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

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and velocity values erroneously calculated by the GPS receiver. The cross product of the position and velocitysolution calculated by the receiver resulted in a value with of 3e19. The magnitude function takes the root sumsquared, 3e192 = 9e38 which exceeded a short float range of 1.7014e+038 (2^127). Typically all divisions,squares etc. are protected in the ATC code, but multiplications are not. The result caused a stack overflow,which in turn caused the safemode activation. The erroneous position and velocity solution was caused by poorgeometry of the GPS constellation. The operational solution was to increase the exception counter.13.4.7.4 Channel Alignment Issues Due to Computer Memory ErrorsOn two occasions, August 12 th , 2004 (Observation 102) and Jan 10 th , 2005 (Observation 135), telemetryindicated that a GPS error flag, channel alignment error, had toggled to the true state, indicating a problem withthe receiver. A detailed analysis of GPS solutions ruled out an actual error state, suggesting that the error bitflipped as a result of a single bit or multi-bit event. While rebooting the receiver would have cleared the error, inboth cases the decision was made to leave the receiver as is. In both instances, the receiver was eventuallyrebooted as part of other vehicle operations.13.4.7.5 Switch to B-Side GPS ReceiverThe last observation regards the switch to the B-side receiver. Since the GPS receivers are not cross strapped,when the vehicle switched from the A-side to the B-side on March 13, 2005, the GPS subsystem switched fromthe A-side to the B-side components as well. While the average percent lock by the B-side components is onlyslightly less than the A-side average (95% vs 98%), Figure 13-43 clearly shows that the day-to-day values varygreatly. Figure 13-43 also shows the percentage of GPS solutions used by the orbit determination group tocalculate the GP-B orbit also dropped after the switch to the B-side hardware. The decrease in usable points isdue to the increase in “stale” data—data from a previous solution still in the GPS memory buffer. When thereceiver is locked and outputting valid GPS solutions, stale data is overwritten by new data. Stale data shouldonly occurs when the receiver is reacquiring the GPS constellation. Analysis of the solution quality indextelemetry shows that the SQI is slightly, but consistently, higher on the B-side than on the A-side receiver, anobservation consistent with the decrease in percent lock seen. Further insight is gleaned by observing that jitterin the clock bias is higher on the B-side. The most likely hypothesis is that the difference is caused by slightdifferences in the performance of the GPS internal oscillators, used to track time between successive PVTsolutions. While only a detailed analysis of the GPS internal oscillators can verify the root cause, availabletelemetry is consistent with this hypothesis. Pre-launch sanity testing did not reveal performance differencesbetween the two oscillators.388 March 2007 Chapter 13 — Other Payload Subsystems Analyses
Figure 13-43. Percent Lock and data points used before and after the switch to the B-sidereceiver on March 4, 2005, day 64.Regardless of the root cause, it is important to note that while the percentage of GPS solutions used by the OrbitDetermination group has decreased since the switch to the B-side receiver, the quality of the solutions has notdecreased, The orbit solution calculated by the group continues to meet mission requirements. Although aperformance difference between the A-side and B-side components is clear, the GPS subsystem has easilyexceeded all mission requirements and pre-launch expectations.13.4.8 ReferencesJ. Ceva, B. W. Parkinson, Multiple Interference in Orbiting Receivers Due to Earth Surface Reflections, ION GPS-93, SaltLake City, Utah, September 1993.C. E. Cohen, B. W. Parkinson, Mitigating Multipath Error in GPS Based Attitude Determination. Reprinted fromGuidance and Control 1991,Vol. 74, Advances in Astronautical Sciences.C. E. Cohen, B. W. Parkinson, Expanding the Performance Envelope of GPS-Based Attitude Determination, ION GPS,Albuquerque, N. M. September 1991.P. Axelrad, B. W. Parkinson, Closed Loop Navigation and Guidance for Gravity Probe B Orbit Insertion, Journal of TheInstitute of Navigation, Vol. 36, No. 1, Spring 1989.J. Li, G.M. Keiser, J.M. Lockhart, P. Shestople, Time Transfer between UTC and Local Vehicle Time for the Gravity Probe BRelativity Mission. Proceedings of both Annual Meetings of Institute of Navigation, pp.560-570, 2004.J. Li, A. Ndili, L. Ward, S. Buchman, GPS Receiver Satellite/Antenna Selection Algorithm for the Stanford Gravity Probe BRelativity Mission. Proceedings of 1999 Institute of Navigation National Technical Meeting, pp.541.J. Li, A. Ndili, L. Ward, S. Buchman, M. Keiser, Analysis of Field-of-View of GPS Antennas and Constraints of the AntennaTransfer Time, Stanford University, GP-B Memo, SDOC 344, Rev -, 1998D. Yale, A. Ndili, J. Li, E Ng, E. Bean, S Buchman, Rolling GPS Receiver Development and Verification Testing for SpaceApplication, Institute of Navigation GPS-99 Conference, Nashville, Tennessee, Proceedings of the 12thInternational Technical Meeting, p. 857.Gravity Probe B — Post Flight Analysis • Final Report March 2007 389
Page 1 and 2:
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
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The Gravity Probe B spacecraft has
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Figure 8-13. Forward -X Thruster Te
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gaFigure 8-15. Aft -X Thruster Temp
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Because there are only two SQUID br
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Because the specifications for SRE
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8.3.2 Critical Mission RequirementT
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Figure 8-19 is a plot of the power
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Battery Performance Summary:Figure
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Figure 8-23. Solar Array Temperatur
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8.3.10 ConclusionThe electrical pow
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8.4.1 TDRSS OperationsFigure 8-28.
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Figure 8-30. Xpndr-A STDN (green),
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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
Page 366 and 367: control the space vehicle without t
Page 368 and 369: Figure 12-3. Helium flow rate predi
Page 370 and 371: helium at 1.8 K. It does not appear
Page 372 and 373: Figure 12-6. Flow meter and ATC flo
Page 374 and 375: were generally within a day or so o
Page 376 and 377: shields) and subsequent instability
Page 378 and 379: 350 March 2007 Chapter 12 — Cryog
Page 380 and 381: 352 March 2007 Chapter 13 — Other
Page 382 and 383: Figure 13-2. ECU-operated heaters i
Page 384 and 385: 13.1.3.1 Vatterfly Valve Operations
Page 386 and 387: 13.1.3.7 Payload MagnetometersThe E
Page 388 and 389: Figure 13-11. ECU performance durin
Page 390 and 391: As we entered the second month of o
Page 392 and 393: During the last month of IOC, prepa
Page 394 and 395: Figure 13-19. ECU heater activity d
Page 396 and 397: Table 13-1. Proton monitor channel
Page 398 and 399: Figure 13-21. Proton Monitor data i
Page 400 and 401: In November, 2004 there was a large
Page 402 and 403: Figure 13-28 shows a correlation th
Page 404 and 405: 13.3.1 About the MagnetometersFigur
Page 406 and 407: 13.3.2 Other Applications for Paylo
Page 408 and 409: Figure 13-35. GPS Antennae Field of
Page 410 and 411: Figure 13-37. Master Antenna Switch
Page 412 and 413: Figure 13-39. Time difference betwe
Page 414 and 415: 13.4.6 On-Orbit ResultsThe GPS comp
Page 418 and 419: E. G. Lightsey, C. E. Cohen, B. W.
Page 420 and 421: Figure 13-45. A Bottom View of the
Page 422 and 423: Figure 13-48. The GMA configuration
Page 424 and 425: Table 13-10. Summary for Helium Gas
Page 426 and 427: 398 March 2007 Chapter 14 — Data
Page 428 and 429: a relatively slow data rate, so we
Page 430 and 431: Figure 14-4. NASA ground stations a
Page 432 and 433: electronic components to recover fr
Page 434 and 435: By a process of elimination, the GP
Page 436 and 437: A special room in the GP-B Mission
Page 438 and 439: Starting on 3 December 1725, Bradle
Page 440 and 441: seemed that aberration of starlight
Page 442 and 443: 14.1.6 Telescope Dither—Correlati
Page 444 and 445: 14.1.6.3 The Telescope Dither Patte
Page 446 and 447: amplifications. Thus, in addition t
Page 448 and 449: 14.2.2 Independent Data Analysis Te
Page 450 and 451: monthly time scales. Though only sh
Page 452 and 453: 424 March 2007 Chapter 15 — Preli
Page 454 and 455: Figure 15-2. A diagram of the GP-B
Page 456 and 457: 15.4 The Two Surprises and Their Im
Page 458 and 459: Near Zeroes.) The exception that we
Page 460 and 461: Figure 15-8. A slide from the GP-B
Page 462 and 463: Figure 15-9. A poster on the effect
Page 464 and 465: 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:
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
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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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