Chapter 3 Constellation Deployment
3.4 Constellation Deployment Results
3.4.1 As-Burn Constellation Results
The current constellation configuration as of December 2007 is five satellites (FM5, FM2, FM6, FM4, and FM1) successfully reaching the 800-km mission orbits. On August 3, 2007 FM3 encountered the solar array drive mechanism malfunction when reaching the 711 km orbit. This anomaly blocks the FM3 thrust burn activity to be deployed at the 800 km mission orbit. The reasons for this anomaly are still under investigation. The constellation deployment status as-of- December 2007 is shown in Figure 3-7. The dash line is the newly planned schedule and the dots recorded the execution results of the thrusting. The relative orbital separation angle, the relative AOL, and the relative altitudes of these four satellites are shown in Table 3-2 [57].
3.4.2 Spacecraft Thrust-Burn Performance Statistics
Figure 3-8 and Table 3-3 show the spacecraft thrust-burn performance statistic results in strip chart and table formats, respectively [57]. Starting from FM4 orbit transfer, the NSPO operations team uses the autopilot scheme to increase the burn success rate and reduce the burn working days. The data show that the FM5 burn working days number 39. However,
seven burns per day for FM4 and FM1 compared to three burns per day for FM5 as deployed earlier. The better spacecraft burn performance indicates that more successful rate has been achieved. The operations team has decreased the planned burn duration from 456 minutes for FM5 to 382.8 minutes for FM1 and also decreased the executed burn duration from 326.1 minutes for FM5 to 329.8 minutes for FM1. These results show that the thrust-burn success rate (= executed burn/planned burn) has been increased by the operations team from 71.5%
for FM5 to 86.2% for FM1. Total burn number has increased from 53 times in FM5 to 71 times in FM1. From Table 3-3 it can be seen that the average orbit transfer height per burn has decreased from 5.4 km/burn for FM5 to 3.4 km/burn for FM1. Additionally, the average burn duration per burn has decreased from 369.4 sec/burn for FM5 to 238.4 sec/burn for FM1.
3.4.3 Spacecraft Mass Property and Moment of Inertia Results
We found that the propellant mass remains in the propellant tank are about 2.0 kg after the orbit-transfer operations are completed for each satellite. It is also expected that the spacecraft mass property (weight and center of gravity) and moment of inertia (MOI) are changed accordingly when propellant mass is changed. It was observed that the spacecraft center of gravity (CG) has a change of -0.7 cm shift in Z-axis before and after orbit-transfer activities, and has a CG shift in -Y and -X axes too. These changes will have a significant impact on the geodesy and earth gravity research [63]-[64]. Table 3-4 shows the spacecraft mass property and moment of inertia results of the six satellites. The spacecraft remaining propellant mass was estimated and provided by Propulsion subsystem. The error of the mass was estimated in the range of ±0.1 kg. Based on computation results, a very minor impact on MOI and CG results was observed due to this error range [57].
In the F3 satellites case, the TBB Boom and the Solar Panels are two portions that are deployed after satellite separation from the launch vehicle. The propellant fuel is also changed after orbit transfer. For the MOI computation, we assume the SAD is at 0o position.
The CG is valid for any SAD position, and therefore applies to the ACS Nadir and Nadir-Yaw Modes. The MOI and CG for six spacecraft were re-computed based on the above propellant mass.
3.5 Conclusion
We have presented a new fundamental operation concept for the F3 spacecraft constellation deployment, orbit-raising results, operations challenges and lessons learned.
With five satellites (FM5, FM2, FM6, FM4, and FM1) successfully reaching the 800-km mission orbits as of December 2007, the F3 mission has verified the “proof-of-concept” of a novel way of performing constellation deployment by taking the advantage of nodal precession. This novel approach has dramatically reduced the spacecraft propellant mass and the complexity of the spacecraft RCS and ACS subsystem design. The success of the constellation deployment of the F3 mission has also provided a powerful demonstration of RO scheme in particular and for the remote-sensing applications of micro-satellite constellations in general. All these technical principles have paved the way for the design of future GNSS RO remote-sensing systems
TABLE 3-1 F3CONSTELLATION SPACECRAFT BUS KEY DESIGN
Mass ~ 54 kg (Dry Weight)
Power: ~ 81 Watts (bus and payload)
Shape Disc-shape of 116cm diameter, 18cm in height Science Data Storage 128 MB
Distributed Architecture Motorola 68302 Microprocessor Attitude Control Magnetic 3-axis Control
Pointing Control = 5° Roll & Yaw, 2 ° Pitch Propulsion Hydrazine Propulsion Subsystem
S-Band Communications HDLC Command Uplink (32 kbps) CCSDS Telemetry Downlink (2 Mbps) Single String Bus Constellation Redundancy
TABLE 3-2 CONSTELLATION DEPLOYMENT STATUS WITH FIVE SATELLITES (FM5,FM2,FM6, FM4, AND FM1)AT FINAL ORBITS AS-OF-2DEC,2007
Items SMA Eccentricity Inclination RAAN (Ωi/5) AOL (Li/5)
SC No. (km) (deg) (deg) (deg)
FM5 799.475 0.0046 71.973 0 0
FM2 799.449 0.0041 72.037 29.9 50.7
FM6 799.444 0.0051 71.982 62.0 104.4
FM4 799.471 0.0072 72.009 90.0 158.2
FM3* 711.047 0.0054 72.012 129.9 Time Variant
FM1 799.475 0.0046 71.973 145.9 262.53
*Note: On 3 Aug. 2007 the FM3 encountered solar array drive mechanism malfunction when reached 711 km orbit.
TABLE 3-3 SPACECRAFT THRUST-BURN PERFORMANCE STATISTICS
Items Total Burn Days
Total Burn Number
Planned Burn
Executed Burn
Successfu l Rate
Total Fuel Used
Total Fuel Mass
Average SMA/burn
Average Duration/burn
SC No. (Days) (no.) (Minutes) (Minutes) (%) (kg) (kg) (km/burn) (sec/burn) FM5 39 53 456 326.1 71.5 4.634 6.671 5.4 369.4 FM2 50 80 646.5 321.7 49.8 4.686 6.651 3.6 241 FM6 36 65 390 294.7 75.6 4.332 6.635 4.4 279.9 FM4 41 90 390.5 307.8 78.8 4.644 6.627 3.2 205.4 FM3 39 74 265.7 190.3 71.6 3.345 6.665 2.7 154.3 FM1 40 71 382.8 329.8 86.2 4.993 6.697 3.4 238.4
TABLE 3-4 SPACECRAFT MASS PROPERTY AND MOMENT OF INERTIA FOR SIX SATELLITES AS-OF-2DEC,2007
Figure 3-1. F3 spacecraft in deployed configuration and its major components.
Figure 3-2. Spacecraft Reaction Control Subsystem block diagram.
Figure 3-3. Reaction Control Subsystem thruster geometry and torque.
Thruster Geometry Cant (10°) Enables 3-Axis Control
Thruster Data:
• 15 msec min. Turn-On time
• 0.2 lbf (BOL), 5:1 Blowdown
R1 R2
Figure 3-4. Reaction Control Subsystem blowdown curve.
Figure 3-5. Functional block diagram of the spacecraft attitude control subsystem.
Figure 3-6. Off-pulsing concept of ACS thrust mode.
Figure 3-7. F3 as-is burn history and deployment timeline.
500 550 600 650 700 750 800 850
4/15/06 7/24/06 11/1/06 2/9/07 5/20/07 8/28/07 12/6/07
Date
Altitude (km)
FM5 FM2 FM6 FM4
FM3
FM1
Figure 3-7. Spacecraft thrust-burn performance statistics.
0 20 40 60 80 100
FM5 FM2 FM6 FM4 FM1
Total Burn Days Total Burn Number Successful Rate % Total Fuel Used %