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

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7.5.2 Successful recovery from multiple CCCA rebootsFor several different reasons, the CCCA, the main processor for the satellite, has rebooted several times. Eachtime a reboot occurs, the vehicle attitude and translation control is off for a short time. Furthermore, all controlsoftware and parameter updates since the latest software installation on July 1, 2004 are cleared from thememory. All of the improvements and fixes are lost and must be reloaded. Through a series of automated loadcommands and manual commands, the vehicle is brought back to a nominal state over a period ranging fromone day to one week.A system of safemode operations has been developed that has left the vehicle in a predictable and recoverablestate for each reboot. The recovery time for a reboot has been reduced from approximately one week to less thanone day. More importantly, the vehicle is typically returned to drag-free operations and pointed to withinarcseconds of the guide star in a matter of hours. A quick recovery time is necessary not only to ensure the safetyof the spacecraft, but also the integrity of the science data.7.5.3 Supporting higher science roll rateOriginally, the GPB spacecraft was optimized for a nominal roll rate of 0.3 rpm. After a request by the scienceteam for a higher roll rate, the team determined that the vehicle could perform sufficiently at a higher roll rate.The team then developed an ATC configuration that supports a roll rate of 0.77 rpm, more than twice as fast asthe baselined roll rate prior to launch. However, the system has performed well and has shown no significantdeficiency due to the higher roll rate.7.5.4 Successful large-scale ditherFigure 7-17 below shows a plot of the large-scale dither operation from the IOC phase of the mission.190 March 2007 Chapter 7 — Attitude & Translation Control Subsystem Analysis
7.5.5 ARP Motion ChallengesFigure 7-17. Large Scale Dither Performance (2004/197)The Attitude Reference Platforms (ARPs) are the mounting location of the control rate gyroscopes, as well asthe roll star trackers. At one time, one set of gyroscopes and one star tracker are used in the control loop thatmaintains the attitude of the vehicle. While thermal effects were expected, the motion of the ARP and rategyroscope housing have introduced disturbances into the rate signal that have presented challenges throughoutmost of the mission. The ARP moves with components of motion at annual, orbit, and roll rates, and all three ofthese components have provided unique challenges to overcome to arrive at the pointing performance thevehicle now achieves.7.5.5.1 Mode 1A vs 1BOne of the most significant operational decisions resulting from ARP motion analysis is that Mode 1B (directmode) was chosen as the science configuration, instead of Mode 1A (observer mode) while pointing at the guidestar. The dependence on the gyroscope signal of the observer would lead to the telescope tracking the ARPmotion rather than keeping the guide star centered in the field of view.As the vehicle rolls around the telescope boresight (the z axis in the body frame), the ARP is heated and cooledin an almost sinusoidal fashion at precisely roll rate. As the ARP deforms, the orientation of the gyroscopehousing changes with respect to the z axis, causing the roll rate of the vehicle to project onto the pitch and yawaxes. This effect shows up in the gyroscope output and yields a fictitious sinusoidal rate signal in both the pitchand yaw axes.Gravity Probe B — Post Flight Analysis • Final Report March 2007 191
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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
Page 168 and 169: 140 March 2007 Chapter 6 — The GP
Page 170 and 171: 3. Payload Integration, Testing and
Page 172 and 173: Figure 6-1. Clockwise from top left
Page 174 and 175: MSFC conducted an in-house Phase A
Page 176 and 177: It is important to note that from t
Page 178 and 179: 6.3.1 Incremental PrototypingThe pe
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Page 182 and 183: Figure 6-9. The Lockheed Martin GP-
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Page 190 and 191: Figure 6-10. MSFC Program Managers/
Page 192 and 193: As described in Chapter 2, the flig
Page 194 and 195: 6.7 Some Observations on the Manage
Page 196 and 197: 168 March 2007 Chapter 6 — The GP
Page 198 and 199: 170 March 2007 Chapter 7 — Attitu
Page 200 and 201: 7.1.2 Vehicle ATC ModesThere are es
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Page 204 and 205: Figure 7-3. Science Telescope Compo
Page 206 and 207: Figure 7-5. Pitch and Yaw Pointing
Page 208 and 209: Figure 7-7. Magnitude of the roll r
Page 210 and 211: Changing the method by which the gy
Page 212 and 213: 7.3.3 Drag-Free Control SystemFigur
Page 214 and 215: 7.3.3.1 DFS - PerformanceThe GP-B d
Page 216 and 217: Figure 7-15. Mass flow effects of a
Page 220 and 221: If the vehicle control system were
Page 222 and 223: accomplish this, the ARPs are mount
Page 224 and 225: 7.5.6.1 South Atlantic AnomalyProto
Page 226 and 227: Figure 7-23. Effects on telescope p
Page 228 and 229: 200 March 2007 Chapter 7 — Attitu
Page 230 and 231: 202 March 2007 Chapter 8 — Other
Page 232 and 233: Figure 8-2. Block Diagram of CDH co
Page 234 and 235: 8.1.1.4 WATCH DOG TIMERFigure 8-4.
Page 236 and 237: of eclipses each day (approximately
Page 238 and 239: Figure 8-8. GSS1 Temperature Trends
Page 240 and 241: 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
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The FSW also met its subsystem leve
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Appendix E, Flight Software Applica
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Table 8-4. SCRs Addressed in On-orb
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The software and macro changes resu
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Figure 8-38 below is an excerpt fro
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Figure 8-40. A-side CCCA Single Bit
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Figure 8-43. A-side CCCA Single Bit
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When single MBEs did not result in
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256 March 2007 Chapter 9 — Gyro S
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9.1 GSS Hardware DescriptionFigure
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significantly reduces and thus pres
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9.1.11 Clock synchronizationThe aft
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Figure 9-8. Block diagram of the LQ
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direction (transverse to the space
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9.2.2.2 Spin-up SuspensionDuring sp
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Figure 9-16. Predicted and measured
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Figure 9-18. The GSS passes rotor c
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Figure 9-20. Representative drag-fr
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Table 9-1. GSS Science Mission Mode
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Table 9-3. GSW application source l
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The Design and Testing of the Gravi
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282 March 2007 Chapter 10 — SQUID
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ate uncertainty). Although we have
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All of the GP-B electronics have be
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10.3 Pre-Launch Ground-Based TestsW
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Figure 10-6. AC Magnetic Shielding
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Figure 10-8. Temperature Error of S
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Figure 10-10. Quiescent SQUID Noise
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Analog control loops on the electro
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The science support applications ru
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Table 10-7. SSW application source
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308 March 2007 Chapter 11 — Teles
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Figure 11-1. Block diagram of TRE a
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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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DateSeverity68 16-Jun-04 Medium Dec
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DateSeverity84 13-Jul-04 Obs F Slig
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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:
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ReqIDLevel 1CSCSRP SafemodeResponse
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ReqIDLevel 1CSCGUP GSS Processing g
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570 March 2007 Appendix F — Acron
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AcronymDefinitionAcronymDefinitionB
Page 602 and 603:
AcronymDefinitionAcronymDefinitionD
Page 604 and 605:
AcronymDefinitionAcronymDefinitionF
Page 606 and 607:
AcronymDefinitionIRUInertial Refere
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AcronymDefinitionAcronymDefinitionM
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AcronymPMPMAPMCPMEPMETPMSPMSUPNPoPO
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AcronymSCMOSCMTSCNSCPASCPMSCRSCSASC
Page 614 and 615:
AcronymDefinitionAcronymDefinitionT
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588 March 2007 Appendix F — Acron
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