Hi,

Here is news about Gravity Probe B mission:

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GRAVITY PROBE B MISSION UPDATE FOR 29 APRIL 2005
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GP-B STATUS AT A GLANCE
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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 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 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 avg.)
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
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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 August 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), and it will remain off for a few 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!
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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.

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UPDATED NASA/GP-B FACTSHEET
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A recently updated NASA Factsheet on the GP-B mission and experiment is now available on our Web site in Adobe Acrobat PDF format. You can download this 6-page fact sheet at: http://einstein.stanford.edu/content/fact_sheet/GPB_FactSheet-0405.pdf

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PREVIOUS GP-B UPDATES
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If you wish to read any of our previous updates, our GP-B Web site includes a chronological archive of all the updates/highlights (with photos and drawings) that we have posted over the past 8 years: http://einstein.stanford.edu/highlights/hlindexmain.html

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OTHER LINKS THAT MAY INTEREST YOU
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* Our GP-B Web site, http://einstein.stanford.edu contains lots of information about the Gravity Probe B experiment, general relativity, and the amazing technologies that were developed to carry out this experiment.


* Visual tour of the GP-B spacecraft and payload from our GP-B Web site: http://einstein.stanford.edu/content/vehicle_tour/index.html


* PDF file containing a 1/20 scale, paper model of the GP-B spacecraft that you can download print out, and assemble: http://einstein.stanford.edu/content/paper_model.


* NASA's Marshall Space Flight Center also has a series of Web pages devoted to GP-B: (http://www.gravityprobeb.com )


* Photo, taken through a telescope by Swiss physics teacher and amateur astronomer Stefano Sposetti, of GP-B spacecraft in orbit, passing near IM Pegasi: http://aida.astronomie.info/sposetti.



* The Harvard-Smithsonian Center for Astrophysics (Cambridge) and York University (Toronto), with contributions from the Observatoire de Paris, have been studying the motions of the guide star, IM Pegasi for over a decade. To find out more, visit: http://www.yorku.ca/bartel/guidestar/


* In addition, you'll find information in the Guide Star FAQ on our Web site: http://einstein.stanford.edu/content/faqs/faqs.html#guidestar and on pages 18-20 of the Gravity Probe B Launch Companion: http://einstein.stanford.edu/highlights/GP-B_Launch_Companion.pdf.


* Track the GP-B satellite on the Web using NASA's Java-based J-Pass satellite tracking application at: http://science.nasa.gov/realtime/JPass/ Also, you can track the GP-B satellite on Personal Digital Assistants (PDAs) using either the Palm OS or Pocket PC operating systems with software from Big Fat Tail Productions: http://www.bigfattail.com.


* The Einstein Exhibition at the Skirball Cultural Center in Los Angeles through May 2005: Information about the Einstein exhibition is available on the Skirball Center Web site: http://www.skirball.org/index.asp?s=exhibit&p=einstein.asp. If you can't make it to Los Angeles, you can visit the AMNH's virtual Einstein exhibit on the Web at: http://www.skirball.org/exhibit/amnh_frame.html.


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NASA - Stanford - Lockheed Martin

Gravity Probe B Program
"Testing Einstein's Universe"
http://einstein.stanford.edu

Bob Kahn
Public Affairs Coordinator

Phone: 650-723-2540
Fax: 650-723-3494
Email: kahn@relgyro.stanford.edu
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Regards,

LelandJ