| Date: | 2004-04-10 08:18:00 | |
| Sender: | Mike Pearlman <Carey Noll <noll@cddisa.gsfc.nasa.gov>> | |
| Subject: | [SLR-Mail] No. 1204: GP-B | |
| Author: | Mike Pearlman | |
| Content: | ******************************************************************************** SLR Electronic Mail 2004-04-10 08:18:00 UTC Message No. 1204 ******************************************************************************** Author: Mike Pearlman Subject: GP-B Dear Colleagues: The Gravity Probe B (GP-B) Satellite is now scheduled for launch on April 19. The satellite will have laser retroreflectors and we anticipate that SLR tracking will begin approximately 5-6 weeks after launch when maneuvring has been completed. The ILRS Governing Board approved the Mission Support request approximately four years ago when the launch was scheduled for late 2001. The mission is scheduled to last for 16 months. GP-B is the relativity gyroscope experiment developed by NASA and Stanford University to test two extraordinary, unverified predictions of Albert Einstein´s general theory of relativity. The experiment relies on very accurate knowledge of the spacecraft position and orientation. SLR is one of several techniques that will be used to achieve and maintain that accuracy. The experiment will check, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting at 642 km altitude directly over the poles. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are warped by the presence of the Earth, and, more profoundly, how the Earth´s rotation drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe. A explanation of the experiment and some of the major subsystems are given at the GP-B website at: http://einstein.stanford.edu/content/story_of_gpb/gpbsty1.html GP-B will be pointed at all times toward a guide star ( IM Pegasus) which is at Right Ascension 343 deg. and Declination 16 deg. The GP- B orbit plane will be exactly aligned with IM Pegasus. The retroreflectors form a ring on the backend of the spacecraft exactly on the center line, pointing exactly in the opposite direction of the star. SLR tracking can only be done for short intervals when the station is on the same side of the Earth as the Pegasus IM. Once tracking is to begin, stations will be supplied with regular predictions and a viewing schedule. Please give this mission your full support. This mission has been in planning for several decades awaiting the development of sufficient technology to make it happen. It is a very exciting mission. Best regards, Mike Pearlman Dr. Michael R. Pearlman Harvard-Smithsonian Center for Astrophysics 60 Garden St. Cambridge MA 02138 tel. (617) 495-7481 fax. (617) 496-0121 e-mail. mpearlman@cfa.harvard.edu From: Carey Noll ******************************************************************************** |