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Gravity Probe B

Testing Einstein's Universe




Item Current Status
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 4:00 PM 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 (See MD Summary below)
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)


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.


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.


Just before the holidays, Swiss amateur astronomer and physics teacher, Stefano Sposetti sent us two new photos of the GP-B spacecraft in orbit, one of which is shown to the right. In this photo, taken on 6 December 2004 (during the spacecraft’s full-sun season), Mr. Sposetti used a 20mm f2.8 photo lens, coupled with a CCD camera on a fixed tripod, with a 60-second exposure to capture a beautiful time exposure of the GP-B spacecraft, rising over a rooftop. You can view other astronomical photos taken by Mr. Sposetti, including photos of the GP-B spacecraft on Mr. Sposetti’s Web page in the Astronomical Image Data Archive (AIDA). As always, we are most grateful to Mr. Sposetti for sending us this extraordinary photo.



If you're going to be in Los Angeles anytime before 30 May 2005, and if you’re interested in Einstein’s life and work, the Einstein Exhibition at the Skirball Cultural Center (just north of the Getty Museum on Interstate 405) is the most comprehensive presentation ever mounted on the life and theories of Albert Einstein (1879-1955). It explores his legacy not only as a scientific genius who re-configured our concepts of space and time, but also as a complex man engaged in the social and political issues of his era. It examines the phenomenon of his fame and his enduring status as a global icon whose likeness has become virtually synonymous with genius.

In this exhibit, you can examine Einstein's report card, inspect his FBI file, and enjoy his family photographs, love letters, and diary entries. Exhibition highlights include scientific manuscripts and original correspondence—including original handwritten pages from the 1912 manuscripts of the special theory of relativity and his 1939 letter to President Roosevelt about nuclear power—and a wealth of other documents from the Albert Einstein Archives at the Hebrew University of Jerusalem.

In addition to these displays of Einstein memorabilia, the exhibit also features a number of interactive components that help provide an understanding of Einstein's revolutionary theories. Furthermore, several “explainers,” identified by their red aprons, are on hand to discuss various aspects of the exhibit and to explain and demonstrate difficult concepts, such as time dilation and warped spacetime. At the end of the exhibit, you’ll find one of GP-B’s gyro rotors on display.

The Einstein exhibition was jointly organized by the American Museum of Natural History (AMNH), the Hebrew University of Jerusalem, and the Skirball Cultural Center. It was designed by the AMNH under the supervision of Dr. Michael Shara, curator of the exhibit and chairman of the museum’s Astrophysics Department. It opened in November 2002 at the AMNH in New York and then traveled to Chicago and Boston, spending about 8 months in each location. It will remain at its final U.S. stop at the Skirball Center in Los Angeles through 29 May 2005, after which time it will move permanently to the Hebrew University in Jerusalem.

Information about the Einstein exhibition is available on the Skirball Center Web site. If you can’t make it to Los Angeles, you can visit the AMNH’s virtual Einstein exhibit on the Web.

Drawing and photo: GP-B Public Affiars Coordinator, Bob Kahn, created the composite photo of the GP-B spacecraft in orbit. The photo of sun spots was taken from the NASA/ESA SOHO Web site. The photos from the Einstein Exhibit are courtesy of the Skirball Cultural Center. Click on the thumbnails to view these images at full size.


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