Chapter 6 Follow-On Mission Trade Analysis and Design
6.3 Follow-On Mission System Architecture and System Design
6.3.1 Follow-On Mission System Architecture
The advanced program team at NSPO is currently at the stage of mission definition design phase. We show here some of the planned mission and spacecraft design features for the follow-on mission. Figure 6-6 shows the proposed F3 follow-on mission system architecture with constellation of 12 satellites that requires three launches. The primary payload of the follow-on satellite will be equipped with next-generation GNSS RO receiver to collect more soundings per receiver by adding Galileo and GLONASS tracking capability.
6.3.2 Spacecraft Bus Design
Based on the F3 satellites design lessons learned, integration and test lessons learned, and the mission operation experiences, the follow-on spacecraft will be a high reliable and robustness satellite and will improve the payload performance by using the next generation Tri-G RO Receiver. The follow-on satellite will be neither a perfect satellite nor a multi-purpose satellite. The follow-on satellite will be designed to provide better attitude performance to reduce the spacecraft recovery time and payload down time.
The proposed spacecraft bus design will be accommodate up to one GNSS RO payload plus two optional additional science payloads. The team will use standard modular design approach for the payload suites. For each science payload suite 5 kg of mass and 5W of power will allocated. And the memory margins will be designed to support additional payload capacity. As for communications subsystem design, identical to F3 Ground System Interface, the team will use S-Band Uplink/Downlink (CCSDS) 2Mbps Downlink and 32Kbps Uplink, respectively. For C&DH subsystem design, the team will use centralized integrated avionic unit with radiation hardness chip and with 1 Gigabytes of SDRAM. For the ACS, pointing performance will be greatly improved over F3 performance based on the lessons learned from the F3 mission operation experiences, the pointing accuracy will be
designed to within ±0.2 deg. (3σ) in Roll/Yaw/Pitch axes, respectively. And the pointing knowledge will be designed to within ±0.2 deg. (3σ) in Roll/Yaw/Pitch axes, respectively.
For EPS Subsystem, the team will use lithium ion battery to improve the battery lessons learned of the current F3 mission. The control algorithm will be a voltage-based algorithm, and the power margins support additional payload capacity. And the aluminum structure will be used for the follow-on mission.
The follow-on spacecraft bus design vs. current F3 design is shown in Table 6-2. Figure 6-7 shows the proposed F3 follow-on mission spacecraft configuration. The benefit and improvement for the follow-on spacecraft will improve payload performance, better attitude performance, simplified operation, simplified orbit transfer, increased data storage, and modular design for and additional science payloads (optional) and launch vehicle interface.
6.3.3 GNSS Payload Design
GNSS RO instrument is the primary payload for the follow-on mission. The manufacturer of the GNSS RO payloads except the GRAS instrument in METOPS-A, are most from the Blackjack technology, which developed by JPL/NASA then transferred to Broad Reach Engineering, such as the following space mission: GPS/MET, SUNSAT, ORSTAD, CHAMP, SAC-C, JASON-1, GRACE (x2), F3 (x6), TERRASAR-X, TCSAT, TanDEM-X, KOMPSAT-5, and IOX.
The GNSS will include 29 operational United States’ GPS satellites, several Russia’s GLONASS (planning to have 18 satellites), and European GALILEO system (plan to have 30 GNSS satellites by 2013). The GNSS RO payload in the follow-on mission will utilize the advanced requirements to be able to receive the US GPS L1/L2/L5 signals, also to receive the GALILEO E1/E5/E6 signals, and to receive Russia’s L1/L2/L5 signals as well. The other advanced requirements for the next generation RO payload are major on the performance improvement from the current GOX payload in F3 in order to achieve more soundings.
The advanced GNSS RO payload should be able to have robust software upload design for modifying the GNSS RO application. The software for the other specific GNSS application or experiment can also be uploaded from ground to GNSS RO payload. JPL’s Tri-G is now currently under development for such requirements and will be available for test flight on 2010.
6.4 Conclusion
The success of the F3 mission has initiated a new age for operational GPS RO soundings and is the world’s first demonstration of the impact of near real-time GPS RO observations in operational global weather forecasting. We provide the proposed follow-on mission definition trade analysis results, especially the system architecture and spacecraft bus and GNSS RO payload design. The follow-on spacecraft design will have robustness design and improve the payload performance by using the next generation GNSS RO payload and provide better attitude performance to reduce the spacecraft recovery time and payload down time. The follow-on mission is expected to have a significantly improved impact on global weather prediction. And its promise for weather and climate research and space weather monitoring is equally far-reaching.
TABLE 6-1 EXPECTED ATMOSPHERIC PROFILES VS.DIFFERENT CONSTELLATION AND
DIFFERENT RECEIVER CAPABILITY.
Satellites in
constellation GPS GALILEO GLONASS GPS+
GALILEO
GPS+GALILEO +GLONASS
High Inc. @72o 500 480 390 980 1,370
Low Inc. @24o 500 470 330 970 1,300
12(=8+4) 6,000 5,720 4,440 11,720 16,160
TABLE 6-2 PROPOSED FOLLOW-ON MISSION SPACECRAFT BUS DESIGN VS.F3DESIGN.
Function Follow-On Design F3 Design Benefit
Weight <50 kg 61 kg (w/ Propellant) Stacked or Single Launch Piggy-Back Launch 3-Axis Gyro, 3-axis MAG, RWA x 3, Torque x 3,
Storage >1.5 G 128 M Increased Data Storage
Simplified Operations
Reduced Mass & Volume Simplified Operations Structure Aluminum Metal Matrix (AlBeMet) Cost Reduced
Payload Interface
Main PL: GNSS RO Rcvr 2 Science PL (Optional)
Primary PL: GOX Secondary PL: TIP, TBB
Modular Design Cost Reduced
Figure 6-1. The relationship between total occultation number and inclination angle for one satellite receiving GPS only.
400 450 500 550 600 650 700
0 10 20 30 40 50 60 70 80 90 100
Inclination angle (deg) O cc u lt a ti o n n u m b er p er s a te ll it e (r ec ei v e g p s o n ly )
400 450 500 550 600 650 700
0 10 20 30 40 50 60 70 80 90 100
Inclination angle (deg)
O cc u lt a ti o n n u m b er p er s a te ll it e (r ec ei v e g p s o n ly )
Figure 6-2. The dependence of data distribution vs. latitude for a 72o inclination angle. The
“equivalent area covered by one occultation” is defined as the average area in square km associated with a single sounding. e.g., one sounding per N km (x N km).
Equivalent area covered by one occultation point (km)
0
Equivalent area covered by one occultation point (km)
Figure 6-3. The dependence of data distribution with inclination angle. The “equivalent area covered by one occultation” is defined as the average area in square km associated with a single sounding. e.g., one sounding per N km (x N km).
500 Equivalent area covered by one occultation point (km)
0 deg Equivalent area covered by one occultation point (km)
0 deg
Figure 6-4. The F3 follow-on constellation with 12 satellites.
Figure.6-5. 6-hr Occultation Distribution with 12-satellite constellation for the F3 follow-on mission (the blue dots are from GPS, the green dots are from GALILEO, and the purple dots are from GLONASS)
-90 90
-180 180
-90 90
-180 180
GPS GALILEO GLONASSGPS GALILEO GLONASS
-90 90
-180 180
-90 90
-180 180
GPS GALILEO GLONASS GPS GALILEO GLONASSGPS GALILEO GLONASSGPS GALILEO GLONASS
Figure 6-6. The F3 follow-on mission system architecture with constellation of 12 satellites.
Fiducial Network Galileo GPS
Data Processing Center TT&C stations (overseas)
TT&C stations (Taiwan)
Satellite Operations
and Control Center Users Users
GLONASS
Follow-On
High-inc
Low-inc
Fiducial Network Galileo GPS
Data Processing Center TT&C stations (overseas)
TT&C stations (Taiwan)
Satellite Operations
and Control Center Users Users
GLONASS
Follow-On
High-inc
Low-inc
Figure 6-7. The proposed F3 follow-on mission spacecraft configuration.