FormoSat-7 / COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere and Climate)
The FormoSat-7 / COSMIC-2 constellation (simply known as FS-7/C-2) is an international collaboration between Taiwan (NSPO) and the United States (NOAA) that will use a constellation of 12 remote sensing microsatellites to collect atmospheric data for weather prediction and for ionosphere, climate and gravity research. NSPO/NARL (National Space Organization/National Applied Research Laboratories) is the designated representative for Taiwan and NOAA (National Oceanic and Atmospheric Administration) is the designated representative for the U.S.
FormoSat-7 / COSMIC-2 is a follow-on mission to the FormoSat-3 / COSMIC mission to meet the RO (Radio Occultation) data continuity requirements of the user community. NOAA and NSPO intend to provide a high-reliability next generation satellite system.
The overall objective of FS-7/C-2 is to advance the capabilities of regional and global weather prediction (including severe weather prediction). The goal is to collect a large amount of atmospheric and ionospheric data primarily for operational weather forecasting and space weather monitoring as well as meteorological, climate, ionospheric, and geodetic research. It is expected to be a much improved constellation system consisting of a new constellation of 12 satellites for an operation mission.
The primary mission payload will be a TriG (third generation) GNSS-RO receiver and will collect more soundings per receiver by adding European Galileo system and Russia's GLONASS (Global Navigation Satellite System) tracking capability, which will produce a significantly higher spatial and temporal density of profiles. These will be much more useful for weather prediction models and also for the severe weather forecasting including typhoons and hurricane, as well as for the related research in the fields of meteorology, ionosphere and climate. 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15)
The constellation is planned to be comprised of 6 satellites at 72º inclination, and 6 satellites at 24º inclination, which will enhance observations in the equatorial region over what is currently being collected with FormoSat-3 / COSMIC. This constellation configuration was chosen because it provides the most uniform global coverage, as shown in Figure 1. Figure 1 shows the global sounding (data point) distribution versus the various orbital inclinations that were considered. 16) 17) 18)
This constellation will produce nearly 12,000 sounding profiles per day, compared to the approximate 2,000 soundings per day currently produced by FormoSat-3 / COSMIC due to the ability of FS-7/C-2 to track three navigation systems’ signals (GPS, GLONASS, and Galileo) versus the ability of FormoSat-3 / COSMIC to track only one (GPS).
Figure 1: Potential satellite inclinations vs. Global sounding coverage for FormoSat-7/COSMIC-2 (image credit: UCAR)
Figure 2: Comparison of sounding distributions for FormoSat-3 / COSMIC and FormoSat-7 / COSMIC-2 (image credit: UCAR)
Responsibilities of FormoSat-7 /COSMIC-2 partner organizations:
NSPO shall be responsible for:
• acquisition, management, and deployment of satellites constellation
• development and management of mission operations
• modification and operations of the SOCC (Satellite Operations Command and Control) station and Taiwan’s TT&C station
• acquisition and management of the Taiwan data processing center.
NOAA shall be responsible for:
• acquisition and management of the GNSS-RO mission payload
• overall management of the data analysis, application, and distribution segment
• acquisition and management of the launch vehicle system
• acquisition and management of the ground receiving stations
• acquisition and management of the data processing centers in the U.S.
NOAA and NSPO shall be jointly responsible for the acquisition and management of the scientific payloads.
Table 1: Partnership responsibilities of the FormoSat-7/COSMIC-2 mission (Ref. 12)
Table 2: Comparison of functions allocated in FormoSat-7(COSMIC-2 and FormoSat-3/COSMIC constellations (Ref. 2)
Figure 4: System architecture of FS-7/C-2 (image credit: NSPO, NOAA) 21)
The project plan is to launch 2 rockets (Minotaur-4 or Falcon-9) with 6 satellites on each rocket. They will be launched and then positioned into their final orbits (nominally 800 km altitude for the 72º inclination orbit and 520 km altitude for the 24º inclination orbit).
The original FormoSat-3 / COSMIC mission had an operational concept of allowing for one data downlink per orbit. The plan for FS-7/C-2 is to allow for 2 data downlinks per orbit, which will considerably reduce the data latency. Consequently, FS-7/C-2 will require more satellite ground stations for receiving the data. As with FormoSat-3 / COSMIC, the data collected by FS-7/C-2 will be downlinked to the tracking station, then transmitted to the COSMIC processing center CDAAC (COSMIC Data Analysis and Archive Center) in Boulder, CO, as well as to the Taiwan processing center TACC (Taiwan Analysis Center for COSMIC) for processing.
The processed products will then be provided to the NOAA GTS (Global Transmission System) for distribution to the worldwide weather prediction centers. Command and control for the FS-7/C-2 constellation will continue to be provided by the NSPO SOCC (Satellite Operations Control Center). Payload operational configurations will continue to be managed by a joint effort between UCAR (University Corporation for Atmospheric Research) and JPL (Jet Propulsion Laboratory) with NOAA and NSPO concurrence for updates and changes.
Table 3: Baseline mission requirements of FS-7/C-2 (Ref. 13)
Status of project in 2011 (Ref. 6):
• The U.S.-Taiwan agreement that is the authorizing document for the FormoSat-7 COSMIC-2 program was signed by both parties in May 2010.
• The Joint Program Office held the FDR (Feasibility Design Review) in May 2010 and the MDR (Mission Definition Review) in August 2010.
• The SRR (System Requirements Review) is scheduled for April 2011, the PDR (Preliminary Design Review) for June 2011, and the CDR (Critical Design Review) for September 2011.
Table 4: FormoSat-7 program master schedule (Ref. 20)
Table 5: FormoSat-7 enhanced satellite design
Figure 5: Illustration of the FS-7/C-2 constellation orbits (image credit: NSPO, NOAA)
Legend to Figure 5:
• Launch No 1: 6 satellites to be launched at low inclination (~ 24.5-28º) and separated by 60º when complete cluster constellation deployment. This inclination provides a better coverage over equatorial and low latitude regions.
• Launch No 2: 6 satellites to be launched at high-inclination-angle (~72º) and separated by 30º when complete final constellation deployment. The higher inclination provides better high latitude coverage.
On Sept. 6, 2012, NSPO awarded a contract to SSTL (Surrey Satellite Technology Ltd., UK) to built 12 minisatellites for the FormoSat-7/COSMIC-2 program. The spacecraft bus contract kick-off ceremony was held at NSPO (National Space Organization) and co-chaired by Dr. Guey-Shin Chang, Director General of NSPO, and Sir Martin Sweeting, Executive Chairman of SSTL. 22) 23)
The first phase is to deploy 6 satellites, each carrying an advanced GNSS receiver, to low-inclination-angle orbits. The launch is targeted in 2016.
Under the contract, SSTL will design and manufacture satellites for the FormoSat-7 program at its facilities in Guildford, UK, with the payloads being produced by NSPO's partners in the USA. NPSO will be responsible for the integration of the majority of the spacecraft at its facilities in Taiwan. The spacecraft design phase is already underway and SSTL is tailoring a new 200 kg platform to the mission requirements.
Spacecraft design: The FS7/C-2 constellation will need to use the same mission control and mission operations ground system network as is being used for the FORMOSAT-3 system. The heritage baseline employed for the spacecraft is the SSTL-100 bus, which has been used on numerous previous missions, and has most recently flown on the UK-DMC2 and Deimos-1 mission. This avionics set provides a large degree of redundancy commensurate with mission lifetimes beyond 5 years. This bus is modified in some areas according to mission specific requirements. 24) 25)
The propulsion system is based on heritage space components, and uses a monopropellant hydrazine system. Four thrusters are employed in order to permit spacecraft attitude control during propulsive maneuvers. Larger reaction wheels are employed to provide adequate control authority. Finally, star cameras are included to improve the attitude knowledge in support of the scientific payloads. One efficiency saving has been implemented by sharing capabilities cross the redundant OBCs (On-Board Computers) and redundant star camera processors, resulting in the need for just three computers. The resulting spacecraft avionics block diagram is shown in Figure 6.
Figure 6: FormoSat-7 spacecraft systerm block diagram (image credit: SSTL, NSPO)
As of 2013, several launchers are still under consideration which require different spacecraft designs (Ref. 24):
1) S/C design for the Minotaur-IV launch option: The most constraining situation is provided with the Minotaur-IV of OSC. The following layout defines the spacecraft configuration for a launch option with the Minotaur-IV launch vehicle.
Figure 7: Preliminary design of theFS-7/C-2 spacecraft and payload accommodation with the Minotaur-IV selection (image credit: NSPO, SSTL)
Table 6: Spacecraft specification with the Minotaur-IV selection
Figure 8: FS-7/C-2 Minotaur-IV compatible design of the launch configuration (image credit: NSPO,Ref. 25)
2) S/C design for the EELV-Grande launch option: This launch configuration provides a much more generous mass and volume allocation for the platform avionics. A more conventional design can be accommodated in this selection, without the need for extensive mass optimization and miniaturization.
Figure 9: FS-7/C-2 ESPA-Grande compatible design of the launch configuration (image credit: NSPO, SSTL)
Figure 10: Schematic view of a FS-7/C-2 spacecraft configuration with the EELV-Grande selection (image credit: NSPO, SSTL)
Table 7: Spacecraft specification with the EELV-Grande selection
Launch: The FORMOSAT-7 program is intended to consist of 2 launches (of 6 satellites each) which are planned to take place in 2016 and 2018, respectively. The launch provider is NOAA.
• First launch: Six satellites will be positioned in a low inclination orbit at a nominal altitude of ~550 km with an inclination of 24.5-28º. Through constellation deployment, they will be placed into 6 orbital planes with 60º separation.
• Second launch: Six satellites will be positioned in a high inclination orbit at a nominal altitude of ~750 km with an inclination of 72º. Through constellation deployment, they will be placed into 6 orbital planes with 30º separation.
Sensor complement: (TriG-RO, VIDI, RF Beacon)
TriG-RO [Tri-GNSS (GPS+ Galileo+GLONASS) Radio Occultation receiver]
NASA/JPL (Jet Propulsion Laboratory) is developing a next-generation GNSS space science receiver, the TriG receiver. The receiver will upgrade the capabilities offered by the current state of the art BlackJack/IGOR GPS science receivers in order to meet NASA’s decadal survey recommendations. This includes the ability to track not only GPS, but additional GNSS signals, including Galileo, CDMA GLONASS and Compass.
Most of the low level signal processing will be done inside multiple reconfigurable FPGAs, which can be updated post-launch to track new in-band GNSS signals as they become available. TriG will greatly increase the amount and quality of data by employing digital beamforming to direct multiple simultaneous high-gain beams at GNSS satellites.
With this new architecture and the availability of Galileo, GLONASS and Compass signals, many more occultations will be observed each day. The TriG receiver will have two processors, one for performing POD (Precise Orbit Determination), and the other dedicated to occultation and other science applications. The science processor will run Linux and can be programmed by scientists in a high-level scripting language, putting the scientist in the driver’s seat when it comes to onboard processing of science data. 26)
TriG technology demonstration: As part of the NASA Instrument Incubator program, JPL developed a prototype of the TriG receiver, namely TOGA (Time-shifted, Orthometric, GNSS Array), and demonstrated dual processor coupling, multi-frequency beamforming, and L5 tracking of both Galileo, GPS, and WAAS L5 signals. 27)
The TriG receiver is a NASA funded instrument. The hardware development is at Moog Broad Reach (formerly Broad Reach Engineering), the software development and complete end-to-end testing is at JPL. 28) 29) 30) 31) 32) 33)
• TriG includes the POD (Precise Orbit Determination) and RO (Radio Occultation) functionalities other than the capability of tracking existing and future GNSS signals. TriG receives all L-band GNSS signals (GPS, Galileo, GLONASS, Compass) and DORIS.
- TriG has separate science processor and the navigation processor (dual processor architecture)
- TriG possesses higher SNR compared to its previous generation receivers
- TriG is tolerant to a total ionizing dose of 40 kRad.
• TriG design is based upon heritage derived from the BlackJack/IGOR receivers that flew on numerous missions with successful operation.
• NASA is scheduled to receive the “in place delivery” of the first fully tested EM (Engineering Model) by early summer of 2013.
• A second EM (with higher Navigation processor throughput capability) is also being built for NOAA in support of the COSMIC -2 program. The NOAA EM is upgraded to allow two additional RF down-converter cards and up to 16 antenna inputs to include surface reflection sensing capability and receiving DORIS signal.
Table 8: Preliminary overview of TriG GRO instrument parameters
For a full-up occultation receiver the spacecraft would also have to accommodate a fore and an aft occultation antenna (2.5 kg each) and a POD antenna (1 kg) with their attendant fields of view, and cables between the antennas and the receiver.
Figure 11: Architecture of the TriG instrument (image credit: JPL)
Figure 12: Conceptual view of the TriG GNSS-RO instrument elements (image credit: JPL)
RFDC = RF-downconversion array
TriG performance features: 34)
• Support for GPS CA, L1 and L2 Semi-Codeless, L2C, and L5
• Supports from 1 to 16 antennas
• Supports POD (Precision Orbit Determination), cm level positioning, mm/sec level velocity
• Supports RO (Radio Occultation) science for weather and climatology
• Supports Reflections science applications (in development).
The TriG receiver requires more capable antennas than those flown on missions such as COSMIC. To maximize the number of ionospheric and atmospheric profiles, the TriG receiver will be capable of tracking legacy and new GPS signals such as L5, L2C and L1C; GLONASS CDMA and Galileo E1 and E5a. 35)
Figure 13: Photo of the TriG instrument with seven 3U slot cPCI chassis (image credit: Moog Broad Reach)
Table 9: Summary of dual processor architecture
Figure 14: Schematic view of the TriG instrument receiver (image credit: NASA/JPL, Garth Franklin)
In 2013, Moog Broad Reach completed the TriG HW development in collaboration with NASA/JPL and has delivered the EM (Engineering Model) HW platform to Jet Propulsion Laboratory. 36)
VIDI ((Velocity, Ion Density and Irregularities) instrument
The USAF (U.S. Air Force) is partnering in FormoSat-7/COSMIC-2 and will provide two space weather payloads that will fly on the first six satellites: RF Beacon transmitters and VIDI (Velocity, Ion Density, and Irregularities) instruments.
VIDI is a space weather instrument of AFRL (Air Force Research Laboratory), Kirtland AFB, Albuquerque, NM. The VIDI instrument includes three packages: 37)
• IVM (Ion Velocity Meter) sensors, aperture plane and associated electronics
• SPLP (SSAEM Planar Langmuir Probe), sensors, aperture plane and associated electronics
• DCPU (Data Combiner/Power Unit) interface box.
All sensors are ram-facing. The IVM can measure the electric field perpendicular to the magnetic field and the ion motions parallel to the magnetic field through measurement of the ion drift velocity vector. Two sensors are part of the IVM package, the RPA (Retarding Potential Analyzer) and a DM (Drift Meter), which together provide data to determine the total ion concentration, the major ion composition, the ion temperature and the ion velocity in the spacecraft reference frame.
The SPLP is designed to measure absolute ion density, ion density fluctuations, and electron temperature. The SPLP has two independent sensor heads: an IT (Ion Trap) and a SP (Surface Probe). The Ion Trap is responsible for absolute ion density and density fluctuation measurements at sample rates up to 1 kHz for the identification of scintillating regions. The Surface Probe primarily measures electron temperature but also provides electron density, spacecraft potential and if necessary can perform the ion density fluctuation measurement. The power and data interface for IVM and SPLP is provided by the DCPU. It provides a single electronic interface between the spacecraft bus and the VIDI sensors.
Figure 15: Illustration of the VIDI-IVM instrumentation (image credit: USAF AFSPC SMC/WMA, Ref. 21)
Figure 16: Illustration of the VIDI-SPLP instrumentation (image credit: USAF AFSPC SMC/WMA)
RF Beacon instrument:
The RF Beacon includes the sensor electronics and antenna. The RF Beacon will transmit a coherent signal at frequencies in the UHF, L-band and S-bands. Ground receivers will intercept the signals and derive information on ionospheric scintillation.
• The ITT antenna design is a cylinder of 25 cm in diameter and 29.1 cm tall.
• The SRI RF beacon antenna unit will be set of 3 nested quadrafilar helix antennae, with outermost and largest element (UHF) to be ~ 14 cm in diameter and 23 cm high, and mounted on a circular base plate/ground plane approximately 25 cm in diameter. The complete antenna unit has a volume of 25 cm x 25 cm x 35 cm.
Figure 17: Overview of COSMIC-2 operational processing (image credit: UCAR, NSPO)
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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.