Hi,

Here is Jan 7 2005 update report about the Gravity Probe B mission.

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GRAVITY PROBE B MISSION UPDATE FOR 7 JANUARY 2005
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Throughout the holiday season, the GP-B spacecraft has remained in
excellent health, with all subsystems performing well and no
anomalous events. The GP-B spacecraft has now completed more than
3,870 orbits over 8.5 months (262 days), and on average, the four
gyros have each made approximately one billion revolutions.

The spacecraft's full-sun season has ended, and it is now
experiencing longer periods of being eclipsed from sunlight by the
Earth during each orbit. It is flying drag-free around gyro #3,
maintaining a constant roll rate of 0.7742 rpm (77.5 seconds per
revolution.) All four gyros are digitally suspended in science mode.
The temperature inside the Dewar is holding steady at 1.82 kelvin,
and it is now less than half full of superfluid helium. We have been
collecting science data for 19 weeks, and we are now approximately
45% of the way through the science phase of the mission. The data
collection process is continuing to proceed smoothly, and the quality
of the data remains excellent.

GP-B's MISSION LIFETIME
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Some readers have inquired how it is that we could have expended over
half the helium in the Dewar and still be less than half way through
the science phase of the mission. The answer is that the Dewar
initially contained enough helium to last for the entire
mission--approximately 16 months--which includes 4 months of
Initialization and Orbit Checkout (IOC), 10 months of science data
collection, and 1-2 months of instrument re-calibration. At the point
last month when the Dewar reached the half-full level, we had
approximately 8 months of helium remaining--enough for 6 more months
of science and 2 months of re-calibration--which is what we need.

GP-B AND THE DEC 26th INDONESSIAN EARTHQUAKE/TSUNAMI
===========================================
Over the past three weeks, we have received numerous inquiries
regarding any possible relationship between GP-B's experimental
measurements and the disastrous earthquake and ensuing tsunami in
South Asia on December 26th. The short answer is that this event had
no effect on the GP-B experimental data, nor did our gyroscopes
detect it. For readers who are interested, more detailed information
follows.

Richard Gross, a scientist at NASA's Jet Propulsion Lab (JPL) in
Pasadena, California, has modeled the coseismic effect on the Earth's
rotation of the December 26 earthquake in Indonesia by using the PREM
model for the elastic properties of the Earth and the Harvard
centroid-moment tensor solution for the source properties of the
earthquake. The result of this modeling is:

Change in length of day: -2.676 microseconds (about one second in a millennium)
X-axis polar motion excitation: -0.670 milliarcseconds (approximately
2 centimeters or 0.8 inches)
Y-axis polar motion excitation: +0.475 milliarcseconds
(approximately 1.5 centimeters or 0.6 inches)

Since the length of the day can only be measured to an accuracy of
about 20 microseconds (20 millionths of a second), this model
predicts that the change in the length-of-day caused by the
earthquake is too small to be observed. And, since the location of
the earthquake was near the equator, this model predicts that the
change in polar motion excitation is also rather small, being about
0.82 milliarcsecond in amplitude. Such a small change in polar motion
excitation will also be difficult to detect.

Nevertheless, at a science conference in Utah last week, Professor
Ulrich Schreiber of the Munich Technical University in Germany
reported that his Earth-based, ultra-precise
"G" ring laser gyroscope was able to detect perturbations in the
Earthís axis as a result of the Indonesian earthquake. This
gyroscope--the largest of its kind in the world--contains a giant
glass ceramic disc, 4.25 meters in diameter, 25 centimeters thick and
weighing 10 tons. It is located in a sealed and pressurized chamber,
eight meters below the surface of the Earth, at the Wettzell
Fundamental Research Station in New Zealand. This instrument was
specifically designed to be able to detect changes in the Earth's
rotation within a day. For more information on the "G" ring laser
gyroscope, see
http://www.spie.org/app/publications/magazines/oerarchive/september/sep96/gyro.html
or http://www.wettzell.ifag.de/publ/publ/IUGG_2003_RinglaserG.pdf

In contrast, the GP-B gyroscopes have not detected any measurable
effect as a result of the Indonesian earthquake and tsunami. GP-B is
measuring the curvature and twisting of space-time around the Earth,
not the planet itself. Our spacecraft is in a circular orbit, 640
kilometers (400 miles) above the earth, always passing over the north
and south poles, but varying in its longitudinal path with each
orbit. The extremely small change in the earth's polar motion
resulting from the Indonesian earthquake/tsunami is simply not
significant enough to appear in our measurements. Also, any small
change in the Earth's polar motion will factor itself out, given the
changing longitude of each orbit.

Our measurements do depend on knowing our spacecraft's position
relative to specific locations on Earth to a high precision, and for
these measurements, we use the Global Positioning System (GPS). It
is possible, though highly unlikely, that if a re-calibration in the
GPS satellites is required, we may need to incorporate some
compensating factors.

Gravity Probe B could conceivably register a change in Earth's polar
orbit, if the change were of immense proportions. For example,
suppose the earth's spin axis were to change position by 3 degrees.
This would significantly affect local space-time, and this change
would be detectable by the science instruments on-board the
spacecraft. However, such a change would require a cataclysmic event,
ten million times larger than the Indonesian earthquake and
tsunami--an event that would mean the end of Planet Earth, as we know
it.

The United States Geological Survey (USGS) maintains a Web page of
Frequently Asked Questions (FAQ) about the December 26th earthquake
and tsunami at:
http://earthquake.usgs.gov/eqinthenews/2004/usslav/neic_slav_faq.html

All of us on the Gravity Probe B team are deeply saddened by human
tragedy that has emerged in the wake of the tsunami. The importance
of the relief efforts cannot be overstated.

NEW PHOTO OF GP-B IN ORBIT FROM AMATEUR ASTRONOMER STEFANO SPOSETTI
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This week, on the Highlights (Home) page of our GP-B Web site, we
have included a new photograph of the GP-B spacecraft in orbit, taken
by Swiss amateur astronomer and physics teacher, Stefano Sposetti. 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 this photo on our GP-B Web site or on Mr.
Sposetti's Web page of the Astronomical Image Data Archive (AIDA):
http://aida.astroinfo.org/sposetti/ As always, we are most grateful
to Mr. Sposetti for sending us this extraordinary photo.


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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