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

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Figure 13-19. ECU heater activity during the Science Phase, from January-May 200513.1.7 ECU transmission of Spacecraft NoiseNoise coupling has been an ongoing issue with the ECU, both prior to launch and during flight. Following is asummary of this issue.13.1.7.1 Pre-Launch ECU Noise CouplingPrior to launch, GP-B processed DR446 that addressed a noise-coupling path between the ECU and the SREsubsystems. Ultimately, this lead to a launch delay from December 2003 to April 2004 to replace a faulty powersupply in the ECU. However, the coupling path between the ECU and the SRE that allowed the detection of thefaulty ECU power supply was not able to be isolated and repaired during this time, and it was deemedacceptable for the performance of the science instrument.13.1.7.2 ECU Noise Coupling On OrbitOnce on orbit, we found that the ECU would occasionally generate coherent noise at a slowly changingfrequency that would couple to the SQUID outputs—primarily to SQUID#1. SQUID#1 and SQUID#3 haveconsistently exhibited a greater sensitivity to external sources of EMI due to the relatively long cables from thetop hat to the forward SRE. Similar noise was observed on the SQUID#1 outputs in early 2005, and it wasdecided then that the ECU could be turned off for extended periods to eliminate this noise source from theSQUID data. The ECU was turned off on April 28, 2005 and was occasionally turned on for system monitoringand heat pulse measurements to the end of helium point on September 29, 2005. Following the depletion ofhelium, the ECU was turned back on permanently.The effect of this coupled noise source on the science data is still to be determined in the post-mission sciencedata analysis effort, but at this time the effect is expected to be small to insignificant.366 March 2007 Chapter 13 — Other Payload Subsystems Analyses
13.2 Proton MonitorThe proton monitor (PM) aboard GP-B is a sophisticated electronic measurement instrument that is capable ofdetecting, counting, and measuring flux and energies of protons in the range 35MeV-525MeV. The purpose ofthis instrument is to provide valuable information about the radiation environment surrounding GP-B,especially the flux of high-energy protons, which can affect or disrupt the performance of sensitive electronicsand science instruments and may contribute to charge build-up on the gyroscopes. This data can also be used tostudy the proton flux density in GP-B’s low-earth orbit, as well as variations in flux that occur with changinggeomagnetic field and geographic location of the spacecraft. Furthermore, there are potential experiments thatthe proton monitor can be used for during the post-science phase of the mission. This report describes thecapabilities, summarizes the to-date performance, and discusses possible post-science applications of the protonmonitor.13.2.1 GP-B Radiation EnvironmentThe Earth’s geomagnetic field acts as a shield, blocking out much of the radiation from the sun and deep space.The shielding effect is strongest over the equator and low latitudes and weakest over the poles and the SAA,where the radiation belt shows a “pothole”, a dip, which scientists explain as a result of the eccentricdisplacement of the center of the magnetic field from the geographical center of the Earth as well as thedisplacement between the magnetic and geographic poles of Earth. Over the poles, the shielding effect is weakerdue to the orientation of the magnetic field. Thus, whenever GP-B passes over the poles or the SAA it is exposedto much higher particle flux than outside of these regions.The radiation environment at the altitude of GP-B’s orbit (640km) is dominated by the flux of trapped particlesin the Earth’s inner radiation belt. Most of these particles are low-energy protons and electrons, but there is asignificant flux of higher energy particles, especially over the SAA and the polar regions and it is the high energyprotons that the GP-B PM is designed to detect.Trapped protons mirror between the magnetic poles, following spiral trajectories around magnetic field lines.Because of this spiral motion, the velocity vector of a trapped proton is approximately perpendicular to themagnetic field vector. This effect makes determining the originating direction of the proton flux more difficultbecause the direction of the source, e.g. the Sun, is not necessarily the direction from which the detector sees thehighest proton flux.Energetic protons can affect the performance of onboard electronics by impacting transistors and flipping oneor more bits. Single and multi-bit errors of this kind can have a severe effect on critical spacecraft electronicsystems, which is why it is important to understand when and how they happen.13.2.2 Proton Monitor Features and SpecificationsThe GP-B PM has 16 channels and is capable of detecting protons in the energy range 35MeV-525MeV, whichexceeds the range and resolution of most past and current satellite detectors in low-earth orbit (POES satellitedetectors have a max of 275MeV, CPA - ~200MeV, SOPA – 50 MeV.) The monitor features two identical 4-layer silicone detectors with 45 degree view angles. The detectors are orthogonal, with one oriented along the –Z axis and the other along the -Y axis of the spacecraft. As the protons enter a detector, they are counted andsorted by energy level into 16 channels, whose configuration is shown in Table 13-1.Gravity Probe B — Post Flight Analysis • Final Report March 2007 367
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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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Page 380 and 381: 352 March 2007 Chapter 13 — Other
Page 382 and 383: Figure 13-2. ECU-operated heaters i
Page 384 and 385: 13.1.3.1 Vatterfly Valve Operations
Page 386 and 387: 13.1.3.7 Payload MagnetometersThe E
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Page 390 and 391: As we entered the second month of o
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Page 404 and 405: 13.3.1 About the MagnetometersFigur
Page 406 and 407: 13.3.2 Other Applications for Paylo
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Page 414 and 415: 13.4.6 On-Orbit ResultsThe GPS comp
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Page 422 and 423: Figure 13-48. The GMA configuration
Page 424 and 425: Table 13-10. Summary for Helium Gas
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Page 438 and 439: Starting on 3 December 1725, Bradle
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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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