WEEKLY UPDATE FOR 29 APRIL 2005:

GRAVITY PROBE B MISSION STATUS AT A GLANCE

Item	Current Status
Mission Elapsed Time	374 days (53 weeks/12.26 months)
Science Data Collection	245 days (35 weeks/8.03 months)
Current Orbit #	5,523 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 97.7%
Attitude & Translation Control (ATC)	X-axis attitude error: 190.9 marcs rms Y-axis attitude error: 91.2 marcs rms
Command & Data Handling (CDH)	B-side (backup) computer in control Multi-bit errors (MBE): 0 Single-bit errors (SBE): 8 (daily average)
Telescope Readout (TRE)	Nominal
SQUID Readouts (SRE)	Nominal
Gyro #1 rotor potential	-3.7 mV
Gyro #2 rotor potential	-4.8 mV
Gyro #4 rotor potential	-4.1 mV
Gyro #3 Drag-free Status	Backup Drag-free mode (normal)

MISSION DIRECTOR'S SUMMARY

As of Mission Day 374, 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.

This past Tuesday, 26 April 2005, the GP-B Dewar team ran another heat pulse meter test to get an update on the amount of liquid helium remaining in the Dewar. Their preliminary results suggest that we have about two weeks more helium than anticipated. Further analysis is in process, and if these results are correct, the helium will be depleted around the end of August or beginning of September. This means that we will be able to continue collecting science data into the first two weeks in July, before beginning a very important series of instrument calibration tests that must be completed before the helium runs out.

Also this past week, we continued fine-tuning our SQUID readout system, analyzing potential sources of noise. To this end, we turned off the telescope dithering motion all day on Wednesday, 27 April 2005 to determine its contribution to experimental noise. Likewise, for the same reason, on Thursday, we turned off the Experiment Control Unit (ECU) for several days. We are in the process of analyzing the results of these noise experiments, which may lead to further fine-tuning of various spacecraft systems.

MISSION NEWS—NO NEWS IS GOOD NEWS!

This past week was a quiet one for the GP-B spacecraft, which has been performing exceptionally well these past few weeks.

Recent patches to the Attitude and Translation Control System (ATC), reported in previous weekly updates, have dramatically improved its pointing performance, which continues to be excellent.

As noted in the Mission Director's summary above, we have been investigating potential sources of noise in various spacecraft systems, including the ECU and the telescope dither routine. The dither (which we will describe in an upcoming Mission News Report) is one of several calibrating routines that is used whenever the telescope is locked onto the guide star.

GP-B Principal Investigator, Francis Everitt, spent this past week at NASA Headquarters in Washington, DC, providing the NASA administration with an update on the progress of GP-B.

Meanwhile, last Thursday, 28 April 2005, was “Bring Your Children to Work Day” here at Stanford. GP-B is always happy to participate in community activities at Stanford, and last Thursday was no exception. For about two hours, 13 children of Stanford staff and faculty were treated to a personal tour of GP-B, led by Educational Outreach Coordinator Shannon Range.

The tour began with an introduction to curved spacetime and the physics of gyroscopes. But, undoubtedly, the highlight of these children's visit was an opportunity to sit at the consoles in the GP-B Mission Operations Center (MOC) and report out some telemetry data for the spacecraft and payload during a GP-B communications pass with a NASA TDRSS (Tracking & Data Relay Satellite System). During this activity, our visitors were in constant contact with Flight Director Kim Owen, using the MOC voice link system, and they were assisted in their data reporting efforts by MOC team members Jerry Aguinaldo and Dave Spencer.

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.

THE EINSTEIN EXHIBITION AT THE SKIRBALL CULTURAL CENTER IN LOS ANGELES

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.

Photos: The Photoshop composite of the GP-B spacecraft in orbit was created by GP-B Public Affairs Coordinator, Bob Kahn. The photos of the Dewar, SRE and ECU electronics boxes, and the MOC, as well as to artist's drawing of the spacecraft locking onto the guide star are from the GP-B Photo & Graphics Archive here at Stanford. 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.

Gravity Probe B

Testing Einstein's Universe