From: LARRY KLAES (ljk4_at_msn.com)
Date: Sat Sep 10 2005 - 02:52:13 UTC
----- Original Message -----
From: Bob Kahn<mailto:kahn_at_relgyro.stanford.edu>
To: gpb-update_at_lists.Stanford.EDU<mailto:gpb-update_at_lists.Stanford.EDU>
Sent: Friday, September 09, 2005 8:30 PM
Subject: Gravity Probe B Update -- September 9, 2005
=============================================
GRAVITY PROBE B MISSION UPDATE FOR 9 SEPTEMBER 2005
==============================================
GP-B STATUS AT A GLANCE
=============================
Mission Elapsed Time: 507 days (72 weeks/ 16.6 months)
--IOC Phase: 129 days (4.2 months)
--Science Phase: 352 days (11.6 months)
--Final Calibration Phase: 26 days
Current Orbit #: 7,482 as of 4:30PM 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
Dewar Temperature: 1.82 kelvin, holding steady
Global Positioning System (GPS) lock: Greater than 96.5%
Attitude & Translation Control (ATC): X-axis attitude error: 149.7 marcs rms
Y-axis error: 179.9 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: +2.4 mV
Gyro #2 rotor potential: +1.7 mV
Gyro #3 rotor potential: +0.5 mV
Gyro #4 rotor potential: +2.6 mV
Gyro #1 Drag-free Status: Backup Drag-free mode
(OFF during some calibration maneuvers)
MISSION DIRECTOR'S SUMMARY
=======================
On Mission Day 507, the Gravity Probe B vehicle
and payload are in good health and all subsystems
are performing nominally.
The helium in the Dewar has lasted throughout
this past week, and thus we have continued with
the calibration tests that we began over three
weeks ago. These tests involve slewing the
telescope (and spacecraft) to "visit" stars (both
real and virtual) in the neighborhood around the
guide star, IM Pegasi. In each case, we visit a
neighboring location for a period of time and
then lock back onto IM Pegasi for several hours.
The purpose of these tests is to calibrate, in
detail, the torques imparted onto the science
gyroscopes by purposely mis-aligning the
telescope (and spacecraft roll axis) from the
direction of the gyro spin axes.
Last weekend, we visited a "virtual star"
(location where no stars visible to the telescope
exist) located 0.1 degree in the direction of
neighboring star HD 216635, northwest of IM
Pegasi. We remained at this location for 24 hours
and then returned to IM Pegasi for 16 hours. We
then repeated this procedure, visiting a location
0.1 degrees in the opposite direction. Then, this
past Tuesday we visited a virtual star location
halfway to the Star HR Pegasi (HD 216672), which
is located to the west of IM Pegasi. After
dwelling in that location for 24 hours, we again
returned to IM Pegasi. And, on Thursday, we
visited a virtual location 0.3 degrees towards HD
216635, remained there for 24 hours and then
returned to IM Pegasi.
This coming weekend, if we still have helium
remaining, we will visit similar virtual star
locations, or possibly real stars, within a
4-degree radius of IM Pegasi, each time visiting
a neighboring location for several hours and then
returning to IM Pegasi. And, as long as there is
still helium, we will continue similar tests into
next weekSand beyond.
GP-B MISSION NEWS--THE HELIUM JUST KEEPS ON FLOWINGS
==========================================
Like Energizer BunnyŽ that "keeps on going," the
helium in the GP-B Dewar just keeps on flowing.
Our Dewar specialists assure us that we are,
indeed, well into the final days--or possibly
hours--of helium. But when will the helium
actually run out? That's anybody's guess (we have
a pool going amongst the remaining team members
here at Stanford).
Estimating the amount of liquid helium remaining
in a 650 gallon Thermos bottle, orbiting 400
miles above the Earth, requires complex
calculations, and there are many variables at
play. Also, there is a considerable margin of
error in these calculations. Our GP-B Dewar
specialists, who modeled the Dewar's life cycle
and have been tracking its performance, have
purposely remained conservative in their
longevity estimates of the helium, so as to
ensure that there would be enough helium to
perform the most important calibration tests.
Following the initial tests, we have been working
our way through a prioritized list of further
tests that will be beneficial in analyzing the
science data. As long as the helium continues to
flow, we will continue working our way through
this list. The consensus here is that the helium
will very likely run out by the beginning of next
week. But, if it lasts longer, we will simply
continue performing these tests.
When the helium actually does run out, we will
post a notice on our Web site and send out a
message to the subscribers of our GP-B Update
email list. NASA will also issue a news release,
and we will then post the content of that release
on our Web site and send it to our email
subscribers. Stay tunedS.
===================
=============================
Our GP-B Web site,
Visual tour of the GP-B spacecraft and payload
PDF file containing a 1/20 scale, paper model of
NASA's Marshall Space Flight Center also has a
Photo, taken through a telescope by Swiss physics
The Harvard-Smithsonian Center for Astrophysics
In addition, you'll find information in the Guide
Track the GP-B satellite on the Web using NASA's
The Einstein Exhibition at the Skirball Cultural
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PREVIOUS GP-B UPDATES
===================
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
OTHER LINKS THAT MAY INTEREST YOU
=============================
<http://einstein.stanford.edu>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.
from our GP-B Web site:
<http://einstein.stanford.edu/content/vehicle_tour/index.html>http://einstein.stanford.edu/content/vehicle_tour/index.html
the GP-B spacecraft that you can download print
out, and assemble:
<http://einstein.stanford.edu/content/paper_model>http://einstein.stanford.edu/content/paper_model
series of Web pages devoted to GP-B:
<http://www.gravityprobeb.com>http://www.gravityprobeb.com
teacher and amateur astronomer Stefano Sposetti,
of GP-B spacecraft in orbit, passing near IM
Pegasi:
<http://aida.astronomie.info/sposetti>http://aida.astronomie.info/sposetti
(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/>http://www.yorku.ca/bartel/guidestar/
Star FAQ on our Web site:
<http://einstein.stanford.edu/content/faqs/faqs.html#guidestar>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>http://einstein.stanford.edu/highlights/GP-B_Launch_Companion.pdf
Java-based J-Pass satellite tracking application
at:
<http://science.nasa.gov/realtime/JPass/>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>http://www.bigfattail.com
Center in Los Angeles has closed.However, you can
visit the American Museum of Natural History's
virtual Einstein exhibit on the Web at:
<http://www.skirball.org/exhibit/amnh_frame.html>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