Landsat-9 — a partnership between NASA and USGS (U.S. Geological Survey) — will continue the Landsat program's critical role in monitoring, understanding and managing the land resources needed to sustain human life. Today's increased rates of global land cover and land use change have profound consequences for weather and climate change, ecosystem function and services, carbon cycling and sequestration, resource management, the national and global economy, human health, and society. 1) 2) 3)
Landsat is the only U.S. satellite system designed and operated to repeatedly observe the global land surface at a moderate scale that shows both natural and human-induced change.
Figure 1: Building on the Landsat Legacy (image credit: NASA)
• In 2016, the Landsat-9 project has been fast-tracked for a December 2020 launch (initially planned for 2023) .The risk reduction of a Landsat data gap is a high priority of the U.S. Sustainable Land Imaging Program. Landsat-9 will be a rebuild of Landsat-8 so it can be launched as soon as possible. 4)
- Hence, NASA HQ amended direction in response to FY16 appropriations and associated congressional language targeting a 2020 launch (Ref. 2).
- In January 2016, the project has been directed to pursue the earliest possible launch date within the spending authority provided in FY16.
- Project has $100M in Congressionally directed spending authority for FY16: $58M of unspent carryover from FY15, $42M in new FY16 funding.
- Substantial progress in FY16 is required for maintaining CY2020 LRD (Launch Readiness Date).
According to Jeff Masek, the project scientist: "With a launch in 2020, Landsat-9 will propel the program into the next half-century of global observations. That's the hallmark of Landsat: the longer the satellites view the Earth, the more phenomena you can observe and understand."
Landsat-9, like Landsat-8, will have a higher imaging capacity than past Landsat missions, allowing more valuable data to be added to the Landsat's global land archive.
Landsat-8, after collecting data for 3.5 years, has already added over 827,000 images to the archive—this represents 12.5 percent of the entire 44-year Landsat data collection—and each day Landsat-8 adds another ~700 new scenes. Landsat-9, like Landsat-8, will be both radiometrically and geometrically better than earlier generation Landsats.
Landsat-9 is essential for informed land use decisions:
Landsat-9 will extend our ability to measure changes on the global land surface at a scale where we can separate human and natural causes of change. When land use and resource availability issues arise, Landsat-9 will help decision makers make informed management decisions. Landsat-9 will thus contribute a critical component to the international strategy for monitoring the health and state of the Earth.
Landsat users can now take advantage of more frequent observations (every 8 days using two satellites). Applications such as weekly tropical deforestation alerts, water quality monitoring, and crop condition reports are now feasible with the constellation.
With increased activity in international and commercial remote sensing, Landsat has emerged as a cornerstone of the global constellation of imagers. The science quality of the Landsat archive, including careful calibration, allows it to serve as a "gold standard" for studies harmonizing multiple sources of satellite imagery.
Landsat-9 will enable informed decision support for key areas such as:
• Tropical deforestation and global forest dynamics: the Landsat archive provides an impartial and unbiased record of Earth's forests for world governments and resource organizations to verify claims of environmental protection and carbon storage.
• Urban expansion: the Landsat record helps us visualize the impact of humankind's convergence on urban centers and to understand the environmental consequences.
• Water use: Landsat-9 will be an invaluable tool for managing water in areas such as the Western U.S. where water is scarce and water usage between agriculture, industry, and residential needs is very competitive.
• Coral reef degradation: Landsat has helped enable global monitoring of Earth's reefs.
• Glacier and ice-shelf retreat: the Landsat archive chronicles changes to 98 percent of Earth's glaciers, and Landsat-9 will continue monitoring them into the future.
• Natural and man-made disasters: Landsat data are regularly used as part of the International Disaster Charter, mapping disaster impacts to save lives.
• Climate change: Landsat data provide a direct view of how almost five decades of climate change have affected Earth's surface and biology.
Some background: Already in April 2015, NASA and the U.S. Geological Survey (USGS) have started work on Landsat- 9, planned to launch in 2023, to extend the Earth-observing program's record of land images to half a century. 5)
Landsat is a remarkably successful partnership," said Sarah Ryker, USGS deputy associate director for climate and land use change, Reston, Virginia. "Last year the White House found that GPS, weather satellites, and Landsat are the three most critical types of Earth-orbiting assets for civil applications, because they're used by many economic sectors and fields of research. Having Landsat-9 in progress, and a long-term commitment to sustainable land imaging, is great for natural resource science and for data-driven industries such as precision agriculture and insurance."
NASA's Goddard Space Flight Center in Greenbelt, Maryland, will lead development of the Landsat-9 flight segment. Goddard will also build the TIRS-2 (Thermal Infrared Sensor-2), which will be similar to the TIRS that the center built for Landsat-8. The new improved TIRS will have a five-year design lifetime, compared to the three-year design lifetime of the sensor on Landsat-8.
With decades of observations, scientists can tease out subtle changes in ecosystems, the effects of climate change on permafrost, changes in farming technologies, and many other activities that alter the landscape.
SLI (Sustainable Land Imaging) 2016-2035:
President Obama's NASA budgets of FY14 and FY15 called for design and initiation of an affordable, sustained,Land Imaging Satellite System (with USGS) to extend the Landsat data record for decades –not just the "next mission". 6)
The SLI program will enable the development of a multi-decade, spaceborne system that will provide users worldwide with high-quality, global, land-imaging measurements that are compatible with the existing 44-year Landsat data record. Landsat-9 is the latest satellite in the Landsat series — it will continue Landsat's irreplaceable record of Earth's land surface upon its 2020 launch. To reduce the build time and a risk of a gap in observations, Landsat-9 will largely replicate its predecessor Landsat-8.
Table 1: Landsat program on-orbit status as of July 2015
Legend to Figure 2:
- a) Limited data of Landsat-4 due to transmitter failure soon after launch. Only 45,172 Landsat-4 TM (Thematic Mapper) scenes from 1982-1993 are available for science users ~10 scenes/day (versus 725 scenes/day from Landsat-8)
- b) Data coverage of Landsat-5 is limited to CONUS (Continental US) and international ground station sites after a transmitter failure in 1987; the MSC (Multispectral Scanner) turned off in August 1995.
- c) Degraded performance due to SLC (Scan Line Corrector) failure in May 2003.
Landsat-9 mission objectives:
• Collect and archive moderate-resolution, reflective and emissive multispectral image data affording seasonal coverage of the global land mass for a period of no less than five years.
• Ensure that Landsat-9 data are sufficiently consistent with data from the earlier Landsat missions, in terms of acquisition geometry, acquisition rates, calibration, coverage characteristics, spectral and spatial characteristics, output product quality, and data availability to permit studies of land cover and land use change over multi-decadal period.
• Distribute standard Landsat-9 data products to users on a nondiscriminatory basis and at no cost to the users.
The Landsat-9 satellite will be constructed at Orbital ATK, NASA awarded a contract in October 2016. Landsat-9 is based on the company's LEOStarTM-3 platform, the medium-class LEO (Low Earth Orbit) spacecraft successfully flown on Landsat-8 and NASA's Fermi and Swift Gamma-ray astrophysics observatories. Landsat-9 will be designed, manufactured and tested by Orbital ATK's Space Systems Group at its facilities in Gilbert, Arizona, the same location and production team that executed the Landsat-8 program. Orbital ATK will also support launch, early orbit operations and on-orbit check-out of the observatory, which is scheduled for launch in December of 2020. 7) 8)
Figure 3: Artist's rendering of the Landsat-9 spacecraft (image credit: Orbital ATK)
A spacecraft description will be added as more information becomes available.
Project development status:
• August 23, 2019: This month, TIRS-2 successfully passed the stringent 12-week testing process at NASA's Goddard Space Flight Center in Greenbelt, Maryland. It was shipped to Northrop Grumman's facility in Arizona, where it and the OLI-2 (Operational Land Imager-2) will be assembled onto the Landsat-9 spacecraft. Landsat-9 is a joint effort of NASA and the U.S. Geological Survey. 9)
Figure 4: Engineers pose with the TIRS-2 instrument, which was built and tested at NASA Goddard (image credit: NASA)
Figure 5: From orbit aboard the Landsat-9 satellite, the TIRS-2 (Thermal Infrared Sensor-2) will measure the temperature of Earth's land surfaces, detecting everything from a smoldering wildfire, to the amount of irrigation used on crop fields, to wispy clouds that are all but invisible to other instruments. First, however, it had to survive tests that simulated the harsh environment of space (video credit: NASA Goddard, Published on Aug 23, 2019)
- Like digital cameras on a smart phone, the TIRS-2 instrument is an imager, said Joel McCorkel, the instrument's deputy project scientist. But while a camera detects light reflected off an object, TIRS-2 detects the thermal energy that an object emits. The hotter a surface is, the more energy the instrument will detect. And since TIRS-2 is a highly-calibrated scientific instrument, not a camera, it provides data that researchers can use to investigate key questions about our home planet.
- TIRS-2 is designed to work in the same way as the first TIRS instrument, which launched on Landsat-8 in 2013 and is still collecting important data on Earth's surface temperature. But the latest version has a couple improvements.
- "The beauty of TIRS-2, is that we had TIRS data from up in orbit and were able to look at what worked, and how we could mitigate what didn't work," said Melody Djam, TIRS-2 instrument deputy project manager at Goddard.
- The TIRS-2 team incorporated a new optical component to shield the instrument's sensor from stray light that had caused problems on the original instrument, requiring software fixes. The first TIRS was also designed, constructed, and integrated in less than three years – which is an incredibly quick turnaround for a satellite's instrument – and so it was only required to last three years. TIRS-2, however, is designed with redundant electronics and other components in order to last at least five years.
- IRS-2 has about 10 main components, and each one was built and tested individually before engineers brought everything together to ensure the instrument worked, Djam said. The engineering team, which included as many as 250 people, then tested the whole instrument both in the clean room, as well as in environmental chambers that simulate the launch and space environments.
- With round-the-clock shifts and successful tests, the team delivered the instrument more than two weeks ahead of its target date. TIRS-2 passed its pre-ship review on Aug. 12 and was trucked to Gilbert, Arizona in two shipments. At the Northrop Grumman facility, the team will reassemble it, test it, and make sure everything is ready to integrate the instrument with the Landsat 9 spacecraft this fall.
Taking Earth's temperatures from orbit
- Landsat satellites have been observing Earth since 1972, building the longest continuous record from space of the planet's forests, farms, cities, and other surfaces. Starting with Landsat-4 and continuing through the first TIRS instrument on Landsat-8, the satellites have carried instruments that can detect thermal energy as well as visible and infrared light – and water managers and others have put these observations to work.
- "Landsat's thermal data is critical for tracking water use in the western United States, where rainfall can be short in supply and managing water resources is critical to ensuring a sustainable supply for farmers, cities, and natural ecosystems," said Bruce Cook, Landsat-9 deputy project scientist at Goddard.
- When plants take up water from the soil, they ‘sweat' it out as they undergo transpiration, cooling them down just as sweating cools people down. By measuring the temperature of growing plants and soils that are cooled by transpiration and evaporation, respectively, Landsat users can create maps that quantify water use and consumption. The accuracy of these maps is increased by TIRS' two thermal bands, which allows researchers to subtract out the effect of atmospheric constituents better than with the single-band thermal data from previous Landsat instruments.
- TIRS also works "behind the scenes" to detect clouds that are difficult to sense with visible data alone, which makes it an important filter for scientists constructing Landsat time series to record disturbances and changes in land cover over time.
- "With TIRS, scientists can better identify clouds, remove those data, and focus on the real land surface," said McCorkel. "This increases the efficiency of their study and the accuracy of their science, whether they're looking at a plot of land or a continent."
• On June 6, 2018, Northrop Grumman Corporation announced it has closed the acquisition of Orbital ATK Inc. ("Orbital ATK"), a global leader in aerospace and defense technologies. Orbital ATK is now Northrop Grumman Innovation Systems, a new, fourth business sector. — Hence, the Landsat-9 spacecraft development news are now going to be reported under the label of Northrop Grumman. 10)
• May 23, 2018: Landsat-9 will continue the Landsat program's critical role in monitoring, understanding and managing the land resources needed to sustain human life. To do so, Landsat-9 will carry two science instruments: the Operational Land Imager 2 (OLI-2) and the Thermal Infrared Sensor 2 (TIRS-2). 11)
Figure 6: Ball Aerospace technicians prepare to install the focal plane assembly, a 14-module detector array, into the OLI-2 (Operational Land Imager 2), one of the key science instruments for Landsat-9 (image credit: Ball Aerospace)
• April 25, 2018: The Landsat-9 Mission Critical Design Review was held April 17-20, 2018 at NASA/GSFC (Goddard Space Flight Center), Greenbelt, MD. NASA and USGS scientists and engineers provided the Standing Review Board (SRB) a status on all segments including the spacecraft, instruments, launch vehicle, and ground system to date. 12)
- The SRB had high praise for the accomplishments and the strengths of the Landsat-9 project team. Highlights noted included the high degree of experience and expertise throughout the project, the close working relationship among agency team members, the project's strong technical maturity, the cost and schedule performance to date, the maturity of plans going forward, and exemplary use of lessons learned. The SRB assigned one request for action (RFA) related to USGS funding reserve levels.
• April 10, 2018: The USGS and NASA held a Landsat-9 Ground System Preliminary Design Review (GPDR) on March 20-22, 2018 in Sioux Falls, South Dakota. The GPDR, which contains the Data Processing and Archive System (DPAS), Ground Network Element (GNE) and Landsat Multi-Satellite Operations Center (LMOC) components, demonstrated that the proposed design of each component satisfies the required functional and performance requirements to continue the Landsat-9 development process. 13)
- With the GPDR a success, the Ground System can now proceed to the Critical Design Review, which is planned for Fall 2018 – continuing to ensure the Landsat-9 mission remains on schedule for a launch readiness date of December 2020.
• March 15, 2018: Northrop Grumman (former Orbital ATK) has been given approval to begin building the NASA Landsat-9 spacecraft after completing a comprehensive design review of the mission. Northrop Grumman is designing and manufacturing the satellite, integrating two science instruments, and supporting launch, early orbit operations and on-orbit check-out of the observatory. 14)
- Representatives from NASA and Northrop Grumman successfully completed a rigorous Critical Design Review (CDR) demonstrating that the program meets all technical performance measures and requirements. The execution of the design review enables the program to effectively transition into manufacturing and prepare for the assembly, test and launch operations phase of the mission. The Landsat-9 spacecraft will be manufactured and tested at the company's Gilbert, Arizona, facility and is currently planned for launch in late 2020. The spacecraft will be operated by the U.S. Geological Survey once in orbit.
- The Critical Design Review took place February 26 through March 1 at Northrop Grumman's facility in Gilbert, Arizona. Landsat-9 will extend the length of the overall Landsat series to half a century, providing the longest continuous record of the Earth's surface as seen from space. Northrop Grumman has built three other Landsat satellites, including Landsat-8, which was launched in 2013, and is providing high quality images in quantities that surpass mission requirements.
• February 14, 2018: Ball Aerospace delivered the TIRS-2 Flight Cryocooler for the Landsat-9 TIRS-2 (Thermal Infrared Sensor-2) instrument ahead of schedule to NASA/GSFC (Goddard Space Flight Center). Achieving this milestone early will allow GSFC additional time and options during the instrument integration and test phase. 15)
- For more than 45 years, Landsat Earth-observing satellite missions have gathered multispectral imagery from space, helping scientists understand the impacts of human activity and natural events on our planet through constant monitoring of land changes. The TIRS-2 instrument aboard Landsat-9 will provide two-band thermal imaging data to measure surface temperature and track land and water usage. The Ball-built cryocooler on the instrument enables TIRS-2 to cool the focal plane and the surrounding enclosure to maintain the sensitivity needed for imaging.
- The TIRS-2 Flight Cryocooler is based upon a Ball family of Stirling Cryocoolers, which are the nation's largest capacity, highest efficiency cryocoolers on orbit to date. The two-stage Flight Cryocooler consists of two CCEs (Cryogenic Control Electronics), one RSE (Redundancy Switch Electronics), a TMU (Thermo Mechanical Unit) and a flight harness set. For TIRS-2, Ball developed redundant electronics and incorporated many design and manufacturing improvements to simplify the fabrication and assembly process.
• December 19, 2017: The USGS and NASA have selected a new Landsat science team, whose primary responsibility is to conduct Landsat-based scientific research and engineering studies, develop useful data products and applications and share the results of its work with the USGS, NASA and others — members will serve a five-year term from 2018 to 2023. 16) 17)
- The new team will conduct scientific research on technical issues critical to the success of the overall Landsat mission, including topics related to data acquisition, product access and formats, new science datasets, practical data applications to be derived from an operational system and other science opportunities for new and past-generation Landsat data.
- Members will evaluate the quality of data when Landsat 9 is launched, which is estimated for December 2020, and help ensure that Landsat 9 data can be successfully integrated into the overall Landsat record. They will also be on the ground floor of discussions for future Landsat missions. In addition, the new team may be called on to assess the viability of Landsat 7 data for scientific or operational purposes as the satellite nears its nineteenth year in orbit. They will also be responsible for looking at opportunities to develop new and advanced applications of Landsat data.
- Previous Landsat Science Teams helped increase the ease of use and expand the utility of Landsat data for users across the nation; greatly increased the size of the Landsat archive by transferring historical data held by international cooperators; and advanced the breadth and accuracy of applications of the 45-year Landsat record.
Table 2: The 2018-2023 USGS-NASA Landsat Science Team members and their areas of study
• December 7, 2017: Landsat-9 has entered its implementation phase, or "Phase C" of its project lifecycle after successfully passing Key Decision Point C (KDP-C). The Landsat-9 project team garnered high praise from NASA Headquarters' APMC (Agency Program Management Council) for the project's exemplary mission formulation performance and for the lockstep collaboration with its partner agency, the U.S. Geologic Survey. 18)
- The implementation phase of the Landsat-9 project lifecycle will be dominated by the fabrication and testing of the Landsat-9 instruments and spacecraft; this phase will last approximately 24 months and will be followed by the observatory integration phase.
Figure 7: A timeline of the Landsat-9 mission development and lifecycle (image credit: NASA)
Mission Schedule and Lifecycle (Figure 7): NASA-managed satellite builds have a mission lifecycle that is divided into incremental phases. Phase A is concept and technology development; Phase B is preliminary design and technology completion; Phase C is final design and fabrication; Phase D is system assembly, integration/testing, and launch readiness; Phase E starts after on-orbit operational checkout and ends at the mission's operational end. 19)
• September 24, 2017: The USGS awarded the prime contract to General Dynamics Mission Systems, with a.i. solutions as one of the subcontractors. Under this contract, General Dynamics will continue to operate Landsat-8 from the existing mission operations center at the GSFC (Goddard Space Flight Center) and will begin design and integration of a new Landsat Multi-satellite Operations Center at GSFC. 20)
- Under the requirements of the contract, a.i. solutions will provide key flight dynamics and mission planning for the ongoing Landsat-8 mission, develop the flight dynamics component of the ground system that will launch and operate on Landsat-9 as well as transition Landsat-8 to the new flight dynamics system once complete.
• September 18, 2017: The Landsat-9 satellite mission team completed a successful Mission PDR (Preliminary Design Review) last week. During the review, the mission team demonstrated to an independent Standing Review Board that all design plans for the Landsat-9 mission are both sound and well integrated. - The PDR is the last milestone before the major Key Decision Point C, scheduled for December 2017, after which the mission officially enters its implementation phase. The review took place from September 12-15 at NASA's Goddard Space Flight Center in Greenbelt, Maryland. 21)
• August 10, 2017: The Landsat-9 spacecraft passed an important progress evaluation milestone in mid-July. The PDR (Preliminary Design Review) for the Orbital ATK-sourced spacecraft was held from July 18–20 in Gilbert, Arizona at the satellite fabricator's facility. 22)
- NASA concluded that the Landsat 9 spacecraft is on track and meeting all of the system and schedule requirements needed for the mission's planned December 2020 launch.
• February 28, 2017: The Landsat-9 TIRS-2 (Thermal Infrared Sensor-2) team at the NASA/GSFC (Goddard Space Flight Center) has successfully completed their ICDR (Instrument Critical Design Review). 23)
• February 27, 2017: USGS and NASA officials will participate in the Landsat-9 SSRR (Spacecraft System Requirements Review) February 28 and March 1 at the Orbital ATK facility in Gilbert, Arizona. 24)
- An independent panel will review the work of the spacecraft vendor to understand system requirements in a number of areas, including being able to control the orientation of Landsat 9 through attitude control, how much redundancy is built into the spacecraft, and how much fuel will be onboard.
- Reviewers will also look at fault management capabilities, which include hardware and software features used to address any potential problems that may arise in orbit. This is the final such review before full-scale spacecraft design and development begins.
• On November 30 – December 1, 2016, USGS EROS hosted the Landsat-9 GSRR (Ground System Requirements Review) in Sioux Falls, SD. This was the first in a series of major project reviews for Landsat-9, which is scheduled for launch December 2020. The GSRR included presentations given to a joint NASA/USGS review panel on the proposed components of the Landsat-9 Ground System. At the conclusion of the review, the panel approved the Landsat-9 Ground System team to proceed to the PDR (Preliminary Design Review) stage. 25)
• Oct. 25, 2016: NASA has awarded a delivery order under the Rapid Spacecraft Acquisition III (Rapid III) contract to Orbital ATK for the Landsat 9 spacecraft. This contract is a 5-year, firm fixed-price delivery order for the purchase of the Landsat-9 spacecraft in the amount of $129.9 million. Orbital will design and fabricate the spacecraft, integrate the mission's two government-furnished instruments, and conduct satellite-level testing, in-orbit satellite checkout, and mission operations support. The work will be performed at the contractor's facilities and at the launch site at Vandenberg Air Force Base in California. 26)
• May 17, 2016: NASA has awarded a sole source contract to BATC (Ball Aerospace and Technology Corporation) of Boulder, Colorado, for the TIRS-2 (Thermal Infrared Sensor-2) instrument Cryocooler for Landsat-9. 27) — TIRS-2 is being upgraded to a Class B instrument, with additional steps being taken to fix the straylight issue affecting the Landsat-8 TIRS instrument.
• On March 4, 2015, the Landsat-9 project was officially directed to initiate activities with strong support from Administration, Congress, NASA, and USGS (Ref. 2).
Figure 8: Overview of spectral band coverage in various missions (HyspIRI, Sentinel-2 of ESA, Landsat-8 and Landsat-7 (image credit: NASA)
What Makes Landsat-9 a Science-Grade Satellite?
Scientific studies rely on science-grade instruments—instruments that record information reliably and accurately. Studying long-term changes to Earth's surface requires carefully calibrated observations to measure subtle changes occurring over decades. The Landsat-9 mission will extend the data record of Earth observations and advance the scientific study of land change and land use into the next half-century. Consistency in Landsat's spatial resolution, calibration, and spectral characteristics over four decades allows long-term, consistent comparisons of historical and current data.
1) Spectral Coverage: For a science-grade instrument, the ability to have broad spectral coverage—the ability to see parts of the light spectrum beyond the visible and VNIR (Near Infrared ) — is essential. Landsat-9 will collect data in three shortwave infrared bands and two thermal infrared bands, in addition to VNIR. These longer wavelength bands play a vital role in water use measurements (evapotransporation), fire scar mapping, volcanic lava flow mapping, and other indices used for land use monitoring.
Because of optical diffraction, the ability to image features at longer wavelengths requires progressively larger telescope apertures. In addition, multiple types of detectors (or even separate instruments) may be required to cover the full spectral range. Thermal detectors must be cooled to very low temperatures (-150º C) in order to be sensitive to the low radiance levels emitted at normal Earth temperatures, which in turn necessitates coolers that can cool to cryogenic temperatures.
2) Accuracy: Radiometric resolution and geometric fidelity: We use the term "science-grade" a lot when describing Landsat's instruments. What we mean by this is that the data collected by Landsat satellites have very strict levels of accuracy that they must live up to—the radiation measurements must be reliable for each of the Landsat spectral bands.
This reliability is what makes comparisons of Landsat data day-to-day, year-to-year and sensor-to-sensor possible. To do scientific research you need to know you can make accurate comparisons.
Radiometric resolution is the ability to measure small differences in radiation over a wide range of brightness levels and geometric fidelity is the ability to know exactly where any given pixel is located. Large optics help by mitigating stray light and ensuring focal plane uniformity (i.e. sameness across the field of the tens-of-thousands of detectors which the telescope focuses light on) to avoid skewed measurements.
The Landsat-9 instruments provide radiometric calibration via onboard sources (blackbody, lamps) and a solar-diffuser system for the reflective bands. Additionally, every full Moon, Landsat-9 (like Landsat-8) will be turned toward the Moon to scan the distant lunar surface multiple times. Since the Moon has no atmosphere, it is the perfect consistent source of light to measure–like a gray card for calibrating a camera's exposure. Data from the Moon is used to both complement and corroborate the results from the other on-board calibration activities.
3) Redundancy: Live long and be precise: Landsat-9 must have sufficient redundancy to ensure the collection of science-grade data over a 5-year mission life. This means that many critical components have a redundant counterpart to minimize the risk of a single point failure. For example, Class B missions like Landsat-9 typically have two of almost every kind of electronics on board (e.g., spacecraft computers, communications electronics, attitude control electronics, instrument control electronics), extra reaction wheels, and extra thrusters. In the event that some primary piece of equipment on the satellite experiences an anomaly that impacts its performance, ground controllers can switch over to the backup unit on the satellite to do the job. But implementing redundancy comes at the expense of higher cost and longer development time, and it also tends to make things bigger and heavier. So a critical element of mission design is performing detailed reliability and risk assessments to determine where redundancy might be most beneficial, and then implementing redundancy as efficiently as possible to provide the needed level of reliability.
Launch: A launch of Landsat-9 is planned for December 2020 from VAFB, CA on an ULA Atlas-V 401 vehicle.
In October 2017, NASA selected ULS (United Launch Services LLC) of Centennial, Colorado, to provide launch services for the Landsat-9 mission. The mission is currently targeted for a contract launch date of June 2021, while protecting for the ability to launch as early as December 2020, on an Atlas-V 401 rocket from Space Launch Complex 3E at Vandenberg Air Force Base in California. 28)
Orbit: Sun-synchronous near-circular orbit, altitude = 705 km, inclination = 98.2º, period = 99 minutes, repeat coverage = 16 days. The Landsat-9 satellite will be in coplanar orbit with Landsat-8, 180º apart. This reduces the repeat coverage to 8 days.
Sensor complement (OLI-2, TIRS-2)
The two NASA science instruments are OLI-2 and TIRS-2. OLI-2 is being constructed by BATC (Ball Aerospace & Technology Corp.), while TIRS-2 is being developed by NASA's Goddard Space Flight Center.
Landsat-9 will fly near-identical copies of the OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor) instruments that were flown on Landsat-8. The TIRS instrument will be upgraded to a risk class B implementation, whereas no changes are planned for OLI. With respect to the Landsat-9 project, these instruments will be referred to as OLI-2 and TIRS-2.
In the four+ decades since Landsat-1 launched, the spectral bands of the Landsat satellites have evolved. Landsat-9, like Landsat-8, has the most evolved of the Landsat spectral bands. 29)
In 1972, Landsat-1 launched with a three-band RBV (Return Beam Vidicon) camera system and a secondary four-band digital MSS (Multispectral Scanner System). The MSS with its scanning mirror whisking back and forth to create an image, seemed to many researchers of the period the antithesis of the high quality camera systems traditionally used in aerial studies. But the secondary MSS instrument proved itself the imaging powerhouse producing superior data. But the four-band MSS was spectrally coarse; it essentially mimicked the color infrared films that became widely used during WWII (World War II).
For follow-on sensors, Landsat management brought together scientists from diverse fields to discuss and recommend spectral channels most useful for answering questions in their research areas. These discussions informed the more sophisticated TM (Thematic Mapper) sensor with its seven spectral bands that flew on the Landsat missions-4 and -5. The Landsat TM band placement has subsequently guided all successive Landsat sensors and is is also echoed in almost all modern passive remote sensing systems—domestic, international, public, commercial, and even those circling about other planets.
Figure 9: MSS aboard Landsats 1–5 had four bands. TM (Thematic Mapper) aboard Landsats-4 & -5 had seven bands. Landsat-7's ETM+ (Enhanced Thematic Mapper Plus) has 8 bands and Landsats-8 &-9 have 11 bands. The atmospheric transmission values for this graphic were calculated using MODTRAN for a summertime mid-latitude hazy atmosphere (circa 5 km visibility), image credit: NASA
Today, Landsat-8 has and Landsat-9 will have eleven spectral bands acquired by the OLI/TIRS and OLI-2 / TIRS-2 instruments, respectively. These new bands help scientists measure high, thin clouds and water quality.
The previous generation sensor, ETM+, supports 8-bit data products, which means means the brightest to the darkest pixels are discriminated with 256 data values. The greater sensitivity of OLI, OLI-2, TIRS, and TIRS-2 instruments allow the signal to be discriminated over 4096 data values (12 bits), and the range has been increased to prevent saturation of very bright targets such as snow.
Table 3: Specification of the OLI-2 and TIRS-2 spectral band requirements
OLI-2 (Operational Land Imager-2)
OLI-2 will continue observations in the visible, near infrared, and shortwave infrared portions of the electromagnetic spectrum and includes two new spectral bands, one of which is designed to support monitoring of coastal waters and the other to detect previously hard to see cirrus clouds that can otherwise unknowingly impact the signal from the Earth's surface in the other spectral bands. 30)
The spatial resolution of its images will be 15 m for the panchromatic band and 30 m for the multispectral bands. The image swath will be 185 km wide, covering wide areas of the Earth's landscape while providing sufficient resolution to distinguish land cover features like urban centers, farms, and forests. Landsat-9's near-polar orbit precesses at the same rate the Earth rotates around the sun, allowing the entire Earth to fall within view every 16 days at the same local solar time.
OLI-2 will, to the extent possible, be a copy of OLI for Landsat-9 to maintain data continuity with Landsat-8 and to minimize cost and risk (Ref. 2).
Figure 10: A diagram of OLI-2 showing its main components (image credit: NASA)
Instrument design: The OLI-2 is a pushbroom sensor. Its focal plane features long arrays of photosensitive detectors. Incident radiation is focused onto the focal plane by a four-mirror anastigmatic telescope. OLI-2 has a 15ºFOV covering a 185 km across-track ground swath.
Landsat-9's photosensitive detectors are divided into 14 modules. There are ~7000 across-track detectors for each OLI-2 spectral band, except the 15 m panchromatic band that has 13,000 detectors. Each spectral band has a specific filter; together the filters are arranged like a "butcher-block" over each module's detector array. The visible and near-infrared detectors are made from Silicon PIN (SiPIN). The shortwave infrared detectors are made from Mercury–Cadmium–Telluride (MgCdTe).
The OLI-2 telescope will view the Earth through its Earth-view baffle. There is a shutter wheel assembly between the Earth-view baffle and the aperture stop. Light enters the telescope via a hole in the shutter wheel during nominal observations. The solar-view baffle is occasionally pointed at the sun so that a diffuser panel can reflect solar illumination into the telescope for calibration purposes. Two lamp assemblies with six small lamps each inside an integrating hemisphere can illuminate the full OLI-2 focal plane through the telescope with the shutter closed as another component of the OLI-2 calibration subsystem.
Figure 11: Drawing of the OLI-2 focal plane showing the 14 detector modules; the "butcher-block" filters are the striped black boxes where the upper and lower detector modules meet (image credit: BATC)
TIRS-2 (Thermal Infrared Sensor-2)
TIRS-2 will be a rebuild of the Landsat-8 TIRS except TIRS-2 will be upgraded to Risk Class B for Landsat-9. The primary Risk Class B improvements are (Ref. 2):
• Redundant MEBs (Main Electronics Boxes)
• Redundant CCEs (Cryocooler Electronics)
• Redundant RSEs (Switch Electronics).
Other TIRS-2 improvements:
• Improved stray light performance through improved telescope baffling
• Improved position encoder for scene select mirror to address problematic encoder on Landsa- 8 TIRS
• Improved thermal blanketing to better protect from micrometeorite impact; in accordance with new GSFC guidelines.
The TIRS-2 instrument is a two-band thermal imaging sensor with a push broom sensor (like OLI-2). Its focal plane has long arrays of photosensitive detectors.
The instrument features a four-element refractive telescope that focuses an f/1.64 beam of thermal radiation onto a focal plane that is cryogenically cooled. TIRS-2 has a 15º FOV to match the 185 km across-track swath of OLI-2. The TIRS-2 focal plane holds three modules with QWIP (Quantum Well Infrared Photodetector) arrays arranged in an alternating pattern along the focal plane centerline.
Spectral filters cover each focal plane module to create TIRS-2's two specified bandwidths. Each QWIP array is 640 detectors long in cross-track allowing for overlap between the arrays to produce an effective linear array of 1850 pixels spanning across the 185 km ground swath.
The FOV is flipped between nadir (Earth) and both an internal blackbody and a deep space view used for on-orbit radiometric calibration using a mirror controlled by a scene select mechanism. This allows the view to be changed without changing the nominal Earth-viewing attitude of the Landsat-9 spacecraft.
A two-stage mechanical cryocooler will cool TIRS-2's focal plane. This permits the QWIP detectors to function at their required temperature of 43 K (-230° C). There will be two radiators mounted to the side of the TIRS-2 instrument structure. One dissipates heat from the cryocooler and the other passively maintains a constant TIRS-2 telescope temperature of 185 K (-88° C).
Figure 12: A diagram of TIRS-2 showing its main components (image credit: NASA)
Figure 13: Left: The TIRS-2 focal plane: the 3 squares in the center of the circuit board are QWIPs. Each QWIP can measure 327,680 pixels. The QWIPs on TIRS-2 will detect two narrow segments of the thermal infrared spectrum. Right: The TIRS-2 cryocooler will look like the one above (image credit: NASA)
On November 30 – December 1, 2016, the USGS EROS hosted the Landsat-9 GSRR (Ground System Requirements Review) in Sioux Falls, SD (South Dakota). This was the first in a series of major project reviews for Landsat-9, which is scheduled for launch in December 2020. The GSRR included presentations given to a joint NASA/USGS review panel on the proposed components of the Landsat-9 Ground System. At the conclusion of the review, the panel approved the Landsat-9 Ground System team to proceed to the PDR (Preliminary Design Review) stage. 31)
Figure 14: Landsat-9 operations concept architecture - identical to Landsat-8 (image credit: USGS)
The ground segment consists of the following elements (Ref. 3):
1) MOC (Mission Operations Center) with the following functions: Command & telemetry, Trending & analysis, Flight dynamics, Science acquisition planning, Primary and backup MOCs at GSFC.
- FOT (Flight Operations Team) performs mission planning and scheduling, command and control, health and status monitoring, orbit and attitude maintenance, mission data management.
- NASA provides MOC and BMOC facility at GSFC as well as NASA institutional services (SN, NEN, NISN, FDF) through on-orbit acceptance.
2) Operations Flight Operations Team:
- NASA leads (USGS supports) mission operations readiness activities, pre-launch, launch and early orbit activities.
- USGS leads operations following on-orbit acceptance.
3) DPAS (Data Processing and Archive System) with the following functions: Provides data ingest, product generation, & image assessment/processing, User Portal web interface for data discovery, product selection & ordering (for Cal/Val), & product distribution Storage and archive services.
- DPAS facility at USGS EROS Center.
4) GNE (Ground Network Element) with the following functions: Ground stations/antennas for X-band image & S-band telemetry data downlink; Generation of S-band command uplink.
- LGN (Landsat Ground Network) stations provide X- and S-band communications with the Observatory.
- LGN stations in Sioux Falls, SD; Fairbanks, AK; and Svalbard, Norway.
- DCRS (Data Collection and Routing Subsystem) gathers mission data from LGN stations into complete intervals to transfer to the DPAS.
Figure 15: USGS/EROS facilities in Sioux Falls, SD (image credit: USGS)
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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 (email@example.com).