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

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The electrical power system is fully functional and is providingadequate power for all operating conditions. Eclipse operation (whenthe spacecraft is in the shadow of the Earth) meets all requirements.There is no evidence of solar array motion that might disturb theexperiment.All other spacecraft subsystems are fully functional. All four gyroshave been checked out and are performing well. They have all beenelectrically suspended in analog mode; digital suspension activities willcommence shortly. The team is in the process of updating data tablesfor the Gyro Suspension System (GSS) to aid in achieving digitalsuspension of the gyros.The spacecraft’s Attitude Control System (ATC) is maintaining astable attitude (relative position in orbit—pitch, yaw and roll). Weexpect to lock onto the Guide Star, IM Pegasi, within a few days, aftercompleting on-orbit re-calibration of the spacecraft’s 16 microthrusters. During thruster re-calibration, it was observed that one ofthe redundant micro thrusters was stuck partially open. It was isolatedand removed from the system, and the flow of helium to the remainingmicro thrusters has been adjusted to compensate for its removal.Overall, one week after launch, it appears that all of the spacecraft’ssubsystems are functioning well—meeting or exceeding missionrequirements, in preparation for beginning the science experiment.7 MAY 2004—MISSION UPDATE: DAY 17As of Mission Day #17, the Gravity Probe B spacecraft continues toperform well, and we are expecting a smooth and successful transitioninto the science phase of the mission.The spacecraft remains in a science mission orbit, within the plane ofthe Guide Star, IM Pegasi. The gyro readout system performancecontinues to exceed expectations, and all four SQUIDs (SuperconductingQuantum Interference Devices) are functional andcalibrated, with very low noise levels. Power and thermal systems meetall of our mission requirements. All spacecraft subsystems continue toperform nominally.All four gyros have been electrically suspended in analog mode, andgyros #1, #2 and #4 are now digitally suspended; we expect gyro #3 totransition from analog to digital suspension shortly.Last weekend, the spacecraft was hit by radiation while passing overthe Earth’s south magnetic pole. This radiation caused data errors inthe spacecraft’s primary (A-side) computer, which exceeded itscapacity for self-correction. Thus, by design, the spacecraftautomatically switched over to the backup (B-side) computer, placedthe spacecraft in a “safe” mode, and put the planned timeline of eventson hold.The automatic switch over from primary to backup computer workedflawlessly. The GP-B mission operations team has since re-booted theprimary computer, restored its data parameters, and then commandedthe spacecraft to switch back to the primary computer, which is onceagain in control. During this incident, the GP-B science instrumentcontinued to function perfectly—as expected—with all four gyrosremaining suspended in their assigned modes.The spacecraft’s Attitude Control System (ATC) is continuing tomaintain a stable attitude (relative position in orbit—pitch, yaw androll). However, the process of locking onto the Guide Star, IM Pegasi,has been delayed a few days by the South Pole radiation incident.14 MAY 2004—MISSION UPDATE: DAY 24As of Day #24 of the mission, all spacecraft subsystems are functioningproperly. The orbit is stable and meets our requirements for nextmonth’s transition into the science phase of the mission, uponcompletion of the spacecraft initialization and orbit checkout.Furthermore, Gravity Probe B has successfully achieved severalimportant milestones over the past week.All four gyroscopes have now been digitally suspended for over aweek. At launch, the gyros were unsuspended. Once on orbit, eachgyro was first suspended in analog mode, which provides coarsecontrol of the gyro’s suspended position within its housing. Analogmode is used primarily as a backup or safe mode for suspending thegyros. Each gyro was then suspended digitally. The digital suspensionmode is computer-controlled; it puts less torque on the gyros thananalog mode and enables their position to be controlled withextremely high precision.At the end of last week, the Gravity Probe B team practiced LowTemperature Bakeout (LTB), in which discs of sintered titanium (verytiny titanium balls, smaller than cake sprinkles) are “warmed up” a fewKelvin, thereby attracting helium molecules to them. This process willremove any remaining helium from the gyro housings after full gyrospin-up. Last week’s practice LTB procedure had the added benefit ofimparting a very small amount of spin-up helium gas to the gyros.Following the practice LTB, the SQUID gyro read-out data revealedthat gyro #1, gyro #3, and gyro #4 were slowly spinning at 0.001, 0.002,and 0.010 Hz, respectively (1 Hz = 60 rpm). Amazingly, the GyroSuspension Systems (GSS) were able to measure gas spin-up forces atthe level of approximately 10 nano-newton (10-8 N). This means thatthe GP-B science team is able to interpret data from gyro spin ratesfour to five orders of magnitude smaller than what was planned for theGP-B science experiment.Earlier this week, the GP-B spacecraft flew “drag-free” around gyro #1,maintaining translation control of the spacecraft to less than 500nanometers. The term, “drag-free,” means that the entire spacecraftliterally floats in its orbit—without any friction or drag—around onethe gyros. Pairs of proportional micro thrusters put out a steady andfinely controlled stream of helium gas, supplied by the dewar, throughits porous plug. Signals from the Gyro Suspension System (GSS)control the output of the micro thrusters, balancing the spacecraftaround the selected gyro. The initial drag-free Control (DFC)checkout lasted 20 minutes, as planned. Then, a two-hour DFC sessionwas tested, during which the spacecraft roll rate was increased andthen returned to its initial rate, maintaining drag-free statusthroughout the test. Achieving DFC indicates that we are on track tomeet the science mission control requirements.Last, but not least, early this week, the Attitude & Translation Controlsystem (ATC) successfully used data from the on-board star sensors topoint the spacecraft towards the guide star, IM Pegasi. This was thefinal step before initiating the dwell scan process, a series ofincreasingly accurate scans with the on-board telescope that enable theATC to lock onto the guide star. Two days ago, the telescope’s shutterwas opened, and a first dwell scan was completed. We are now in thefinal stages of repeating the dwell scan to home in on the guide starand lock onto it. Photo: ATC Engineers with the Attitude Controlsystem before it was placed on the spacecraft, circa May 2001.474 March 2007 Appendix C — Weekly Chronicle of the GP-B Mission
21 MAY 2004—MISSION UPDATE: DAY 31One month into the mission, all spacecraft subsystems are continuingto perform well. The spacecraft’s orbit remains stable and meets ourrequirements for next month’s transition into the science phase of themission, upon completion of the spacecraft initialization and orbitcheckout. The four gyroscopes are suspended, and we have indicationsthat they are rotating slightly in their housings.Last weekend, the team successfully performed a procedure to reducemagnetic flux that had built up around the gyroscope rotors (spheres).Magnetic flux is a measure of the number of magnetic field linespenetrating a surface. To ensure that the SQUID readouts receiveclean signals from the gyroscopes and to provide the highest possibledegree of accuracy during the GP-B science experiment, any magneticflux around the gyroscope rotors must be minimized.We reduce magnetic flux by turning on heaters and flowing heliumgas, warmed to 10 Kelvin, through the Probe. This process also drivesoff any residual helium remaining in the well of the dewar, where theProbe sits. The flux reduction procedure went smoothly, and when itwas completed, the level of trapped flux remaining within the gyroswas almost imperceptible. In fact, gyroscope #4, which previously hadthe highest amount of trapped magnetic flux of all the gyros now hasthe lowest level.The flux reduction procedure added heat to the dewar, therebyincreasing the pressure inside to its maximum allowable level. Theincreased pressure during this stress period caused some of thespacecraft’s micro thrusters to become unstable, resulting in thespacecraft pointing in the wrong direction and triggering a“safemode.”still on track for completion within 60 days after launch, at which timethe 13-month science data collection will begin. This will be followedby a two-month final calibration of the science instrument assembly.28 MAY 2004—MISSION UPDATE: DAY 38At five weeks past launch, the Gravity Probe B team is now about halfway through the Initialization and Orbit Checkout (IOC) phase of themission. Thus far, the team has successfully transmitted over 5,000commands to the spacecraft, which remains healthy on orbit. Allspacecraft subsystems are continuing to perform well. The spacecraft’sorbit is stable, meeting our requirements for next month’s transitioninto the science phase of the mission. All four gyros are now digitallysuspended, and the team is in the process of locking the on-boardtelescope onto the guide star, IM Pegasi.This past week, the team began spinning up the gyros. During thiscomplex and delicate process, which spans the entire second half ofIOC, each of the four gyros undergoes a series of spin-up and testingsequences, the first of which gets the gyros spinning—but at a veryslow speed. Because the correct performance of the gyros is critical tothe success of the experiment, the team is proceeding through thespin-up process slowly, painstakingly monitoring and checking theperformance of the gyros throughout the process.In preparation for spin-up, the digital suspension system for each gyrowas first tested. This was accomplished by suspending each gyro in thecenter of its housing, electrically “nudging” it slightly off center in oneof eight directions (the corners of a cube), and monitoring itsautomatic re-centering. This checkout was first performed under lowvoltage conditions (fine control) and then under high voltageconditions (secure hold). Photo: The Forward GSS unit prior toinstallation and flight, circa May 2001.To begin the actual spin-up process, ultra-pure helium gas was flowedover gyro #1 and gyro #4 for 15 seconds, which started them spinningat approximately 0.125 Hz (7.5 rpm). While these gyros were slowlyspinning, the suspension test was repeated under high voltageconditions on gyros #2 and #3. During this high voltage suspensiontest on gyro #3, the team discovered an error in its command template,which turned off the high voltage amplifier to gyro #1 and caused it tolose suspension. There was no damage to gyro#1.The 16 micro thrusters are arranged in clusters of four, and localfeedback loops within each cluster enable the thrusters tocommunicate with each other and automatically adjust their flowrates. Ground commands were issued to isolate the unstable thrusters,which resolved the thruster cross-talk issue and enabled the spacecraftto re-orient itself. The thrusters are now functioning properly, thespacecraft’s attitude has been corrected, and it is once again pointingtowards the guide star.The flux reduction operation and subsequent thruster instability andattitude problems has delayed locking the spacecraft onto the guidestar, which will be our next major activity. While we have used upsome of the contingency days built into the Initialization & OrbitCheckout (IOC) schedule, this phase of the Gravity Probe B mission isMore than 1,000 commands have now been sent to the GyroSuspension System (GSS), and this was the first error found.Discovering an error in these numerous, intricate command templateswas exactly the kind of situation that the painstaking gyro spin-upprocess was designed to identify; it enabled the team to correct thecommand template for gyro #3 without serious consequences. Also, asa further precaution, the team has thoroughly reviewed the commandtemplates for the remaining three gyros. Gyros #2 and #3 have nowbeen spun-up to 0.26 Hz (15 rpm) and 0.125 Hz (7.5 rpm) respectivelywithout incident, and gyro #1 is currently being spun-up, as well.Over the past week, much progress has been made towards the goal oflocking the spacecraft’s on-board telescope onto the guide star. Thepointing error of the spacecraft has been reduced to within 385 arcseconds(0.11 degrees). This allows the on-board telescope to see theguide star over a portion of a spacecraft roll cycle. The team is in theprocess of fine-tuning the spacecraft’s attitude by adjusting thenavigational gyroscope in the Attitude and Translation Control (ATC)system, so that the telescope will be able to see the guide starthroughout the entire spacecraft roll cycle, and the team hopes to lockonto the guide star by the beginning of next week.Gravity Probe B — Post Flight Analysis • Final Report March 2007 475
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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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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
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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
Page 498 and 499: 470 March 2007 Appendix C — Weekl
Page 500 and 501: 16 April 2004—Vehicle is Prepared
Page 504 and 505: 4 JUNE 2004—MISSION UPDATE: DAY 4
Page 506 and 507: SQUIDs to detect their rotation spe
Page 508 and 509: 17 JULY 2004—MISSION UPDATE: DAY
Page 510 and 511: indicate that we have reduced the t
Page 512 and 513: C.4 Science Mission Phase: 8/27/04
Page 514 and 515: • GP-B also has an independent da
Page 516 and 517: free suspension parameters to de-tu
Page 518 and 519: We have received inquiries about a
Page 520 and 521: One of the effects of geomagnetic s
Page 522 and 523: egan transmitting, one-by-one, stat
Page 524 and 525: 28 JANUARY 2005—GRAVITY PROBE B M
Page 526 and 527: magnetic pole. This event triggered
Page 528 and 529: 8 APRIL 2005—GRAVITY PROBE B MISS
Page 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
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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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Page 588 and 589:
ReqIDLevel 1CSCSRM Solid StateRecor
Page 590 and 591:
Page 592 and 593:
Page 594 and 595:
ReqIDLevel 1CSCSRP SafemodeResponse
Page 596 and 597:
ReqIDLevel 1CSCGUP GSS Processing g
Page 598 and 599:
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
Page 610 and 611:
AcronymPMPMAPMCPMEPMETPMSPMSUPNPoPO
Page 612 and 613:
AcronymSCMOSCMTSCNSCPASCPMSCRSCSASC
Page 614 and 615:
AcronymDefinitionAcronymDefinitionT
Page 616:
588 March 2007 Appendix F — Acron
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