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

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On Tuesday afternoon (19-April), GP-B Principal Investigator,Francis Everitt, delivered a Physics Colloquium to a packedauditorium at Stanford entitled: “The Gravity Probe B Flight Mission:A Stanford Physics-Engineering Partnership”. In this lecture,Professor Everitt explained some of the finer points of GP-B's varioustechnologies, emphasizing in each case the interdisciplinarycollaborations required to produce these extraordinary technologicalinnovations.29 APRIL 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 374 days (53 weeks/12.26 months)Science Data Collection: 245 days (35 weeks/8.03 months)Current Orbit #: 5,523 as of 5:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 0, Single-bit errors (SBE): 8 (dailyaverage)This past Tuesday, 26 April 2005, the GP-B dewar team ran anotherheat pulse meter test to get an update on the amount of liquid heliumremaining in the dewar. Their preliminary results suggest that we haveabout two weeks more helium than anticipated. Further analysis is inprocess, and if these results are correct, the helium will be depletedaround the end of August or beginning of September. This means thatwe will be able to continue collecting science data into the first twoweeks in July, before beginning a very important series of instrumentcalibration tests that must be completed before the helium runs out.Also this past week, we continued fine-tuning our SQUID readoutsystem, analyzing potential sources of noise. To this end, we turned offthe telescope dithering motion all day on Wednesday, 27 April 2005 todetermine its contribution to experimental noise.Likewise, for the same reason, on Thursday, we turned off theExperiment Control Unit (ECU) for several days. We are in theprocess of analyzing the results of these noise experiments, which maylead to further fine-tuning of various spacecraft systems.6 MAY 2005—GRAVITY PROBE B MISSION UPDATEMission Elapsed Time: 381 days (54 weeks/12.49 months)Science Data Collection: 252 days (36 weeks/8.26 months)Current Orbit #: 5,627 as of 5:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 1, Single-bit errors (SBE): 9 (dailyaverage)Further analysis of the results of the heat pulse test run on Tuesday, 26April 2005, to determine the amount of liquid helium remaining in thedewar, confirms the preliminary prediction that the helium in thedewar will be depleted in late August or early September. Based onthese results, the GP-B mission operations team is planning tocomplete readout calibrations, some of which can be done while weare still collecting science data, by the beginning of August. Gyrotorque calibrations, which cannot be done during the science phase ofthe mission because they involve placing small torques (forces) on thegyro rotors, will commence early in August and continue until thehelium runs out.Our telescope pointing and guide star capture times continue to beexcellent, thanks to recent fine-tuning of the spacecraft's Attitude andTranslation Control system (ATC) parameters. We have alsodetermined that we can reduce some noise in the SQUID ReadoutElectronics system (SRE) by turning off the Experiment Control Unit.However, we will now periodically power on the ECU for about 6hours in order to obtain certain readouts that require informationfrom the ECU.Finally, a memory location in the B-side (backup) flight computer thatis now controlling the spacecraft sustained a multi-bit error (MBE) lastSaturday, 30 April 2005. The memory location affected is not currentlybeing used. Following new procedures developed a few weeks ago,when we were experiencing an increased level of MBEs, our computeroperations team quickly uploaded a patch to correct the contents ofthe affected memory location.Also this past week, the GP-B Anomaly Review Board met todetermine whether or not to change the pre-programmed safemodetrigger and response to MBEs detected in the main flight computer.After a lengthy discussion, it was decided to change the safemodetrigger condition from 3 to 9 MBEs and the response actions from502 March 2007 Appendix C — Weekly Chronicle of the GP-B Mission
simply stopping the timeline (halting execution of the command setcurrently loaded into the computer) to automatically rebooting thecomputer. These changes ensure that if the error occurs in a memorylocation that increments the error counter at 10 Hz, the computer willautomatically reboot immediately, rather than possibly freezing upand waiting for up to 8 hours for an “aliveness” test to trigger a reboot.13 MAY 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 388 days (55 weeks/12.72 months)Science Data Collection: 259 days (37 weeks/8.49 months)Current Orbit #: 5,726 as of 5:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 0, Single-bit errors (SBE): 9 (dailyaverage)Our telescope pointing and guide star capture times continue to beexcellent. The Experiment Control Unit continues to remain offduring most orbits, resulting in reduced noise in the SQUID ReadoutElectronics system (SRE). Once a week, we power the ECU back on fora few hours in order to obtain and check certain readouts, such as thedewar temperature, that are provided by the ECU.The NASA Distinguished Public Service Medal is awarded to anindividual whose distinguished accomplishments contributedsubstantially to NASA's mission. Contributions must be soextraordinary that other forms of recognition by NASA would beinadequate. This is the highest honor that NASA confers to anindividual who is not a government employee.Because the spacecraft has been in orbit for over a year now, we areable to conduct an analysis of the external temperature and solar arrayefficiencies by comparing current data from these systems with datacollected a year ago.In preparation for the end of the GP-B mission, which is fastapproaching, we have begun delegating tasks to complete our finalmission report, which we will deliver to NASA in July.GP-B PRINCIPAL INVESTIGATOR FRANCIS EVERITTHONORED BY NASAFollowing is a copy of the press release we sent out earlier this week,announcing this award.Stanford experimental physicist Francis Everitt has been awarded aNASA Distinguished Public Service Medal. NASA Deputy DirectorFred Gregory presented the medal to Everitt on April 27 at an awardsceremony at NASA Headquarters in Washington, D.C. Everitt isprincipal investigator of the Gravity Probe B (GP-B) experiment, acollaboration between Stanford University, NASA and LockheedMartin Corp. that is testing predictions of Albert Einstein's 1916general theory of relativity (his theory of gravitation) by means of fourultra-precise gyroscopes that have been orbiting the Earth in a satellitefor just over a year.Everitt obtained his doctorate at the University of London (ImperialCollege) in 1959 for research under Nobel laureate P. M. S. Blackett.He then spent two years at the University of Pennsylvania working onliquid helium. In 1962, Everitt joined William Fairbank and LeonardSchiff in the Stanford Physics Department as the first full-timeresearch worker on the GP-B experiment. His efforts advanced thestate of the art in the areas of cryogenics, magnetics, quantum devices,telescope design, control systems, quartz fabrication techniques,metrology and, most of all, gyroscope technology. His leadership asthe principal investigator for GP-B advanced the GP-B program fromthe concept and technology development stages to the experiment'slaunch on April 20, 2004, and its ensuing orbital operations.“None of us at the beginning had any idea how long it would take forthe GP-B spacecraft to fly and take the science data,” Everitt said whenasked about the long life of the project. “But speaking for myself, Ihave never been bored.”Gravity Probe B was developed on the Stanford campus in the W. W.Hansen Experimental Physics Laboratory (HEPL). The current onorbitGP-B mission operations center (MOC) is located in HEPL,where the science data is currently processed as well. From the MOC,the GP-B spacecraft is commanded with ground antennas in Alaska orGravity Probe B — Post Flight Analysis • Final Report March 2007 503
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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
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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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Description of the GP-B experience:
Page 480 and 481: Figure 16-1. Six interacting transl
Page 482 and 483: 16.1.3.2 Training and certification
Page 484 and 485: Description of the GP-B experience:
Page 486 and 487: Below is an edited summary of six a
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Page 490 and 491: 462 March 2007 Appendix A — Gravi
Page 492 and 493: Apogee altitude659.1 km (409.6 mile
Page 494 and 495: 466 March 2007 Chapter B — Spacec
Page 496 and 497: Gravity Probe B — Post Flight Ana
Page 498 and 499: 470 March 2007 Appendix C — Weekl
Page 500 and 501: 16 April 2004—Vehicle is Prepared
Page 502 and 503: The electrical power system is full
Page 504 and 505: 4 JUNE 2004—MISSION UPDATE: DAY 4
Page 506 and 507: SQUIDs to detect their rotation spe
Page 508 and 509: 17 JULY 2004—MISSION UPDATE: DAY
Page 510 and 511: indicate that we have reduced the t
Page 512 and 513: C.4 Science Mission Phase: 8/27/04
Page 514 and 515: • GP-B also has an independent da
Page 516 and 517: free suspension parameters to de-tu
Page 518 and 519: We have received inquiries about a
Page 520 and 521: One of the effects of geomagnetic s
Page 522 and 523: egan transmitting, one-by-one, stat
Page 524 and 525: 28 JANUARY 2005—GRAVITY PROBE B M
Page 526 and 527: magnetic pole. This event triggered
Page 528 and 529: 8 APRIL 2005—GRAVITY PROBE B MISS
Page 532 and 533: Norway or through the NASA space ne
Page 534 and 535: Dewar Temperature: 1.82 kelvin, hol
Page 536 and 537: visitors on a tour of the GP-B faci
Page 538 and 539: test, we are planning on running fi
Page 540 and 541: contractor at the Goddard Space Fli
Page 542 and 543: On Wednesday, we visited the star H
Page 544 and 545: Gyro Suspension System (GSS): All 4
Page 546 and 547: The helium in the dewar has now sur
Page 548 and 549: the all the spacecraft status data.
Page 550 and 551: 522 March 2007 Appendix D — Summa
Page 552 and 553: Figure D-2 below shows the distribu
Page 554 and 555: DateSeveritySubtypeTitle Descriptio
Page 556 and 557: DateSeverity24 26-Apr-04 Obs F Nois
Page 558 and 559: DateSeverity40 11-May-04 Obs T Dwel
Page 562 and 563: DateSeverity68 16-Jun-04 Medium Dec
Page 564 and 565: DateSeverity84 13-Jul-04 Obs F Slig
Page 568 and 569: DateSeverity116 26-Sep-04 Obs F SG3
Page 570 and 571: DateSeverity132 20-Dec-04 Obs F Unc
Page 572 and 573: DateSeverity149 5-Mar-05 Obs T Few
Page 574 and 575: DateSeverity169 04-Jun-05 Obs F MBE
Page 576 and 577: DateSeverity191 04-Oct-05 Obs A GSS
Page 578 and 579: 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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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
Page 608 and 609:
AcronymDefinitionAcronymDefinitionM
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AcronymPMPMAPMCPMEPMETPMSPMSUPNPoPO
Page 612 and 613:
AcronymSCMOSCMTSCNSCPASCPMSCRSCSASC
Page 614 and 615:
AcronymDefinitionAcronymDefinitionT
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588 March 2007 Appendix F — Acron
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