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Gravity Probe B

Testing Einstein's Universe



Item Current Status
Mission Elapsed Time 388 days (55 weeks/12.72 months)
Science Data Collection 259 days (37 weeks/8.49 months)
Current Orbit # 5,726 as of 5:00 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 96.6%
Attitude & Translation Control (ATC)

X-axis attitude error: 202.6 marcs rms
Y-axis attitude error: 90.7 marcs rms

Command & Data Handling (CDH) B-side (backup) computer in control
Multi-bit errors (MBE): 0
Single-bit errors (SBE): 9 (daily average)
Telescope Readout (TRE) Nominal
SQUID Readouts (SRE) Nominal
Gyro #1 rotor potential -2.3 mV
Gyro #2 rotor potential -3.1 mV
Gyro #4 rotor potential -2.7 mV
Gyro #3 Drag-free Status Backup Drag-free mode (normal)


As of Mission Day 388, the Gravity Probe B vehicle and payload are in good health. All four gyros are digitally suspended in science mode. The spacecraft is flying drag-free around Gyro #3.

Our telescope pointing and guide star capture times continue to be excellent. The Experiment Control Unit continues to remain off during most orbits, resulting in reduced noise in the SQUID Readout Electronics system (SRE). Once a week, we power the ECU back on for a few hours in order to obtain and check certain readouts, such as the Dewar temperature, that are provided by the ECU. 

Because the spacecraft has been in orbit for over a year now, we are able to conduct an analysis of the external temperature and solar array efficiencies by comparing current data from these systems with data collected a year ago.

In preparation for the end of the GP-B mission, which is fast approaching, we have begun delegating tasks to complete our final mission report, which we will deliver to NASA in July.


Following is a copy of the press release we sent out earlier this week, announcing this award.

Stanford experimental physicist Francis Everitt has been awarded a NASA Distinguished Public Service Medal. NASA Deputy Director Fred Gregory presented the medal to Everitt on April 27 at an awards ceremony at NASA Headquarters in Washington, D.C. Everitt is principal investigator of the Gravity Probe B (GP-B) experiment, a collaboration between Stanford University, NASA and Lockheed Martin Corp. that is testing predictions of Albert Einstein's 1916 general theory of relativity (his theory of gravitation) by means of four ultra-precise gyroscopes that have been orbiting the Earth in a satellite for just over a year.

The NASA Distinguished Public Service Medal is awarded to an individual whose distinguished accomplishments contributed substantially to NASA's mission. Contributions must be so extraordinary that other forms of recognition by NASA would be inadequate. This is the highest honor that NASA confers to an individual who is not a government employee.

Everitt obtained his doctorate at the University of London (Imperial College) in 1959 for research under Nobel laureate P. M. S. Blackett. He then spent two years at the University of Pennsylvania working on liquid helium. In 1962, Everitt joined William Fairbank and Leonard Schiff in the Stanford Physics Department as the first full-time research worker on the GP-B experiment. His efforts advanced the state of the art in the areas of cryogenics, magnetics, quantum devices, telescope design, control systems, quartz fabrication techniques, metrology and, most of all, gyroscope technology. His leadership as the principal investigator for GP-B advanced the GP-B program from the concept and technology development stages to the experiment's launch on April 20, 2004, and its ensuing orbital operations.

"None of us at the beginning had any idea how long it would take for the GP-B spacecraft to fly and take the science data," Everitt said when asked about the long life of the project. "But speaking for myself, I have never been bored."

Gravity Probe B was developed on the Stanford campus in the W. W. Hansen Experimental Physics Laboratory (HEPL). The current on-orbit GP-B mission operations center (MOC) is located in HEPL, where the science data is currently processed as well. From the MOC, the GP-B spacecraft is commanded with ground antennas in Alaska or Norway or through the NASA space net. HEPL supports a number of collaborative scientific research programs that cross traditional university departmental boundaries. The GP-B space mission itself was a successful interdepartmental collaboration of the Stanford Physics and Engineering departments.

"HEPL is one of the few places in the United States where an interdisciplinary experiment such as Gravity Probe B could be successfully carried out," said HEPL Director Robert Byer, a professor of applied physics.



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.



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.

Drawings & Photos: The schematic diagram of the GP-B experiment was created by GP-B Public Affairs Coordinator, Bob Kahn. The photos of the ECU electronics box and spacecraft solar panels are from the GP-B Photo & Graphics Archive here at Stanford. The photo of Francis Everitt at the NASA Awards Ceremony is courtesy of Renee Bouchard, NASA Photographer. The close-up photos of the award medals and certificate, as well as the photo of Francis Everitt standing with colleagues from Stanford were taken by GP-B Public Affairs Coordinator, Bob Kahn. Finally, 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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