Hi,
Here is the GP-B Mission report:
#--------------------------------------
==============================================
GRAVITY PROBE B MISSION UPDATE FOR 18 FEBRUARY 2005
==============================================
GP-B STATUS AT A GLANCE
====================
Mission Elapsed Time: 304 days (43 weeks/10.0 months)
Science Data Collection: 175 days (25 weeks/5.75 months)
Current Orbit #: 4,486 as of 2:00PM 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 98.6%
Attitude & Translation Control (ATC): X-axis attitude error: 173.2 marcs rms
Y-axis attitude error: 264.0 marcs rms
Command & Data Handling (CDH): Multi-bit errors (MBE): 0
Single-bit errors (SBE): 4,704 (daily avg.)
Telescope Readout (TRE): Nominal
SQUID Readouts (SRE): Nominal
Gyro #1 rotor potential: -2.7 mV
Gyro #2 rotor potential: +6.1 mV
Gyro #4 rotor potential: -7.8 mV
Gyro #3 Drag-free Status: Backup Drag-free mode (normal)
MISSION DIRECTOR'S SUMMARY
========================
As of Mission Day 304, the Gravity Probe B vehicle and payload are in good health, with all systems functioning nominally and more than five months of science data collected. All four gyros are digitally suspended in science mode and the spacecraft is flying drag-free around Gyro #3.
This past week was again a relatively quiet one for GP-B. Solar flare activity is low, and solar radiation levels are normal.
Guide star capture times (time required to re-lock the telescope onto the guide star as the spacecraft emerges from behind the Earth each orbit) are averaging approximately one minute, which is excellent.
The brightness table was updated for two of the stars that are monitored by the spacecraft's star trackers, and this significantly improved the star tracker's performance. Brightness tables for other stars in the star tracker catalog will be updated next week.
Mission News -- Heat Pulse Meter Test in Progress
====================================
During this time of year for our orbit, the front end of the spacecraft is pointed towards the sun, warming the Forward Equipment Enclosure (FEE) slightly more than our models had predicted. Thus, for the past few weeks, the flow rate of the helium escaping from the Dewar has been slightly higher than anticipated, which may slightly reduce the length of the mission. When the Dewar has only 3-5 weeks of helium remaining, we will conclude the science phase and begin our instrument re-calibration, and this requires at least 3 weeks.
To determine how much helium is currently left in the Dewar, the GP-B Dewar team is in the process of performing another heat pulse meter operation. The heat pulse test works in the following way: The amount of heat that it takes to warm an object by a specified amount depends on the type of material, its temperature, and its mass. Thus, if the "specific heat" (the amount of heat needed to warm a kilogram of material by one degree kelvin) is known, it is a simple matter to measure the mass by applying a known amount of heat (usually with an electric heater) and measuring the resultant temperature rise. In the case of the GP-B Dewar, the situation is simplified by the fact that heat distributes itself virtually instantaneously throughout superfluid helium. The amount of heat used in the test must be large enough to cause a measurable temperature change (approximately 10 millikelvin) but not so large as to appreciably shorten the mission lifetime.
The Dewar team expects to complete their analysis of the heat pulse data next week, and we will report the results in next week's update. Our current expectation is that the science phase of the mission will conclude towards the end of June, and the results of the heat pulse meter operation will help us determine whether or not the current mission time line is correct.
================================================
CORRECTIONS AND CLARIFICATIONS TO LAST WEEK'S HIGHLIGHTS
================================================
Last week's highlights included a few errors, such as my inadvertent reversing the IM Pegasi minimum and maximum magnitude values. (Star magnitude is an inverse scale, so for IM Pegasi, minimum light=6.0; maximum light=5.7).
Also, based on feedback I received this week from our GP-B colleagues at the Harvard-Smithsonian Center for Astrophysics (Cambridge) and York University (Toronto), I have revised some of the information in last week's highlights to improve both its accuracy and its clarity. You can view these revisions on our GP-B Web site,
http://einstein.stanford.edu, by scrolling to the bottom of this week's Web highlights and clicking the "Previous Highlights" link or by choosing February 11, 2005 in the chronological highlights archive on our Web site (see below).
===================
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
=============================
OTHER LINKS THAT MAY INTEREST YOU
=============================
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.htmlPDF 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.
==========================
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.
To subscribe to this list, 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 (not in the Subject line.)
--
**********************************
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
**********************************
#-------------------------------------------
Regards,
LelandJ
