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Mission status

• January 17, 2022: Since 2019, SpaceX has been launching an increasing number of internet satellites into orbit around Earth. The satellite constellation, called Starlink, now includes nearly 1,800 members orbiting at altitudes of about 550 kilometers. Astronomers have expressed concerns that that these objects, which can appear as streaks in telescope images, could hamper their scientific observations. 69)

- To quantify these effects, a team of researchers studied archival images captured by the National Science Foundation (NSF)-funded Zwicky Transient Facility (ZTF), an instrument that operates from Caltech's Palomar Observatory near San Diego. ZTF scans the entire night sky every two days, cataloguing cosmic objects that explode, blink, or otherwise change over time. This includes everything from supernovae to near-Earth asteroids. The Zwicky team members say they decided to specifically study the effects of Starlink satellites because they currently represent the largest low-Earth orbit, or LEO, constellation, and they have well-characterized orbits.

- The findings, reported in the January 17 issue of The Astrophysical Journal Letters, shows 5,301 satellite streaks appear in archival images taken between November 2019 and September 2021. 70) — The streaks are most apparent in so-called twilight observations, those taken at dawn or dusk, which are important for finding near-Earth asteroids that appear close to the sun in the sky. ZTF has discovered several asteroids of this nature, including 2020 AV2, the first asteroid spotted with an orbit that fits entirely within the orbit of Venus.

- "In 2019, 0.5 percent of twilight images were affected, and now almost 20 percent are affected," says Przemek Mróz, study lead author and a former Caltech postdoctoral scholar who is now at the University of Warsaw in Poland.

- In the future, the scientists expect that nearly all of the ZTF images taken during twilight will contain at least one streak, especially after the Starlink constellation reaches 10,000 satellites, a goal SpaceX hopes to reach by 2027.

- "We don't expect Starlink satellites to affect non-twilight images, but if the satellite constellation of other companies goes into higher orbits, this could cause problems for non-twilight observations," Mróz says.

- Yet despite the increase in image streaks, the new report notes that ZTF science operations have not been strongly affected. Study co-author Tom Prince, the Ira S. Bowen Professor of Physics, Emeritus, at Caltech, says the paper shows a single streak affects less than one-tenth of a percent of the pixels in a ZTF image.

- "There is a small chance that we would miss an asteroid or another event hidden behind a satellite streak, but compared to the impact of weather, such as a cloudy sky, these are rather small effects for ZTF."

- Prince says that software can be developed to help mitigate potential problems; for example, software could predict the locations of the Starlink satellites and thus help astronomers avoid scheduling an observation when one might be in the field of view. Software can also assess whether a passing satellite may have affected an astronomical observation, which would allow astronomers to mask or otherwise reduce the negative effects of the streaks.

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Figure 31: The streak from a Starlink satellite appears in this image of the Andromeda galaxy, taken by the Zwicky Transient Facility (ZTF), during twilight on May 19, 2021. The image shows only one-sixteenth of ZTF's full field of view (image credit: Caltech Optical Observatories/IPAC)

- The new study also looked at the effectiveness of visors on the Starlink satellites, which SpaceX added beginning in 2020 to block sunlight from reaching the spacecraft. According to the ZTF observations, the visors reduce the satellite brightness by a factor of about five. That dims the satellites down to an apparent brightness level of 6.8 magnitude (the brightest stars are first magnitude, and the faintest stars we can see with our eyes are about sixth magnitude).

- This is still not dim enough to meet standards outlined by the Satellite Constellations 1 (SATCON1) workshop in 2020, a gathering sponsored by the NOIRLab (National Optical-Infrared Astronomy Research Laboratory) and the AAS (American Astronomical Society) to bring together astronomers, policymakers, and other experts to discuss the impact of large satellite constellations on astronomy and society. The group called for all LEO satellites to be at seventh magnitude or fainter.

- The study authors also note their study is specific to ZTF. Like ZTF, the upcoming Vera C. Rubin Observatory, under construction in Chile, will also survey the sky nightly, but due to its more sensitive imager, astronomers predict that it may be more negatively affected by satellite streaks than ZTF.

- ZTF (Zwicky Transient Facility) is funded by NSF and an international collaboration of partners. Additional support comes from the Heising-Simons Foundation and Caltech. ZTF data are processed and archived by Caltech's IPAC astronomy center. NASA supports ZTF's search for near-Earth objects through the Near-Earth Object Observations program.

• September 16, 2021: Two years after the close approach of a Starlink satellite with a European Space Agency satellite alarmed some in the space industry, SpaceX says it’s working closely with a wide range of satellite operators to ensure safe space operations. 71)

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Figure 32: SpaceX says it's working closely with a number of government and commercial satellite operators to coordinate close approaches involving Starlink satellites with their spacecraft (image credit: SpaceX)

- In September 2019, ESA announced it maneuvered an Earth science satellite called Aeolus when the agency determined it would pass dangerously close to a Starlink satellite. The incident was exacerbated by a breakdown in communication between ESA and SpaceX in the days leading up to the close approach.

- After that incident “we went to work coordinating” with both commercial and government satellite operators, said David Goldstein, principal guidance navigation and control engineer at SpaceX, during a panel discussion at the AMOS (Advanced Maui Optical and Space Surveillance Technologies Conference) here Sept. 16 (AMOS 14-17, September 2021, Wailea, Maui, Hawai'i).

- The best-known example of that coordination is a Space Act Agreement between NASA and SpaceX announced in March. Under the terms of that agreement, SpaceX agreed to move its Starlink satellites in the event of any close approaches with NASA spacecraft, a move intended to avoid scenarios when both parties maneuvered their satellites.

- In addition to that agreement, Goldstein said the company has a Cooperative Research and Development Agreement with the U.S. Space Force and a “good working relationship” with ESA and the European Union’s Space Surveillance and Tracking program.

- Those partnerships extend even to OneWeb, a company that complained in Federal Communications Commission filings about a close approach one of its newly launched satellites had with a Starlink satellite in March. “We have a great working relationship with OneWeb after that conjunction in March,” Goldstein said. “Just fantastic coordination at the operational level.”

- He specifically praised OneWeb for its support for the ongoing Inspiration4 crewed mission, saying “they jumped through a lot of hoops” to provide updated information about the orbits of its satellites. Goldstein appeared by video on the panel from SpaceX’s headquarters because, he said, he is providing collision avoidance support for Inspiration4, which launched Sept. 15 for what’s scheduled to be a three-day mission.

- Other companies SpaceX is working with regarding space traffic management include Astroscale, which is developing technologies to service satellites and remove orbital debris, and United Launch Alliance. The work with ULA, he said, is to address “launch COLA [collision avoidance] sorts of issues.”

- SpaceX recently signed a contract with LeoLabs, which provides commercial space traffic management services using data from a network of tracking radars it operates. “They’re doing great work, and we’re super proud of the accomplishments they’ve had and the help they’re providing to us and others,” he said.

- Goldstein also expressed interest in Slingshot Beacon, a collaboration platform developed by Slingshot Aerospace to help satellite operators share space traffic information. That tool, he said, could make it easier for companies to share data and coordinate potential conjunctions.

- One of the more controversial aspects of Starlink is its automated collision avoidance system, where the satellites maneuver 12 hours before the time of closest approach if the risk of a collision exceeds a set threshold.

- Goldstein said he did not have up-to-date information on the number of such maneuvers the Starlink fleet has performed to date. However, he said the company informed the FCC that, from December 2020 through May 2021, Starlink satellites made more than 2,000 collision avoidance maneuvers.

- “The average per satellite during that time is one to two,” he said. “That’s not a terribly high number for that many spacecraft.” SpaceX currently has nearly 1,700 Starlink satellites in orbit.

- Goldstein appeared on a panel that was discussing developing “right of way” procedures for determining who should maneuver in the event of a close approach. “We need a sense of urgency to address things that we can do to avoid the Kessler Syndrome,” or a runaway growth of orbital debris. “There are things that we can do to make space safer, and we all need a sense of urgency to do what we can to avoid that.”

• May 13, 2021: SpaceX will install ground stations within Google’s data centers for its Starlink broadband satellites under a new cloud partnership. 72)

- The alliance aims to expand the reach of Google Cloud customers to their data, services and applications without the need for nearby cell towers.

- After connecting to a Starlink constellation that is becoming increasingly available worldwide, they can increase performance by running applications within Google data centers.

- SpaceX president and chief operating officer Gwynne Shotwell said that, in return, Starlink customers will leverage Google’s infrastructure and capabilities for secure connections.

- Urs Hölzle, senior vice president of infrastructure at Google Cloud, said in a statement: “Applications and services running in the cloud can be transformative for organizations, whether they’re operating in a highly networked or remote environment.

- “We are delighted to partner with SpaceX to ensure that organizations with distributed footprints have seamless, secure, and fast access to the critical applications and services they need to keep their teams up and running.”

- They expect to provide enterprise customers with new services based on this partnership in the second half of this year.

- Although there are currently more than 1,550 Starlinks in orbit following SpaceX’s latest launch May 9, the company remains in beta testing.

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Figure 33: A row of servers inside Google's data center in Douglas County, Georgia (image credit: Google)

Battle in the clouds

- Starlink’s Google partnership appears to be more integrated than an alliance announced in October with Microsoft, which will also use the satellites to expand cloud services.

- Microsoft said Starlink will support its new space-focused, modular cloud business called Azure Space, which will offer mobile cloud computing data centers that can be deployed anywhere in the world.

- O3b internet satellites that SES operates in medium Earth orbit (MEO) also empower that initiative, supporting customers who use space-based data but are unwilling to invest in ground infrastructure directly to process and analyze it.

- SES is jointly investing with Microsoft in Azure Orbital ground stations and MEO gateways, primarily targeting the Earth observation market.

- The Luxembourg-based company became the first satellite operator in 2019 to implement ONAP, an open-source platform telecoms companies use to automate their networks, with network functions virtualization (NFV) technology on Azure cloud services.

- Cloud computing companies and satellite operators are increasingly coming together to drive down costs and improve network access amid improving virtualization technologies.

- In September, Microsoft unveiled a “ground-station as a service” business called Azure Orbital to compete with AWS Ground Station, which is part of Amazon’s cloud-computing branch Amazon Web Services (AWS).

- Meanwhile, Amazon is developing its own LEO broadband constellation called Project Kuiper.

- Although Project Kuiper has yet to launch a single satellite, Amazon has set aside $10 billion to accelerate its development.

- In 2018, established LEO satellite operator Iridium Communications partnered with AWS to develop a network called CloudConnect, targeting the market for connecting internet of things (IoT) devices to the internet.

- Established broadband operators with satellites in geostationary orbit (GEO) have also been ramping up their cloud partnerships in recent years.

- Intelsat, Inmarsat and Viasat, for example, are working with Microsoft as an ‘ExpressRoute’ partner, helping send customer data to the Azure network of fiber-linked data centers.

• March 8, 2021: SpaceX is seeking regulatory permission to connect moving vehicles to its rapidly expanding Starlink constellation, branching the broadband network out of fixed homes and offices. 73)

- The company is asking the FCC (Federal Communications Commission) for authorization similar to the blanket license it already has for up to a million end-user customer Earth stations.

- David Goldman, SpaceX’s director of satellite policy, said in a regulatory filing that its Earth Stations in Motion (ESIM) equipment is “electrically identical to its previously authorized consumer user terminals but have mountings that allow them to be installed on vehicles, vessels and aircraft, which are suitable for those environments.”

- SpaceX recently told the FCC it has more than 10,000 Starlink users in the United States and abroad, after launching more than 1,100 high-speed internet satellites.

- The possibility of diversifying into more markets will raise eyebrows in the satellite mobility industry, as Elon Musk’s launch company continues to raise sizable funding rounds to back its capital-intensive plans.

- Satellite operators Inmarsat, SES and Intelsat are among those likely to feel the most disruption in the land-mobile market, Northern Sky Research principal analyst Brad Grady said.

- Depending on the exact form factors and use cases, Grady said mobile-satellites service (MSS) businesses at Inmarsat and Iridium Communications might see disruption akin to when maritime products transitioned to VSATs (Very-Small-Aperture Terminals).

- However, antenna maker Kymeta and other players in the communications on the pause (COTP) market segment are likely to feel more of an impact from early Starlink adoption.

- “Right now, there really isn’t a high-bandwidth/low latency form factor solution for that market segment that would match the terminal form factor of Starlink,” Grady said.

- “Perhaps once [SES’ next-generation constellation] mPower and their terminal segment develops in the next couple of years we’ll see another competitor there, but the COTP market is a far easier nut to crack in my view.”

- Almost all other non-GEO high-throughput satellite (HTS) constellations have been diversifying into other markets, and Grady said investors and industry have already “priced-in” Starlink as a competitive threat, potential partner or solution as they prepare for its eventual entrance.

- Starlink is likely eying opportunities at Tesla, Musk’s electric vehicle and energy company, which makes cars that currently rely on terrestrial telecoms companies for connectivity.

- Last year, SpaceX sought FCC permission to test Starlink services on private jets, as well as the vessels its rockets land on for reuse.

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Figure 34: Starlink's $499 self-install starter kit includes a phased array antenna that industry veterans say likely costs SpaceX $1,000 or more to manufacture (image credit: SpaceX)

• February 19, 2021: To realize his dream of satellite-powered internet, tech billionaire Elon Musk needs to install antennas around the world. In northern France, a village hopes he'll decide to keep those antennas far away. 74)

- Saint-Senier-de-Beuvron, population 350, is none too thrilled to have been picked as a ground station for Musk's Starlink project for broadband from space.

- "This project is totally new. We don't have any idea of the impact of these signals," said Noemie Brault, a 34-year-old deputy mayor of the village just 20 km (12 miles) from the majestic Mont Saint-Michel abbey on the English Channel.

- "As a precaution the municipal council said no," she explained.

- Musk, founder of SpaceX and electric carmaker Tesla, plans to deploy thousands of satellites to provide fast internet for remote areas anywhere in the world.

- It's a high-stakes battle he is waging with fellow billionaire Jeff Bezos of Amazon as well as the London-based start-up OneWeb.

- Antennas on the ground will capture the signals and relay them to individual user terminals connected by cable.

- Starlink's contractor had already secured French regulatory approval to install nine "radomes" — three-meter-tall globes protecting the antennas — in Saint-Senier, one of four sites planned for France.

- In December, Saint-Senier issued a decree to block construction on the field.

- But the refusal was based on a technicality, and the contractor, Sipartech, told AFP (Agence France Presse) that it plans to refile its request, which the council will likely be unable to block.

- "That worries us because we have no data" on the eventual effects of the signals on the health of humans or animals, said Brault, herself a farmer.

- "And when you hear that he wants to implant a chip in people's brains, it's frightening," she said, referring to Musk's Neuralink project.

- 'Not technophobes'

- Francois Dufour, a Greens council member and retired farmer, said he believes residents had reason to worry.

- "The risks from electromagnetic waves is something we've already seen with high-voltage power lines, which have disturbed lots of farmers in the area," he said.

- Besides, "social networks, internet, they exist already — why do we need to go look for internet on the moon?" he said.

- France's national radio frequency agency ANFR, which approved Starlink's stations, says they present no risks to residents, not least because they will be emitting straight up into the sky.

- There are already around 100 similar sites across France dating from the first satellite launches from 50 years ago, it adds.

- That hasn't convinced Jean-Marc Belloir, 57, who worries that his cows will start producing less milk.

- "On our farm, we're always online. My cows are linked up; my smart watch warns me when they're going to calve," Belloir said. "But when you see the range of these antennas, there has to be some research" on the potential impacts.

- Still, he baptized his latest calf "SpaceX du Beuvron," combining Musk's firm with the name of the creek that runs through his village.

- "We're not attacking Elon Musk," said Anne-Marie Falguieres, who lives just 60 meters from the future Starlink station with her husband and two children.

- "We're not technophobes. I'm a guide on the bay, I have an internet site, my husband works from home. But these antennas are completely new, at least in France, and we want to know if they're dangerous or not," she said.

- She also thinks the project is hardly necessary and unlikely to interest many, based on reports from the US.

- "In the testing phase, they made you pay $500 for the dish and then you had to pay $100 a month for a subscription," she said. "I don't think everyone's going to be able to pay that."

• February 4, 2021: SpaceX disclosed in a public filing on Thursday that its Starlink satellite internet service now has “over 10,000 users in the United States and abroad.” 75)

- “Starlink’s performance is not theoretical or experimental ... [and] is rapidly accelerating in real time as part of its public beta program,” SpaceX wrote in a filing with the Federal Communications Commission.

- Elon Musk’s company began a public beta program of Starlink in October, with service priced at $99 a month, in addition to a $499 upfront cost to order the Starlink Kit, which includes a user terminal and Wi-Fi router to connect to the satellites.

- The company is offering the service to select customers in the northern U.S., Canada, and the U.K.

- Starlink is SpaceX’s ambitious project to build an interconnected internet network with thousands of satellites, known in the space industry as a constellation, designed to deliver high-speed internet to consumers anywhere on the planet. The FCC two years ago approved SpaceX to launch 11,943 satellites, with the company aiming to deploy 4,425 satellites in orbit by 2024.

- SpaceX noted in the filing that Starlink’s service is “meeting and exceeding 100/20 Mbit/s throughput to individual users,” while the vast majority of users were seeing latency “at or below 31 milliseconds.”

- The update on Starlink’s customer base came in a petition to the FCC, with SpaceX asking that Starlink be designated an “Eligible Telecommunications Carrier” or ETC.

- The company noted that receiving this designation is necessary for Starlink to provide service to regions in “Alabama, Connecticut, New Hampshire, New York, Tennessee, Virginia and West Virginia.”

- SpaceX was awarded access to those regions under the FCC’s Rural Digital Opportunities Fund, an auction to bring broadband services to rural areas.

- The FCC in December awarded SpaceX with nearly $900 million in federal subsidies in the first phase of the auction.

- “Designating Starlink Services as an ETC is in the public interest because it will enable the company to receive support that will facilitate rapid deployment of broadband and voice service to the Service Areas at speeds and latency comparable to terrestrial systems in urban locations,” SpaceX wrote in the filing on Thursday.

- “Starlink Services respectfully requests that the Commission grant this petition by June 7, 2021 in order for Starlink Services to meet the Commission’s deadline for ETC designation for the purposes of receiving RDOF support.”

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Figure 35: A Starlink user terminal installed on the roof of a building in Canada (image credit: SpaceX)

- SpaceX’s rapid Starlink user growth is notable given the service has been in a public beta for just over three months.

- But customer demand was apparent before Starlink began offering early access, as SpaceX said in July that it received interest in the service from “nearly 700,000 individuals” across the United States. Those individuals’ interest came within the first two months of SpaceX allowing potential customers to sign up on the company’s website for updates on service availability.

• January 18, 2021: The German Astronomical Society (AG), the German association of amateur astronomers (VdS) and the Society of German-Speaking Planetariums (GDP) comment on the rapid increase in the number of satellites in the night sky. Artificial satellites have significant impact on the perception of the natural starry sky and the exploration of our universe. 76)

- Astronomical research institutes, observatories and planetariums have received a large number of concerned inquiries in recent months. The reason for this is the many satellites launched into Earth orbit by the private US space company SpaceX since May 2019, which are moving across the sky in groups.

- With Starlink, SpaceX hopes to provide a satellite-based network of high-speed internet connections worldwide. The final constellation will consist of more than 30,000 satellites, which far exceeds the number of all satellites in Earth orbit to date. Other companies such as OneWeb, Amazon and others are planning or in some cases already enacting similar projects. German companies also have corresponding plans to launch large numbers of microsatellites cheaply into Earth orbits. Astronomy is aware of the importance of connecting remote regions of the Earth to the internet, as well as other technological developments. Nevertheless, implementation via the enormous increase in artificial satellites in the sky also entails considerable restrictions and risks, the consequences of which must be weighed responsibly and reduced as far as possible.

- For astronomers, the protection of the night sky as a unique cultural heritage of mankind is a central concern. The experience of this natural wonder is already severely impaired in large parts of the world by inefficient and excessive artificial lighting. An uninterrupted view of the starry sky will no longer be possible due to the large number of light-reflecting artificial satellites, even in regions of the Earth that have so far been largely untroubled by light pollution. Even before the launch of the first Starlink satellites, numerous artificial satellites were observable in the night sky. With tens of thousands of additional objects orbiting the Earth, it is a realistic scenario that several thousand satellites passing over the firmament will obstruct stargazing in the night sky. Their number would then exceed that of the stars visible to the naked eye.

- This will forever change the night sky, the sight of which has fascinated and inspired mankind since the beginning. In addition, the exploration of the universe for professional and amateur astronomy will be significantly affected. Images of night landscapes and celestial objects, which have always carried the fascination of astronomy to the general public and contributed to general education, will be significantly affected. Astronomy forms the basis for our exploration and use of space. With the development of sophisticated observatories, many advances have been made in the exploration of our universe. Modern telescopes scan the sky and peer into the depths of space, furthering our understanding of the universe. However, these observations are significantly threatened by the multitude of satellites. Of particular note are studies of the dynamic universe. Optical telescopes for wide-field imaging will be impacted (such as the future Vera C. Rubin Observatory), as well as the tracking and monitoring of small bodies in the solar system that could potentially collide with Earth. In addition to optical astronomy, observations in infrared and radio wavebands from space will also be significantly affected.

- Radio astronomy is already increasingly disturbed by man-made signals, for example by the steadily growing volume of mobile communications. Therefore, scientists set up their observatories in very remote areas. However, the expected large number of satellites will operate around the globe so there will be no escape for radio astronomy either. German researchers do not only operate Europe’s largest radiotelescope, the 100-m telescope at Effelsberg near Bonn, but they are also involved in a large number of state-of-the-art radio observatories around the world, such as the Atacama Large Millimeter Array (ALMA) and the Square Kilometer Array (SKA) under construction in Australia and South Africa. These sites will then also be affected.

- The current development also poses a threat to manned and unmanned space flight, as it inevitably increases the risk of collisions.

- The degradation of the night sky has a global impact, but the approval of satellite launches is done exclusively by national authorities, such as the Federal Communications Commission in the US. We hereby express our concern about this and call for international regulations for satellite constellations to ensure the protection of the night sky over the entire electromagnetic spectrum for research and as a human cultural asset.

• January 9, 2021: The FCC (Federal Communications Commission) will allow SpaceX to launch 10 Starlink satellites into polar orbit on an upcoming mission, but deferred a decision on a much broader modification of SpaceX’s license. 77)

- In an order published Jan. 8, the FCC granted SpaceX permission to launch 10 Starlink satellites into a 560-kilometer orbit with an inclination of 97.6 degrees. Those satellites will launch on a Falcon 9 no earlier than Jan. 14 as part of Transporter-1, a dedicated smallsat rideshare mission.

- SpaceX had been lobbying the FCC for weeks for permission to launch Starlink satellites into a polar orbital plane as the FCC considers a modification of the company’s license to lower the orbits of satellites originally authorized for higher altitudes. That included a Nov. 17 request to launch 58 satellites into a single polar orbital plane, citing “an opportunity for a polar launch in December” that it did not identify.

- In a Jan. 5 filing with the FCC, SpaceX said it spoke with FCC officials the previous day about this request. “SpaceX confirmed that if it receives the proper authorization, its forthcoming Transporter-1 mission will include 10 Starlink satellites targeted for operation in polar orbits,” the company stated.

- SpaceX argued in filings that adding at least some satellites into polar orbits would allow it to begin service in Alaska, which is not in the coverage area of existing Starlink satellites launched into mid-inclination orbits. The company said in its November filing that “launching to polar orbits will enable SpaceX to bring the same high-quality broadband service to the most remote areas of Alaska that other Americans have come to depend upon, especially as the pandemic limits opportunities for in-person contact.”

- Other satellite operators opposed the move. In a Nov. 19 filing, Viasat said that “commercial expediency” was not a sufficient reason for the FCC to grant SpaceX permission for launching satellites into polar orbit, raising concerns about the reliability of Starlink satellites and the orbital debris hazards they pose.

- The FCC, in its order, concluded that allowing SpaceX to launch the 10 Starlink satellites into polar orbits was in the public interest. “We find that partial grant of ten satellites will facilitate continued development and testing of SpaceX’s broadband service in high latitude geographic areas in the immediate term pending later action to address arguments in the record as to both grant of the modification as a whole and the full subset of polar orbit satellites,” the order stated.

- It rejected Viasat’s opposition to the request, stating that allowing the 10 satellites “does not present concerns in connection with the issues raised by commenters.” That included orbital debris concerns about failed Starlink satellites. “We conclude that the addition of these ten satellites is unlikely to have any significant incremental effect on the operations of other satellites in the relevant orbital altitudes,” the order stated.

- The FCC, though, deferred a decision on SpaceX’s overall license modification request to lower the orbits of those satellites. In the order, the FCC didn’t state when it expected to rule on the full request.

• December 8, 2020: Observations conducted by the Murikabushi Telescope of Ishigakijima Astronomical Observatory in Japan confirmed that dark coating can reduce satellite reflectivity by half. There are concerns that numerous artificial satellites in orbit could impair astronomical observations, but these findings may help alleviate such conditions. 78) 79)

- Today's growing demand for space-based services has spawned a wave of satellite constellation projects which operate numerous artificial satellites in orbit. Since these satellites can shine by reflecting sunlight, the astronomy community has raised concerns about their potential impact on astronomical observations. In January 2020, SpaceX launched "DarkSat," an experimental satellite with an anti-reflective coating, and asked astronomers to assess how much this coating can reduce the satellite reflectivity. Brightness measurements of artificial satellites have already been conducted, but until now, there was no verification that a dark coating actually achieves the expected reflectivity reduction.

- The Murikabushi Telescope of Ishigakijima Astronomical Observatory can observe celestial objects simultaneously in three different wavelengths (colors). Comparing multicolor data obtained under the same conditions provides more accurate insight into how much the coating can reduce the satellite brightness. Observations conducted from April to June 2020 revealed for the first time in the world that artificial satellites, whether coated or not, are more visible at longer wavelengths, and that the black coating can halve the level of surface reflectivity of satellites. Such surface treatment is expected to reduce the negative impacts on astronomical observations. Further measures will continue to be implemented to pave the way for peaceful coexistence between space industries and astronomy.

• December 7, 2020: The Federal Communications Commission (FCC) on Monday awarded SpaceX's Starlink Internet venture $885 million in a broadband services auction for rural America. It was the fourth-largest award in recent competitive bidding. 80)

- The win provides new funding to Starlink, which recently provided free public testing in limited areas of the northwestern United States and Canada. The money also will help Starlink move toward bringing better-quality and faster Internet service to rural areas.

- Elon Musk's company has more than 900 Starlink communications satellites in orbit and intends to launch hundreds more.

- SpaceX won bids to provide broadband in 35 states, more states than any of the 180 companies that bid in the recent auction, which covered 49 states.

- The contracts are a significant win for SpaceX, said Shagun Sachdeva, who has worked as an analyst covering large satellite constellations and recently founded her own consulting company, France-based Kosmic Apple.

- "If SpaceX manages to get government and military contracts for Starlink, as they seem to be successfully doing so far, they can keep the commercial costs low enough to gain a decent market share," Sachdeva said.

- The FCC funding and recent public testing mean SpaceX is "most definitely one of the front runners now" in providing broadband service, she said.

- The companies that won more funding than SpaceX were LTD Broadband, which operates in the Upper Midwest, at $1.32 billion; Connecticut-based Charter Communications, $1.22 billion; and Rural Electric Cooperation Consortium, a nationwide collection of rural utilities, at $1.1 billion.

- SpaceX Starlink satellites operate at LEO (Low Earth Orbit) altitudes of roughly 550 km according to SpaceX.

- Winning bids in the auction allows SpaceX to submit formal applications for contract Internet service in rural areas. SpaceX has advertised Starlink at $99 a month after the purchase of a satellite dish receiver for $499, but the FCC funding is to be used partly to lower those costs for rural areas.

August 26, 2020: Light pollution problem from large satellite constellations for astronomy
A new report offers ways both astronomers and satellite developers can reduce the effect megaconstellations have on ground-based astronomy, but warned that no combination of measures can entirely eliminate the problem. 81)

- The report released Aug. 25 by the AAS (American Astronomical Society) and the National Science Foundation’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory) is the outcome of a four-day workshop called ”Satellite Constellations 1 Workshop Report” (SATCON1) held nearly two months ago. That workshop brought together more than 250 people, including both astronomers and satellite operators, to evaluate how to minimize the effect satellite constellations would have on astronomy.

- For more than a year, astronomers have expressed concern that constellations of thousands of satellites could interfere with their observations. The satellites, visible through reflected sunlight, can leave bright streaks as they pass through the fields of view of telescopes.

- The workshop concluded that while there are a number of ways to reduce the problem, there is no panacea. “No combination of mitigations will eliminate the impact of satellite constellations on optical astronomy,” said Connie Walker of NOIRLab, one of the co-chairs of the workshop, in an Aug. 25 press conference. The exception, she said, was not to launch such systems at all, but acknowledged “it’s not viable for industry.”

- Instead, the report offered a set of recommendations to mitigate the effects of megaconstellations on astronomy, including ways for companies to reduce the brightness of their satellites and the amount of time they are visible in the night sky. Those steps include placing satellites in orbits no higher than 600 kilometers, as well as darkening them and controlling their attitude to reduce their reflectivity.

- Even before the SATCON1 workshop, astronomers had been working with SpaceX on mitigation measures along the lines of those steps described in the report. The Starlink satellites operate at an altitude of 550 kilometers, and the company has tested measures to both darken the satellites to reduce their reflectivity as well as to install visors to block sunlight from hitting reflective surfaces.

- The first “VisorSat” satellite launched in June and, earlier this month, reached its operational orbit. Astronomers said it was still too soon to measure its effectiveness. “We don’t have a complete set of observations yet,” said Lori Allen of NOIRLab, who chaired a SATCON1 working group on observations. “We do have some initial observations, but those are still under analysis.”

- Allen said that the effort to measure the brightness of VisorSat had been affected by observatories that remain closed because of the pandemic. However, some amateur satellite observers have observed the first VisorSat this month and estimate its brightness at seventh magnitude, enough of a reduction to reduce the worst impacts on astronomy.

- The efforts to reduce the brightness of Starlink satellites are much further along than those of other satellite constellations, such as OneWeb and Amazon’s Project Kuiper. OneWeb, which paused the deployment of its constellation after filing for Chapter 11 bankruptcy in March, worries astronomers because its satellites are in orbits 1,200 kilometers high, making them visible longer each night. The company also recently filed a proposal to operate as many as 48,000 additional satellites.

- “SpaceX is leading the charge in terms of trying to understand these issues and designing mitigations on their satellites,” said Tony Tyson, chief scientist of the Vera Rubin Observatory and chair of a SATCON1 working group devoted to mitigation measures.

- “Others are getting interested,” he added, notably OneWeb and Amazon, which participated in the workshop, “but we’re nowhere near any kind of down-to-earth engineering discussions on how to do this.”

- The report included recommendations for astronomers as well, such as development of software to plan observations to avoid or minimize the number of satellites passing through the field of view, as well as software to identify and remove trails created by passing satellites. It also recommended astronomers and satellite operators work together to coordinate observations of satellites to measure changes in brightness over time, and to share more accurate satellite position data to enable astronomers to more effectively avoid satellites.

- “We need to greatly increase the precision of publicly available positions” of satellites, said Jeff Hall of Lowell Observatory, the other co-chair of the SATCON1 workshop. “They’re not accurate enough for observatories to work around some of the issues that we’re facing.”

- The report did not examine regulatory or policy issues involving satellite megaconstellations and astronomy. That will be the subject of a second workshop tentatively scheduled for the first half of 2021.

- The SATCON1 workshop is not the only study of the topic. The NSF commissioned a report from the independent JASON scientific advisory group on the effects megaconstellations have on astronomy in general. Ralph Gaume, director of the NSF’s astronomical sciences division, said at an Aug. 25 meeting of the Astro2020 decadal survey steering committee that he received an initial “letter report” from the group a week ago, and expected the final report around October 1.

- Phil Puxley, vice president for special projects at the Association of Universities for Research in Astronomy, which operates NOIRLab for the NSF, noted at the SATCON1 briefing that astronomers previously built observatories in remote locations to avoid terrestrial light pollution. But with constellations, he said, “there are no remote locations that are immune. There is no place to hide.”

• August 25, 2020: Satellite Constellations 1 Workshop Report (SATCON1). The content of Table 1 contains only the Executive Summary of the SATCON1 paper. 82)

Existing and planned large constellations of bright satellites in low-Earth orbit (LEOsats) will fundamentally change astronomical observing at optical and near-infrared (NIR) wavelengths. Nighttime images without the passage of a Sun-illuminated satellite will no longer be the norm. If the 100,000 or more LEOsats proposed by many companies and many governments are deployed, no combination of mitigations can fully avoid the impacts of the satellite trails on the science programs of current and planned ground-based optical-NIR astronomy facilities. Astronomers are just beginning to understand the full range of impacts on the discipline. Astrophotography, amateur astronomy, and the human experience of the stars and the Milky Way are already affected. This report is the outcome of the Satellite Constellations 1 (SATCON1) workshop held virtually on 29 June–2 July 2020. SATCON1, organized jointly by NSF’s NOIRLab and AAS with funding from NSF, aimed to quantify better the impacts of LEOsat constellations at optical wavelengths and explore possible mitigations.

Recent technology developments for astronomical research — especially wide-field imaging on large optical telescopes — face significant challenges from the new ability in space and communication technologies to launch many thousands of LEOsats rapidly and economically. This troubling development went unnoticed by our community as recently as 2010, when New Worlds, New Horizons — the most recent National Academies’ decadal survey of astronomy and astrophysics — was issued. In the last year, the sky has changed, with growing numbers of satellite trails contaminating astronomical images.

Many astronomical investigations collect data with the requirement of observing any part of the sky needed to achieve the research objective with uniform quality over the field of view. These include studies that are among the highest priorities in the discipline: stellar populations in the Milky Way and neighboring galaxies; searches for potentially hazardous near-Earth objects; identification of gravitational wave sources such as neutron star mergers; and wide-area searches for transiting exoplanets. At a minimum, a fraction of the area being imaged is lost to the trails or significantly reduced in S/N (signal-to-noise ratio). However, many of these areas of research also include a time-critical aspect and/or a rare, scientifically critical target. Such a missed target, even with low probability, will significantly diminish the scientific impact of the project. For example, if a near-Earth object is not recovered, its orbital parameters are lost. If the transit of a promising super-Earth exoplanet candidate is missed, the orbital timing may not be recovered. If the optical counterpart of a gravitational wave source is lost in the few percent of pixels in satellite trails, its rapid fading may preclude subsequent identification. Detailed simulations beyond the scope of this workshop are required to better quantify the potential scientific cost of losing uniform full area coverage in these cases.

Even more challenging simulations are required to understand the impact on very large samples (e.g., from Vera C. Rubin Observatory) that are limited not by small number statistics but rather by systematic uncertainties. One measure of precision cosmology, for example, is the gravitational weak lensing shear that elongates faint galaxy images, and more complex modeling is needed to understand the major impact these satellites will have on this field.

Initial visibility simulations have shown the significant negative impacts expected from two communications-focused LEOsat constellations, Starlink (launched by Space Exploration holdings, LLC [SpaceX]), and OneWeb. For SATCON1, simulations were performed of the visibility of LEOsats with 30,000 second-generation Starlink satellites below 614 km and ~48,000 OneWeb satellites at 1200 km, in accord with the FCC filings for these projects. For all orbital heights, the visibility of sunlit satellites remains roughly constant between sunset and astronomical twilight (Sun 18 degrees below the horizon). The key difference between lower (~600 km) and higher (~1200 km) orbits is the visibility in the dark of night between astronomical twilights: higher altitude constellations can be visible all night long during summer, with only a small reduction in the number visible compared to those in the twilight.

Mitigation of the most damaging impacts on scientific programs is now being actively explored by the professional astronomy community worldwide. These investigations have benefited from collaboration with SpaceX, the first operator to launch a substantial constellation of LEOsats (538 satellites over 9 launches as of July 2020). Changes are required at both ends: constellation operators and observatories. SpaceX has shown that operators can reduce reflected sunlight through satellite body orientation, Sun shielding, and surface darkening. A joint effort to obtain higher accuracy public data on predicted locations of individual satellites (or ephemerides) could enable some pointing avoidance and mid-exposure shuttering during satellite passage. Observatories will need to adopt more dynamic scheduling and observation management as the number of constellation satellites increases, though even these measures will be ineffective for many science programs.

SATCON1 was attended by over 250 astronomers and engineers from commercial operators (mainly from SpaceX since they are furthest along in their work on this issue), as well as other stakeholders, and reached a number of conclusions and recommendations for future work. The organizers hope that the collegiality and spirit of partnership between these two communities will expand to include other operators and observatories and continue to prove useful and productive. Our findings and recommendations should serve as guidelines for observatories and satellite operators alike to use going forward, even as we work toward a more detailed understanding of the impacts and mitigations.

Table 1: Impact of Satellite Constellations on Optical Astronomy and Recommendations toward Mitigations

• May 15, 2020: Every two weeks, late in the evening, people are able to see a swarm of strikingly bright points of light crossing the night sky. An array of images and spectacular videos of such sightings circulate on social media. Word soon gets around that these glowing strings of light are not, in fact, an alien fleet. Rather, they are the Starlink satellites from SpaceX, the US space company run by Elon Musk, streaking across the night sky in 'trains'. 83)

- This visual spectacle and the ambitious project behind it, which is on an enormous scale, are fascinating. Felix Huber and Manfred Gaida explain the background to the project in an interview. They talk about the impact that these strings of light have on astronomy and space, and answer the questions that people sent to DLR when it put out a call on social media.

- Felix Huber is Director of DLR Space Operations and Astronaut Training. This is the central institution for spaceflight operations in Germany. Manfred Gaida is an astronomer and researcher at the DLR Space Administration and an expert on satellite-based space research and optical astronomy.

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Figure 36: Eye-catching newcomers to the sky (image credit: Giancarlo Foto4U CC-BY 2.0)

• April 27, 2020: SpaceX Chief Executive Elon Musk said April 27 that he hopes to test a new way to reduce the brightness of the company’s Starlink satellites on the next launch for the broadband megaconstellation. 84)

- In a briefing to a committee working on the next astrophysics decadal survey, Musk said the experimental “VisorSat,” along with a new approach for orienting Starlink satellites as they raise their orbits, should address concerns raised by astronomers that the Starlink constellation could interfere with their observations.

- “Our objectives, generally, are to make the satellites invisible to the naked eye within a week, and to minimize the impact on astronomy, especially so that we do not saturate observatory detectors and inhibit discoveries,” Musk said.

- SpaceX first attempted to address the brightness problem with an experimental “DarkSat” included in a batch of Starlink satellites launched in January. The satellite used what the company described as experimental darkening treatments over reflective surfaces, like its antennas, in an effort to reduce the amount of sunlight it reflects and thus make it darker.

- While DarkSat has shown some promise, appearing about one magnitude darker than untreated Starlink satellites, the company is moving in a different direction. “We found an option that is even better than that, which is basically to give the satellites shades,” he said.

- Musk and others at SpaceX have previously discussed a sunshade that they compared to a patio umbrella that would deploy from a satellite, keeping the antennas in shadow. Musk, at the committee meeting, described a concept called VisorSat that would deploy panels, like sun visors mounted on a car windshield, to block the sun.

- “We have a radio-transparent foam that will deploy nearly upon the satellite being released, and it blocks the sun from reaching the antennas,” he said. “They’re sun visors, essentially: they flip out and block the sun and prevent reflections.” He predicted that the visors would have a “massive effect” on the brightness of the satellites.

- SpaceX is planning test VisorSat on the company’s next Starlink launch. “It’s a bit of a challenge, but that’s our goal,” he said. He didn’t say how many satellites would be equipped with visors, or when the launch was scheduled. SpaceX has been performing Starlink launches at the rate of at least one a month so far this year, most recently April 22.

- A second effort involves the brightness of the satellites as they raise their orbits after launch. Musk said the satellites appear bright because of the orientation of the solar panels, which are aligned differently during orbit raising than once at their operational orbit.

- As soon as this week, Musk said SpaceX will try an “orientation roll” to change the alignment of the solar panels relative to the Earth, reducing the amount of sunlight they reflect to the ground. “Early indications are this will have a significant effect on the brightness during orbit raise,” he said. “The satellites will be significantly less visible from the ground.”

- The measures SpaceX has taken have come after months of discussions with astronomers, who have been worried about the effects a full constellation of Starlink satellites — about 12,000 according to current plans, with proposals for up to 30,000 more — would have on astronomy. The situation was of particular concern to those operating telescopes with wide fields of view, like the Vera Rubin Observatory under construction in Chile, where Starlink satellites would be visible in a large fraction of images taken each night.

- In a separate presentation to the committee earlier in the day, Tony Tyson, chief scientist for the Rubin Observatory, said the concern was that the brightness of unmodified Starlink satellites would cause “nonlinear crosstalk,” or severe image artifacts, in the observatory’s camera. “We would be left with all of these fake trails, fake galaxies, etc., in our data, damaging the science,” he said.

- SpaceX has already made progress darkening the satellites, with newer satellites about one magnitude darker than the original “v0.9” satellites launched in May 2019 even without the darkening treatments used on DarkSat. If the satellites can be made about a factor of two darker than DarkSat, Tyson said a technique to correct for the nonlinear crosstalk can work, although it is computer intensive and won’t correct for the original streak left in the images by passing satellites.

- The new approaches won’t address the issue of brightness of existing Starlink satellites, but Musk said their lifetime is limited. He estimated the initial generation of satellites will be deorbited in about three to four years to make way for improved satellites. “We’ll just have far greater throughput capability with version two” of the Starlink satellites, he said.

- While the focus of the committee presentation and subsequent discussion, which lasted for more than an hour, was on Starlink, there was some talk about the role SpaceX could play in supporting space-based astronomy, which is not affected by Starlink or other megaconstellations.

- “I’m very excited about the future of space-based telescopes that could be very large,” he said. He mentioned Starship, the company’s next-generation large reusable launch system, which will begin regular flights “I think within a couple of years,” he promised. “It allows for space telescopes to be transported to orbit at probably an order of magnitude lower cost than in the past.”

- “I’m pretty interested in trying to figure out how to help launch and possibly build a big observatory in space,” he said, offering to meet with astronomers to discuss mission concepts. “Like a planet imager or something like that.”

• March 19, 2020: SpaceX, the largest commercial satellite constellation operator in the world, has ambitious plans of installing 12,000 satellites in low-orbit over a span of several years, as part of its Starlink project to provide low-cost broadband internet service. 85)

A well-known astronomer and satellite tracker has voiced concerns that efforts to scan the skies for potentially dangerous near-Earth asteroids might be in jeopardy due to ambitious plans by SpaceX to deploy over 12,000 satellites in low-Earth orbit over the next several years.

The study "The Low Earth Orbit Satellite Population and Impacts of the SpaceX Starlink" by Jonathan McDowell from the Harvard-Smithsonian Center for Astrophysics analyses the impact that the broadband service mega-constellation could have on different observatories. 86)

The research, still awaiting peer review and accepted for pre-print publication in Astrophysical Journal Letters, states:

"Astronomers - and casual viewers of the night sky - must expect a future in which the low Earth orbit population includes tens of thousands of relatively large satellites."

The researcher has modelled how many satellites in a constellation of 12,000 that the FCC has already approved for SpaceX would be lit up by the Sun and above the horizon from three different latitudes on Earth.

"We see that several hundred satellites are above the horizon at all times of night; during winter twilight, and all summer night long, most of them are illuminated," writes McDowell.

Since Elon Musk's SpaceX began launching batches of satellites in 2019, astronomers have been voicing concerns that the expanding number of huge satellite constellations, driven by Starlink's target plan of installing up to 42,000 satellites in low orbit could wreak havoc on scientific observations of space.

Both skywatchers and astronomers were shocked by the bright lights of the satellites that were obstructing the view for major telescopes and potentially corrupting between 30 to 40 percent of astronomical images.

Satellites from companies other than SpaceX, such as OneWeb pose a similar problem, as many observatories with particularly wide fields of view, like the Vera C. Rubin Observatory currently under construction in Chile, are likely to be impacted.

According to a recent study from the European Southern Observatory (ESO), satellite mega-constellations are projected as "severely" affecting between 30 and 50 percent of observations taken by the Rubin Observatory.

"However, there appear to be other science projects which may be more severely affected... For example, searches for near-Earth asteroids include observations taken in twilight, a time when the satellites are illuminated year-round," writes McDowell.

The astronomer has recently been expounding the importance of continued, unhampered observation of asteroids that may pose a danger to the Earth due to the close proximity in which they move.

When it comes to detection of near-Earth objects travelling close to the Sun, researchers typically search for them after sunset, when Starlink's satellites illuminate the sky.

While urging additional regulation, which he claimed might help solve the issue, he stressed measures being proposed at the moment are not effective.

There has been no official comment from SpaceX.

Previously, to allay concerns, SpaceX CEO Elon Musk stated the company would work with astronomers to develop solutions to mitigate any impact on scientific observation. In response to the criticism, Elon Musk tweeted in May 2019 that the amount of light the satellites have been sending down toward Earth would be studied and measures to mitigate the effects would be taken by modifying them to be less reflective.

"Agreed, sent a note to Starlink team last week specifically regarding albedo reduction. We'll get a better sense of value of this when satellites have raised orbits and arrays are tracking to Sun."

Meanwhile, the company continues to launch new batches of satellites, as a Falcon 9 rocket is geared up to carry 60 more satellites to space on 18 March.

SpaceX has plans to have over 1,500 satellites in space by the end of the year, with the long-term plan for the mega-constellation aiming at 42,000 satellites that would beam high-speed internet to every corner of the globe.

• March 5, 2020: Astronomers have recently raised concerns about the impact of satellite mega-constellations on scientific research. To better understand the effect these constellations could have on astronomical observations, ESO commissioned a scientific study of their impact, focusing on observations with ESO telescopes in the visible and infrared but also considering other observatories. The study, which considers a total of 18 representative satellite constellations under development by SpaceX, Amazon, OneWeb and others, together amounting to over 26 thousand satellites [1], has now been accepted for publication in Astronomy & Astrophysics. 87) 88)
Note [1]: Many of the parameters characterizing satellite constellations, including the total number of satellites, are changing on a frequent basis. The study assumes 26,000 constellation satellites in total will be orbiting the Earth, but this number could be higher.

The study finds that large telescopes like ESO's Very Large Telescope (VLT) and ESO's upcoming Extremely Large Telescope (ELT) will be "moderately affected" by the constellations under development. The effect is more pronounced for long exposures (of about 1000 s), up to 3% of which could be ruined during twilight, the time between dawn and sunrise and between sunset and dusk. Shorter exposures would be less impacted, with fewer than 0.5% of observations of this type affected. Observations conducted at other times during the night would also be less affected, as the satellites would be in the shadow of the Earth and therefore not illuminated. Depending on the science case, the impacts could be lessened by making changes to the operating schedules of ESO telescopes, though these changes come at a cost [2]. On the industry side, an effective step to mitigate impacts would be to darken the satellites.
Note [2]: Examples of mitigation measures include: computing the position of the satellites to avoid observing where one will pass; closing the telescope shutter at the precise moment when a satellite crosses the field of view; and constraining observations to areas of the sky that are in Earth’s shadow, where satellites are not illuminated by the sun. These methods, however, are not suitable for all science cases.

The study also finds that the greatest impact could be on wide-field surveys, in particular those done with large telescopes. For example, up to 30% to 50% of exposures with the US National Science Foundation's Vera C. Rubin Observatory (not an ESO facility) would be "severely affected”, depending on the time of year, the time of night, and the simplifying assumptions of the study. Mitigation techniques that could be applied on ESO telescopes would not work for this observatory although other strategies are being actively explored. Further studies are required to fully understand the scientific implications of this loss of observational data and complexities in their analysis. Wide-field survey telescopes like the Rubin Observatory can scan large parts of the sky quickly, making them crucial to spot short-lived phenomena like supernovae or potentially dangerous asteroids. Because of their unique capability to generate very large data sets and to find observation targets for many other observatories, astronomy communities and funding agencies in Europe and elsewhere have ranked wide-field survey telescopes as a top priority for future developments in astronomy.

Professional and amateur astronomers alike have also raised concerns about how satellite mega-constellations could impact the pristine views of the night sky. The study shows that about 1600 satellites from the constellations will be above the horizon of an observatory at mid-latitude, most of which will be low in the sky — within 30 degrees of the horizon. Above this — the part of the sky where most astronomical observations take place — there will be about 250 constellation satellites at any given time. While they are all illuminated by the Sun at sunset and sunrise, more and more get into the shadow of the Earth toward the middle of the night. The ESO study assumes a brightness for all of these satellites. With this assumption, up to about 100 satellites could be bright enough to be visible with the naked eye during twilight hours, about 10 of which would be higher than 30 degrees of elevation. All these numbers plummet as the night gets darker and the satellites fall into the shadow of the Earth. Overall, these new satellite constellations would about double the number of satellites visible in the night sky to the naked eye above 30 degrees [3].
Note [3]: It is estimated that about 34,000 objects greater than 10 cm in size are currently orbiting the Earth. Of these, about 5500 are satellites, including about 2300 functional ones. The remainder are space debris, including rocket upper stages and satellite launch adapters. About 2000 of these objects are above the horizon at any given place at any one time. During twilight hours, about 5–10 of them are illuminated by the Sun and bright enough to be seen with the naked eye.

These numbers do not include the trains of satellites visible immediately after launch. Whilst spectacular and bright, they are short lived and visible only briefly after sunset or before sunrise, and — at any given time — only from a very limited area on Earth.

The ESO study uses simplifications and assumptions to obtain conservative estimates of the effects, which may be smaller in reality than calculated in the paper. More sophisticated modelling will be necessary to more precisely quantify the actual impacts. While the focus is on ESO telescopes, the results apply to similar non-ESO telescopes that also operate in the visible and infrared, with similar instrumentation and science cases.

Satellite constellations will also have an impact on radio, millimeter and submillimeter observatories, including the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX). This impact will be considered in further studies.

ESO, together with other observatories, the International Astronomical Union (IAU), the American Astronomical Society (AAS), the UK Royal Astronomical Society (RAS), and other societies, is taking measures to raise the awareness of this issue in global fora such as the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) and the European Committee on Radio Astronomy Frequencies (CRAF). This is being done while exploring with the space companies practical solutions that can safeguard the large-scale investments made in cutting-edge ground-based astronomy facilities. ESO supports the development of regulatory frameworks that will ultimately ensure the harmonious coexistence of highly promising technological advancements in low Earth orbit with the conditions that enable humankind to continue its observation and understanding of the Universe.

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Figure 37: This annotated image shows the night sky at ESO's Paranal Observatory around twilight, about 90 minutes before sunrise. The blue lines mark degrees of elevation above the horizon. A new ESO study looking into the impact of satellite constellations on astronomical observations shows that up to about 100 satellites could be bright enough to be visible with the naked eye during twilight hours (magnitude 5–6 or brighter). The vast majority of these, their locations marked with small green circles in the image, would be low in the sky, below about 30 degrees elevation, and/or would be rather faint. Only a few satellites, their locations marked in red, would be above 30 degrees of the horizon — the part of the sky where most astronomical observations take place — and be relatively bright (magnitude of about 3–4). For comparison, Polaris, the North Star, has a magnitude of 2, which is 2.5 times brighter than an object of magnitude 3. The number of visible satellites plummets towards the middle of the night when more satellites fall into the shadow of the Earth, represented by the dark area on the left of the image. Satellites within the Earth's shadow are invisible. (image credit: ESO/Y. Beletsky/L. Calçada)

• June 14, 2019: SpaceX’s ambitious Starlink project could eventually launch more than 10,000 satellites into orbit and rewrite the future of the internet. But Elon Musk’s company SpaceX has been taking heat from the astronomical community after an initial launch in late May released the first 60 satellites. The satellites with a mass of 227 kg were clearly visible in Earth’s night sky, inspiring concern that they could increase light pollution, interfere with radio signals, and contribute to the growing issue of space debris. 89)

This week, the American Astronomical Society, the International Astronomical Union, the British Royal Astronomical Society, and the International Dark-Sky Association (IDA) all issued statements expressing concern about Starlink’s potential to damage astronomical research by leaving bright streaks through images.

“The Starlink affair has raised the attention of the astronomy community in a way that I’ve not seen during my couple of decades in it,” says John Barentine, director of public policy at the IDA, which lobbies against light pollution. “I hope that this moment is the wake-up call that is needed to prompt a new discussion in the international community about the nature of outer space, especially near the Earth, in a commercial context.”

Musk had repeatedly assured people on Twitter that his satellites wouldn’t be visible at night, so the light caught some people by surprise. However, the satellites’ initial brightness is intended to wane as they climb higher into their permanent orbits.

“The observability of the Starlink satellites is dramatically reduced as they raise orbit to greater distance and orient themselves with the phased array antennas toward Earth and their solar arrays behind the body of the satellite,” a spokesperson for SpaceX said in an email.

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Figure 38: Telescopes at Lowell Observatory in Arizona captured this image of galaxies on May 25, their images marred by the reflected light from more than 25 Starlink satellites as they passed overhead (image credit: Victoria Girgis/Lowell Observatory)

But Barentine and other astronomers aren’t so sure, especially given that this is only the beginning for Starlink. Plus, many other companies — including Amazon, Boeing, OneWeb, Telesat, LeoSat, and even Facebook — are planning other so-called “mega-constellations” for connecting the masses online.

“There are billions of people around the world who lack access to broadband internet,” a spokesperson for Amazon’s Project Kuiper said in an email. “Our vision is to provide low-latency, high-speed broadband connectivity to many of these unserved and underserved communities around the world .... Many of our satellite and mission design decisions are, and will continue to be, driven by our goals of ensuring space safety and taking into account concerns about light pollution.”

But there are already 22,000 artificial objects currently in orbit. And as the microlaunch space race kicks into high gear, that number is destined to double. Communications satellites aren’t the only things headed up, either. One group even proposed launching orbiting billboards that would shine ads back down to Earth. And an artist recently launched the “Humanity Star” – a purely artistic light beacon.

“Space is already crowded, and roughly doubling the number of objects in low- and near-Earth orbit will only add to the visual pollution of the night sky,” Barentine says. “Being in a dark place and seeing one satellite fly over every few minutes is one thing. But seeing literally dozens of them at any given time for hours every night is another story entirely.”

Part of the reason this problem stands to get worse, according to astrophysicist Laura Forczyk, is “there is no regulatory body in the United States that directs companies as to the kind of light pollution or the brightness of satellites. This is a fairly new topic and as always the government regulations are behind technology.”

But Forczyk, owner of the space consulting firm Astralytical, also says that changing the night skies isn’t the same thing as losing the night sky — and it’s a little too early to know what the total impact is going to be. After all, the Starlink satellites still haven’t reached their final orbit. “We’re very reactive when it comes to these kinds of things,” she says, but emphasizes miscommunication from both sides.

Whether the problem stands to worsen or not, most experts see the growth of these mega-constellations as inevitable.

“I don’t think we’re going to be able to create political will to stop the satellites because there is so much commercial potential and politicians tend to respond to economics,” says Phil Metzger, a planetary scientist at the University of Central Florida and a former NASA physicist. However, he says future designs of satellites can ensure they’ll cause less interference with on-the-ground astronomy.

“We can change the surface of the spacecraft so it is more absorptive and less reflective or we can even make it more transparent,” Metzger says. “We do have the ability to make electrical conductors completely transparent so we don’t need metal. You could have glass with transparent conductors in the glass ... I think we’ll probably be doing all of these things in the future.”


• January 9, 2020: The aerospace company SpaceX launched 60 of its Starlink broadband Internet satellites into orbit on 6 January 2020 — including one, called DarkSat, that is partially painted black. The probe is testing one strategy to reduce the brightness of satellite ‘megaconstellations’, which scientists fear could interfere with astronomical observations. 90)

Various companies plan to launch thousands of Internet satellites in the coming years; SpaceX, of Hawthorne, California, aims to launch 24 batches of Starlinks this year. By the mid-2020s, thousands to tens of thousands of new satellites could be soaring overhead. Bright streaks caused by light reflecting off them could degrade astronomical images.

“I was complaining to my wife that I can’t sleep very well these days because of this,” says Tony Tyson, a physicist at the University of California, Davis, and chief scientist of the Vera C. Rubin Observatory, a major US telescope under construction in Chile. (It was renamed this week from the Large Synoptic Survey Telescope to honor the late Rubin, who discovered evidence for the existence of dark matter.)

Astronomers discussed the potential impacts of the satellites on various telescopes, and what could be done about them, on 8 January at a meeting of the American Astronomical Society in Honolulu, Hawaii. “2020 is the window to figure out what makes a difference in reducing the impact,” says Jeffrey Hall, director of Lowell Observatory in Flagstaff, Arizona, and chair of the society’s committee on light pollution.

“SpaceX is absolutely committed to finding a way forward so our Starlink project doesn’t impede the value of the research you all are undertaking,” Patricia Cooper, SpaceX’s vice-president for satellite government affairs, told a session at the astronomy meeting.

Star light, star bright: Three batches of Starlinks have been launched, for a total of about 180 satellites so far. They are most obvious in the night sky immediately after launch, before they boost their orbits to higher altitudes where they are farther away and appear dimmer. It’s not yet clear how significant a problem Starlinks will be for astronomy; scientists have complained about trails in their images since the first launch, but if the company ultimately moves to paint most of the Starlinks black, the impact could be substantially reduced.

Many astronomers panicked in June, soon after SpaceX launched the first batch of 60 Starlinks and telescopes began photographing their trails. Their brightness came as a surprise, says Patrick Seitzer, an astronomer at the University of Michigan in Ann Arbor. “The new megaconstellations coming online have the potential to be brighter than 99% of everything else in Earth orbit, and that’s where the concern comes from,” he says.

Several factors contribute to their puzzling brightness, astronomers reported at the meeting. SpaceX says the position of the solar panels might have something to do with it: at lower elevations, before the orbit boost, the satellites’ panels are positioned like an open book to reduce drag. That temporary orientation could make them reflect more sunlight. The speed at which a satellite moves across a telescope’s field of view is also important — the slower it moves, the more brightness accumulates per pixel of imagery.

There are no regulations that control how bright or dim a satellite needs to be, notes Ralph Gaume, director of the astronomical-sciences division of the US National Science Foundation in Alexandria, Virginia.

Twilight zone: Calculations suggest the Starlink trails will interfere with astronomy most significantly during the hours surrounding twilight and dawn. That’s a particular problem for observations that need to be made during twilight, such as searches for some near-Earth asteroids. And on short summer nights, the satellite trails could be visible all night long.

The Rubin Observatory is particularly vulnerable because it will scan huge amounts of the sky very frequently. When it begins operating in 2022, it will photograph the entire night sky every three days, for ten years.

Tyson’s team is working on possible software fixes for the anticipated satellite trails, such as ways to electronically erase trails and other glitches they induce in astronomical images. But “we’re still left with all the complexity of having all these things removed and all these systematic errors”, Tyson says.

If telescope operators know precisely where each satellite will appear and at what time, they can swivel the telescope to point at a different part of the sky that does not have a satellite in it, says Tyson. That’s feasible if there are 1,000 satellites, but not if there are tens of thousands, because the telescope loses so much time maneuvering that “it’s hopeless”, he says.

That leaves darkening as a leading option. With DarkSat, SpaceX engineers painted surfaces on the satellite that scatter light or reflect light diffusely, says Cooper. That could make them faint enough to be invisible to anyone looking up at a typical night sky — but almost certainly still visible to most astronomical research telescopes.

“It’s still going to be very much a part of astronomers’ lives,” says Jonathan McDowell, an astronomer at the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts. “Just not a part of everyone’s lives.”



1) Matt Williams, ”SpaceX’s Starlink Constellation Construction Begins. 2,200 Satellites Will go up Over the Next 5 years,” Universe Today, 16 April 2019, URL: https://www.universetoday.com/141980/
spacexs-starlink-constellation-construction-begins-2200-satellites-will-go-up-over-the-next-5-years/

2) https://en.wikipedia.org/wiki/Starlink_(satellite_constellation)

3) Elon Musk, ”Starlink,” August 20, 2019, https://www.starlink.com/

4) Jason Rainbow, ”Starlink’s head of India resigns as SpaceX refunds preorders,” SpaceNews, 4 January 2021, URL: https://spacenews.com/starlinks-head-of-india-resigns-as-spacex-refunds-preorders/

5) Jason Rainbow, ”India orders halt on Starlink presales until it gives regulatory approval,” Space News, 29 November 2021, URL: https://spacenews.com/
india-orders-halt-on-starlink-presales-until-it-gives-regulatory-approval/

6) Jason Rainbow, ”All future Starlink satellites will have laser crosslinks,” SpaceNews, 26 August 2021, URL: https://spacenews.com/all-future-starlink-satellites-will-have-laser-crosslinks/

7) Jason Rainbow, ”Viasat wants FCC to review Starlink’s government funding,” SpaceNews, 1 June 2021, URL: https://spacenews.com/viasat-wants-fcc-to-review-starlinks-government-funding/

8) Jeff Foust, ”FCC approves Starlink license modification,” SpaceNews, 27 April 2021, URL: https://spacenews.com/fcc-approves-starlink-license-modification/

9) Jeff Foust, ”SpaceX adds to latest funding round,” SpaceNews, 15 April 2021, URL: https://spacenews.com/spacex-adds-to-latest-funding-round/

10) J. D. Harrington, ”NASA, SpaceX Sign Joint Spaceflight Safety Agreement,” NASA Commercial Space, Press Release 21-011, 18 March 2021, URL: https://www.nasa.gov
/press-release/nasa-spacex-sign-joint-spaceflight-safety-agreement

11) ”SpaceX launches public beta test of Starlink Internet service,” Space Daily, 27 October 2020, URL: https://www.spacedaily.com/reports/
SpaceX_launches_public_beta_test_of_Starlink_Internet_service_999.html

12) ”SpaceX, Microsoft partner in global satellite Internet project,” Space Daily, 21 October 2020, URL: https://www.spacedaily.com/reports/
SpaceX_Microsoft_partner_in_global_satellite_Internet_project_999.html

13) ”FCC Authorizes SpaceX To Deploy A Million Antennas For Starlink Satellites,” Satnews Daily, 23 March 2020, URL: http://www.satnews.com/story.php?number=280640621

14) Stephen Clark, ”SpaceX’s brisk Starlink launch cadence to continue next week,” Spaceflight Now, 14 January 2020, URL: https://spaceflightnow.com/2020/01/14/
spacexs-brisk-starlink-launch-cadence-to-continue-next-week/

15) Jeff Foust, ”SpaceX, astronomers working to address brightness of Starlink satellites,” Space News, 8 January 2020, URL: https://spacenews.com/
spacex-astronomers-working-to-address-brightness-of-starlink-satellites/

16) ”SpaceX seeking many more satellites for space-based internet grid,” Space Daily, 16 October 2019, URL: http://www.spacedaily.com/reports/
SpaceX_seeking_many_more_satellites_for_space-based_internet_grid_999.html

17) Eric Ralph, ”SpaceX CEO Elon Musk reveals radical Starlink redesign for 60-satellite launch,” Tesla Rati, 11 May 2019, URL: https://www.teslarati.com/spacex-starlink-satellites-tease-revolutionary-design/

18) Stephen Clark, ”FCC approves SpaceX’s plan to operate Starlink satellites at lower altitude,” Spaceflight Now, 30 April 2019, URL: https://spaceflightnow.com/2019/04/30/
fcc-approves-spacexs-plan-to-operate-starlink-satellites-at-lower-altitude/

19) Eric Ralph, ”SpaceX’s first dedicated Starlink launch announced as mass production begins,” Tesla Rati, 8 April 2019, URL: https://www.teslarati.com/spacex-starlink-first-launch-date/

20) ”SpaceX gets nod to put 12,000 satellites in orbit,” Phys.org, 16 November 2018, URL: https://phys.org/news/2018-11-spacex-satellites-orbit.html

21) ”SpaceX Receives FCC's Stamp of Approval to Launch 4,425 Broadband Satellites,” Satnews Daily, 2 April 2018, URL: http://www.satnews.com/story.php?number=1759391214

22) Jon Brodkin, ”FCC approves SpaceX plan to launch 4,425 broadband satellites,” ars Technica, 30 March 2018, URL: https://arstechnica.com/information-technology/2018/03/
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23) ”SpaceX launches Falcon 9 with PAZ, Starlink demo and new fairing,” NASA Spaceflight.com, 22 February 2018, URL: https://www.nasaspaceflight.com/
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24) Jeff Foust, ”SpaceX passes 2,000 Starlink satellites launched,” SpaceNews, 18 January 2022, URL: https://spacenews.com/spacex-passes-2000-starlink-satellites-launched/

25) Jeff Foust, ”SpaceX kicks off 2022 with Starlink launch,” SpaceNews, 6 January 2022, URL: https://spacenews.com/spacex-kicks-off-2022-with-starlink-launch/

26) Jeff Foust, ”Falcon 9 sets reuse milestone with Starlink launch,” SpaceNews, 18 December 2021, URL: https://spacenews.com/falcon-9-sets-reuse-milestone-with-starlink-launch/

27) Jason Rainbow, ”SpaceX breaks annual launch record as it deploys 48 more Starlink satellites,” SpaceNews, 02 December 2021, URL: https://spacenews.com/
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28) Stephen Clark, ”SpaceX launch starts deployment of new Starlink orbital shell,” Spaceflight Now, 13 November 2021, URL: https://spaceflightnow.com/2021/11/13/
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29) Jeff Foust, ”SpaceX launches first dedicated polar Starlink mission,” SpaceNews, 14 September 2021, URL: https://spacenews.com/spacex-launches-first-dedicated-polar-starlink-mission/

30) Stephen Clark, ”New version of SpaceX’s Starlink internet satellites to begin launching Monday,” Spaceflight Now, 13 September 2021, URL: https://spaceflightnow.com/2021/09/
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31) Jeff Foust, ”SpaceX sets Falcon 9 fairing reuse mark with Starlink launch,” SpaceNews, 26 May 2021, URL: https://spacenews.com/spacex-sets-falcon-9-fairing-reuse-mark-with-starlink-launch/

32) ”Recent Launch Starlink Mission,” SpaceX, 15 May 2021, URL: https://www.spacex.com/launches/

33) Jeff Foust, ”SpaceX launches Starlink satellites and rideshare payloads,” SpaceNews, 15 May 2021, URL: https://spacenews.com/spacex-launches-starlink-satellites-and-rideshare-payloads/

34) ”Recent Launch Starlink Mission,” SpaceX, 9 May 2021, URL: https://www.spacex.com/launches/

35) Jeff Foust, ”SpaceX sets booster reuse milestone on Starlink launch,” SpaceNews, 9 May 2021, URL: https://spacenews.com/spacex-sets-booster-reuse-milestone-on-starlink-launch/

36) Jeff Foust, ”SpaceX continues Starlink deployment with latest launch,” SpaceNews, 4 May 2021, URL: https://spacenews.com/spacex-continues-starlink-deployment-with-latest-launch/

37) Jeff Foust, ”SpaceX launches Starlink satellites,” SpaceNews, 29 April 2021, URL: https://spacenews.com/spacex-launches-starlink-satellites/

38) Jeff Foust, ”SpaceX launches another set of Starlink satellites as it nears global coverage,” SpaceNews, 7 April 2021, URL: https://spacenews.com/
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39) Jeff Foust, ”SpaceX marks anniversary of first launch with Starlink mission,” SpaceNews, 24 March 2021, URL: https://spacenews.com/spacex-marks-anniversary-of-first-launch-with-starlink-mission/

40) Jeff Foust, ”SpaceX sets new booster reuse mark with Starlink launch,” SpaceNews, 14 March 2021, URL: https://spacenews.com/spacex-sets-new-booster-reuse-mark-with-starlink-launch/

41) Jeff Foust, ”SpaceX launches Starlink satellites and expands international service,” SpaceNews, 11 March 2021, URL: https://spacenews.com/
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42) Stephen Clark, ”SpaceX sticks 75th Falcon rocket landing after launching 60 more Starlink satellites,” Spaceflight Now, 4 March 2021, URL: https://spaceflightnow.com/2021/03/04/
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43) Jeff Foust, ”SpaceX launches Starlink satellites, but booster landing fails,” SpaceNews, 16 February 2021, URL: https://spacenews.com/spacex-launches-starlink-satellites-but-booster-landing-fails/

44) Jeff Foust, ”Falcon 9 launches Starlink satellites,” SpaceNews, 4 February 2021, URL: https://spacenews.com/falcon-9-launches-starlink-satellites/

45) Stephen Clark, ”SpaceX smashes record with launch of 143 small satellites,” Spaceflight Now, 24 January 2021, URL: https://spaceflightnow.com/2021/01/24/
spacex-launches-record-setting-rideshare-mission-with-143-small-satellites/

46) Jeff Foust, ”SpaceX surpasses 1,000-satellite mark in latest Starlink launch,” SpaceNews, 20 January 2021, URL: https://spacenews.com/spacex-surpasses-1000-satellite-mark-in-latest-starlink-launch/

47) Stephen Clark, ”SpaceX sets new rocket reuse records with successful Starlink launch,” Spaceflight Now, 20 January 2021, URL: https://spaceflightnow.com/2021/01/20/
spacex-sets-new-rocket-reuse-records-with-successful-starlink-launch/

48) Stephen Clark, ”SpaceX launches 60 more Starlink satellites on 100th Falcon 9 flight,” Spaceflight Now, 25 November 2020, URL: https://spaceflightnow.com/2020/11/25/
spacex-launches-60-more-starlink-satellites-on-100th-falcon-9-flight/

49) Stephen Clark, ”SpaceX adds another 60 satellites to Starlink network,” Spaceflight Now, 24 October 2020, URL: https://spaceflightnow.com/2020/10/24/spacex-adds-another-60-satellites-to-starlink-network/

50) Stephen Clark, ”SpaceX launches another batch of Starlink satellites,” Spaceflight Now, 18 October 2020, URL: https://spaceflightnow.com/2020/10/18/spacex-launches-another-batch-of-starlink-satellites/

51) Jeff Foust, ”Falcon 9 investigation ongoing as SpaceX continues Starlink launches,” SpaceNews, 18 October 2020, URL: https://spacenews.com/
falcon-9-investigation-ongoing-as-spacex-continues-starlink-launches/

52) Stephen Clark, ”SpaceX breaks cycle of scrubs with successful Falcon 9 launch,” Spaceflight Now, 6 October 2020, URL: https://spaceflightnow.com/2020/10/06/
spacex-breaks-cycle-of-scrubs-with-successful-falcon-9-launch/

53) Stephen Clark, ”SpaceX launches more Starlink satellites, beta testing well underway,” Spaceflight Now, 3 September 2020, URL: https://spaceflightnow.com/2020/09/03/
spacex-launches-more-starlink-satellites-beta-testing-well-underway/

54) Stephen Clark, ”SpaceX adds more satellites to ever-growing Starlink network,” Spaceflight Now, 18 August 2020, URL: https://spaceflightnow.com/2020/08/18/
spacex-adds-more-satellites-to-ever-growing-starlink-network/

55) Stephen Clark, ”SpaceX closes out busy week with launch of more Starlink satellites,” Spaceflight Now, 7 August 2020, URL: https://spaceflightnow.com/2020/08/07/
spacex-closes-out-busy-week-with-launch-of-more-starlink-satellites/

56) ”SpaceX launched 10th Starlink batch,” Space Daily, 07 August 2020, URL: https://www.spacedaily.com/reports/SpaceX_launched_10th_Starlink_batch_999.html

57) Caleb Herny, ”SpaceX launches 58 Starlink satellites, three Planet SkySats on Falcon 9,” SpaceNews, 13 June 2020, URL: https://spacenews.com/
spacex-launches-58-starlink-satellites-three-planet-skysats-on-falcon-9/

58) ”SpaceX sets new mark in rocket reuse 10 years after first Falcon 9 launch,” Spaceflight Now, 4 June 2020, URL: https://spaceflightnow.com/2020/06/04/
spacex-sets-new-mark-in-rocket-reuse-10-years-after-first-falcon-9-launch/

59) ”SpaceX launch boosts Starlink network to 480 satellites,” Space Daily, 4 June 2020, URL: https://www.spacedaily.com/reports/SpaceX_launch_boosts_Starlink_network_to_480_satellites_999.html

60) ”SpaceX Successfully Launches 60 Starlink Satellites but is Unsuccessful with Recovery of First Stage,” Satnews Daily, 18 March 2020, URL: http://www.satnews.com/story.php?number=61076689

61) Stephen Clark, ”Falcon 9 rocket overcomes engine failure to deploy Starlink satellites,” Spaceflight Now, 18 March 2020, URL: https://spaceflightnow.com/2020/03/18/
falcon-9-rocket-overcomes-engine-failure-to-deploy-starlink-satellites/

62) Stephen Clark, ”SpaceX delivers more Starlink satellites to orbit, booster misses drone ship landing,” Spaceflight Now, 17 February 2020, URL: https://spaceflightnow.com/2020/02/17/
spacex-delivers-more-starlink-satellites-to-orbit-booster-misses-drone-ship-landing/

63) Stephen Clark, ”SpaceX boosts 60 more Starlink satellites into orbit after weather delays,” Spaceflight Now, 29 January 2020, URL: https://spaceflightnow.com/2020/01/29/
spacex-boosts-60-more-starlink-satellites-into-orbit-after-weather-delays/

64) Stephen Clark, ”SpaceX launches more Starlink satellites, tests design change for astronomers,” Spaceflight Now, 7 January 2020, URL: https://spaceflightnow.com/2020/01/07/
spacex-launches-more-starlink-satellites-tests-design-change-for-astronomers/

65) Stephen Clark, ”Successful launch continues deployment of SpaceX’s Starlink network,” Spaceflight Now, 11 November 2019, URL: https://spaceflightnow.com/2019/11/11
/successful-launch-continues-deployment-of-spacexs-starlink-network/

66) Chris Gebhardt, ”Falcon 9 launches first Starlink mission – heaviest payload launch by SpaceX to date,” NASA Spaceflight.com, 23 May 2019, URL: https://www.nasaspaceflight.com
/2019/05/first-starlink-mission-heaviest-payload-launch-spacex/

67) ”Sixty Launched ... 11,940 Left to Go ... as SpaceX Successfully Sends Off Their First Batch of Starlink Satellites,” Satnews Daily, 24 May 2019, URL: http://www.satnews.com/story.php?number=179808724

68) ”SpaceX launches first satellites of its internet network,” Space Daily, 24 May 2019, URL: http://www.spacedaily.com/reports/SpaceX_launches_first_satellites_of_its_internet_network_999.html .

69) ”Palomar Survey Instrument Analyzes Impact of Starlink Satellites,” Caltech News, 17 January 2022, URL: https://www.caltech.edu/about/news/
palomar-survey-instrument-analyzes-impact-of-starlink-satellites

70) Przemek Mróz, Angel Otarola, Thomas A. Prince, Richard Dekany, Dmitry A. Duev, Matthew J. Graham, Steven L. Groom, Frank J. Masci, and Michael S. Medford,”Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations,” The Astrophysical Journal Letters, Volume 924, Number 2, Published: 14 January 2022, https://doi.org/10.3847/2041-8213/ac470a, URL: https://iopscience.iop.org/article/10.3847/2041-8213/ac470a/pdf

71) Jeff Foust, ”SpaceX emphasizes coordination with other satellite operators,” SpaceNews, 16 September 2021, URL: https://spacenews.com/spacex-emphasizes-coordination-with-other-satellite-operators/

72) Jason Rainbow, ”Starlink teams up with Google for ground infrastructure,” SpaceNews, 13 May 2021, URL: https://spacenews.com/starlink-teams-up-with-google-for-ground-infrastructure/

73) Jason Rainbow, ”SpaceX takes aim at satellite mobility operators with Starlink expansion,” SpaceNews, 8 March 2021, URL: https://spacenews.com/
spacex-takes-aim-at-satellite-mobility-operators-with-starlink-expansion/

74) ”French village says 'non' to Elon Musk's space-age internet,” Space Daily, 19 February 2021, URL: https://www.spacedaily.com/reports/
French_village_says_non_to_Elon_Musks_space-age_internet_999.html

75) Michael Sheetz, ”SpaceX says its Starlink satellite internet service now has over 10,000 users,” CNBC, 4 February 2021, URL: https://www.cnbc.com/2021/02/04/
spacex-starlink-satellite-internet-service-has-over-10000-users.html

76) ”Statement on Satellite Constellations,” Press Release, AG (Astronomische Gesellschaft), 18 January 2021, URL: https://idw-online.de/de/news761318

77) Jeff Foust, ”FCC grants permission for polar launch of Starlink satellites,” SpaceNews, 9 January 2021, URL: https://spacenews.com/fcc-grants-permission-for-polar-launch-of-starlink-satellites/

78) ”Dark coating can reduce satellite reflectivity,” Science Daily, 8 December 2020, URL: https://www.sciencedaily.com/releases/2020/12/201208090000.htm

79) Takashi Horiuchi, Hidekazu Hanayama, and Masatoshi Ohishi, ”Simultaneous Multicolor Observations of Starlink's Darksat by the Murikabushi Telescope with MITSuME,” The Astrophysical Journal, Volume 905, Number 1, Published: 7 December 2020, https://doi.org/10.3847/1538-4357/abc695

80) ”SpaceX wins $885 million for Starlink broadband service,” Space Daily, 7 December 2020, URL: https://www.spacedaily.com/reports/SpaceX_wins_885_million_for_Starlink_broadband_service_999.html

81) Jeff Foust, ”Report outlines measures to reduce impact of satellite constellations on astronomy,” SpaceNews, 26 August 2020, URL: https://spacenews.com/
report-outlines-measures-to-reduce-impact-of-satellite-constellations-on-astronomy/

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84) Jeff Foust, ”SpaceX to test Starlink “sun visor” to reduce brightness,” SpaceNews, 27 April 2020, URL: https://spacenews.com/spacex-to-test-starlink-sun-visor-to-reduce-brightness/

85) ”Killer asteroid hunt in jeopardy, new study claims,” Space Daily, 19 March 2020, URL: https://www.spacedaily.com/reports/Killer_asteroid_hunt_in_jeopardy_new_study_claims_999.html

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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net)

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Minimize GOES-R Continued


Sensor complement (ABI, SUVI, EXIS, GLM, SEISS, MAG)

The GOES (Geostationary Operational Environmental Satellite) family of satellites has a history of supporting meteorological and climate observations dating back to 1974.

Unlike the GOES-I/M and GOES-N/P series, the 3rd generation GOES-R series spacecraft do not contain a “sounder”. Legacy sounding products are derived based on ABI data through the GS (Ground System). - Instead, a GLM (Geostationary Lightning Mapper) will greatly improve storm hazard identification and increase warning lead-time during both day and night, providing continuous monitoring of lightning activity. In addition, the satellite will contain a similar, but more powerful, suite of solar ultraviolet imaging and space weather monitoring equipment in comparison to previous GOES satellites.

On the GOES-R “family tree” of instruments, there are three general classifications for the instrument payloads:

Nadir-pointing

- Earth-pointed “business end” of GOES

- Highly stable, precision pointed platform

- Dynamically isolated from the rest of the spacecraft

- Supports operation of the ABI and GLM

Solar-pointing

- Utilizes a Sun Pointing Platform (SPP) housed on the solar array yoke

- The SPP provides a stable platform that tracks the seasonal and daily movement of the sun relative to the spacecraft

- Supports operation of the SUVI and EXIS

In-Situ

- SEISS and the Magnetometer provide localized measurements of particles and fields in geosynchronous orbit

- Accommodation challenges include: a) a wide variance in Field-of-View (FOV) requirements for the SEISS sensors, and, b) a boom to provide relative magnetic isolation for the Magnetometer.

Instrument

Instrument provider

Objectives and improvement

ABI (Advanced Baseline Imager)

Harris (formerly ITT Corporation, Ft Wayne, IN)

Hurricane track & intensity forecast

SUVI (Solar Ultra Violet Imager)

Lockheed-Martin Advanced Technology Corp (LM ATC), Palo Alto, CA

Power blackout forecasts due to solar flares

EXIS (Extreme Ultra Violet and X-ray Irradiance Sensor)

Laboratory for Atmospheric and Space Physics (LASP), Boulder, CO

Solar flare warnings for communications and navigation

GLM (Geostationary Lightning Mapper)

Lockheed-Martin Advanced Technology Corp (LM ATC), Palo Alto, CA

Thunderstorm & tornado warning lead time,
Aviation flight route planning

SEISS (Space Environmental In-Situ Suite)

Assurance Technology Corporation (ATC), Carlisle, MA

Energetic particle forecasts

MAG (Magnetometer)

Procured as part of the spacecraft contract, Lockheed Martin, Newtown, PA

 

Table 2: Overview of the GOES-R sensor complement 77) 78)


ABI (Advanced Baseline Imager):

ABI is the next-generation (3rd) multispectral imager, a 2-axis scanning radiometric imager, intended to begin a new era in US environmental remote sensing with greatly improved capabilities and features (more spectral bands, faster imaging cycles, and higher spatial resolution than the current imager generation of GOES-N to -P). The ABI instrument is a significant advancement over current imager generation.

The overall objectives of ABI are to provide high-resolution imagery and radiometric information of the Earth's surface, the atmosphere and the cloud cover (measurement of the emitted and solar reflected radiance simultaneously in all spectral channels). Data availability, radiometric quality, simultaneous data collection, coverage rates, scan flexibility, and minimizing data loss due to the sun, are prime requirements of the ABI system. 79) 80) 81) 82) 83) 84) 85)

The instrument is providing 16 bands of multispectral data, with two bands in VIS (0.47 µm & 0.64 µm) and 14 bands in IR (0.86 µm to 13.3 µm). The spatial resolution is band-dependent, the IGFOV (Instantaneous Geometric Field of View) ranges from 0.5 km at nadir for broadband visible, 1.0 km for SWIR, and 2.0 km for MWIR and TIR data. The instrument features three “imaging sectors” with a simultaneous observation capability, referred to as: FD (Full Disk), CONUS, and Mesoscale. Full Disk includes the synoptic Earth view from GEO. The CONUS (Contiguous USA) sector covers a target area of 5000 km x 3000 km; the Mesoscale sector covers a nominal region of 1000 km x 1000 km (at nadir projection). 86)

ABI has two imaging modes, namely Mode 3 and Mode 4. Mode 3 imaging can provide 1 FD image, 3 CONUS and 30 Mesoscale images, every 15 minutes. Mode 4 can provide 30 Mesoscale images every 15 minutes as well as a Full Disk every 5 minutes.

The following four requirements of the NWS (National Weather Service) are considered with highest priority: 87)

1) Continuous instrument operation capability including the eclipse phases at the vernal equinoxes of the GEO orbit

2) Simultaneous observation capability for the modes “full-disk” and “CONUS” (Contiguous USA).

3) Improvement of the temporal instrument imagery resolutions.

- Full-disk Earth observation within 15 minutes

- CONUS, or the equivalent of a nadir-viewed rectangle (3000 km x 500 km) every 5 minutes (goal of 1 minute)

- Imagery of minimum size 1000 km x 1000 km (nadir) every 30 seconds

- A capability must exist to observe concurrently the CONUS and full-disk imagery along with all other imaging activities, such as space locks, blackbody calibrations, and star observations

4) Improvement of the spatial resolution of the imagery. The current GOES Imager spatial resolution (1 km in VIS and 4 km in IR) must be doubled for ABI. The intent is to allow for better identification and tracking of cloud and moisture signatures.

The band selection has been optimized to meet all cloud, moisture, and surface observation requirements. The phenomena observed and the various applications are:

• VIS band (0.64 µm): Daytime cloud imaging, snow and ice cover, severe weather onset detection, low-level cloud drift winds, fog, smoke, volcanic ash, flash flood analysis, hurricane analysis, winter storm analysis

• SWIR band (1.6 µm): Daytime cloud/snow/ice discrimination, total cloud cover, aviation weather analysis for icing, smoke from low-burn-rate fires

• MWIR band (3.9 µm): Fog and low-cloud discrimination at night, fire identification, volcanic eruption and ash, daytime reflectivity for snow/ice

• MWIR band (7.0 µm): Middle-tropospheric water vapor tracking, jet stream identification, hurricane track forecasting, mid-latitude storm forecasting, severe weather analysis

• TIR band (11.2 µm): Continuous day/night cloud analysis for many general forecasting applications, precipitation estimates, severe weather analysis and prediction, cloud drift winds, hurricane strength and track analysis, cloud top heights, volcanic ash, winter storms, cloud phase/particle size (in mid-band products)

• TIR band (12.3 µm): Continuous cloud monitoring for numerous applications, low-level moisture, volcanic ash trajectories, cloud particle size (in mid-band products)

• TIR band (13.3 µm): Cloud top height assignments for cloud-drift winds, cloud products for ASOS supplement, tropopause delineation, cloud opacity.

Application spectrum of the five additional bands.

• VIS band (0.47 µm): This band is used for aerosol detection and visibility estimation

• VIS band (0.86 µm): This band provides synergy with AVHRR/3 band 2. The band is used for determining vegetation amount, aerosols and ocean/land studies.

• SWIR band (1.378 µm): This band is similar to a MODIS band. It does not see into the lower troposphere due to water vapor sensitivity, thus it provides excellent daytime sensitivity to very thin cirrus.

• TIR band (8.5 µm): This band permits the detection of volcanic cloud with sulfuric acid aerosols, thin cirrus in conjunction with 11 µm band and determination of cloud microphysical properties with the 11.2 µm and 12.3 µm bands. This includes a more accurate delineation of ice from water clouds during day or night

• TIR band (10.3 µm): The band permits the determination of microphysical properties of clouds with the 11.2 and 12.3 µm bands. This includes a more accurate determination of cloud particle size during the day or night.

In May 2001, NASA awarded formulation phase contracts to three companies: ITT Industries' Aerospace/Communications Division, Fort Wayne, IN; BATC (Ball Aerospace & Technologies Corp.) of Boulder, CO; and Raytheon SBRS (Santa Barbara Remote Sensing), Goleta, CA. Under terms of the contracts, each company developed detailed engineering plans for the future instrument. In Sept. 2004, NASA on behalf of NOAA has selected ITT Industries to design and develop the ABI instrument.

Note: In 2011, the ITT Corporation split into three companies: ITT, Xylem, and ITT Exelis. The ABI instrument was developed at ITT Exelis in Fort Wayne, IN.

Requirement

2nd generation GOES Imager

ABI of GOES-R

No of spectral bands

5

16

Data rate

2.6 Mbit/s

75 Mbit/s

Spatial resolution:
0.64 µm (VIS)
Other VNIR bands < 2 µm
Bands > 2 µm


~ 1 km
N/A
4 km


0.5 km
1.0 km
2.0 km

Time for full disk scan

26 minutes

15 or 5 minutes

Absolute INR (Image Navigation and Registration)

54 µrad

21 µrad (EW), 21 µrad (NS)

Registration between images (15 minutes)

36 µrad

16 µrad (0.5, 1.0 km)
21 µrad (2.0 km)

Cross-channel image co-registration

50 µrad (VIS to IR)
28 µrad (IR to IR)

6.3 µrad (0.5, 1.0 to2 km)
5.2 µrad (0.5, 1.0 to1 km)

VIS (reflective bands) calibration

No

Yes

Table 3: Key performance parameter comparison of 2nd and 3rd generation imagers (Ref. 91)

Requirement

Threshold

Spatial resolution

VIS (0.64 µm)
Other VNIR bands
All other bands (> 2 µm)

0.5 km (14 µrad IGFOV)
1 km (28 µrad IGFOV)
2 km (56 µrad IGFOV)

Spatial coverage

Full disk
CONUS (3000 km x 5000 km)
Mesoscale (1000 km x 1000 km)

4 per hour (every 15 min one image)
12 per hour
Every 30 s, may impact CONUS or full disk

Operation during eclipse

Yes

Data timelines (when scanning is complete)

CONUS: <1 minute Full disk: <6 minutes

Simultaneity

Within 5 s for all bands at any FOV Within 30 s for any adjacent (n/S) pixels Within 15 s for any adjacent (E/W) pixels

Number of spectral bands

8 (threshold), 12 (goal) Star sensing capability required

Spectral bands (µm), 8 bands at minimum

0.64±0.05, 1.61±0.03; 3.9±0.1; 6.15±0.45; 7.0±0.2; 10.7±0.5; 12.0±0.5; 13.3±0.3

Spectral bands (µm), goal of four additional bands

0.86±0.05, 1.375±0.015, 8.5±0.2, 10.35±0.25

Navigation

<1.0 km (28 µrad)

Registration within frame

<1 km (28 µrad)

Line-to-line registration

<25 km (7 µrad)

Registration image to image, VIS, IR

<0.75 km (<21 µrad), <1.0 km (<28 µrad)

Band-to-band co-registration, VIS-IR, IR-IR

<1.0 km (<28 µrad), <15% of FOV

On-orbit calibration

VIS, IR (goal)

Pre-launch to ±5%, On-board to ±3% 0.2 K repeatability, 1.0 K absolute accuracy

IR band linearity

±1%

Total instrument mass, power, volume

<125 kg, <256 W, <0.8 m3

Lifetime

Ground storage On-orbit storage Mean mission life Design life

2 years 2 years 8.4 Years 10 years

Table 4: Requirements overview for the ABI instrument

Band No

FWHM wavelength range (µm)

Center wavelength (µm)

Nominal IGFOV (km)

Prime measurement objectives and use of sample data

Instrument heritage

1

0.45-0.49

0.47

1

Daytime aerosol over land, coastal water mapping

MODIS

2

0.59-0.69

0.64

0.5

Daytime clouds fog, insolation, winds

Current GOES imager/sounder

3

0.846-0.885

0.885

1

Daytime vegetation/burn scar and aerosols over water, winds

VIIRS, spectrally modified AVHRR/3

4

1.371-1.386

1.378

2

Daytime cirrus cloud

VIIRS, MODIS

5

1.58-1.64

1.61

1

Daytime cloud-top phase and particle size, snow

VIIRS, spectrally modified AVHRR/3

6

2.225-2.275

2.25

2

Daytime land/cloud properties, particle size, vegetation, snow

VIIRS, similar to MODIS

7

3.80-4.00

3.90

2

Surface and cloud, fog at night, fire, winds

Current GOES imager

8

5.77-6.6

6.19

2

High-level atmospheric water vapor, winds, rainfall

Current GOES imager

9

6.75-7.15

6.95

2

Mid-level atmospheric water vapor, winds, rainfall

Current GOES imager

10

7.24-7.44

7.34

2

Lower-level water vapor, winds and SO2

Spectrally modified current sounder

11

8.3-8.7

8.5

2

Total water for stability, cloud phase, dust, SO2, rainfall

MAS (MODIS Airborne Simulator)

12

9.42-9.8

9.61

2

Total ozone, turbulence, winds

Spectrally modified current sounder

13

10.1-10.6

10.35

2

Surface and cloud

MAS

14

10.8-11.6

11.2

2

Imagery, SST, clouds, rainfall

Current GOES sounder

15

11.8-12.8

12.3

2

Total water, ash, SST

Current GOES sounder

16

13.0-13.6

13.3

2

Air temperature, cloud heights and amounts

Current GOES sounder/GOES-12 + imager

Table 5: Overview of the spectral band allocation for the ABI instrument

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Figure 40: Schematic view of the ABI instrument (image credit: ITT) 88)

Support mode

FOV (Field of View)

0.5 km resolution

1 km resolution

2 km resolution

Full disk diameter

17.76º

22141 pixels

11070 pixels

5535 pixels

CONUS height

4.8129º

6000 pixels

3000 pixels

1500 pixels

CONUS width

8.0215º

10000 pixels

5000 pixels

2500 pixels

Meso height/width

1.6043º

2000 pixels

1000 pixels

500 pixels

Table 6: Approximate number of ABI pixels for various support modes (Ref. 81)

ABI cryocooler: NGAS (Northrop Grumman Aerospace Systems) has developed and tested a two-stage pulse tube (PT) cooler of JAMI (Japanese Advanced Meteorological Imager) heritage flown on the Japanese MTSAT-1R mission (launch Feb. 26, 2005). The ABI cooler system incorporates an integral HEC (High Efficiency Cryocooler) pulse tube cooler and a remote coaxial cold head. The two-stage cold head was designed to provide large cooling power at 53 K and 183 K, simultaneously. 89) 90)

NGAS evolved the design from on-orbit pulse tube cooler designs that the company has built and launched over the past decade. No failures have been experienced on any of these coolers on the seven satellite systems launched to date; some of these coolers are now approaching 11 years of failure-free operation.

The PFM (Proto-Flight Module) cooler system for ABI consists of a linear pulse tube cold head that is integral to the compressor assembly and a coaxial remote pulse tube cold head; the two cold head design affords a means of cooling a detector array to its operational temperature while remotely cooling optical elements (to reduce effects of radiation on imager performance) and a second detector array. The two cooler systems are referred to as TDU (Thermo-Dynamic Units); in addition, there are two associated CCE (Cooler Control Electronics) units that provide power and control functions to the TDUs.

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Figure 41: Illustration of the PFM TDU (image credit: NGAS)

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Figure 42: The CCE (Cooler Control Electronics) device (image credit: NGAS)

The TDU has a size of 370 mm x 350 mm x 130 mm (width x depth x height) with a mass of 5.5 kg. The size of CCE is 235 mm x 205 mm x 85 mm (width x depth x height) with a mass of 3.8 kg. The requirements on the cooler call for: 2.27 W of cooling at 53.0 K and 5.14 W of cooling at 183.1 K.

INR (Image Navigation and Registration):

Since ABI uses multiple focal plane modules for the channels of detector grids, the channel-to-channel registration can present a challenge if relative motion occurs from one focal plane module to another. This is especially the case given the ABI channel-to-channel registration requirements are at sub-pixel levels. 91)

INR on the current GOES program preceding GOES-R (2nd generation) employs image motion compensation (IMC) on board the spacecraft/imager to assure the image line of sight is accurately pointed to desired locations on the Earth scene. Once the image data are processed on ground, a series of manual landmarking registration techniques are applied to the image to improve the location of features in the image relative to known landmarks within the scene. The landmarking updates are also used to update the IMC coefficients for the following day’s operation.

ABI INR relies on a ground-based real time image navigation process to achieve increased knowledge accuracy using precise encoder readings and star image data. During an Earth scene collection, the instrument uses attitude information provided by the spacecraft to compensate for the spacecraft’s attitude motion; however the precise image navigation and registration is achieved through ground processing to determine where the image data were actually collected relative to the fixed grid scene.

ABI collects scene image data as well as star measurements to maintain line of sight knowledge. Image navigation uses ground processing algorithms to decompress, calibrate and navigate the image samples from the focal plane module detectors. The navigated samples are then re-sampled using a 4 x 4 sample kernel to form the 14 µrad pixels which form the Earth disk image.

Image collection performance for the ABI is governed by the attitude knowledge provided by the spacecraft, the control accuracy of the pointing servo control for the instrument and the diurnal line of sight variation. Per the GOES-R GIRD (General Interface Requirements Document), the spacecraft provides the following information to allow the instrument to collect scenes:

- Quaternion: ~ 100 µrad uncertainty (sampled at 1 Hz)

- Attitude rate measurements: < 20 µrad drift over 15 minutes (sampled at 100 Hz)

- Spacecraft position: 35 m in-track, 35 m cross-track and 70 m radial over 15 minutes (sampled at 1 Hz)

- Spacecraft velocity: < 6 cm/sec uncertainty per axis (sampled at 1 Hz).

Reference frame definitions: Image navigation and registration uses data and measurements defined in a number of different coordinate frames. The primary reference frame is J2000 which is the inertial frame in which the star catalog coordinates are defined. Star coordinates are updated to a True of date frame and then to an EFC (Earth Centered Fixed) coordinate frame with the X-axis oriented to the station longitude for GOES. Orbit determination and body axis attitude reporting are done relative to a frame defined by the velocity vector and nadir referred to as to ORF (Orbit Reference Frame). The ABI instrument alignment is referenced to a frame relative to the spacecraft body axis frame referred to as the IMF (Instrument Mounting Frame) and line of sight is referenced to a frame relative to the instrument mounting frame. ABI commanding and image navigation is defined relative to the Fixed Grid Frame defined as an ideal Geosynchronous orbit located at the GOES east or GOES west station longitude.

Requirement

EW (3σ)

NS (3σ)

Navigation (Absolute location of any pixel)

±21 µrad

±21 µrad

Frame-to-Frame Registration: 0.47, 0.64, 0.865, and 1.61 µm channels.
Frame-to-frame registration error is the difference in navigation error for any given pixel in two consecutive images within the same channel.

±16 µrad

±16 µrad

Frame-to-Frame Registration: 1.378, 2.25, 3.9, 6.185, 6.95, 7.34, 8.5, 9.61, 10.35, 11.2, 12.3, and 13.3 µm channels

±21 µrad

±21 µrad

Within Frame Registration: Angular separation of any two pixels in a Frame

±21 µrad

±21 µrad

Swath-to-Swath Registration

± 5.2 µrad

± 5.2 µrad

Channel-to-Channel Registration: 2 km to 2 km, 1 km, 0.5 km (wavelength/detector dependent)

± 6.3 µrad

± 6.3 µrad

Channel-to-Channel Registration: 1 km to 1 km, 0.5 km (wavelength/detector dependent)

± 5.2 µrad

± 5.2 µrad

Table 7: GOES-R INR metric performance requirements

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Figure 43: Reference frames used in the INR process (image credit: ITT)

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Figure 44: ABI image navigation and registration process (image credit: ITT)

ABI's advanced design will provide users with twice the spatial resolution, six times the coverage rate, and more than three times the number of spectral channels compared to the current GOES Imagers. The operations flexibility permits consistent collection of Earth scenes, eliminating time gaps in coverage by the need to prioritize some areas over others. These improvements will allow tomorrow’s meteorologists and climatologists to significantly improve the accuracy of their products, both in forecasting and nowcasting. 92)

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Figure 45: Photo of the ABI instrument (image credit: ITT) 93)


ABI Images: 94)

The ABI (Advanced Baseline Imager) will provide a paradigm shift in the United States’ geostationary weather imaging over the current GOES Imager:

• More than three times the channels (16 vs. 5)

• Four times the number of pixels (0.5, 1, and 2 km vs. 1 and 4 km)

• More than five times the temporal resolution (5 minute Full Disk vs. 26 minutes)

However, its most unique feature is its operational flexibility - one instrument seamlessly interleaving the collection of multiple images of different sizes, locations, and repetition intervals plus the ability to collect scan data in any direction. This enables the high temporal resolution imaging of severe weather events (hurricanes, typhoons, tornados, etc.) or vicarious calibration observations (e.g., moon, deserts, etc.) without interrupting Full Earth Disk and regional image collections.

ABI’s ability to interleave image collections ensures all regions will be imaged far more frequently than with the current imagers. Hence, ABI’s image collections can be simplified to just three standard images:

• Full Disk

• CONUS Continental United States (`lower 48 states')

• Mesoscale (aka meso)

The sizes of these images are provided in Table 8 and their locations are provided in Table 9. Note that all images are defined in radians. Degrees and kilometer equivalents are provided for convenience. (The size in kilometers is based on the conversion factor of 28 µrad/km.) This information is also provided visually in Figure 46, Figure 47, and Figure 48.

Mesoscale images can be located anywhere within the ABI FOR (Field of Regard). In Figure 6 some possible locations are shown (nadir, tornado in the mid-West, hurricane off the coast of Florida, lunar observation).

ABI Image

Shape

Size (degrees)

Size (radians)

km at nadir

Height

Width

Height

Width

Height

Width

Full Disk

Circle

17.4º diameter

0.303687

N/A

CONUS

Rectangle

4.81º

8.02º

0.084

0.140

3000 km

5000 km

Mesoscale

Square

1.60º

1.60º

0.028

0.028

1000 km

1000 km

Table 8: Sizes of the ABI operational images

ABI Image

Satellite Longitude

Center Offset

Center Location

NS (rad)

EW (rad)

Latitude

Longitude

Full Disk

all

nadir

CONUS GOES-R East

75º W

0.086240

-0.031360

30.083º N

87.097º W

CONUS GOES-R West

137º W

0.086240

0.000000

29.967º N

137.000º W

CONUS GOES-R Central

89.5º W

0.084560

-0.005040

29.294º N

91.406º W

Mesoscale (meso)

all

Within 10º of nadir

Table 9: Locations of the ABI operational images

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Figure 46: ABI Full Disk Images for GOES-R West and East (image credit: Harris Corp.)

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Figure 47: ABI CONUS Images for GOES-R West, Central, and East (image credit: Harris Corp.)

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Figure 48: ABI Mesoscale Images – Representative Locations Shown (image credit: Harris Corp.)

Note that the size of a “Full Disk” image varies by payload:

• GOES-R ABI: 17.4 degree diameter circle (Earth only)

• Himawari AHI: 17.8 degree diameter circle (Earth plus limb and space)

• GEO-KOMPSAT-2A AMI: 17.8 degree diameter circle (Earth plus limb and space)

• MTG FCI: 17.7 degree diameter circle (Earth plus limb)

ABI Timelines:

An ABI scene definition defines the scan patterns needed to collect a desired image. Each scene is a collection of individual swaths. The ABI timeline defines when to collect each swath of each scene.

ABI currently has two operational timelines, created by Harris based on our customer’s requirements:

1) Continuous Full Disk (CFD)

• Timeline: ABI Scan Mode 4

• Images collected:

- 5-minute Full Disk images

2) Flex Mode (aka Storm Watch)

• Timeline: ABI Scan Mode 3

• Images collected (seamlessly interleaved):

- 30-second Mesoscale

- 5-minute CONUS

- 15-minute Full Disk

All operational ABI timelines include observations for radiometric and geometric calibration. All timelines start with a space look and blackbody observation and collect a space look at least every 30 seconds for radiometric calibration. Hence, blackbody observations occur at least every 15 minutes, far more frequently than required to meet the IR calibration accuracy requirements. All operational ABI timelines include visible stars observations on average at least every 100 s and IR stars observations on average at least every 300 s for navigation (i.e., geometric calibration).

Because the gain of the visible and near IR (VNIR) channels change far slower than the MWIR and LWIR channels, observations of the solar calibration target are required far less frequently than blackbody observations. Hence, observations of the solar calibration target are not included in the operational timelines. They are collected using a custom timeline, which is run approximately every two weeks at the start of the operational mission and less frequently later in the mission.

Custom scenes and timelines can be defined and uploaded at any time during the mission life. One such custom timeline has already been defined by Harris and is loaded in the ABI EEPROM (Electrically Erasable Programmable Read-Only Memory):

Super Flex Mode

• Timeline: ABI Scan Mode 6

• Images collected:

- 30-second Mesoscale

- 5-minute CONUS

- 10-minute Full Disk

This is not currently an operational timeline. However, it is expected to become an operational timeline once the GOES-R ground system parameters are updated to include processing and distribution of Full Disk image products on 10-minute intervals (in addition to the current 5 and 15 minute intervals) and the users’ systems have been updated to receive Full Disk products on 10-minute intervals.

ABI Images

Timeline Repetition Intervals (minutes)

Scan Mode 4 (Continuous Full Disk)

Scan Mode 3 (Flex Mode)

Scan Mode 6 (Super Flex Mode)

Full Disk

5

15

10

CONUS

5

5

Mesoscale #1

0.5

1

0.5

1

Mesoscale #2

1

1

Table 10: Images collected by the baseline ABI timelines

In the Scan Mode 3 and 6 timelines, a mesoscale image is collected every 30 seconds. However, ABI provides the user the option to define two different mesoscale image locations (Meso 1 and Meso 2) and collect both of them at 1 minute intervals. This means two severe weather events can be monitored simultaneously. — This is not an operational requirement for ABI. It is an enhancement provided by Harris to ensure our customers have the flexibility to address more than just the baseline scenarios.

ABI’s interleaved image collection approach can be easily seen in the “time-timeiii” diagram for the Scan Mode 3 Timeline provided in Figure 49. This diagram takes the 900 second timeline, breaks it into 30-second intervals and stacks them from top to bottom in sequential order. It is “read” chronologically just like reading a paragraph – left to right from the top to the bottom.

• This diagram shows how the mesoscale images are collected at precisely 30 second intervals and the CONUS images are at precisely 5-minute (300-second) intervals.

- When two mesoscale images are defined, their collections alternate, so there is no change in the timing of the timeline execution.

• The start of each Full Disk swath collection is staggered so the time interval across the swath boundary is precisely 30 seconds for all points.

• Nadir stares are added in time periods where there are no operational images to collect (no data is downlinked during nadir stares).

• Note that every Full Disk swath includes an autonomous space look observation. In time intervals where no Full Disk swaths are collected, explicit space look observations are performed.

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Figure 49: “Time-Time” diagram for ABI Scan Mode 3 timeline (image credit: Harris Corp.)


SUVI (Solar Ultra Violet Imager):

SUVI is a sun-pointed instrument, a normal-incidence multilayer-coated telescope, with the overall objective to provide information on solar activity and the effects of the sun on the Earth and the near-earth space environment. The SUVI provides narrowband imaging in the soft X-ray to EUV wavelength range (9.4 nm - 30.4 nm) at a high cadence (up to 3 images/s). SUVI will monitor the entire dynamic range of solar X-ray features including coronal holes and solar flares and will provide data regarding the rapidly changing conditions is the Sun’s atmosphere. These data are used for geomagnetic storm forecasts and for observations of solar energetic particle events related to flares. SUVI will continue the mission performed by the current GOES-M/P series SXI (Solar X-ray Imager) instrument. 95) 96)

In Sept. 2007, NASA awarded to LM ATC a contract to build the SUVI instrument. 97) In December 2009, SUVI has met all the requirements of a CDR (Critical Design Review). 98)

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Figure 50: Photo of the SUVI instrument assembly (image credit: LM ATC)

Status of SUVI:

- In November 2012, the Lockheed Martin team met the requirements of a Pre-Environmental Review (PER). The Lockheed Martin SUVI instrument has met all requirements of the PER.

- The next major review will be the Pre-Ship or Pre-Storage Review in May 2013. The team is on plan for instrument delivery in Oct. 2013 to the Lockheed Martin Space Systems facility in Denver for integration with the spacecraft. 99)

- Dec. 2013: A Lockheed Martin team has completed the SUVI (Solar Ultraviolet Imager) instrument. The instrument will be delivered in 2014 for integration with the first GOES-R spacecraft at Lockheed Martin's Space Systems facility in Denver. 100)

- April 2014: Lockheed Martin has delivered the SUVI instrument for GOES-R integration. 101)


EXIS (Extreme Ultra Violet and X-ray Irradiance Sensor):

EXIS contains two full disk instruments, the EUVS (EUV Sensor) and the XRS (X-Ray Sensor). The EUVS is a full disk detector measuring EUV flux in the 5 - 127 nm range as compared to the 10 – 126 nm range for GOES-N. EUV radiation plays a key role in heating the thermosphere and creating the ionosphere. The EXIS instrument has been designed and developed at LASP (Laboratory for Atmospheric and Space Physics) at the University of Colorado, Boulder, CO (PI: Frank Eparvier). 102) 103)

NOAA requires the realtime monitoring of the solar irradiance variability that controls the variability of the terrestrial upper atmosphere (ionosphere and thermosphere). 104)

• The EUVS device monitors solar variations that directly affect satellite drag/tracking and ionospheric changes, which impact communications and navigation operations. This information is critical to understanding the outer layers of the Earth’s atmosphere.

- Through a combination of measurements and modeling, EUVS determines the solar EUV spectral irradiance in the 5 -127 nm range.

- Pre-GOES-R EUVS: Transmission grating spectrographs covering five broad bandpasses.

- EUVS for GOES-R: Three reflection grating spectrographs measuring specific solar emission lines from which fullspectrum is reconstructed with a model.

• The XRS instrument monitors solar flares that can disrupt communications and degrade navigational accuracy, affecting satellites, astronauts, high latitude airline passengers, and power grid performance.

- XRS measures the solar soft x-ray irradiance in two bandpasses at 0.05-0.4 nm and 0.1-0.8 nm

- Pre-GOES-R XRS: Ionization chamber instruments with limited dynamic range (solar min unresolved in noise and bright flares clipped)

- XRS for GOES-R: Solid state detectors that capture full dynamic range of solar variability.

Device

Parameter

Requirement

Design

XRS

Spectral range

0.05 - 0.8 nm

0.05 - 0.8 nm

Dynamic range

10-9 - 10-3 W/m2

10-9 - 10-3 W/m2

SNR (Signal/Noice Ratio)

1:1 over 10 minute avearge

> 30:1 over 10 minute average

Data product accuracy

≤20% over mission life

14% over mission life

Cadence

≤3 s

3 s

EUVS

Specral range

5 - 127 nm

5 - 127 nm (data product)

Spectral resulution

From 5-35 nm: 10 nm bins
From 35-115 nm: 40 nm bins
Lyman-α (121.6 nm): 10 nm (FWHM)

5-115 nm; 5 nm bins

117-127 nm; 10 nm bin

SNR

1:1 over 10 minute avearge

> 20:1 over 10 minute average

Data product accuracy

≤20% over mission life

18% over mission life

Cadence

≤30 s

27 s

Table 11: Key measurement requirements of EXIS

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Figure 51: Illustration of the EXIS instrument (image credit: LASP, NOAA) 105)

EXIS subsystems

EUVS (Extreme Ultraviolet Sensor)
XRS (X-Ray Sensor)
EXEB (EUVS/XRS Electrical Box)
SPS (Sun Positioning Sensor)

Instrument mass, power

30 kg, 40 W

Data rates

7.2 kbit/s (X-band), 0.9 kbit/s (L-band)

Instrument envelope

76 cm x 30 cm x 37 cm

Thermal control

Active control , 2 zones

Table 12: EXIS instrument parameters

XRS monitors solar flares and helps predict solar proton events that can penetrate Earth’s magnetic field. The XRS is important in monitoring X-ray input into the Earth's upper atmosphere and alerts scientists to X-ray flares that are strong enough to cause radio blackouts and aide in space weather predictions (this is different from the SUVI instrument which monitors solar flares via images on the X-ray spectrum). EXIS will provide more information on solar flares and include a more complete and detailed report of solar variability than is currently available.

The EUVS will measure changes in the solar extreme ultraviolet irradiance which drive upper atmospheric variability on all time scales. EUV radiation has major impacts on the ionosphere. An excess can result in radio blackouts of terrestrial high frequency communications at low latitudes. EUV flares also deposit large amounts of energy in Earth’s upper atmosphere (thermosphere) causing it to expand into Low Earth Orbiting satellites, causing increased atmospheric drag and reduce the lifetime of satellites by degrading items such as solar panels.


GLM (Geostationary Lightning Mapper):

GLM is also referred to as LMS (Lightning Mapper Sensor). The GLM mission consists of an optical imaging instrument of GHCC (Global Hydrology and Climate Center) at NASA/MSFC (Marshall Space Flight Center, Huntsville, AL). The prime objective is to measure from GEO the total lightning activity on a continuous basis (under both day and nighttime conditions) over the Americas (North and South) and portions of the adjoining oceans. The GLM will provide continuous measurements of lightning and ice-phase precipitation. These measurements will be used to:

- Diagnose and forecast the transient evolution of severe storm events, such as tornadoes, microbursts, hail storms and flash floods

- Improve mesoscale model forecasts and satellite-based retrievals of convective properties

- Improve forecast models through rapid-update assimilation of lightning data

- Examine the seasonal to interannual variability of storms and to develop a lightning climatology.

GLM permits the study of the electrosphere over dimensions ranging from the Earth's radius down to individual thunderstorms. The instrument is capable of detecting all types of lightning phenomena at a nearly uniform coverage (detection of storm formulation and severity). Near real-time data transmission to MSFC is required for processing and quality assurance and redistribution of the data within 1 minute of reception. 106) 107) 108) 109)

Imager type

Staring CCD array imager with 1372 x 1300 pixels, pixel size (variable) 30 x 30 µm

Spectral wavelength

777.4 nm (filter center wavelength, single bandpass)

Lens focal length, lens f number

134 mm, 1.2

Lens FOV

±8º

Ground sample distance

8-14 km

Threshold

< 4.0 J m-2 sr-1 → A lightning event is identified whenever the selected signal difference threshold is exceeded

Flash efficiency

80%

Event rate

1 x 10 -5 s-1

SNR, dynamic range

6, > 100

Detection efficiency, false alarm rate

> 90% of total events, <5% of total events

Measurement accuracy

Location: 1 pixel; intensity: 10%; time tag at frame rate

Temporal resolution

2 ms frame rate (500 frames/s)

Instrument mass, power

125 kg, 290 W

Data downlink communication

Data rate: 7.7 Mbit/s; modulation: PCM; quantization = 14 bit

Table 13: Specification of the GLM instrument

In Sept. 2007, a NASA/NOAA contract was awarded to LM ATC (Lockheed Martin Advanced Technology Corporation) of Palo Alto, CA to build the GLM instrument. 110)

The GLM instrument consists of a staring imager optimized to detect and locate lightning. The major subsystems of the instrument are: an imaging system, a focal plane assembly, real-time event processors, a formatter, power supply, and interface electronics. The imaging subsystem is a fast f/1.2 telescope with a 12 cm aperture diameter and a 1 nm bandwidth interference filter. A broadband blocking filter is placed on the front surface of the filter substrate to maximize the effectiveness of the narrowband filter.

GLM is a camera system that can be described in the usual terms of imaging systems (resolution, spectral response, distortion, noise, clock rates, bit depth, etc.), the science data output of the GLM instrument consists primarily of events, not images. To understand how GLM detects lightning, it helps to think of it as an event detector, and set aside for a moment our usual thoughts about cameras.

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Figure 52: Photo of the GLM engineering unit (image credit: GHCC, NOAA)

Event filtering approaches: The daytime lightning signals tend to be buried in the background noise; hence, special techniques are implemented to maximize the lightning signal relative to this background noise.

• Spatial filtering is used which matches the IFOV of each detector element in the GLM focal plane array to the typical cloud-top area illuminated by a lightning stroke (i.e., in the order of about 10 km). This results in an optimal sampling of the lightning scene relative to the background illumination.

• Spectral filtering is obtained by using a narrowband interference filter centered on a strong optical emission line (e.g., OI at 777.4 nm) in the lightning spectrum. This method further maximizes the lightning signal relative to the reflected daylight background.

• GLM employs temporal filtering which takes advantage of the difference in lightning pulse duration which is on the order of 400 µs versus the background illumination which tends to be constant on the time scale of seconds. In an integrating sensor, such as GLM, the integration time specifies how long a particular pixel accumulates charge between readouts. The lightning SNR improves as the integration period approaches the pulse duration. An integration time of 2 ms (technological limit) is used to minimize pulse splitting and maximize lightning detectability.

• Since the ratio of the background illumination to the lightning signal often exceeds 100 to 1 at the focal plane, a fourth technique, a modified frame-to-frame background subtraction is implemented to remove the slowly varying background signal from the raw data coming off the GLM focal plane. Each real-time event processor generates an estimate of the background scene imaged at each pixel of its section of the focal plane array. This background scene is updated during each frame readout sequence and, at the same time, the background signal is compared with the off-the-focal-plane signal on a pixel-by-pixel basis. When the difference between these signals exceeds a selected threshold, the signal is identified as a lightning event and an event processing sequence is initiated.

Principle of event detection: As a digital image processing system, GLM is designed to detect any positive change in the image that exceeds a selected detection threshold. This detection process is performed on a pixel-by-pixel basis in the RTEP (Real Time Event Processor) by comparing each successive value of the pixel (sampled at 500 Hz in the incoming digital video stream) to a stored background value that represents the recent history of that pixel. The background value is computed by an exponential moving average with an adjustable time constant k (Ref. 111).

The large data rate of about 5 Gbit/s is read out from the focal plane of GLM into several RTEPs for event detection and data compression. Each RTEP detects weak lightning flashes from the intense but slowly evolving background. The RTEP continuously averages the output from the focal plane over a number frames on a pixel-by-pixel basis to generate a background estimate. It then subtracts the average background estimate of each pixel from the current signal of the corresponding pixel. The subtracted signal consists of shot noise fluctuating about zero with occasional peaks due to lightning events. When a peak exceeds the level of a variable threshold, it triggers comparator circuits and is processed by the rest of the electronics as a lightning event.

An event is a 64-bit data structure describing the identity of the pixel, the camera frame (i.e. time) in which it occurred, its intensity with respect to the background, and the value of the background itself. Performing on-board image processing in the RTEPs, and reporting changes in the Earth scene by exception only (when an event is triggered) reduces the downlink data bandwidth of the instrument to a reasonable level, from 14 bit/pixel x (1372 x 1300) pixels/frame x 500 frames/s = 12.5 Gbit/s of raw video data to just ~6 Mbit/s of processed event data.

Operating at the Limits of Noise: The intensity of lightning pulses, like many phenomena in nature, approximately follows a power law. There are relatively fewer bright and easily detectable events, and a “long tail” of dim events that eventually get drowned out by instrument noise. To achieve high detection efficiency, GLM must reach as far into this long tail as possible by operating with the lowest-possible detection threshold. The challenge of lightning event detection is then to lower the detection threshold so low that it starts flirting with instrument noise, where random excursions in the value of a pixel can trigger a so-called “false” event that does not correspond to an optical pulse.


Architectural drivers: 111)

The GLM instrument, as built, is the result of years of trade-off studies and prototype testing that refined the present design. The architecture of GLM was driven by a number of important considerations, each of them with the common goal of maximizing lightning detection efficiency. The following list summarizes these considerations.

Patented Variable Pixel Pitch: The GLM CCD was designed such that the GSD (Ground Sample Distance), i.e. the projected area of each pixel on the Earth’s surface, is approximately constant with a target value of 8 km matched to the typical size of a storm cell. When following the development of severe thunderstorms it is important to track the lightning flash rate of individual storm cells, and therefore constant ground sample distance over the Earth is necessary.

RTEP (Real Time Event Processor) adjustability: A deliberate choice was made to separate imaging from event detection, by functionally partitioning the instrument into a Sensor Unit that performs digital video imaging and an Electronics Unit that performs digital signal processing. This partitioning approach, while it does cost mass and power, allows digital event detection algorithms and parameters to be more flexibly developed and optimized to operate reliably at the limits of instrument noise.

In the RTEP, it is critically important to be able to select the threshold on a pixel-by-pixel basis. The following simulated example provides further insight into the need for controlling TNR (Threshold-to-Noise Ratio)) in each pixel. Figure 53 shows a typical cloud scene near the terminator, simulated as GLM would see it, where grazing illumination creates a lot of contrast in the cloud tops.

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Figure 53: Small portion of cloud scene, as viewed by GLM (image credit: Lockheed Martin STAR Labs)

Because shot noise is of roughly the same order as electronics noise, pixels containing sunlit cloud tops will have more total noise than adjacent pixels containing shaded cloud tops. The total noise in each pixel (1σ, in units of DN) is simulated in Figure 54; note that it varies by several counts over small spatial scales.

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Figure 54: Total noise, 1σ (DN), image credit: Lockheed Martin STAR Labs

If one were to apply a single global detection threshold to this entire 90 x 90 pixel scene, selected such that the false event rate stayed below 100 events/s over this portion of the cloud scene, the global threshold would need to be 25 counts and the TNR would vary widely across the scene:

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Figure 55: Threshold-to-noise ratio achieved by selecting a single detection threshold of 25 (image credit: Lockheed Martin STAR Labs)

As a result, the false event rate is dominated by the brightly sunlit pixels, and detection efficiency suffers in pixels with shaded cloud tops (yellow, orange and red). - GLM does not use a global threshold in recognition of the fact that shot noise varies significantly from pixel to pixel due to the highly variable illumination of cloud tops. The event detection threshold is selected by the RTEP for each individual pixel from a 32-element lookup table indexed by the top five bits of the background in that pixel. Instead of applying a global threshold of 25, a different threshold value is selected for each pixel as shown in Figure 56. In this example, the threshold values were determined by the same criterion to keep the false event rate less than 100 events/sec.

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Figure 56: Detection thresholds selected on a pixel-by-pixel basis (image credit: Lockheed Martin STAR Labs)

Note how a higher threshold is applied to brightly sunlit pixels, and a threshold less than 25 is applied to shaded pixels, enhancing detection efficiency in all the pixels shaded blue. In this example the false event rate is evenly distributed across this scene, as revealed by the uniformity of the corresponding TNR map, obtained simply by dividing the threshold by the total noise (Figure 57):

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Figure 57: Threshold-to-noise ratio when detection threshold is selected on a pixel-by-pixel basis (image credit: Lockheed Martin STAR Labs)

By controlling TNR on a pixel-by-pixel basis and preventing a few bright pixels from dominating the false event budget, GLM can maximize detection efficiency by lowering the threshold in each pixel to its optimal value, peering deeper into the noise and detecting the dimmest optical pulses in the long tail of the lightning intensity distribution. Threshold tables can be uploaded to the instrument and will be optimized during post-launch test.

Of course, detection thresholds are only one aspect of a robust RTEP design, and a number of other adjustable parameters are available to fine-tune the behavior of the background tracking. For example, RTEP settings can be adjusted to accommodate repeated events in the same pixel (to detect the continuing current events that often spark forest fires), to reduce spurious jitter events at contrast boundaries induced by minute disturbances in the instrument line of sight, or to mitigate the impact of stray light when entering and exiting eclipse. The GLM RTEP design benefits directly from years of on-orbit experience with the LIS (Lightning Imaging Sensor) flying on the TRMM satellite.

Narrow Band Filter: The true test of a lightning mapper is its ability to detect dim lightning events emanating from a bright, zenith-illuminated cloud top. Clouds are nearly Lambertian reflectors with an albedo that sometimes approaches unity, so a large amount of undesired reflected sun light is present in the vicinity of the oxygen triplet. The worst-case spectral radiance of the cloud background is estimated in Figure 58, for all seasonal and diurnal illumination conditions.

This background cloud radiance creates shot noise which can drown out dimmer lightning events. It is necessary to cut down the background signal using optical filters that have the narrowest feasible bandpass while still passing the majority of the lightning oxygen triplet. GLM contains three filters of increasingly narrow spectral width: a SRF (Solar Rejection Filter) at ~30 nm FWHM that performs the task of rejecting the bulk of out-of-band radiation, a SBF (Solar Blocking Filter) at ~3 nm FWHM, and the key NBF (Narrow Band Filter) at ~1 nm FWHM. Due to their large size and stringent spectral requirements, these filters pushed the boundaries of manufacturing capabilities.

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Figure 58: Worst-case 100% albedo Lambertian cloud spectral radiance at 777 nm, with atmospheric loss (mW/sr/cm2/µm),image credit: Lockheed Martin STAR Labs

Frame Rate and CCD Well Depth: GLM detects the individual optical pulses caused by lightning, on top of a bright background of sunlit clouds. In order to detect these pulses with good signal to noise, the frame rate must be optimized. The average duration of a lightning optical pulse is shown in Figure 59.

The frame rate should be closely matched to the average duration of the pulse. If the frame rate is too low, then additional background is detected with no additional signal, lowering signal to noise. If the frame rate is too high, then the signal is split into adjacent frames, reducing signal to noise. The GLM frame rate is 500 Hz, well matched to the duration of the lightning optical pulses. The frame rate and the CCD well depth must also be matched. Lightning most often occurs in optically thick clouds, in the afternoon when the clouds are well illuminated by the Sun. The CCD well depth must be large enough to accommodate the expected background from bright clouds, at the frame rate matched to the pulse duration, and with the optical filters matched to the oxygen triplet emission line. The GLM CCD has a well depth of approximately 2 million electrons to be able to accommodate the bright background while leaving room to detect lightning events. The frame rate, CCD well depth, and optical filters work together to optimize the signal to noise ratio for detecting lightning optical pulses.

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Figure 59: Typical lightning optical pulse profile (image credit: Lockheed Martin STAR Labs)

Coherency Filter: The GLM hardware is designed to detect events, including many events caused by noise, and sends all these events to the ground for further processing. The first step in the processing is to remove the non-lightning events from the data stream. The flashes are then identified by reviewing the remaining events. The ground processing algorithms include many filters designed to remove events not caused by lightning, including radiation hits and glint from Sun on the ocean. Most of the filters are based on work done on the LIS (Lightning Imaging Sensor). The most important filter is the coherency filter. This filter relies on the fact that true lightning events are coherent in time and space, whereas noise events are not. This is the filter that enables GLM to operate at the edge of the noise, sending many noise events to the ground and detecting fainter lightning events in the process.

As viewed from space, any given lightning flash will generate several to several tens of optical pulses. Flashes can be up to several seconds long, and contain multiple optical pulses detected in the same pixel or adjacent pixels. A noise event will not have this coherent behavior. Although many noise events may be triggered over the course of several seconds, they are unlikely to be in the same or adjacent pixels. The coherency filter calculates the probability that any given event is a noise event, based on the event intensity, the electronics noise, and the photon noise of the background. When another event occurs in this same pixel or an adjacent pixel, the filter calculates the probability that both of these events are noise events, based on the new event intensity, the instrument and photon noise, and the time elapsed between the two events. When two events have a sufficiently low probability of both being noise, the events are reported as lightning events. This probability threshold is adjustable to allow more or less stringent filtering of the data as desired by the user community.

Performance:

The overall performance of GLM is measured in terms of the fraction of the lightning flashes that are detected and reported. We call this the detection efficiency. In order to do this calculation, one must know the characteristics of lightning flashes. For our truth data set,high-altitude airplane data is used which provides the distribution function of the energy density of the brightest pulse in a flash. The event detection thresholds of GLM is compared, converted into the energy density units using the instrument calibration data, to the distribution function of the brightest pulse in a flash. The threshold applied to a given pixel depends on the background in that pixel. An 80% cloud background albedo is assumed and the background of each pixel at a given time and illumination is calculated. The project can then determine which threshold will be selected for each pixel, and determine the detection efficiency of each pixel. Figure 60 shows an example of a predicted detection efficiency map.

The vertical banding visible in the areas east of the terminator (dark red) corresponds to a different detection threshold being selected, resulting in a step change in the detection efficiency. Areas on the sunlit limb (light blue) have the lowest detection efficiency under these illumination conditions. When averaged over 24 hours and over the entire field of view, GLM is expected to detect 80% of lightning flashes.

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Figure 60: Calculated detection efficiency of each GLM pixel, in percent, at 4 PM local time as seen from GOES-East satellite (image credit: Lockheed Martin STAR Labs)

In conclusion, GLM will gather more spaceborne lightning data in the first few weeks of operations,than has been collected in the entire history of space flight. Hemispherical coverage combined with round-the-clock operation at 500 frames/s will enable near real-time reporting of lightning flashes, giving unprecedented insight into the energetics of severe weather.

GLM has the potential to reduce fuel consumption of the air transport network by providing near real-time lightning maps, augmenting traditional radar detection to optimize air traffic management around areas of convective weather.

Long-term trending of GLM lightning data will provide continuity with data sets from LIS (Lightning Imaging Sensor) flown on the TRMM satellite, and contribute to our understanding of decadal changes in the Earth’s climate.

Most importantly, GLM lightning data will be used in operational data products to forecast tornado activity with significantly greater warning time and reliability. Increased warning time and fewer false tornado warnings will save lives.


SEISS (Space Environmental In Situ Suite):

In Aug. 2006, NASA in coordination with NOAA awarded a contract to ATC (Assurance Technology Corporation) of Carlisle, MA to design and develop the SEISS package. 112) 113)

The SEISS instrument package monitors the near-Earth particle and electromagnetic environment in real-time. Monitoring of geomagnetically trapped electrons and protons; electrons, protons, and heavy ions of direct solar origin; and galactic background particles.

The SEISS package consists of the following instruments:

EHIS (Energetic Heavy Ion Sensor), was designed and developed at NHU (New Hampshire University). The objective of EHIS is to measure the proton, electron, and alpha particle fluxes at GEO. This includes particles trapped within Earth’s magnetosphere and particles arriving directly from the sun and cosmic rays which have been accelerated by electromagnetic fields in space. The information will be used to help scientists protect astronauts and high altitude aircraft from high levels of harmful ionizing radiation. The EHIS device incorporates a unique system design called ADIS (Angle Detecting Inclined Sensor).

MPS (Magnetospheric Particle Sensor). MPS is a three-axis vector magnetometer to measure the magnitude and direction of the Earth's ambient magnetic field in three orthogonal directions in an Earth referenced coordinate system. The magnetometer will provide a map of the space environment that controls charged particle dynamics in the outer region of the magnetosphere.

MPS-LO: The sensor measures electron and proton flux over an energy range of 30ev to 30kev. MPS-LO will be able to tell scientists the amount of charging by low energy electrons that the GOES-R spacecraft is undergoing. Spacecraft charging can cause ESD and arcing between two differently charged parts of the spacecraft. This discharge arc can cause serious and permanent damage to the hardware on board a spacecraft, which affects operation, navigation and interferes with measurements being taken.

MPS-HI: The sensor will monitor medium and high energy protons and electrons which can shorten the life of a satellite. High energy electrons are extremely damaging to spacecraft because they can penetrate and pass through objects which can cause dielectric breakdowns and result in discharge damage inside of equipment.

SGPS (Solar and Galactic Proton Sensor). The objective of SGPS is to measure the solar and galactic protons found in the Earth's magnetosphere. The data provided by SGPS will assist the Space Weather Prediction Center's Solar Radiation Storm Warnings. These particular measurements are crucial to the health of astronauts on space missions, though passengers on certain airline routes may experience increased radiation exposure as well. In addition, these protons can cause blackouts of radio communication near the Earth's poles and can disrupt commercial air transportation flying polar routes. The warning system allows airlines to reroute planes that would normally fly over Earth’s poles.

The instrument suite also includes the DPU (Data Processing Unit). Data from SEISS will drive solar radiation storm portion of NOAA space weather scales and other alerts and warnings and will improve energetic particle forecasts.

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Figure 61: Illustration of the SEISS instrument package (image credit: GOES-R project)


MAG (Magnetometer):

The MAG will provide measurements of the space environment magnetic field that controls charged particle dynamics in the outer region of the magnetosphere. These particles can be dangerous to spacecraft and human spaceflight. The geomagnetic field measurements are important for providing alerts and warnings to many customers, including satellite operators and power utilities. GOES Magnetometer data are also important in research, being among the most widely used spacecraft data by the national and international research community. The GOES-R Magnetometer products will be an integral part of the NOAA space weather operations, providing information on the general level of geomagnetic activity and permitting detection of sudden magnetic storms. In addition, measurements will be used to validate large-scale space environment models that are used in operations. The MAG requirements are similar to the tri-axial fluxgates that have previously flown. GOES-R requires measurements of three components of the geomagnetic field with a resolution of 0.016 nT and response frequency of 2.5 Hz. 114)

The MAG device is provided by Lockheed Martin, Newton, PA and is boom mounted on GOES-R.

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Figure 62: Illustration of the boom-mounted MAG device (image credit: GOES-R project)




Ground Segment (GS) of the GOES-R series:

For the first time in GOES history, the GOES-R series will also be delivered with an integrated GS (Ground System) that provides a cohesive capability to provide data processing, control, and monitoring capabilities in an integrated system. 115) 116)

• In May 2009, NOAA selected the Harris Corporation - Government Communications Systems Division of Melbourne, FLA, to develop the GOES-R ground system, which will capture, process and distribute information from NOAA's next generation geostationary satellite series to users around the world. 117) 118) 119) 120) 121) 122) 123) 124)

• In February 2015, Harris Corporation has delivered all hardware and completed installation and integration of the GOES-R ground segment IT infrastructure supporting operational systems at NOAA Satellite Operations Facility (NSOF) in Suitland, Maryland, Wallops Command and Data Acquisition Station (WCDAS) in Wallops, Virginia, and the Consolidated Backup (CBU) in Fairmont, West Virginia. — The system includes 2,100 servers, 149 racks of network equipment, 317 workstations, and storage services totaling three petabytes (3 PB). The system also contains 454 blade servers with 3,632 cores for product processing and distribution across all environments, delivering approximately 40 trillion floating point operations per second of processing power. 125)


The GS is comprised of a core development effort made up of mission management, product generation, product distribution, and enterprise management elements and supported by hardware and software infrastructure. Mission management will provide the primary data receipt and command and control as well as mission planning, scheduling, and monitoring functionality in order to support the satellite operations processes of the GOES-R series.

The product generation element will process raw instrument data into higher order products, including the creation of a direct broadcast data stream to be distributed hemispherically to the GOES user community. Product distribution will provide data dissemination capabilities to ensure GOES-R products reach the user community, including dedicated pathways to the NWS (National Weather Service) for low-latency, high-availability imagery.

The enterprise management element provides an integrated monitoring and reporting capability that will enable a comprehensive view of system status, while Infrastructure provides a pooled set of hardware and software resources to be used by the elements. In addition, the GS will provide a RBU (Remote Backup Facility), new and upgraded antenna capabilities to NOAA, and will develop a user distribution and access portal known as the GOES-R Access Subsystem.

The ground segment contract baseline and options include:

• Development of the core ground segment

- Mission management element

- Enterprise management element

- Product generation element

- Subset of product generation element: a) GRB (GOES Rebroadcast), b) AWIPS (Advanced Weather Information Processing System) distribution

- Internal telecommunications/networks (i.e., intra-site)

- Option 1: improved latency / option 2: additional L2+ products

• Total ground segment integration and checkout

- Integration of GFP systems, including antennas and GAS (GOES-R Access Subsystem)

- Interfaces to external systems, including CLASS and ADRS (Ancillary Data Relay System)

• Transition to NOAA operations.

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Figure 63: Architectural overview of the GOES-R Ground System (image credit: GOES-R GS Project)

Function

GOES-N

GOES-R

Instrument data downlink

2.62 Mbit/s

~55 Mbit/s (ABI only)

Rebroadcast

2.11 Mbit/s (GVAR)

~30 Mbit/s (GRB)

Level 1b products

2.11 Mbit/s (GVAR)

~30 Mbit/s

Level 2/3 products

< 4.7 Mbit/s

TBS

Product latency

Near real-time to hrs (product dependent)

Near real-time to 15 minutes (product dependent)

No of types of products

42

TBS

Planned data outage

> 300 hrs / yr

< 3 hrs / yr

CLASS data storage per satellite

N/A

Daily: 1.9 TB; Yearly: 670 TB

Temporary storage

30 hrs of raw data; 7 days of product data

5 days of raw data; 7 days of product data

Table 14: GOES-N and GOES-R data transfer differences


GOES-R Ground Segment Sites:

The GOES-R GS will operate from three sites:

1) NSOF (NOAA Satellite Operations Facility) in Suitland, MD. NSOF will house the primary Mission Management (MM), Product Generation (PG), and Product Distribution (PD) functions.

2) WCDAS (Wallops Command and Data Acquisition Station), located at Wallops, VA. WCDAS will provide space communications services and selected Ground Segment functions.

3) RBU (Remote Backup) facility. RBU is a geographically isolated site, located in Fairmont, WV (West Virginia). RBU will function as a completely independent backup for designated MM, PG and PD functions for the production and delivery of critical cloud and moisture imagery products, and GOES Rebroadcast (GRB) data,and will be capable of remote operation from the NSOF and WCDAS. The RBU station will have visibility to all operational and on-orbit spare satellites. The Enterprise Management (EM) function supports GS components across all locations.

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Figure 64: GOES-R Ground Segment Architecture (image credit: GOES-R GS Project, Ref. 124)

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Figure 65: Operational sites of the GOES-R Ground Segment (image credit: GOES-R GS Project)

Spacecraft commands are generated by GS operators and are uplinked to the satellite through the primary command interface at the WCDAS (Wallops Command and Data Acquisition Station), located at Wallops, VA. Commands may also be generated at the NSOF (NOAA Satellite Operations Facility) in Suitland, MD and sent terrestrially to WCDAS for uplink via dedicated, high availability telecommunications circuits. Commands may also be generated from the RBU site in Fairmont, WV or may be distributed from one of the other two sites to RBU for uplink.

For GOES-R operations, the NSOF and WCDAS together comprise the “primary” sites and may be considered in certain respects as a single system. WCDAS provides the Earth-space communications functions, while primary console operations and higher-level product data functions are provided by NSOF. The RBU consolidates the mission-critical functionality of the NSOF and WCDAS into a single “backup” site that can operate completely independently.

Spacecraft telemetry data is received and processed at WCDAS during primary operations and at RBU in non-nominal or contingency situations. Telemetry includes both spacecraft health and safety information (engineering telemetry) and raw instrument data. Engineering telemetry is monitored by the system to support anomaly detection and resolution. Engineering telemetry is made available to operators at NSOF via terrestrial distribution.

Mission management provides the primary mission operations as well, including real-time console operations, offline engineering and trending, bus and instrument health and safety and performance monitoring, anomaly detection and resolution, procedure development, spacecraft resource accounting, and special operations planning and execution. These functions occur at NSOF and WCDAS during primary mission operations.

One key function associated with mission management operations is mission planning and scheduling. The GS will provide maneuver planning and scheduling for routine operations as well as special operations such as station keeping, annual yaw flips, and engineering or science investigations outside of normal operations.

Mission management also includes a detailed product monitoring function. Product monitoring enables the operations team to identify anomalies in the instrument data being generated by the GS. Product monitoring is focused on Level 1b processed data included in the GRB (GOES Rebroadcast) data stream. It also provides for the monitoring of the signal quality of the uplinked and downlinked communications signals to ensure integrity of the received data.

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Figure 66: RBU (Remote Backup) Facility, Fairmont, W.VA (image credit: GOES-R GS Project, Ref. 124)

GOES-R GS Antenna System:

Associated with the development of the GS is a set of new and upgraded antennas to support the transmission and receipt of GOES-R series satellite data, along with legacy GOES mission data. At WCDAS and RBU, these antennas will provide for raw data and telemetry receipt from the spacecraft in X-band. They will support command uplinking in S-band and will provide for the uplink of GRB L1b data at X-band. They will also be capable of receiving GRB data to perform quality monitoring of the GRB downlink in L-band.

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Figure 67: Notional view of of a 16.4 m antenna station (image credit: NOAA, Harris)

At WCDAS, three new 16.4 m antennas will be installed into the existing NOAA antenna infrastructure. One of the existing 18 m antennas will be replaced, and two additional antennas will be added. All three antennas will support both the GOES-R series and legacy GOES missions. They will be designed to operate through a Category 2 hurricane without performance degradation.

Three new antenna stations will also be installed at the GOES-R RBU site. These stations will be functionally identical to the WCDAS antennas and will also be capable of operating under more stressing conditions of ice and snow. Although the current GOES-R series mission does not include backup for legacy GOES at the RBU, the antennas at RBU will be capable of supporting both missions.

At NSOF, the existing 9.1 m antennas will be upgraded to be capable of receiving both GRB and legacy GVAR (GOES Variable) downlinks. This data receipt provides the primary path through which L1b data is sent to NSOF from WCDAS. Because the NSOF antennas are currently in use supporting GOES operations, they will be taken offline one at a time to be upgraded, tested, and re-installed.

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Figure 68: Antenna system architecture components at each facility (image credit: NOAA, Harris)

In addition to the primary data streams, the GOES-R series antennas will support a set of Unique Payload Services. The HRIT/EMWIN (High Rate Information Transmission/Emergency Manager’s Weather Information Network) is uplinked in S-band and downlinked in L-band at WCDAS and RBU. The HRIT/EMWIN broadcast provides low-resolution GOES imagery and products, along with emergency weather forecasts and warnings generated by the NWS (National Weather Service). - In parallel, the GOES-R series system will support the collection of in-situ environmental sensor data from DCS (Data Collection System) platforms and will transpond commands to DCS platforms using the GOES-R antennas at WCDAS. Interfaces between the Antenna System and the HRIT/EMWIN and DCS systems will mirror those in place at WCDAS today, but with new and upgraded capabilities to support more DCS terminals and higher data rate signals for HRIT/EMWIN.


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Figure 69: Photo of WCDAS (Wallops Command Data Acquisition Station), Wallops Island, VA (image credit: GOES-R GS Project, Ref. 124)


Core Ground Segment Functions:

The key functions of the Ground Segment are as follows:

1) MM (Mission Management):

The MM element provides the primary interface between the GS and the Space Segment. It is responsible for the following functional areas (Ref. 115):

• Space-ground communications

• Command generation

• Telemetry (TT&C) processing

• Mission operations

• Product monitoring.

Space-ground communications functions are necessary to process the radio-frequency (RF) signals received from the satellite into usable information, and to generate the RF signals transmitted from the GS back to the satellite. The antenna system being developed for GOES-R falls under the mission management element and serves as the front-end for transmission and receipt of the RF signals. An intermediate frequency (IF) interface between the antenna system and core GS passes these signals into the space-ground communications hardware, which turns them into information to be sent throughout the system.

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Figure 70: Ground segment functions (image credit: NOAA)


2) PG (Product Generation):

Raw data is received at WCDAS and processed through the antenna system and space-ground communications hardware until CCSDS-formatted packets are recovered. Those packets containing raw instrument data are recovered and processed to Level 0 (L0) data (reprocessed, unreconstructed instrument data at full resolution with communications artifacts removed). This L0 data is in turn radiometrically corrected (calibrated) and geometrically corrected (navigated) to produce a L1b radiance data set. For GLM (Geostationary Lightning Mapper) data, the data set is further processed algorithmically to produce a higher order Level 2+ (L2+) product. GLM L1b and L2+ data, along with the L1b data from all other instruments, is packaged for distribution via the GRB uplink. GRB is sent from PG through the space-ground communications equipment to be uplinked from WCDAS at X-band. The GRB link is transponded onboard the GOES-R Series satellites and downlinked in L-band within the satellite coverage area down to a 5º elevation angle. GRB data is freely available to any users within the coverage area who possess the appropriate equipment to receive the data.

GRB distribution is the primary means of providing L1b instrument data from WCDAS to NSOF. L1b is received at NSOF through the antenna system and is processed back to L1b data sets. This L1b data is then further processed through a set of algorithms to create higher order (L2+) science products. These include the GOES-R KPP (Key Performance Parameter) product of Cloud and Moisture Imagery, which is the critical higher order product required for mission success.

A total of 65 End-Products have been identified for the GOES-R GS. Of these, 56 are generated based on data from the ABI. ABI products focus on atmospheric, ocean, and land data and include subcategories such as clouds, radiation, and precipitation. In addition, the GLM will provide near real-time lightning data End-Products, and the space weather instruments will generate an additional 8 Level 1b End-Products. Each product has a set of performance parameter characteristics that identify the product’s resolution, accuracy, refresh rate, latency, and precision.

The algorithms are implemented by the GS development contractor based on ATBDs (Algorithm Theoretical Basis Documents) generated by NOAA’s Center for Satellite Applications and Research (STAR) in the case of L2+ End-Products and provided by the instrument vendor in the case of L1b End-Products. The capability to deliver these products is divided into three phases known as Releases. The implementations will be validated against a reference data set to ensure that the output of the implemented algorithm correlates with the STAR implementation.

Depending on the algorithm used for generation of each L2+ product, ancillary data inputs may be required to create a given product. These ancillary inputs are aggregated from multiple sources such as numerical weather prediction models and snow/ice analyses through the ADRS (Ancillary Data Relay System). ADRS is being developed in conjunction with the GOES-R GS and will be configurable to meet algorithm needs over the life of the mission. ADRS will provide the ancillary data to the PG L2+ processing system to support the generation of these higher order products. Currently, 20 of the L2+ End-Products listed above require ancillary data inputs.

The PUG (Product Definition and Users' Guide) is defined in the following reference: 126)


3) PD (Product Distribution):

Once the End Products are generated, the core GS PD (Product Distribution) element ensures that data and products are provided to the appropriate entities. The core GS distributes data to the GAS (GOES-R Access Subsystem) via a dedicated network interface located at NSOF. GAS is the primary source of L2+ data for the majority of GOES users Data is also provided directly to NWS via the AWIPS (Advanced Weather Interactive Processing System) interface and to NOAA’s CLASS (Comprehensive Large Array-data Stewardship System) via dedicated interfaces.

The GOES-R Access System is being developed as a component of an overall upgrade of NOAA’s ESPC (Environmental Satellite Processing Center) under the ESPDS (Environmental Satellite Processing and Distribution System) development effort. GAS will consist of a seven-day storage repository and a data distribution interface supporting both subscription-based and ad hoc data requests. GAS will also provide an API (Application Programming Interface) designed to support direct machine-machine distribution of data and products to outside systems. GAS will receive the L1b and L2+ products described in Figure 63, along with ancillary data, metadata, Instrument Calibration Data, sample outlier files for the ABI, and mission operations data (schedules, satellite configuration, operations schedules, and other operational information).

The core GS PD element will also provide sectorized cloud and moisture imagery directly to the NWS via the AWIPS interface. This interface is a high availability, low latency distribution channel that ensures that the NWS receives critical KPP data. The core GS will provide a product sectorization capability that will be configurable based on the following parameters:

• Geographic coordinate corner points

• Map projection (Mercator, Lambert conformal, Polar Stereographic, or Fixed Grid)

• Spatial resolution

• Bit depth

• ABI channel

• Periodicity.

A “stressing case” consisting of a representative set of AWIPS data has been defined between the GOES-R GS and the NWS and is being used to provide a baseline capability for the system’s performance. The system will remain operationally configurable to respond to changing NWS needs within the parameters defined above.

All Level 0, L1b, and L2+ GOES-R data and products will be archived in NOAA’s CLASS repository for long-term preservation. This data repository serves as the primary storage for long-term climatological studies, as well as serving as the data source for users requiring data older than the previous seven days. These non-operational users will interface with the CLASS via a we-based interface outside of the GOES-R system. In addition, Instrument Calibration Data, calibration coefficients, ancillary data, and L2+ parameter tables will be stored to enable detailed analysis and reprocessing by the meteorological and climatological communities. The GS-CLASS interface will be sized to support the distribution of over 2.5 TB of data per day per satellite.

Figure 71 depicts the complete flow of data from the satellite’s instruments through the products’ distribution to the user community.

GoesR_Auto2

Figure 71: The data flow of the GOES-R mission (image credit: GOES-R GS Project)


4) EM (Enterprise Management):

The EM element of the core GS supports operational functions by supervising the overall systems and networks of the core GS. In the GOES-R context, supervision is the ability to monitor, report, and enable an operator response to anomalous conditions. EM functions underpin the infrastructure that links the MM, PG, and PD functions and supports automation. While direct control of various systems may be implemented within the individual elements, EM provides a higher layer of supervision across the GS. GS operators at all sites will have access to the EM functionality for insight to their local site and to the distributed GS components, infrastructure, and interfaces.

The EM status is generally reported through an event message generated by a core GS component. Event messages provide a standardized means of communicating particular status information or alerts to EM from the other core GS components. As the EM functionality receives status and other information provided by the distributed GS functions, operators would be able to monitor, trend, and perform other supervisory activities. Components of the GS that are not a part of the core GS will report EM status through a core GS element (e.g., the Antenna system will report via MM and the GAS will report through PD).

In addition to status and monitoring, EM provides configuration and asset management functionality for the GS. The GS uses a consolidated CMART (Configuration Management and Anomaly Reporting and Tracking) system to manage the configuration of software builds, licenses, and database schema. CMART also provides the ability to distribute software and database updates throughout the GS. The anomaly reporting and tracking components of CMART generates anomaly trouble tickets and supports the prioritization, tracking, and resolution of anomalies throughout the development and operations life cycle.


5) IS (Infrastructure):

Although not explicitly defined in the Government requirements, an Infrastructure element is being implemented within the core GS. Infrastructure provides a set of common services for the core GS that are utilized by multiple elements. These services include a network fabric, consolidated storage, database services, and an enterprise service bus. The network fabric is an IP (Internet-Protocol)-based network that provides intra-element and inter-element connectivity. It also provides connectivity across GS sites, connects to external interfaces, and supports a defense-in-depth IT (Information Technology) security strategy.

Consolidated storage provides a set of storage media and file structures that enable both short-term and long-term storage within the GS. The database services enable element-level databases through the use of relational database clusters. Finally, the enterprise service bus supports a common set of message exchanges for both intra-and inter-element communication. Consolidation of infrastructure functions under a common element enables more efficient hardware utilization, supports a standard design and implementation of common GS-wide functions, increases system flexibility, and helps centralize the management of the common functions of the system.

The GAMCATS (GOES-R Antenna Monitor, Control, and Test Subsystem) performs an analogous function to EM for the Antenna system. GAMCATS provides monitoring, control, and test functionality for the antenna control unit, receive elements, transmit elements, control ports of the switching system, RF switching, BITE (Built-In Test Equipment), environmental and fire suppression system monitoring, waveguide dehydrator, and other related equipment across all sites. During normal operations, the GOES-R antennas and associated equipment at both WCDAS and RBU will be monitored and controlled from the WCDAS operations room, with backup monitoring by operators at NSOF via remote GAMCATS workstation. GAMCATS will provide status information to the core GS MM element via event messages, and these will be relayed to the core GS EM element to provide a consolidated view of the GS status (Ref. 115).

GoesR_Auto1

Figure 72: Overview of GOES-R data distribution (image credit: NOAA)




GOES-R UPS (Unique Payload Services):

The GOES-R Unique Payload Services suite consists of transponder payloads providing communications relay services in addition to the primary GOES mission data. The UPS suite consists of the following elements: 127)

DCS (Data Collection System)

HRIT/EMWIN (High Rate information Transmission / Emergency Managers Weather Information Network).

GRB (GOES-R Rebroadcast). GOES-R Rebroadcast is the primary space relay of Level 1b products and will replace the GOES VARiable (GVAR) service. GRB will provide full resolution, calibrated, navigated, near-real-time direct broadcast data. The content of the data distributed via GRB service is envisioned to be the full set of Level 1b products from all instruments onboard the GOES-R series spacecraft. This concept for GRB is based on analysis that a dual-pole circularly polarized L-band link of 12 MHz bandwidth may support up to a 31-Mbps data rate – enough to include all ABI channels in a lossless compressed format as well as data from GLM, SUVI, EXIS, SEISS, and MAG.

Function

GVAR (GOES VARiable Format)

GRB (GOES Rebroadcast)

Full Disk Image

30 minutes

5 minutes (Mode 4), 15 min (Mode 3)

Other modes

Rapid Scan, Super Rapid Scan

3000 km x 5000 km (CONUS: 5 minute)
1000 km x 1000 km (Mesoscale: 30 seconds)

Polarization

None

DCP (Dual Circular Polarized)

Receiver center frequency

1685.7 MHz (L‐band)

1686.6 MHz (L‐band)

Data rate

2.11 Mbit/s

31 Mbit/s

Antenna coverage

Earth coverage to 5º

Earth coverage to 5º

Data sources

Imager and Sounder

ABI (16 bands), GLM, SEISS, EXIS, SUVI, MAG

Space weather

None

~2Mbit/s

Lightning data

None

0.5 Mbit/s

Table 15: Transition from GVAR to GRB (Ref. 123)

SARSAT (Search and Rescue Satellite Aided Tracking) System. NOAA operates the SARSAT system to detect and locate mariners, aviators, and other recreational users in distress almost anywhere in the world at anytime and in almost any condition. This system uses a network of satellites to quickly detect and locate distress signals from emergency beacons onboard aircraft, vessels, and from handheld PLBs (Personal Locator Beacons. The SARSAT transponder that will be carried onboard the GOES-R satellite will provide the capability to immediately detect distress signals from emergency beacons and relay them to ground stations - called Local User Terminals. In turn, this signal is routed to a SARSAT Mission Control Center and then sent to a Rescue Coordination Center which dispatches a search and rescue team to the location of the distress.

The GOES-R series continues the legacy GEOSAR (Geostationary Search and Rescue) function of the SARSAT system onboard NOAA’s GOES satellites which has contributed to the rescue of thousands of individuals in distress. The SARSAT transponder will be modified slightly for GOES-R by being able to operate with a lower uplink power (32 dBm) enabling GOES-R to detect weaker signal beacons.

Over its history, the SAR (Search and Rescue) office at NASA's Goddard Space Flight Center in Greenbelt, Maryland, has developed emergency beacons for personal, nautical and aeronautical use, along with ground station receivers that detect beacon activation. Space segment SAR instruments fly on many spacecraft in various orbits around the Earth. The GOES SAR transponders are geostationary, meaning that they appear "fixed" relative to a user on the surface due to their location over the equator and orbital period of 24 hours. 128)

"The SAR space segment isn't just one instrument in one orbit," said Tony Foster, SAR's deputy mission manager. "Rather it's a series of instruments aboard diverse satellites in various orbits, each working together to provide first responders with highly accurate locations."

The GOES search and rescue transponders, unlike SAR instruments in other orbits, are only able to detect the beacon signals, not help to determine location. This detection rapidly alerts the global SAR network, Cospas-Sarsat, of a distress beacon's activation. This gives the system valuable time to prepare before the signal's origin can be determined by SAR instruments on low-Earth-orbiting satellites.

Additionally, beacons with integrated GPS technology can send their location data through GOES to the SAR network. The network can then alert local first responders to the location of the emergency without the aid of the low-Earth-orbiting constellation of search and rescue instruments.

NASA's SAR team provides on-orbit testing, support and maintenance of the search and rescue instrument on GOES. The GOES satellites and SAR instruments are funded by NOAA.

"We are proud to support the Cospas-Sarsat program by hosting a search and rescue transponder aboard our satellites," said Tim Walsh, GOES-R series program acting system program director. "SAR is one of the many NOAA-NASA collaborations that translate into life-saving technology."

In the future, first responders will rely on a new constellation of instruments on GPS and other Global Navigation Satellite Systems currently in medium-Earth orbit, an orbit that views larger swathes of the Earth than low-Earth orbit due to higher altitudes. These new instruments will enable the SAR network to locate a distress signal more quickly than the current system and calculate their position with accuracy an order of magnitude better, from 1 km to approximately 100 meters.

In the meantime, the SAR transponders aboard GOES cover the time between the activation of a distress signal and detection by SAR instruments in low-Earth orbit.

"NASA's SAR office dedicates itself to speed and accuracy," said Lisa Mazzuca, SAR mission manager. "The instruments and technologies we develop endeavor to alert first responders to a beacon's activation as soon as possible. The GOES search and rescue transponders are crucial to this goal, providing near-instantaneous detection in the fields of view of the Earth."


DCS (Data Collection System):

The objective of DCS is to collect near real-time environmental data from more than 19,000 data collection platforms located in remote areas where normal monitoring is not practical. The DCS receives data from platforms on ships, aircraft, balloons and fixed sites. These data are used to monitor seismic events, volcanoes, tsunami, snow conditions, rivers, lakes, reservoirs, ocean data, forest fire control, meteorological and upper air parameters.

The transmissions can occur on predefined frequencies and schedules, in response to thresholds in sensed conditions, or in response to interrogation signals. The transponder on board the GOES satellite detects this signal and then rebroadcasts it so that it can be picked up by other ground-based equipment. Federal, state and local agencies then monitor the environment through the transmission of observations from these surface-based data collection platforms. The platforms can be placed in remote locations and left to operate with minimal human intervention. The Data Collection System thus allows for more frequent and more geographically complete environmental monitoring. Enhancements to the DCS program during the GOES-R era include expansion in the total number of user-platform channels from 266 to 433.

GoesR_Auto0

Figure 73: Data flows of the DCS (image credit: NOAA/NESDIS, Ref. 127)


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127) “GOES-R Unique Payload Services (UPS),” URL: http://www.goes-r.gov/spacesegment/ups.html

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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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