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

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shields) and subsequent instability in the bath temperature that will disturb the vapor equilibrationprocess. Even in a system such as ours, where the vent rate is actively controlled, the long-term stability israrely adequate due to environmental variation over various time scales (roll, orbital, diurnal) and due toelectronics and sensor drift.Figure 12-9. HPM data analyzed under three different assumptions together with extrapolated linear trendlines.12.10 Magnetic Shielding PerformanceThis section describes two aspects of GP-B’s magnetic shielding performance that are related to the cryogenicsystem: trapped flux in the gyro rotors and AC shielding.12.10.1 Rotor Trapped FluxGP-B has a unique magnetic shield system that provides an ultra-low magnetic field environment for thescience instrument. Considerable effort was also made to ensure that the materials used in constructing theProbe and the science instrument did not degrade this environment. The primary reason for this requirement isthe need to keep the magnetic flux in the gyro rotors below 9 microgauss (0.9 nT) uniform field equivalent.The trapped flux in the gyro rotors measured on orbit is smaller than 4 μG for all gyroscopes as shown inTable 12-2. (The readout system is only capable of measuring the component of trapped flux that threads thepickup loop and varies in time as the rotor rotates.) The trapped field in gyro 4 is more than an order ofmagnitude smaller. The table also compares the trapped field to the magnitude of the equivalent Londonmoment field for each rotor. These results indicate that the superconducting shield is nominal and that therewas no degradation of the shield as a result of launch conditions.348 March 2007 Chapter 12 — Cryogenic Subsystem Analysis
Table 12-2. Measured trapped field compared to the London moment equivalent field in each of the gyrorotors.GyroNo.Trapped field (μG) (Uniformfield equivalent and asaligned late in mission)12.10.2 AC ShieldingLondon moment equiv.field (μG)The second function of the magnetic shielding system is to prevent time-varying fields from coupling to thereadout pickup loops and contaminating the science signal. In this regard, the shields built into the dewar aresupplemented by superconducting cylindrical local shields around each gyro and by the diamagnetic effect ofthe superconducting rotors themselves. As it turns out, the limits on the AC magnetic shielding derived fromthe data while the gyros were caged early in the mission were not as tight as the limits obtained from the groundverification, which were 2x10 -12 (-234 db) attenuation. In any case, no evidence of a signal with the signature ofa leakage field was observed above the noise. In addition, the fact that the ambient dc field is nominal is goodprima facie evidence that the AC shielding has not been degraded from the ground test result.12.11 Probe Vacuum PerformanceRatio of trapped field toLondon moment1 3.1 57 0.0552 1.3 44 0.0293 0.859 59 0.0144 0.2 47 0.005Vacuum in the Probe is important during science data acquisition because of the damping effect residualhelium has on the gyro rotors. Of particular concern is differential damping wherein the component of spinalong the roll axis decays at a different rate than the component transverse to the roll axis. This can cause aprecession if the spin and roll axes are not exactly aligned. In order to keep this effect to an acceptable level,there is a requirement that the Probe pressure be less than or equal to 2x10 -10 torr after the low temperaturebakeout. In the absence of other damping torques, residual pressure can be determined by measurement of thespin-down decay time. In actuality, the spin-down decay time varied between 7,000 years for gyro 3 and 25,700years for gyro 4, however. This variability, along with other evidence, supports the contention that the spindownrates were dominated by some other mechanism (possibly patch effect) rather than by gas damping. Byusing the longest decay time, however, an upper limit of ~1.5x10 -11 torr (2 nPa) can be placed on the residualgas pressure—a result that is an order of magnitude below the requirement, demonstrating ample margin.Gravity Probe B — Post Flight Analysis • Final Report March 2007 349
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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
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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
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
Page 342 and 343: Figure 11-3. CLL switch states duri
Page 344 and 345: Table 11-3. Dates and UTC times whe
Page 346 and 347: Figure 11-7. Low Gamma Angle Data S
Page 348 and 349: s N+w i= sign+w i++−+−w i−w i
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Page 352 and 353: Figure 11-14. Y axis, B side RMS po
Page 354 and 355: Figure 11-17. X axis, B side curren
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Page 358 and 359: Figure 11-24. Scaled summed current
Page 360 and 361: Figure 11-26 through Figure 11-29 s
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Page 364 and 365: 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
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Page 372 and 373: Figure 12-6. Flow meter and ATC flo
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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
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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
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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:
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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
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AcronymDefinitionAcronymDefinitionD
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AcronymDefinitionAcronymDefinitionF
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AcronymDefinitionIRUInertial Refere
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AcronymDefinitionAcronymDefinitionM
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AcronymPMPMAPMCPMEPMETPMSPMSUPNPoPO
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AcronymSCMOSCMTSCNSCPASCPMSCRSCSASC
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AcronymDefinitionAcronymDefinitionT
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588 March 2007 Appendix F — Acron
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