GOLD (Global-scale Observations of the Limb and Disk)
GOLD (Global-scale Observations of the Limb and Disk) Hosted Payload in GEO
The GOLD project is a mission of opportunity and part of NASA's Explorer Program, designed to provide frequent, low-cost access to space for heliophysics and astrophysics missions with small to mid-sized spacecraft. The mission is a collaboration between LASP (Laboratory for Atmospheric and Space Physics) at the University of Colorado in Boulder, CO, UCF (University of Central Florida) in Orlando, FL, and the commercial communications satellite company, SES-GS (Government Solutions), Reston, VA. Note: In 2011, SES-GS was introduced as part of the global SES family. 1) 2) 3) 4) 5)
UCF was awarded a $55 million NASA grant to build and launch into space an instrument the size of a microwave oven that will provide unprecedented imaging of the Earth's upper atmosphere. The award is the largest single grant in UCF's history, and UCF will become the first Florida university to lead a NASA mission. 6)
GOLD is a NASA Explorer mission of opportunity to build and launch an instrument to provide unprecedented imaging of the Earth's upper atmosphere from a geostationary orbit. The information collected by the GOLD mission will have a direct impact on understanding space weather and its impact on communication and navigation satellites, which we've come to rely on for everything from television programming to cell phone coverage and GPS in our vehicles.
In addition to providing the compact instrument, LASP will provide project management, systems engineering, safety and mission assurance, instrument operations, and Education and Public Outreach (E/PO) for the mission. Under the leadership of GOLD PI (Principal Investigator) Richard Eastes of UCF, UCF will oversee the project, and build the data center that will collect, process, and distribute the science data for the mission.
An important aspect of the mission is that GOLD will be one of the first NASA science missions to fly as a hosted payload on a commercial communications satellite. This is by far the most cost-effective way to put a science instrument into geostationary orbit, where it can observe nearly a full hemisphere of the Earth all of the time.
The goal of the GOLD imaging mission is the study of the boundary layer between Earth and space and to address four primary science questions:
1) How do geomagnetic storms alter the temperature and composition structure of the thermosphere?
2) What is the global-scale response of the thermosphere to solar extreme-ultraviolet variability?
3) How significant are the effects of atmospheric waves and tides propagating from below on thermospheric temperature structure?
4) How does the nighttime equatorial ionosphere influence the formation and evolution of equatorial plasma density irregularities?
Figure 1: GOLD mission: Discovering how the upper atmosphere acts as a weather system (image credit: GOLD Team)
GOLD is a NASA PI (Principal Investigator) mission, lead by Richard W. Eastes of UCF (University of Central Florida). UCF will oversee the project and build the data center that will collect, process and distribute the data for the mission. LASP will build the compact instrument, which will operate in a geostationary orbit, and SES-GS is scheduled to launch the hosted payload on one of its communication satellites in 2017.
Other members of the GOLD team that will be supporting the mission include NCAR (National Center for Atmospheric Research), UCB (University of California at Berkeley), Computational Physics Inc., and NOAA (National Oceanic and Atmospheric Administration).
Figure 2: Overview of the GOLD mission time schedule (image credit: GOLD Team, Ref. 4)
SES-14 is a geostationary communications satellite operating in C- and Ku-bands across the Americas and the North Atlantic region, which uses electric propulsion for initial orbit raising and all on-orbit maneuvers. The spacecraft is being built by Airbus Space and Defence, based on the Eurostar E3000 EOR (Electric Orbit Raising) platform, which exclusively uses electric propulsion for orbit raising. SES-14 will replace SES's satellite NSS-806 and add new capacity. 7)
The satellite combining power and flexibility will have a double mission. The first will be a wide-beam payload of C- and Ku-band, covering the Americas plus a link to Europe. The other payload, called HTS (High Throughput Satellite) with numerous user beams, will combine an on-board processor with multi-beam coverage of the Americas and the North Atlantic. The Ku-band wide beams will bring augmented capacity to serve growing video neighborhoods in the Americas and support existing VSAT services. The HTS Ku-band multi-spot beams (20) are ideal for traffic-intensive data applications such as mobile backhaul, maritime and aeronautical services.
SES-14 will carry seven antennas. It will have a take-off weight of 4,200 kg and an electric power of 16 kW. The satellite is scheduled for launch in late 2017 and its electric propulsion system will enable it to reach geostationary orbit in four months, depending on the type of launcher used.
Figure 3: Illustration of the SES-14 spacecraft (image credit: Airbus DS)
Electric propulsion makes it possible to reduce the mass of satellites, leading to lower launch costs for a given mission and/or a more capable satellite for a given mass. Airbus Defence and Space has been using electric propulsion for station keeping for more than ten years, and is building the first large satellites using only electric propulsion for initial orbit raising. 8)
Figure 4: Illustration of electric propulsion versus chemical propulsion for orbit raising from GTO into GEO (image credit: Airbus DS)
GOLD will transmit data from a geostationary orbit at a fast pace, to build up a full-disk view every half hour, providing detailed large-scale measurements of the response of the upper atmosphere to forcing from the Sun, the magnetosphere, and the lower atmosphere.
Hosted GOLD payload:
Flying as a hosted payload on a commercial communications satellite, GOLD takes advantage of the resource margins available in the early years of the commercial mission's planned 15-year life. This hosted payload approach is a pathfinder for cost-effective NASA science missions. 9)
The affordable ride to GEO makes it possible for an Explorer-class Mission of Opportunity to perform FUV (Far UltraViolet) imaging of nearly a complete hemisphere on a 30-minute cadence. This global-scale, high-cadence imaging will enable GOLD to distinguish between spatial and temporal variations in the TI (Thermosphere Ionosphere) system caused by geomagnetic storms, variations in solar EUV, and forcing from the lower atmosphere.
The most significant difference between developing instrumentation for a NASA-owned mission and accomplishing the same task for a commercial satellite is that communications satellites are procured on a faster schedule - 24 to 36 months from satellite contract to launch - than the instrument development. GOLD has partnered with SES Government Solutions (SES-GS), the comsat mission owner-operator, to define instrument interfaces and requirements that will be included in the eventual Request for Proposal to candidate spacecraft vendors. SES-GS launches 3 to 4 missions per year, which allows the GOLD-SES-GS partnership to match the instrument's launch readiness date with a suitable mission.
Figure 5: Artist's rendition of the SES-14 coverage; the hosted payload GOLD will examine the response of the upper atmosphere to forcing from the Sun, the magnetosphere and the lower atmosphere (image credit: NASA) 10)
• December 22, 2017: SES-14 has arrived safely at the Guiana Space Center in Kourou, French Guiana, in preparation for launch by an Ariane 5 vehicle in January 2018. 11)
- SES-14 was built by Airbus Defence and Space and is an electric satellite. It will rely fully on electric propulsion and will be equipped with an electric plasma propulsion system for orbit raising and in-orbit maneuvers. The new spacecraft also features a Digital Transparent Processor (DTP), which increases payload flexibility and will provide customized bandwidth solutions to SES's customers.
Figure 6: The GOLD instrument (the gray and white object located on the front right corner of the top deck) has completed environmental testing and is shown here on the SES-14 spacecraft in preparation for a scheduled January 2018 launch date (image credit: Airbus DS) 12)
• May 23, 2017: SES-GS (Société Européenne des Satellites-Government Solutions) today announced the successful integration of NASA's GOLD (Global-Scale Observations of the Limb and Disk) hosted payload with the SES-14 communication satellite. 13) 14)
- Marking a significant milestone in the lead up to launch, GOLD was integrated onto the SES-14 satellite in preparation for a series of environmental tests at Airbus Defence and Space in Toulouse, France. Airbus DS is building the SES-14 satellite for SES-GS.
Figure 7: The GOLD instrument is hoisted up and installed onto the SES-14 commercial communications satellite, which is being assembled at Airbus Defence and Space in Toulouse, France (image credit: Airbus DS)
• January 4, 2017: A NASA instrument that will study the upper atmosphere and the impact of space weather on Earth is a step closer on its journey into space. The LASP-built instrument was shipped to Airbus Defence and Space in Toulouse, France, for integration on the SES-14 communications satellite. 15)
- GOLD is a pathfinder for NASA's use of commercial spacecraft for science missions. UCF and LASP partnered with SES Government Solutions (SES-GS), based in Reston, VA, to provide GOLD with its ride into geostationary orbit on the SES-14 satellite that is owned and operated by SES, the parent company of SES-GS.
Figure 8: The GOLD instrument arrives in its shipping container at Airbus Defence & Space in Toulouse, France on January 4, 2017 (image credit: Airbus DS)
• December 1, 2016: Photo of the GOLD science team and the GOLD instrument. 16)
Figure 9: Members of the GOLD science team gather with the instrument in a LASP clean room on December 1, 2016, just after the instrument went through its pre-ship review ahead of shipment to Airbus Defence and Space in Toulouse, France (image credit: LASP)
Launch: The GOLD payload was launched as a hosted payload on the SES-14 communication satellite of SES-GS (SES Government Solutions) on 25 January 2018 (22:20 UTC). SES-14 was built by Airbus DS. The launch vehicle was Ariane-5 ECA and the launch complex was ELA-3 in Kourou (flight VA241). - The second communication satellite on this flight was Al Yah-3 of Yahsat. Built by Orbital ATK, Al Yah-3 will support broadband Internet and data services over Africa and Brazil for Yahsat Satellite Communications Company of Abu Dhabi.
According to Arianespace, a few seconds after ignition of the upper stage, the second tracking station located in Natal, Brazil, did not acquire the launcher telemetry. This lack of telemetry lasted throughout the rest of powered flight. Subsequently, both satellites were confirmed separated, acquired and they are on orbit. SES-14 and Al Yah 3 are communicating with their respective control centers. Both missions are continuing. 17)
Both satellites, SES-14 and Al Yah-3, use all-electric propulsion for orbit raising in GTO (Geosynchronous Transfer Orbit) and in-orbit maneuvers.
The University of Colorado announced in April 2015 that it had awarded a five-year contract to SES- GS VA, to host a NASA-funded science instrument on board SES-14, a communications satellite to be stationed over the Americas. 18)
The contract award, made by the University of Colorado, a partner in the project, will give the GOLD payload the ride it needs to geostationary orbit on board SES-14, a communications satellite to be stationed over the Americas. From there, the microwave-sized device will transmit data of how Earth's upper atmosphere responds to solar impacts back to scientists for analysis. 19)
Orbit of SES-14: Geostationary orbit, altitude of 35,786 km, location = 47.5º W.
SES-14 will fulfill two primary missions: its C-band wide beams are specifically designed for SES's expanding cable neighborhood in Latin America, while its Ku-band HTS spot beams will provide expansion capacity to serve the dynamic aeronautical and maritime markets and other traffic-intensive applications, such as cellular backhaul or broadband delivery services.
With the launch of Al Yah-3, Yahsat's commercial Ka-band coverage will be extended to an additional 20 markets, reaching 60% of Africa's population and over 95% of Brazil's population. - Al Yah-3 will be positioned at 20 West Longitude.
The Al Yah-3 satellite carries 53 active Ka-band user beams and four gateway beams, and produces approximately 8.0 kW of payload electrical power. The Ka-band spot beams provide two-way communications services to facilitate high-speed delivery of data to end-user applications such as broadband Internet and corporate networking as well as IP backhaul for telecommunications service providers.
Al Yah-3 was built by Orbital ATK using its new GEOStar-3 hybrid platform, the first application of this platform.
• September 17, 2018: NASA's GOLD ( Global-scale Observations of the Limb and Disk) instrument powered on and opened its cover to scan the Earth for the first time, resulting in a "first light" image of the Western Hemisphere in the ultraviolet. 20) 21)
- The instrument was launched from Kourou, French Guiana, on 25 January 2018, onboard the SES-14 satellite and reached geostationary orbit in June 2018. After checkout of the satellite and communications payload, GOLD commissioning—the period during which the instrument performance is assessed—began on 4 September.
- Team scientists conducted one day of observations on 11 September, during instrument checkout, enabling them to produce GOLD's "first light" image shown here. Commissioning will run through early October, as the team continues to prepare the instrument for its planned two-year science mission.
- "GOLD is an amazing technological breakthrough," said GOLD Principal Investigator Richard Eastes, a research scientist at LASP. "After years of reviews, testing, testing, and more testing, the instrument is finally making observations of the Earth. The main act has begun. It's a testament to the engineering and science teams, who were responsible for building and calibrating the instrument, that we've reached this significant mission milestone."
- Along with NASA's ICON (Ionospheric Connection Explorer), scheduled for launch later this fall, GOLD is a key element of NASA's program to explore Earth's boundary with space, as the two missions explore this unpredictable near-Earth region to determine how it responds to solar and atmospheric inputs.
Figure 10: Shown here is the "first light" image of ultraviolet atomic oxygen emission (135.6 nm wavelength) from the Earth's upper atmosphere captured by NASA's GOLD instrument. It was taken at approximately 6 a.m. local time, near sunrise in eastern South America. The colors correspond to emission brightness, with the strongest shown in red and the weakest in blue. This emission is produced at altitudes around 160 km (note how it extends above the Earth's surface on the horizon), when the Earth's upper atmosphere absorbs high energy photons and particles. The aurora, at the top and bottom of the image, and daytime airglow, on the right hand side, are also visible. An ultraviolet star, 66 Ophiuchi (HD 164284), is visible above the western horizon of the Earth. Outlines of the continents and a latitude-longitude grid have been added for reference (image credit: LASP/GOLD science team)
- "The successful launch of GOLD and acquisition of initial data is a fantastic result," said Bill McClintock, GOLD instrument scientist at LASP. "Its data will help us understand the critical role the Sun plays in space weather and allow us to better protect astronauts and our technological assets that we've become so reliant upon in today's society."
- Changes in near-Earth space can affect our lives on Earth by disrupting the use of satellites for communications and navigation. The result can be lost messages, aircraft flight delays, interruptions in GPS signals, and satellite TV outages. Incoming solar energy can also damage spacecraft electronics and detectors, and expose astronauts to health risks from radiation. The more we understand about the fundamental nature of our space environment, the better we can protect these interests.
- Scientists expect to begin operations of the GOLD instrument in early October 2018.
• September 4, 2018: The high-powered SES-14 satellite, positioned at 47.5 degrees West, is now operational and is serving Latin America, the Caribbean, North America, North Atlantic and West Africa. 22)
- The commercial communications satellite also carries a hosted payload for NASA's GOLD (Global-scale Observations of the Limb and Disk) mission. GOLD will provide unprecedented imaging of the Earth's upper atmosphere from geostationary orbit to deepen scientists' understanding of the boundary between Earth and space.
• February 23, 2018: The Independent Enquiry Commission formed after the Ariane 5 launcher's trajectory deviation during its January 25, 2018 mission issued its conclusions on Thursday, February 22. The anomaly's cause is perfectly understood and recommendations are clearly identified. Arianespace and ArianeGroup are immediately implementing the Independent Enquiry Commission's recommended corrective measures. The current Soyuz and Ariane 5 launch campaigns are continuing at the Guiana Space Center in French Guiana for the two launches planned in March. 23)
Table 1: Results of the anomaly report of the Independent Enquiry Commission
• January 29, 2018: NASA's GOLD mission powered on the GOLD instrument for the first time after launch on Jan. 28, 7:23 p.m. EST. The systems engineers successfully established communication with the GOLD instrument and its detector doors opened when commanded. After their tests, the engineers powered off the instrument the same day, at 7:40 p.m. EST. The instrument will remain powered off until its host satellite, SES-14, reaches geostationary orbit and GOLD operations commence later this year. 24)
- GOLD will investigate the dynamic intermingling of space and Earth's uppermost atmosphere and seek to understand what drives change in this critical region. Resulting data will improve forecasting models of the space weather events that can impact life on Earth, as well as satellites and astronauts in space.
• January 26, 2018: Both spacecraft launched on Flight VA241 – SES-14 and Al Yah 3 – have been acquired and are operating in orbit nominally, despite a trajectory deviation experienced during the mission. This was confirmed by the satellites' operators, SES and Yahsat, respectively. 25)
- SES has informed NASA there is minimal impact on the SES-14 satellite carrying the agency's GOLD instrument after a launch anomaly on Jan. 25, 2018. The satellite will reach geostationary orbit four weeks later than originally planned. As the spacecraft is in good health, we expect no effect on the quality of observations and data. Originally, science operations were expected to start in mid-October. Our partners are working to maintain that timeline as closely as possible. We will provide updates as they become available. 26)
GOLD (Global-scale Observations of the Limb and Disk) instrument
GOLD is a result of collaboration among several world-leading entities. NASA/GSFC in Greenbelt, Maryland, is providing overall NASA program management. The GOLD instrument is being designed and built at LASP (Laboratory for Atmospheric and Space Physics) at the University of Colorado, Boulder, CO. Richard Eastes, the PI of UCF/FSI (University of Central Florida/Florida Space Institute), oversees the GOLD mission. UCF will be responsible for disseminating the data products. CU/LASP is responsible for the mission and home of the Science Data Center for the mission. 27) 28) 29)
In addition to LASP, the GOLD mission partners include NCAR (National Center for Atmospheric Research), UCB ( University of California at Berkeley), Computational Physics Inc. and NOAA (National Oceanic and Atmospheric Administration). UCF is the first Florida university to lead a NASA mission.
GOLD is a high-resolution FUV (Far Ultraviolet) imaging spectrograph with two identical channels. The objective is to provide global-scale imaging and limb scans, with a 30 minute cadence. GOLD will image the Earth in the far-ultraviolet from 132 to 162 nm.
The science objectives of the GOLD mission are:
• Determine how geomagnetic storms alter the temperature and composition of Earth's thermosphere.
• Analyze the global-scale response of the thermosphere to solar extreme-ultraviolet variability.
• Investigate the significance of atmospheric waves and tides propagating from below on the temperature structure of the thermosphere.
• Resolve how the structure of the equatorial ionosphere influences the formation and evolution of equatorial plasma density irregularities.
The GOLD instrument is a dual channel imaging spectrograph, each capable of all measurements, with a mass of 37 kg, a power consumption of 72 W (average), a size of 40 x 30 x 70 cm, and a data rate of ~6 Mbit/s.
Focal length of telescope: 150 mm, entrance pupil size 30 mm x 30 mm.
Figure 11: Illustration of the GOLD imaging spectrograph (image credit: GOLD Team)
The GOLD imager has two identical and independent optical channels, each capable of performing every required measurement. These interface to the SES-14 spacecraft through a single processor assembly, which commands each channel independently. Images produced by the instrument are routed to a dedicated transponder for immediate downlink to an SES ground station. The raw images are stored at the ground station until transmission to LASP is confirmed. These are then sent over ground line to the University of Central Florida where high-level data processing converts the raw data into maps of thermosphere composition and temperature. 30)
Each channel contains an ultraviolet spectrograph equipped with an imaging detector that covers 132 to 162 nm. This wavelength range contains important emissions from the main constituents of the thermosphere—atomic oxygen (135.6 nm) and molecular nitrogen (the Lyman-Birge-Hopfield (LBH) band system 132 – 162 nm). Two selectable entrance slits, which are 0.2 mm and 0.4 mm wide, respectively, enable the two spectral resolutions of 0.2 nm and 0.4 nm required for measuring temperature and composition. The optical layout of a single channel is shown here in Figure 12.
Figure 12: Shown here is a labeled drawing of the GOLD instrument, which uses a pair of independent, identical channels (image credit: GOLD Team)
A single-mirror telescope equipped with a plane scan mirror images the spectrograph entrance slit onto the atmosphere. During an observation, a precision mechanism rotates the mirror so that the slit image sweeps east-west across the Earth's atmosphere. The slit is only tall enough to cover a single hemisphere (either north or south). This is accommodated by tilting the mirror through approximately 4.5º. In this configuration, one face of the mirror projects the slit onto the northern hemisphere and the other face projects it onto the southern hemisphere, as illustrated in the left panel of Figure 13. A third 2.6 mm wide entrance slit is used for stellar occultations. In this configuration, which is illustrated in the right panel of Figure 13, the scan mirror is positioned near the limb of the Earth and remains motionless as the star drifts through it. This enables GOLD to measure the absorption of starlight by the atmosphere in order to measure the density of molecular oxygen, which is a minor constituent of the thermosphere.
Figure 13: Left panel: Disk scans are performed with two swaths across the northern and southern hemispheres, respectively. Right panel: The slit remains motionless during stellar occultations (image credit: GOLD Team)
Figure 14: An illustration of typical GOLD LBH emission data from a single channel for a single slit position. On the left is an image of LBH emission intensity displayed on a logarithmic scale in the range from 10 – 104 brightness units. Here, the slit is positioned in the northern hemisphere near the sub-spacecraft longitude. On the right is a display of an LBH spectrum obtained at a single location along the slit. The actual image will have a spectrum for each row of the detector (image credit: GOLD Team)
GOLD measures composition and temperature simultaneously:
• Two identical channels
• Each channel fully independently in all observing modes
- disk images and limb scans
- dayside: T and O/N2
- nightside: O+ density
- stellar occultations
- full disk maps and limb scans with 30 minute cadence
- limiting resolution is ~50 km
• A single channel can perform all measurements with reduced cadence or reduced spatial resolution
Proven measurement techniques will be used:
• Temperature obtained on disk from rotational shape of N2 LBH (Lyman-Birge-Hopfield) bands
• O/N2 composition measured using ratio of 135.6 doublet to LBH bands
• Temperature on limb determined by slope of emission altitude profile
• O+ at night observed using 135.6 recombination emission
• O2 profile on limb from stellar occultations.
Figure 15: Daytime FUV (Far-Ultraviolet) spectrum (image credit: GOLD Team)
GOLD will observe space weather response to forcing:
Figure 16: Modeled changes (from TIEGCM) in upper atmosphere during a geomagnetic storm, one example of the space weather effects that GOLD will observe (image credit: GOLD Team)
GOLD provides a new perspective on T-I (Thermosphere-Ionosphere) system:
• Unprecedented, simultaneous imaging of composition and temperature
• Able to separate changes in time from changes in location
• Capability for continuous, real time data availability is inherent to the mission
• Provides context for ground-based and LEO measurements
• Observations will be concurrent with NASA's ICON (Ionospheric Connection Explorer) mission.
"GOLD's imaging represents a new paradigm for observing the boundary between Earth and space," said Bill McClintock, senior research scientist at LASP working on the project. "It will revolutionize our understanding of how the sun and the space environment affect our upper atmosphere."
Figure 17: Photo of the GOLD instrument (image credit: LASP)
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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 (firstname.lastname@example.org).