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

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8 APRIL 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 353 days (50 weeks/11.57 months)Science Data Collection: 224 days (32 weeks/7.34 months)Current Orbit #: 5,210 as of 4:00 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): 7 (dailyaverage)1 APRIL 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 346 days (49 weeks/11.50 months)Science Data Collection: 217 days (31 weeks/7.11 months)Current Orbit #: 5,10 as of 4:00 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 (on 3/26), Single-bit errors (SBE): 9(daily average)Last Saturday, the Gyro Suspension (GSS) computer for gyro #4reported a multi-bit error (MBE). Upon investigation of this MBE, theGSS team determined that it was in a memory location that wouldsoon be accessed by a program command sequence. To avert thecomputer reboot problems that the spacecraft has been experiencingfor the past three weeks, the team sent commands to the flightcomputer halting the mission timeline. Then, as described in lastweek's Mission News, computer specialists used the Integrated TestFacility (ITF) simulator at Lockheed Martin to determine the correctvalue for the afflicted memory location and uploaded a patch to repairthat location. After this repair, the team sent a revised commandtimeline to the GSS computer and resumed normal operations.Because of the team's intervention, the guide star lock was not lost andthe spacecraft remained in drag-free flight throughout this period.Also, gyro #4 remained digitally suspended in science (data collection)mode. Complete recovery from this MBE took only a few hours,thanks to the diligence of the team.Investigations into the root causes of the recent spate of MBEssuggests the possibility that the scrub routine which is checking thememory cells of the on-board Command & Control ComputerAssembly (CCCA) could trigger a safemode response on a single MBEif that error occurs in certain locations. As a result, the team has reprogrammedthe safemode response for the MBE test to automaticallystop the mission timeline, rather than rebooting the computer.Also this past week, the GP-B team continued work on the Attitudeand Translation Control system (ATC) and the telescope detectors.The purpose of these adjustments is to enable the spacecraft to remainunder control of the science gyros (rather than the navigation controlgyros) in all orbits through the South Atlantic Anomaly (SAA) region.For a number of weeks now, the spacecraft has been experiencingdegraded attitude performance in the South Atlantic Anomaly (SAA)region. As a short-term fix for this problem, we have beencommanding the Attitude and Translation Control system (ATC) toswitch from the science telescope to the spacecraft's navigationalgyroscopes for controlling the spacecraft's attitude while in the SAAregion. This has increased the spacecraft's stability in the SAA, butsince we only use relativity data collected when the science telescope isin control of the ATC, we have effectively been losing science data inthose orbits where the spacecraft passes through the SAA undernavigational gyro control.Over these past few weeks, our Attitude and Translation Control(ATC) group has been working very hard to fine tune the ATC systemso that the science telescope can remain in control of the spacecraft'sattitude in the SAA region. Three weeks ago, we made some progresson this issue by shrinking our defined boundaries of the SAA region,thus reducing the number of orbits affected. Two weeks ago, the ATCgroup made further progress by changing the ATC gain settings(similar to adjusting the volume control on a radio). Finally, this pastweek, the ATC group adjusted the gain settings on the TelescopeReadout Electronics (TRE). This past week's adjustments, incombination with those previously made, have mitigated this issue.The science telescope is now able to remain locked on the guide star inall passes through the SAA, and we are once again collecting sciencedata in all orbits.Also this past week, we started making detailed plans for the postscienceinstrument re-calibration phase, estimated to begin early inJuly.15 APRIL 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 360 days (51 weeks/11.80 months)Science Data Collection: 231 days (33 weeks/7.57 months)Current Orbit #: 5,316 as of 9:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steady500 March 2007 Appendix C — Weekly Chronicle of the GP-B Mission
Command & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 0, Single-bit errors (SBE): 6 (dailyaverage)Around February of this year, we entered a GP-B “season” where thefront of the spacecraft is pointing towards the sun. Many of theelectronics boxes on-board the spacecraft are located in the ForwardEquipment Enclosure (FEE), and we are in the process of investigatingthe possibility that the spacecraft's sunward orientation may be acontributing factor to the increase in multi-bit errors (MBEs) weexperienced a few weeks ago, as well as some of the attitude controlissues we have experienced recently—especially in the South AtlanticAnomaly (SAA) region.This past week, we made further progress operating the spacecraftthrough the SAA region. In analyzing the SAA attitude data we havecollected recently, our ATC group noticed some interesting patterns.They have now investigated these patterns and determined that a datatype conversion routine was causing data values exceeding a certainthreshold to become corrupted. This situation was greatly exacerbatedin the SAA region, where the telescope's detectors were being floodedwith stray protons, which causes a noticeable increase in thesecorrupted data values.As reported in last week's update, we addressed these SAA attitudeproblems by shrinking our defined size of the SAA region andreducing the gains on both the ATC system and the telescopedetectors. These gain reductions have provided a work-around for thisdata corruption problem by re-scaling the data values so that they nolonger exceed the threshold in the SAA region. As a result, ourspacecraft can now point at the guide star throughout the SAA regionwith the same precision as it does outside the SAA.Also last week, we exercised the Ultraviolet Discharge procedure onscience gyros #1, #2, and #4, followed later by drag-free gyro #3. Thisprocedure reduces the electrostatic charge that builds up on the gyrorotors over time. The rotors build up a charge in two ways: first, theprocess of suspending the rotors electrically deposits some chargedparticles on them, and second, protons from the sun are constantlybombarding the spacecraft, especially over the SAA region, and someof these protons strike the rotors and leave a residual charge on them.Finally, this past week, we began planning for another heat pulse testto determine the level of liquid helium remaining in the dewar. Wealso continued our detailed planning for the post-science instrumentre-calibration phase, estimated to begin early in July.22 APRIL 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 367 days (52 weeks/12.00 months)Science Data Collection: 238 days (34 weeks/7.80 months)Current Orbit #: 5,419 as of 9:00 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 mission operations team performed routine tasks over this pastweek related to the electrostatic discharge of Gyro #3 (the “drag-free”gryo) and minor dewar pressure oscillations. After performing anumber of tests on Gyro #3 early in the week, it was discharged onThursday to -3.0 mV, using ultraviolet light, as explained in last week'supdate.The Attitude and Translation Control (ATC) group reports that thetime required to re-lock onto the guide star as the spacecraft emergesfrom behind the Earth each orbit continues to be excellent, includingone guide-star capture (re-locking) this weekend that took only 20seconds.Gravity Probe B — Post Flight Analysis • Final Report March 2007 501
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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
Page 478 and 479: 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
Page 488 and 489: 460 March 2007 Chapter 16 — Lesso
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 530 and 531: On Tuesday afternoon (19-April), GP
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
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550 March 2007 Appendix E — Fligh
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ReqIDLevel 1CSCDMP DataMgmtProcessi
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ReqIDLevel 1CSCLevel2 CSC Level 3 C
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Page 586 and 587:
Page 588 and 589:
ReqIDLevel 1CSCSRM Solid StateRecor
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Page 592 and 593:
Page 594 and 595:
ReqIDLevel 1CSCSRP SafemodeResponse
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ReqIDLevel 1CSCGUP GSS Processing g
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570 March 2007 Appendix F — Acron
Page 600 and 601:
AcronymDefinitionAcronymDefinitionB
Page 602 and 603:
AcronymDefinitionAcronymDefinitionD
Page 604 and 605:
AcronymDefinitionAcronymDefinitionF
Page 606 and 607:
AcronymDefinitionIRUInertial Refere
Page 608 and 609:
AcronymDefinitionAcronymDefinitionM
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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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