Hi,
Here is the GP-B mission update. The mission is now past the half-way
point and remain on track to deliver data about Einstein's concept of
space-time and gravity. I can hardly wait for the completion of the
mission and the analysis and release of the data to see what we might learn.
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GRAVITY PROBE B MISSION UPDATE FOR 4 FEBRUARY 2005
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GP-B Status At a Glance
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Mission Elapsed Time: 290 days (41 weeks/9.5 months)
Science Data Collection: 161 days (23 weeks/5.25 months)
Current Orbit #: 4,281 as of 4:00PM PST
Spacecraft General Health: Good
Roll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)
Gyro Suspension System (GSS): All 4 gyros digitally suspended in science mode
Dewar Temperature: 1.82 kelvin, holding steady
Global Positioning System (GPS) lock: Greater than 98.5%
Attitude & Translation Control (ATC): X-axis attitude error: 206.1 marcs rms
Y-axis attitude error: 302.1 marcs rms
Command & Data Handling (CDH): Multi-bit errors (MBE): 1; Single-bit errors (SBE): See MD Summary below
Telescope Readout (TRE): Nominal
SQUID Readouts (SRE): Nominal
Gyro #1 rotor potential: -2.4 mV
Gyro #2 rotor potential: +8.3 mV
Gyro #4 rotor potential: -8.0 mV
Gyro #3 Drag-free Status: Backup Drag-free mode (normal)
Mission Director's Summary
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As of Mission Day 290, the Gravity Probe B vehicle and payload remain in good health, with all systems functioning nominally and over five months of science data collected.
Last weekend, on both Saturday and Sunday, the spacecraft's main computer (CCCA) erroneously displayed a dramatic increase in single-bit errors (SBE). We observed similar SBE increases in July 2004 and one other time since then. In both previous cases, the SBE count quickly returned to normal, and we were unable to determine the root cause of the erroneous increase. SBEs are self-correcting, so no particular action is required, but we are monitoring this situation. Also, this past Tuesday, a new multi-bit error (MBE) was discovered in a memory location of the CCCA computer. A command was subsequently sent to reload this memory location, clearing the MBE.
The health of the spacecraft's Proton Monitor is still under investigation. Telemetry indicates that it is powered on, but the data appears to be corrupt. Note that the science mission is NOT affected by the loss of the Proton Monitor. The Proton Monitor Engineering unit is continuing to investigate this failure.
We have been notified that the sun spot which caused the GP-B science telescope to lose track of the guide star two weeks ago, will be coming around to the front side of the sun on 5 February 2005. Geomagnetic activity around the Earth tends to increase after the appearance of sun spots. Thus, we have added extra telemetry passes and increased sensitivity to this issue during the next two weeks.
Mission News
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This past week, we passed the halfway mark in the science phase of the mission, which began on 27 August 2004 and is anticipated to last approximately 10 months through the end of June, depending on the supply of superfluid helium in the Dewar. Each of our four gyroscopes has now completed over a billion revolutions, and they have all been generating copious amounts of relativity data, which we are busily processing and preparing for analysis.
On Tuesday (1 February 2005), our NASA management team from Marshall Space Flight Center in Huntsville, AL., visited us for a scheduled GP-B status review. During the review, GP-B team members presented detailed reports on each of the spacecraft's systems and subsystems. With the exception of the Proton Monitor, all reports were good-the spacecraft's power is positive, the ATC is performing well, and temperatures are stable. During this review, we also added a new item concerning elevated proton flux from solar activity to our existing risk management plan.
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NASA - Stanford - Lockheed Martin
Gravity Probe B Program
"Testing Einstein's Universe"
http://einstein.stanford.eduBob Kahn
Public Affairs Coordinator
Phone: 650-723-2540
Fax: 650-723-3494
Email: kahn@relgyro.stanford.edu
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Regards,
LelandJ
