Hi,

Here is a recent status report of Graviety Probe B.

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GRAVITY PROBE B MISSION UPDATE -- June 4, 2004
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Please Note: During the Initialization & Orbit Checkout (IOC) Phase
of the GP-B mission, we will update our Web site and send out this
email update once a week (usually on Thursday or Friday) to keep you
apprised of our progress. From time to time, we may send out extra
updates, as warranted by mission events.

After six weeks in orbit, the spacecraft continues to be healthy,
with all subsystems performing well. Over the past two weeks, with
the arrival of summer in the Northern Hemisphere, the spacecraft
emerged from being partially eclipsed by the Earth each orbit to
being in full sunlight continuously. The spacecraft's orbit is stable
and meets our requirements for transition into the science phase of
the mission. All four gyros remain digitally suspended, and all are
spinning very slowly. Progress in locking the on-board telescope onto
the guide star, IM Pegasi, has been slower than anticipated, but late
this afternoon, we achieved this important milestone. (We'll have
more information about locking onto IM Pegasi in next week's update.)

This past week, the team started performing a highly methodical and
painstaking series of calibration tests on the four science
gyroscopes. These tests begin at very low gyro spin rates of 0.333 Hz
(20 rpm) or less. This enables the team to exercise and check out the
software command templates that control the tests, without risk of
damage to the gyro rotors or housings, which could occur at higher
speeds. We accomplish these calibration tests by briefly applying
voltages asymmetrically to the suspension electrodes on a given gyro,
causing that gyro rotor (sphere) to move off center by a few
micrometers (10-6 meters) or less, and then re-centering it.

During these initial calibration tests, the team discovered that the
performance characteristics of the gyros on orbit are slightly
different from the simulator predictions on which the original
command templates were based. As a result of these differences,
during one of the initial tests, gyro #4 touched one of its
electrodes, and stopped spinning. A simple modification to the
spin-up command templates is now in process. Once the on-orbit
performance characteristics of each gyro is well understood, the team
will repeat these tests at gradually increasing spin rates.

The team also exercised the Ultraviolet Discharge procedure to reduce
the electrostatic charge, which builds up on the gyro rotors over
time. The rotors build up a charge in two ways: first, the process of
suspending the rotors electrically deposits some charged particles on
them, and second, protons from the sun are constantly bombarding the
spacecraft, especially over the South Atlantic Ocean-the so-called
"South Atlantic Anomaly"- and some of these protons strike the rotors
and leave a residual charge on them.

We use ultraviolet light to remove the build-up of electrostatic
charge from the gyro rotors. Each gyro housing is fitted with fiber
optic cables that run from the gyro housings, up through the top hat
of the probe and out to an ultraviolet light source in the Experiment
Control Unit (ECU) box, mounted on the spacecraft frame. UV light is
beamed through the fiber optics onto the gyro rotors to discharge
them. Reducing the level of charge is important because it increases
the sensitivity and accuracy of the Gyroscope Suspension System (GSS).

The spacecraft is being controlled from the Gravity Probe B Mission
Operations Center, located here at Stanford University. The
Stanford-NASA/MSFC-Lockheed Martin operations team is continuing to
perform superbly.

LEARN MORE ABOUT IOC & GRAVITY PROBE B
==================================
If you are interested in following the IOC procedures more closely,
you'll find a schedule and description of them on pages 12-14 of the
"Gravity Probe B Launch Companion." You can download a copy of this
document, in Adobe Acrobat PDF format, from
http://einstein.stanford.edu/highlights/GP-B_Launch_Companion.pdf.

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.

Our Web site also includes a 3 1/2 minute Quicktime streaming video
clip of the launch, edited by Mark Shwartz and Delana Lindsey of the
Stanford News Service. We will be posting more video clips on the Web
site soon.

LEARN MORE ABOUT OUR GUIDE STAR, IM PEGASI
=====================================
For an overview about why we chose IM Pegasi as our guide star, and
its importance to the GP-B mission, see the Guide Star FAQ on our Web
site: http://einstein.stanford.edu/content/faqs/faqs.html#guidestar

Also, the ETH Institute of Astronomy in Zurich, Switzerland, is
working with the Harvard-Smithsonian Center for Astrophysics to
provide detailed optical information about the GP-B guide star, IM
Pegasi. You can find out about the ETH Institute's work in monitoring
magnetic activity on IM Pegasi and the Doppler Imaging Technique used
for this purpose at:
http://www.astro.phys.ethz.ch/staff/berdyugina/private/GP/gravity_probe.html

TRACK THE GP-B SATELLITE ON THE WEB OR WITH YOUR PDA
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You can 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, Big Fat Tail Productions (http://www.bigfattail.com) has
created shareware satellite tracking software that runs on Personal
Digital Assistants (PDAs) using either the Palm OS or Pocket PC
operating systems. Like all PDA shareware, you can try out either
version for free. If you like the software and decide to use it, Big
Fat Tail asks that you pay a nominal shareware fee.

FOLLOW THE GP-B MISSION ELSEWHERE ON THE INTERNET
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In addition to our Stanford GP-B Web site, the ELV Missions Virtual
Launch Center Web page on the John F. Kennedy Space Center Web site
has information and several streaming video clips covering the GP-B
mission. The URL is: http://www.ksc.nasa.gov/elvnew/gpb/vlcc.htm.
(You can view these video clips free of charge, but you will need to
have either the Real Media Player or Windows Media Player installed
on your computer to view them.)

NASA's Marshall Space Flight Center Gravity Probe B.com Web page
(http://www.gravityprobeb.com ) has a number of great photos from the
GP-B launch, including photos of the spacecraft separation, as well
as other information about Gravity Probe B.


ABOUT THE GPB-UPDATE EMAIL LIST
============================
The email distribution list for this GP-B Weekly Highlights update is
maintained on the Stanford University email lists server. These email
updates are automatically sent to GP-B program internal email
distribution lists at Stanford, Lockheed Martin, and NASA. If your
email address is not included in one of these distribution lists, you
have subscribed--or been subscribed by someone else--to this email
list.

If this email update was forwarded to you by someone else and you
wish to subscribe, simply send an email message to
"majordomo@lists.Stanford.edu" with the command "subscribe
gpb-update" in the body of the message (not in the Subject line).

You can unsubscribe at any time by sending an email message to
"majordomo@lists.Stanford.edu" with the command, "unsubscribe
gpb-update" in the body of the message.

--
**********************************
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