STATUS UPDATE AS OF 30 DECEMBER 2005:

GRAVITY PROBE B MISSION STATUS AT A GLANCE

Item	Current Status
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 4:00 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 digitally suspended
Gyro Spin Rates	~0.5 rpm (same as spacecraft roll rate)
Dewar Temperature	~170 kelvin (and rising ~0.9 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): 3 (Triggered reboot of CCCB backup computer on 12/21) Single-bit errors (SBE): Data Not Available

MISSION DIRECTOR'S SUMMARY

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.

GP-B MISSION NEWS—NASA REPORT & DATA ANALYSIS PROCEEDING AS PLANNED

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.

NEXT SCHEDULED GP-B STATUS UPDATE & MISSION NEWS ON 27 JANUARY

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.

UPDATED NASA/GP-B FACT SHEET AVAILABLE FOR DOWNLOADING

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 composite photo of the GP-B spacecraft orbiting the dark side of the Earth and the Data Analysis collage were created by GP-B Public Affairs Coordinator, Bob Kahn.Tthe drawings of the Dewar and gyro suspension system and the photo of the Gyro Suspension System (GSS) electronics are from the GP-B Image Archive here at Stanford. Click on the thumbnails to view these images at full size.

Gravity Probe B

Testing Einstein's Universe