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Gravity Probe B

Testing Einstein's Universe



Item Current Status
Mission Elapsed Time 591 days (84.4 weeks/19.4 months)
IOC Phase
129 days (4.2 months)
Science Phase
352 days (11.6 months)
Final Calibration Phase
43 days (1.3 months)
Extended Science Phase
4 days
Post Mission Phase
63 days
Current Orbit # 8,720 as of 5:00 PM PST
Spacecraft General Health Good
Roll Rate Normal at 0.4898 rpm (122.5 seconds per revolution)
Gyro Suspension System (GSS) All 4 gyros electrostatically caged against their housing walls in preparation for re-suspension
Gyro Spin Rates 0 rpm (not spinning)
Dewar Temperature ~137 kelvin (and rising ~1.3 kelvin/day)
Global Positioning System (GPS) lock Nominal
Attitude Control System (ATC)

Nominal for post-mission operation
Pointing Error (XY/Pitch-Yaw): 0.39 degrees rms
Roll Phase (Z Axis) Error: 7.6 degrees rms

Telescope Readout (TRE) Pointing performance too low to lock onto guide star
Command & Data Handling (CDH) B-side (backup) computer in control
Multi-bit errors (MBE): 1 (during past month; memory location patched)
Single-bit errors (SBE): Data Not Available


On Mission Day 591, the Gravity Probe B vehicle and payload are in good health. All active subsystems, including solar arrays/electrical power, Experiment Control Unit (ECU), flight computer, star trackers and magnetic torque rods, gyro suspension system (GSS), and telescope detectors--are performing nominally.

The temperature in the Dewar is now at ~137 kelvin, and it is still rising at a rate of approximately 1.3 kelvin per day. The spacecraft remains in a safe configuration, and we are communicating with it regularly, monitoring the Dewar and probe as they continue to warm up.

Over the past month, our telescope experts have been monitoring data from the telescope detectors, observing their performance as the telescope views the stellar background in the vicinity of the guide star. In part, the telescope team is looking for the presence of “dark current,” a signal produced by the detectors due to due to infrared and ultraviolet light from the faint stars surrounding mission guide star IM Peg. To this end, they have been periodically cycling the shutter on the spacecraft's sunshade open and closed to observe the difference between current generated by the detectors with no light entering the telescope (shutter closed) and stellar background light entering the telescope (shutter open).

We are also preparing to re-suspend all four gyros digitally. To this end, we have caged each of the gyro rotors--that is, each rotor is being electrostatically held against the protruding lands (nubs) on one of the six suspension electrodes in its housing wall to remove static charge. This is essentially how the gyro rotors were configured for launch. To re-suspend them digitally, we will follow a slightly modified version of the suspension procedures we used after launch at the beginning of the mission. Once digitally suspended, the rotors will spin very slowly--less than 2 Hz (120 rpm)--and at this point, we have no plans to spin them up any faster.

For the most part, we are only performing maintenance operations on the spacecraft. Our main focus is analyzing the science data we have collected, and we are also continuing work on our final report to NASA.


This past Wednesday, 30 November 2005, Tony Lyons, NASA's GP-B Program Manager from Marshall Spaceflight Center (MSFC) in Huntsville, AL, came to Stanford to present a special NASA Group Achievement Award to the entire GP-B team, including team members from both Stanford and Lockheed Martin. Generally, NASA Group Achievement Awards are given out during an awards ceremony at NASA Headquarters in Washington DC in June of each year. However, Tony Lyons felt that the successful completion of the GP-B flight mission, one of the most complex missions that NASA has ever flown, was a significant enough accomplishment to warrant special consideration. With the help of Rex Geveden, NASA GP-B Program Manager from 1995-2003 and now Associate Administrator at NASA Headquarters, Lyons arranged for the Award to be presented this month at Stanford, so that as many members of the Stanford-Lockheed Martin team as possible could participate.

At 3:30 PM on Wednesday afternoon, about 70 employees of Lockheed Martin who had all worked on GP-B in recent years arrived at Stanford in two busses. They were joined by more than 40 GP-B employees and contractors from Stanford--both current members of the team and a number of former Stanford team members. Also present were Bob Cannon, Stanford Emeritus Professor of Aeronautics & Astronautics and one of the three founders of GP-B, Blas Cabrera, Professor of Physics and Associate Director of the WW Hansen Experimental Physics Lab (HEPL) under which GP-B is administered, and Arthur Bienenstock, Vice Provost and Dean of Research and Graduate Policy at Stanford.

The award ceremony, which lasted an hour, began with welcoming remarks by GP-B Program Manager, Gaylord Green, who served as the Master of Ceremonies. Following Green's opening remarks, Tony Lyons also welcomed everyone on behalf of NASA and MSFC.

“We are here to recognize the end of the GP-B [flight] mission, after 17 months of cryogenic operation,” said Lyons. “…And isn't it just incredible to be here! I can't help but think about all those times over the years when I wondered whether we would ever launch…and here we are, at the end of the mission.”

Lyons went on to say that a model of the GP-B spacecraft sits in a heritage gallery at MSFC among models of all the other Marshall space programs, including Saturn launch vehicles, Sky Lab, the Moon Buggy, the International Space Station, the Chandra Observatory, the Hubble Telescope, and many others. Furthermore, administrators recently decided to use a photo of the GP-B spacecraft as a symbol of scientific space exploration on a new MSFC poster. Lyons concluded his remarks by explaining that in addition to this being a special award ceremony, the Group Achievement Award being given to the GP-B team is the highest team award that NASA can give to any of its programs.

The citation on the award reads: “For exceptional dedication and highly innovative scientific and engineering accomplishments leading to the successful execution and completion of the Gravity Probe B Science Mission.” The award is signed by NASA Administrator Michael Griffin, and individual copies were prepared for each and every member of the team. A photo of the award certificate is shown to the right. Each of the individual certificates that were given out includes the member's name.

Following the remarks by Tony Lyons, Professor Cabrera, representing the HEPL Labs, congratulated the team and talked briefly about the beginnings of the GP-B experiment over 40 years ago and the remarkable interdisciplinary collaboration required in bringing the experiment to fruition. He was followed by Dean Bienenstock, who expressed Stanford University's pride in the accomplishments of GP-B and special joy in commemorating the unique cooperation and collaboration between Stanford, MSFC, and Lockheed Martin that has resulted in a successful GP-B mission.

Then, not unlike a college commencement ceremony, Gaylord Green called up each member of the team--one by one, commenting on each person's contribution--to receive an individual award certificate. After all of the certificates, over 100 in all, had been given out, the GP-B team had a few special awards of its own to distribute. Framed photos of the GP-B launch, signed by all of the GP-B senior managers around the matte, were given to GP-B founder, Bob Cannon, Tony Lyons, and GP-B Dewar Specialist Mike Taber, who will soon be retiring.

At the end of the ceremony, there were a few concluding remarks and anecdotes. Jeff Smith, a senior manager at Lockheed Martin, re-emphasized the importance of the teamwork and cooperation that was the hallmark of the successful GP-B collaboration. Brad Parkinson, Co-Principal Investigator praised the longstanding leadership of Francis Everitt, GP-B's principal investigator, which drew a resounding ovation from the team. Finally, Francis Everitt addressed the group, remarking that the lives of everyone on the team changed at 9:57:23 am PDT on 20 April 2004, when GP-B lifted off the launch pad at Vandenberg AFB. Everitt then noted that in celebrating the teams recent accomplishments, it was also important to remember the contributions of “two of the masters” who started GP-B, but have since passed away--Bill Fairbank and Leonard Schiff. He finished by recognizing the GP-B Science team that is busily analyzing the data and optimistically looked forward to announcing the results in April 2007.

We concluded the ceremony with a group photo, which is shown to the right. Then the group enjoyed some refreshments and had an opportunity to reminisce about the “good old days of GP-B.”


Our final regularly scheduled update of 2005 will be at the end of this month. Of course, we will send out a timely update if there are any important changes in the spacecraft's status, or if noteworthy events occur here at GP-B in the meantime.


We recently updated our NASA Factsheet on the GP-B mission and experiment. You'll now find this 6-page document (Adobe Acrobat PDF format) listed as the last navigation link under "What is GP-B" in the upper left corner of this Web page. You can also click here to download a copy.

Photos & Drawings: The "Blue Gyro" photo was taken by photographer Mark Gottlieb. The photos the telescope detectors and Gyro Suspension System (GSS) electronics, plus the drawings of the payload and gyro suspension system are from the GP-B Image Archive here at Stanford. All photos of the NASA Awards Ceremony were taken by GP-B Public Affairs Coordinator, Bob Kahn. Click on the thumbnails to view these images at full size.


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