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

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14.2.2 Independent Data Analysis TeamsThe Stanford team has formed two independent, internal teams to attack the data analysis task. This was doneprimarily for internal quality control: two teams, processing the exact same data, should produce very similarresults. The results are compared formally on a regular basis where discrepancies are noted and investigated.These comparisons will unearth subtle software coding errors, which may go undetected if only a single analysispackage is used. Each team, while working under the constraint of using the same source data, has considerablelatitude in what methods of analysis to apply during each of the data analysis phases. This has the beneficialeffect of better understanding the nature of the source data and what signal processing techniques are mosteffective in estimating the performance of the four science gyroscopes.To provide a benchmark for both of the teams, sets of “truth model data” are constructed and are run on the twodata analysis packages. In these truth model cases, the signal structure, instrument calibrations, and noises areprecisely known and can be analyzed in a relatively straightforward way without sophisticated signal processingtools. Both data analysis packages should return identical results when run on such truth data; if they do not,this test reveals a fundamental difference in the algorithms that may be rectified quickly. Once the algorithmsagree on “truth”, they will be re-benchmarked regularly to ensure that evolutionary changes in the codes do notcompromise their ability to correctly analyze straightforward data sets.14.2.3 Data GradingThe Gravity Probe B science data consists of approximately 5300 guide star valid intervals during which theinstrument is able to measure the orientation of each of the four gyroscopes with respect to the line of sight tothe guide star. Due to vehicle anomalies or environmental effects, not all of these intervals contain valid sciencemeasurement data. If these data are used in the analysis algorithms, significant errors in the overall results maybe introduced.Consequently, a data grading scheme is used to separate the compromised data from the clean science data. Thegrading system does not remove data from the set, but simply flags segments of the data that do not meet anestablished grading criteria. Roughly 20 criteria have been set to flag sub-standard data on a gyro-by-gyro basis.The criteria chosen are primarily a function of vehicle state, such as “guide star out of view,” “vehicle in eclipse”,“loss of drag-free control,” “SQUID unlocked;” these all directly affect the validity of the data being sent fromthe spin axis readout system.During data analysis runs, the analyst selects the grading criteria that will apply during the run. Then, databaseextraction tools will then return the data that meet the grading criteria. Immediately, the same algorithm can berun with different grading criteria to assess the sensitivity of the result to various types of low quality data.420 March 2007 Chapter 14 — Data Collection, Processing & Analysis
14.2.4 Data Analysis “Standard Model”The data analysis effort revolves around a “standard model” for how the vehicle operates and how vehicleconfiguration affects the performance of the gyroscopes. This model evolves as the team’s knowledge of theoperation and performance of the vehicle increases during the analysis efforts. In addition to the 1) IndependentAnalysis teams, 2) the Truth Modeling Efforts, and 3) the Data Grading system, the data analysis team focusesits efforts on six primary areas of vehicle performance (Figure 14-8):1. Precession dynamics and torques: Understand the overall drift of the gyroscope and how it relates torelativistic effects and classical (Newtonian) effects.2. Orbital and Annual Aberration: Model and compensate for the apparent motion of the guide star due tospace vehicle motion.3. Vehicle Pointing: Assess the pointing of the space vehicle during guide star valid (GSV) and guide starinvalid (GSI) periods using all on-board sensors (ATC, telescope, science gyroscopes). Determinerelative scale factor between telescope readout of pointing and science gyroscope readout of pointing.4. Roll Phase Measurement: Measure and quantify errors in the roll phase of the vehicle over the mission(time history of the clocking of the vehicle with respect to the orbital plane).5. Spin Axis Orientation Measurement: Model and calibrate the SQUID readout system and compensatefor effects of vehicle pointing in the science signal.6. Polhode and Scale Factor Modeling: Model and remove the effects of the time varying polhode period onthe SQUID scale factor. Compensate for systematic errors in gyro orientation measurements due to theslow damping of the gyroscope polhode path.Figure 14-18. Components of the GP-B Data Analysis Standard Model (equations shown are significantlysimplified and are of iconic value only)Phase 1 activities focus primarily on improving the accuracy of all the terms that go into the standard model,based on vehicle data, and setting performance limits on the ultimate resolution of the experiment. Phase 2 and3 activities focus on the precession dynamics, effects of anomalies, and polhode models that span weekly orGravity Probe B — Post Flight Analysis • Final Report March 2007 421
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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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Page 400 and 401: In November, 2004 there was a large
Page 402 and 403: Figure 13-28 shows a correlation th
Page 404 and 405: 13.3.1 About the MagnetometersFigur
Page 406 and 407: 13.3.2 Other Applications for Paylo
Page 408 and 409: Figure 13-35. GPS Antennae Field of
Page 410 and 411: Figure 13-37. Master Antenna Switch
Page 412 and 413: Figure 13-39. Time difference betwe
Page 414 and 415: 13.4.6 On-Orbit ResultsThe GPS comp
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Page 418 and 419: E. G. Lightsey, C. E. Cohen, B. W.
Page 420 and 421: Figure 13-45. A Bottom View of the
Page 422 and 423: Figure 13-48. The GMA configuration
Page 424 and 425: Table 13-10. Summary for Helium Gas
Page 426 and 427: 398 March 2007 Chapter 14 — Data
Page 428 and 429: a relatively slow data rate, so we
Page 430 and 431: Figure 14-4. NASA ground stations a
Page 432 and 433: electronic components to recover fr
Page 434 and 435: By a process of elimination, the GP
Page 436 and 437: A special room in the GP-B Mission
Page 438 and 439: Starting on 3 December 1725, Bradle
Page 440 and 441: seemed that aberration of starlight
Page 442 and 443: 14.1.6 Telescope Dither—Correlati
Page 444 and 445: 14.1.6.3 The Telescope Dither Patte
Page 446 and 447: amplifications. Thus, in addition t
Page 450 and 451: monthly time scales. Though only sh
Page 452 and 453: 424 March 2007 Chapter 15 — Preli
Page 454 and 455: Figure 15-2. A diagram of the GP-B
Page 456 and 457: 15.4 The Two Surprises and Their Im
Page 458 and 459: Near Zeroes.) The exception that we
Page 460 and 461: Figure 15-8. A slide from the GP-B
Page 462 and 463: Figure 15-9. A poster on the effect
Page 464 and 465: electrostatic patches, located at o
Page 466 and 467: Last summer (2006), Mac Keiser devi
Page 468 and 469: 440 March 2007 Chapter 15 — Preli
Page 470 and 471: 442 March 2007 Chapter 16 — Lesso
Page 472 and 473: 16.1.1.3 Flight science downlink da
Page 474 and 475: Description of the GP-B experience:
Page 476 and 477: Lessons:1. Perform all tests with a
Page 480 and 481: Figure 16-1. Six interacting transl
Page 482 and 483: 16.1.3.2 Training and certification
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
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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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