GP-B Post-Flight AnalysisÃ¢Â€Â”Final Report - Gravity Probe B - Stanford ...

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Figure 9-8. Block diagram of the LQE control architecture.This algorithm is implemented in a radiation-hardened digital computer based on a Power PC-derived BritishAerospace (formerly Lockheed-Martin Federal Systems) RAD6000 processor running at 16.368 MHz within thesuspension electronics package. To achieve maximum performance from the processor, a custom single-thread,non-preemptive real time operating system was written for this application. During peak demand periodsduring spin-up operations, the processor is loaded to 96% of its capacity; science operation requiresapproximately 65% of capacity The code for this application is small, however, only occupying 500 kB ofmemory. The range of external accelerations that can be handled by the digital control algorithm is shown inFigure 9-10.Figure 9-9. Simulated response of adaptive LQE controller showing constant excursion for varying disturbanceThe digital controller is able to operate over 8 orders of magnitude of force disturbances while minimizing thetorques on the gyroscope rotors. The primary science mode digital suspension operates over a specific forcerange from 10 7 m/s 2 to 10 2 m/s 2 and bandwidths of 1.5 Hz to 8 Hz, respectively, at a sample rate of 220 Hz. The264 March 2007 Chapter 9 — Gyro Suspension Subsystem (GSS) Analysis
spin-up controller bandwidth is not adaptive, has a 660 Hz sample rate, and has been designed to reject thedisturbances from the spin-up gas flow. During spin-up, electrostatic torques are not a concern, thus acomputationally simpler, fixed control scheme is used. This system is also able to suspend a gyroscope in thelaboratory in 1 g conditions, and can apply up to 1600 VDC to provide the required electric fields to suspend onthe ground for performance testing. Computer systems are notoriously unreliable in a space radiationenvironment. Three all-analog backup control systems are also provided to suspend the gyroscope in the eventof a computer fault.Figure 9-10. Suspension Controllers and Modes of Operation showing the 8 ordersof magnitude of operation for this system.The spin-up backup controller is used during gas flow operations, and the two science mode backups are activeduring the remainder of the mission. The all-analog controllers are robust proportional/derivative (PD) designswith a force-to-voltage nonlinearity inversion circuit to allow good control over the range of motion of the rotorin the housing. The primary role of these controllers is to prevent the rotor from contacting the housing wall,thus an integral term in the controller is not needed which significantly simplifying the design of thesecompensators. An analog arbiter (see the FSU block diagrams above) monitors computer health and rotorposition and will autonomously switch into the appropriate backup controller in the event of a computer faultor a large position excursion of the rotor. This architecture permits the controller to operate over the required 8orders of force magnitude, providing reliable suspension of the rotors (via prime and backup systems), andminimize electrostatic torques on the rotor via the variable bandwidth adaptive control law.9.2.2 Controller performance on OrbitThe GSS system performed very well on orbit and was able to successfully suspend, support spin-up, and alignthe spin axes of the gyros to mission requirements.9.2.2.1 Science SuspensionBecause of the robustness and simplicity of the control algorithms, the gyroscopes were initially suspendedusing the analog backup control system. Figure 9-11 shows a snapshot of the trajectory of the Gyro 2 positionon its inaugural on-orbit suspension. The gyro was initially sitting on the housing wall in the C electrode axisGravity Probe B — Post Flight Analysis • Final Report March 2007 265
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Post Flight Analysis — Final Repo
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Signatures & ApprovalsPrepared byPu
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Table of ContentsPreface . . . . .
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6.8 Sources and References . . . .
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11 Telescope Readout Subsystem (TRE
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14 Data Collection, Processing & An
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xiv March 2007 Table of Contents
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Figure 3-4. The GP-B dewar—one of
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Figure 8-5. The Seasons of GP-B . .
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Figure 11-20. Pointing angle differ
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Figure 14-9. In the Anomaly Room, t
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xxiv March 2007
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Table 13-3. GP-B payload magnetomet
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xxviiiMarch 2007
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2 March 2007 Chapter 1 — Executiv
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facility, it was necessary to recas
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spacetime around with them as they
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After years of work and the inventi
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axis of a gyroscope rotor changes i
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Figure 1-8. Clockwise, from top lef
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“management experiment.” This w
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Attitude-Control Gyroscopes. Two pa
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Any significant deviation from “g
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established, ranging from Level 1 (
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1.14 The Broader Legacy of GP-BAt l
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24 March 2007 Chapter 2 — Overvie
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Figure 2-1. GP-B Historical Time Li
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Applied Physics Laboratory, of the
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William Fairbank once remarked: “
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In Einstein’s view, space and tim
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y a mere 1.1 inches. You can see th
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Figure 2-10. Schematic diagram of t
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Figure 2-12. Final assembly of the
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Sun Shield. The sun shield is a lon
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2.1.8 The Broader Legacy of GP-BWhe
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2.3 Spacecraft SeparationThe Solar
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Flight Anomalies.) Furthermore, a d
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Table 2-2. Weekly summary of IOC ac
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2.4.3.2 Guide Star AcquisitionAbout
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A second mass trim operation had be
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On Friday, 2 July 2004, the spin ra
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Low temperature bakeout was first p
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2.5.1.3 Lockheed Martin Team Phase-
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Monthly Highlights of the GP-B Scie
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2.6.1 Overview of the Calibration P
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Weekly Highlights of the GP-B Final
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66 March 2007 Chapter 3 — Accompl
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It was in this pristine, near-zero
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Each quartz rotor is coated with a
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Figure 3-3. Functional diagram of a
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Based on data from the on-board tel
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Ideally, the telescope should have
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Figure 3-9. Schematic diagram of st
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used. The star trackers are essenti
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Result: By using the porous plug, w
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Solution: Create a tetrahedral lapp
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Constraint 2: The exhaust tube must
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Result: The on-orbit gyroscope spin
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spacecraft's subsystems for the dur
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Constraint 3: Keep the spacecraft p
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Technology Category Specific Implem
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96 March 2007 Chapter 4 — GP-B On
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Any significant deviation from “g
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packages, one for each Ping load an
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In addition to these software packa
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Table 4-6. Features & benefits of W
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This software added considerable ef
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It is said that “an experiment is
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Table 4-10. Significant Events/Sour
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Figure 4-5. Pictorial depiction of
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Figure 4-7. Eta-Average Error Assoc
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4.4.4.2 OD Using SLR DataFigure 4-9
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4.4.5 ConclusionsFigure 4-11. Compa
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Overall, the storage issues did not
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Table 4-11. ITF equipment listEQUIP
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124 March 2007 Chapter 5 — Managi
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5.2 Overview of GP-B Anomalies in O
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Figure 5-1. Anomaly Review Team Org
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5.3.3.1 Anomaly Investigation and R
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5.3.5 Anomaly Identification and Re
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5.4.3 Risk Management ApproachThe r
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Table 5-1. Summary of Open GP-B ris
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138 March 2007 Chapter 5 — Managi
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140 March 2007 Chapter 6 — The GP
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3. Payload Integration, Testing and
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Figure 6-1. Clockwise from top left
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MSFC conducted an in-house Phase A
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It is important to note that from t
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6.3.1 Incremental PrototypingThe pe
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alignment, and act as an accelerome
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Figure 6-9. The Lockheed Martin GP-
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Furthermore, a fourth electronic sy
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positive thermal connections betwee
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astrophysics/cosmology. Many of the
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Figure 6-10. MSFC Program Managers/
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As described in Chapter 2, the flig
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6.7 Some Observations on the Manage
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168 March 2007 Chapter 6 — The GP
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170 March 2007 Chapter 7 — Attitu
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7.1.2 Vehicle ATC ModesThere are es
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The output of the pressure transduc
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Figure 7-3. Science Telescope Compo
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Figure 7-5. Pitch and Yaw Pointing
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Figure 7-7. Magnitude of the roll r
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Changing the method by which the gy
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7.3.3 Drag-Free Control SystemFigur
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7.3.3.1 DFS - PerformanceThe GP-B d
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Figure 7-15. Mass flow effects of a
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7.5.2 Successful recovery from mult
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If the vehicle control system were
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accomplish this, the ARPs are mount
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7.5.6.1 South Atlantic AnomalyProto
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Figure 7-23. Effects on telescope p
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200 March 2007 Chapter 7 — Attitu
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202 March 2007 Chapter 8 — Other
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Figure 8-2. Block Diagram of CDH co
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8.1.1.4 WATCH DOG TIMERFigure 8-4.
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of eclipses each day (approximately
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Figure 8-8. GSS1 Temperature Trends
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Figure 8-10. Forward Dewar Vacuum S
Page 242 and 243: The Gravity Probe B spacecraft has
Page 244 and 245: Figure 8-13. Forward -X Thruster Te
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Page 248 and 249: Because there are only two SQUID br
Page 250 and 251: Because the specifications for SRE
Page 252 and 253: 8.3.2 Critical Mission RequirementT
Page 254 and 255: Figure 8-19 is a plot of the power
Page 256 and 257: Battery Performance Summary:Figure
Page 258 and 259: Figure 8-23. Solar Array Temperatur
Page 260 and 261: 8.3.10 ConclusionThe electrical pow
Page 262 and 263: 8.4.1 TDRSS OperationsFigure 8-28.
Page 264 and 265: Figure 8-30. Xpndr-A STDN (green),
Page 266 and 267: Figure 8-32. Plot of TDRS AGC vs Te
Page 268 and 269: The FSW also met its subsystem leve
Page 270 and 271: Appendix E, Flight Software Applica
Page 272 and 273: Table 8-4. SCRs Addressed in On-orb
Page 274 and 275: The software and macro changes resu
Page 276 and 277: Figure 8-38 below is an excerpt fro
Page 278 and 279: Figure 8-40. A-side CCCA Single Bit
Page 280 and 281: Figure 8-43. A-side CCCA Single Bit
Page 282 and 283: When single MBEs did not result in
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Page 286 and 287: 9.1 GSS Hardware DescriptionFigure
Page 288 and 289: significantly reduces and thus pres
Page 290 and 291: 9.1.11 Clock synchronizationThe aft
Page 294 and 295: direction (transverse to the space
Page 296 and 297: 9.2.2.2 Spin-up SuspensionDuring sp
Page 298 and 299: Figure 9-16. Predicted and measured
Page 300 and 301: Figure 9-18. The GSS passes rotor c
Page 302 and 303: Figure 9-20. Representative drag-fr
Page 304 and 305: Table 9-1. GSS Science Mission Mode
Page 306 and 307: Table 9-3. GSW application source l
Page 308 and 309: The Design and Testing of the Gravi
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Page 312 and 313: ate uncertainty). Although we have
Page 314 and 315: All of the GP-B electronics have be
Page 316 and 317: 10.3 Pre-Launch Ground-Based TestsW
Page 318 and 319: Figure 10-6. AC Magnetic Shielding
Page 320 and 321: Figure 10-8. Temperature Error of S
Page 322 and 323: Figure 10-10. Quiescent SQUID Noise
Page 324 and 325: Analog control loops on the electro
Page 326 and 327: The science support applications ru
Page 328 and 329: Table 10-7. SSW application source
Page 336 and 337: 308 March 2007 Chapter 11 — Teles
Page 338 and 339: Figure 11-1. Block diagram of TRE a
Page 340 and 341: Additionally, the warm electronics
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Figure 11-3. CLL switch states duri
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Table 11-3. Dates and UTC times whe
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Figure 11-7. Low Gamma Angle Data S
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s N+w i= sign+w i++−+−w i−w i
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expression, which otherwise on a po
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Figure 11-14. Y axis, B side RMS po
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Figure 11-17. X axis, B side curren
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Figure 11-20. Pointing angle differ
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Figure 11-24. Scaled summed current
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Figure 11-26 through Figure 11-29 s
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334 March 2007 Chapter 12 — Cryog
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12.2 Temperature / pressure control
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control the space vehicle without t
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Figure 12-3. Helium flow rate predi
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helium at 1.8 K. It does not appear
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Figure 12-6. Flow meter and ATC flo
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were generally within a day or so o
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shields) and subsequent instability
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350 March 2007 Chapter 12 — Cryog
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352 March 2007 Chapter 13 — Other
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Figure 13-2. ECU-operated heaters i
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13.1.3.1 Vatterfly Valve Operations
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13.1.3.7 Payload MagnetometersThe E
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Figure 13-11. ECU performance durin
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As we entered the second month of o
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During the last month of IOC, prepa
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Figure 13-19. ECU heater activity d
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Table 13-1. Proton monitor channel
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Figure 13-21. Proton Monitor data i
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In November, 2004 there was a large
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Figure 13-28 shows a correlation th
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13.3.1 About the MagnetometersFigur
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13.3.2 Other Applications for Paylo
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Figure 13-35. GPS Antennae Field of
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Figure 13-37. Master Antenna Switch
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Figure 13-39. Time difference betwe
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13.4.6 On-Orbit ResultsThe GPS comp
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and velocity values erroneously cal
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E. G. Lightsey, C. E. Cohen, B. W.
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Figure 13-45. A Bottom View of the
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Figure 13-48. The GMA configuration
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Table 13-10. Summary for Helium Gas
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398 March 2007 Chapter 14 — Data
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a relatively slow data rate, so we
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Figure 14-4. NASA ground stations a
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electronic components to recover fr
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By a process of elimination, the GP
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A special room in the GP-B Mission
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Starting on 3 December 1725, Bradle
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seemed that aberration of starlight
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14.1.6 Telescope Dither—Correlati
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14.1.6.3 The Telescope Dither Patte
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amplifications. Thus, in addition t
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14.2.2 Independent Data Analysis Te
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monthly time scales. Though only sh
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424 March 2007 Chapter 15 — Preli
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Figure 15-2. A diagram of the GP-B
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15.4 The Two Surprises and Their Im
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Near Zeroes.) The exception that we
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Figure 15-8. A slide from the GP-B
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Figure 15-9. A poster on the effect
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electrostatic patches, located at o
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Last summer (2006), Mac Keiser devi
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440 March 2007 Chapter 15 — Preli
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442 March 2007 Chapter 16 — Lesso
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16.1.1.3 Flight science downlink da
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Description of the GP-B experience:
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Lessons:1. Perform all tests with a
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Figure 16-1. Six interacting transl
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16.1.3.2 Training and certification
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Below is an edited summary of six a
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460 March 2007 Chapter 16 — Lesso
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462 March 2007 Appendix A — Gravi
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Apogee altitude659.1 km (409.6 mile
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466 March 2007 Chapter B — Spacec
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Gravity Probe B — Post Flight Ana
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470 March 2007 Appendix C — Weekl
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16 April 2004—Vehicle is Prepared
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The electrical power system is full
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4 JUNE 2004—MISSION UPDATE: DAY 4
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SQUIDs to detect their rotation spe
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17 JULY 2004—MISSION UPDATE: DAY
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indicate that we have reduced the t
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C.4 Science Mission Phase: 8/27/04
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• GP-B also has an independent da
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free suspension parameters to de-tu
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We have received inquiries about a
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One of the effects of geomagnetic s
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egan transmitting, one-by-one, stat
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28 JANUARY 2005—GRAVITY PROBE B M
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magnetic pole. This event triggered
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8 APRIL 2005—GRAVITY PROBE B MISS
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On Tuesday afternoon (19-April), GP
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Norway or through the NASA space ne
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Dewar Temperature: 1.82 kelvin, hol
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visitors on a tour of the GP-B faci
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test, we are planning on running fi
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contractor at the Goddard Space Fli
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On Wednesday, we visited the star H
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Gyro Suspension System (GSS): All 4
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The helium in the dewar has now sur
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the all the spacecraft status data.
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522 March 2007 Appendix D — Summa
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Figure D-2 below shows the distribu
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DateSeveritySubtypeTitle Descriptio
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DateSeverity24 26-Apr-04 Obs F Nois
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DateSeverity40 11-May-04 Obs T Dwel
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Page 562 and 563:
DateSeverity68 16-Jun-04 Medium Dec
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DateSeverity84 13-Jul-04 Obs F Slig
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Page 568 and 569:
DateSeverity116 26-Sep-04 Obs F SG3
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DateSeverity132 20-Dec-04 Obs F Unc
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DateSeverity149 5-Mar-05 Obs T Few
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DateSeverity169 04-Jun-05 Obs F MBE
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DateSeverity191 04-Oct-05 Obs A GSS
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550 March 2007 Appendix E — Fligh
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ReqIDLevel 1CSCDMP DataMgmtProcessi
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ReqIDLevel 1CSCLevel2 CSC Level 3 C
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Page 586 and 587:
Page 588 and 589:
ReqIDLevel 1CSCSRM Solid StateRecor
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Page 592 and 593:
Page 594 and 595:
ReqIDLevel 1CSCSRP SafemodeResponse
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ReqIDLevel 1CSCGUP GSS Processing g
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570 March 2007 Appendix F — Acron
Page 600 and 601:
AcronymDefinitionAcronymDefinitionB
Page 602 and 603:
AcronymDefinitionAcronymDefinitionD
Page 604 and 605:
AcronymDefinitionAcronymDefinitionF
Page 606 and 607:
AcronymDefinitionIRUInertial Refere
Page 608 and 609:
AcronymDefinitionAcronymDefinitionM
Page 610 and 611:
AcronymPMPMAPMCPMEPMETPMSPMSUPNPoPO
Page 612 and 613:
AcronymSCMOSCMTSCNSCPASCPMSCRSCSASC
Page 614 and 615:
AcronymDefinitionAcronymDefinitionT
Page 616:
588 March 2007 Appendix F — Acron
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