Gravity Probe B

 2004-014A

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The Gravity Probe B satellite was designed to carry the Stanford relativity gyroscope experiment, measuring Einsteinian gravitomagnetic 'frame dragging'.

Prime contractor is officially Stanford. The GP-B spacecraft was built by Lockheed Martin/Sunnyvale, with the special dewar constructed by Lockheed Martin/Palo Alto and the relativity experiment developed by Stanford. The mission is managed by NASA-MSFC. Launch is by Delta 7920-10. Mass of GP-B is 3145 kg (alloc 3322 kg). Probably 350 kg of He so 2805 kg dry. Size is 6.43 l 2.64 dia with 4.0? span across panels.

Orbit 639 x 659 x 90.007

GP-B will observe IM Peg (V=5).

GP-B operations:

IOC 40-60 days Science mission phase 13-16 months Calibration phase 2-3 months

The GP-B relativity mission has completed collecting science data. Its superconducting gyroscopes were held at low temperatures in a liquid helium dewar during the primary mission which began in the spring of 2004. On August 15, the satellite was switched to collect calibration data, moving its pointing from its primary target IM Peg to look at a variety of other bright stars in the final days before the helium ran out. To the suprise of the Stanford-based science team, the dewar remained cold for three weeks longer than expected, allowing extra calibrations to be done. On September 26, GP-B went back to IM Peg to collect yet more science data, but the helium finally did run out three days later, and the gyros began to spin down from 4300 revs per minute to only 120 rpm. When data analysis is complete in early 2007, the GP-B team expect to be able to determine the general relativistic rotation of local space-time caused by the Earth's rotation over the past year.

GP-B was placed in hibernation in May 2006 pending any future experiment funding.

GP-B
Date	Time	Event	Orbit
2004 Apr 20	1657:24	Launch by Delta 7920	V SLC2W
		T+1:26 SRM sep
		T+2:11 SRM 7-9 sep
		T+4:23 Stage 1 MECO
		T+4:31 Stage 1 sep
		T+4:37 SES-1
		T+4:41 Fairing sep
	1708:40	T+11:16 SECO-1	167 x 652 x 90.014
	1759:02	T+1:01:38 SES-2 17s
	1759:18	T+1:01:54 SECO-2	637 x 659 x 90.011
		T+1:07 Solar panel deloy
	1812:24	T+1:15:00 Stage 2 sep
		T+1:34 SES-3 evasive 4.8s	298 x 635 x 90.41
		T+1:42 SES-4 depletion	182 x 631 x 94.56
2004 Apr 21			97.59 641 x 645 x 90.01
2005 Sep 29		Dewar depletion, end of primary mission
2006 May		Hibernation mode, end of mission
2006 Sep		Preps for use by AF Academy from training, research
2007 May		Beginning of USAFA use
2009		GP-B returned to Stanford control
2010 Nov		GP-B dormant but operational
2010 Dec 8		Decommissioned

Payload:

• Aperture cover, hinged

• Liquid helium dewar, 2441l.

• Gyroscopes (4), 1.8K cyro

• Quartz Telescope 14cm, f = 3.81m, mirror 0.142m dia

• Electrostatic levitation ssytem

• GPS receivers, 2