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

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Figure 3-3. Functional diagram of a SQUID pickup loop measuring the London Moment around a GP-B gyrorotor (left) and four SQUID readouts—one for each gyro (right).Using the London moment to monitor the gyroscope's orientation was the perfect readout scheme for GravityProbe B—it is extremely sensitive, extremely stable, applicable to a perfect sphere, and-most important, it exertsnegligible torques (forces) on the gyroscope.3.2.1.3 The Dewar: A 9’ Tall, 8’ Wide ThermosOne of the greatest technical challenges for Gravity Probe B was keeping the science instrument just aboveabsolute zero, at approximately 2.3 Kelvin (-270.9 celsius or -455.5 fahrenheit) constantly for 16 months orlonger.Figure 3-4. The GP-B dewar—one of the largest and most sophisticated dewars ever flownThe science instrument is kept at this supercold temperature, by placing it in a special 2,441 liter (645-gallon)dewar, or thermos, about the size of a mini van, that is filled with liquid helium in a superfluid state. This ninefoottall Dewar is the main structure of the GP-B satellite itself. In its 640-kilometer (400-mile) high polar orbit,the GP-B satellite is low enough to be subjected to heat radiating from the Earth's surface, and it is also subjectedto alternating hot and cold cycles, as it passes from intense sunlight into the Earth's shadow every ninety-sevenminutes. Throughout the life of the mission, key portions of the science instrument had to be maintained at aconstant temperature to within five millionths of a degree centigrade.72 March 2007 Chapter 3 — Accomplishments & Technology Innovations
Figure 3-5. Cross sectional schematic of the dewarDuring the mission, the dewar's insulating chamber remained a vacuum, which limited the amount of heatpenetrating through the outside wall into the inner chamber containing the science instrument. In addition, itincludes several other devices for maintaining the necessary cryogenic temperature:1. Multilayer insulation—multiple reflective surfaces in the vacuum space to cut down radiation2. Vapor-cooled shields—metal barriers, suitably spaced, cooled by the escaping helium gas3. Porous Plug—invented at Stanford, and engineered for space at NASA Marshall Space Flight Center inHuntsville, AL, Ball Aerospace in Boulder, CO, and the Jet Propulsion Laboratory in Pasadena, CA. Thisplug allows helium gas to evaporate from the Dewar's inner chamber, while retaining the superfluidliquid helium inside. See section 3.2.3.1for a more complete description of the porous plug.When there was still helium in the dewar, virtually no heat could penetrate from the outside wall through thevacuum and multilayer insulation inside. However, a small amount of heat (about as much as is generated bythe message indicator lamp on a cell phone) did leak into the Dewar from two sources:1. Conduction of heat flowing from the top of the Dewar into the liquid helium2. Radiation leaking down through the telescope bore into the liquid helium.The porous plug controls the flow of this evaporating helium gas, allowing it to escape from the Dewar, butretaining the superfluid helium inside. The plug is made of a ground-up material resembling pumice. Theevaporating helium gas climbed the sides of the inner tank near the plug and collected on its surface, where itevaporated through the pores in the plug, much like sweating in the human body.The evaporating helium provided its own kind of refrigeration. As the helium gas evaporated at the surface ofthe porous plug, it drew heat out of the liquid helium remaining in the Dewar, thereby balancing the heat flowinto the Dewar. You can feel this effect on your skin when you swab your skin with water. As the liquidevaporates off your skin, it draws heat energy with it, leaving your skin a tiny bit cooler than before.The helium gas that escaped through the porous plug was cycled past the shields in the outer layers of theDewar, cooling them (thus the name, “vapor-cooled shields”), and then it was used as a propellant for eightpairs of micro thrusters that are strategically located around the spacecraft.Gravity Probe B — Post Flight Analysis • Final Report March 2007 73
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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 (
Page 50 and 51: 1.14 The Broader Legacy of GP-BAt l
Page 52 and 53: 24 March 2007 Chapter 2 — Overvie
Page 54 and 55: Figure 2-1. GP-B Historical Time Li
Page 56 and 57: Applied Physics Laboratory, of the
Page 58 and 59: William Fairbank once remarked: “
Page 60 and 61: In Einstein’s view, space and tim
Page 62 and 63: y a mere 1.1 inches. You can see th
Page 64 and 65: Figure 2-10. Schematic diagram of t
Page 66 and 67: Figure 2-12. Final assembly of the
Page 68 and 69: Sun Shield. The sun shield is a lon
Page 70 and 71: 2.1.8 The Broader Legacy of GP-BWhe
Page 72 and 73: 2.3 Spacecraft SeparationThe Solar
Page 74 and 75: Flight Anomalies.) Furthermore, a d
Page 76 and 77: Table 2-2. Weekly summary of IOC ac
Page 78 and 79: 2.4.3.2 Guide Star AcquisitionAbout
Page 80 and 81: A second mass trim operation had be
Page 82 and 83: On Friday, 2 July 2004, the spin ra
Page 84 and 85: Low temperature bakeout was first p
Page 86 and 87: 2.5.1.3 Lockheed Martin Team Phase-
Page 88 and 89: Monthly Highlights of the GP-B Scie
Page 90 and 91: 2.6.1 Overview of the Calibration P
Page 92 and 93: Weekly Highlights of the GP-B Final
Page 94 and 95: 66 March 2007 Chapter 3 — Accompl
Page 96 and 97: It was in this pristine, near-zero
Page 98 and 99: Each quartz rotor is coated with a
Page 102 and 103: Based on data from the on-board tel
Page 104 and 105: Ideally, the telescope should have
Page 106 and 107: Figure 3-9. Schematic diagram of st
Page 108 and 109: used. The star trackers are essenti
Page 110 and 111: Result: By using the porous plug, w
Page 112 and 113: Solution: Create a tetrahedral lapp
Page 114 and 115: Constraint 2: The exhaust tube must
Page 116 and 117: Result: The on-orbit gyroscope spin
Page 118 and 119: spacecraft's subsystems for the dur
Page 120 and 121: Constraint 3: Keep the spacecraft p
Page 122 and 123: Technology Category Specific Implem
Page 124 and 125: 96 March 2007 Chapter 4 — GP-B On
Page 126 and 127: Any significant deviation from “g
Page 128 and 129: packages, one for each Ping load an
Page 130 and 131: In addition to these software packa
Page 132 and 133: Table 4-6. Features & benefits of W
Page 134 and 135: This software added considerable ef
Page 136 and 137: It is said that “an experiment is
Page 138 and 139: Table 4-10. Significant Events/Sour
Page 140 and 141: Figure 4-5. Pictorial depiction of
Page 142 and 143: Figure 4-7. Eta-Average Error Assoc
Page 144 and 145: 4.4.4.2 OD Using SLR DataFigure 4-9
Page 146 and 147: 4.4.5 ConclusionsFigure 4-11. Compa
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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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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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ReqIDLevel 1CSCSRM Solid StateRecor
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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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