Hi,

Here is the news from the Gravity Probe B folts:

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GRAVITY PROBE B MISSION UPDATE FOR 30 DECEMBER 2005
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GP-B STATUS AT A GLANCE
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Mission Elapsed Time: 619 days (88.4 weeks/ 20.3 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: 91 days
Current Orbit #: 9,134 as of 4:00PM PST
Spacecraft General Health: Good
Roll Rate: Normal at 0.4898 rpm (2.04 minutes per revolution)
Gyro Suspension System (GSS): All 4 gyros digitally suspended
Gyro Spin Rates: ~0 rpm (spinning slightly due to spacecraft roll)
Dewar Temperature: ~170 K and rising ~0.9 K/day
Global Positioning System (GPS) lock: Nominal
Attitude Control System: Nominal for post-mission operation
Pointing Error: (XY/Pitch-Yaw Axes) 0.39 degrees RMS;
Roll Phase (Z Axis) Error: 7.6 degrees RMS
Telescope Readout: Pointing performance too low to lock onto guide star
Command & Data Handling (CDH): B-side (backup) computer in control
Multi-bit errors (MBE): 3 (Triggered reboot of CCCB Backup Computer on 12/21/05)

MISSION DIRECTOR'S SUMMARY
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On Mission Day 619, 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. We continue to communicate with the spacecraft regularly, monitoring the Dewar and probe as they continue to warm up, and collecting status data from various instruments on-board.

The temperature inside the Dewar has now warmed to ~170 kelvin, and its rate of temperature rise has slowed to ~0.9 kelvin per day. By comparison, various devices on the exterior frame of the spacecraft are registering average temperatures of ~0 centigrade (~273 kelvin). The temperature inside the Dewar will eventually reach thermal equilibrium with the outside temperature, but its rate of rise will continue to decrease so that it will approach the equilibrium temperature very gradually.

About two weeks ago, having caged and removed static charge from all four gyros, we re-suspended each of them digitally. The digital suspension mode, which was used throughout the flight mission, is computer-controlled and enables the gyro rotors to be positioned with great precision. When the gyro rotors were caged, they were basically spinning with the spacecraft's roll rate, and thus when they were re-suspended, they have continued to spin at that rate (~0.5 rpm). At present, we have no plans to do anything further with the gyros.

On Wednesday 21 December 2005, the CCCB backup computer that is controlling all spacecraft operations sustained three multi-bit errors (MBEs). This triggered an excessive MBE safemode response, which re-booted the backup computer. Having worked through similar scenarios a number of times during the Science Phase of the mission, it took our two-person mission operations team about a day to fully recover from this computer re-boot, eventually returning all spacecraft systems to nominal operation.
It is important to emphasize that at this point in the mission, we are only performing maintenance operations on the spacecraft. Our main focus is analyzing the science data we have collected and finishing our final report to NASA. In this regard, our final report to NASA, which is over 450 pages long, is now in the final stages of completion. Our science data analysis is proceeding according to plan. We are in the process of analyzing approximately 1 terabyte (1,000 gigabytes) of data collected from the spacecraft. Two independent analysis teams here at GP-B are working on the data, frequently comparing their results for both quality control and to ensure the validity of the data analysis algorithms.

The main part of the data analysis is expected to be completed late this summer (July-August 2006). At this point, the Harvard-Smithsonian Center for Astrophysics (CfA) will provide our science team with their ultra-precise measurements of the proper motion of the guide star, IM Pegasi. In the final step of the analysis, our science team will combine the gyroscope results with the CfA proper motion measurements of IM Pegasi to arrive at the final experimental results. These results will then be carefully and critically reviewed by international experts in general relativity and data analysis to ensure that our statement of the effects observed are as accurate as possible. Only after this review is complete--early in 2007--will we make a formal and public announcement about the results of this unprecedented test of General Relativity.

Best wishes from all of us here on the GP-B team for a very happy new year.

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NEXT SCHEDULED GP-B UPDATE ON JANUARY 27, 2006
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Our next regularly scheduled update will be at the end of January. 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.

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PREVIOUS GP-B UPDATES
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If you wish to read any of our previous updates, our GP-B Web site includes a chronological archive of all the updates/highlights (with photos and drawings) that we have posted over the past 8 years: http://einstein.stanford.edu/highlights/hlindexmain.html

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OTHER LINKS THAT MAY INTEREST YOU
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* Our GP-B Web site, http://einstein.stanford.edu contains lots of information about the Gravity Probe B experiment, general relativity, and the amazing technologies that were developed to carry out this experiment.


* Visual tour of the GP-B spacecraft and payload from our GP-B Web site: http://einstein.stanford.edu/content/vehicle_tour/index.html


* PDF file containing a 1/20 scale, paper model of the GP-B spacecraft that you can download print out, and assemble: http://einstein.stanford.edu/content/paper_model.


* NASA's Marshall Space Flight Center also has a series of Web pages devoted to GP-B: http://www.gravityprobeb.com


* Photo, taken through a telescope by Swiss physics teacher and amateur astronomer Stefano Sposetti, of GP-B spacecraft in orbit, passing near IM Pegasi: http://aida.astronomie.info/sposetti



* The Harvard-Smithsonian Center for Astrophysics (Cambridge) and York University (Toronto), with contributions from the Observatoire de Paris, have been studying the motions of the guide star, IM Pegasi for over a decade. To find out more, visit: http://www.yorku.ca/bartel/guidestar/


* In addition, you'll find information in the Guide Star FAQ on our Web site: http://einstein.stanford.edu/content/faqs/faqs.html#guidestar and on pages 18-20 of the Gravity Probe B Launch Companion: http://einstein.stanford.edu/highlights/GP-B_Launch_Companion.pdf


* Track the GP-B satellite on the Web using NASA's Java-based J-Pass satellite tracking application at: http://science.nasa.gov/realtime/JPass/ Also, you can track the GP-B satellite on Personal Digital Assistants (PDAs) using either the Palm OS or Pocket PC operating systems with software from Big Fat Tail Productions: http://www.bigfattail.com


* The Einstein Exhibition at the Skirball Cultural Center in Los Angeles has closed.However, you can visit the American Museum of Natural History's virtual Einstein exhibit on the Web at: http://www.skirball.org/exhibit/amnh_frame.html


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NASA - Stanford - Lockheed Martin
Gravity Probe B Program
"Testing Einstein's Universe"
http://einstein.stanford.edu

Bob Kahn
Public Affairs Coordinator

Phone: 650-723-2540
Fax: 650-723-3494
Email: kahn@relgyro.stanford.edu
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Regards,

LelandJ