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Mission Photos:

Gravity Probe B
Courtesy of Stanford University

Mission Objectives:

Gravity Probe B (GP-B) is the relativity gyroscope experiment being developed by NASA and Stanford University to test two extraordinary, unverified predictions of Albert Einstein's general theory of relativity.

The experiment will check, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting at 400-mile 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.

Mission Instrumentation:

Gravity Probe B has the following instrumentation onboard:

  • Four gyroscopes
  • Quartz telescope
  • GPS receiver
  • Retroreflector array
Mission Parameters:
Sponsor: United States
Expected Life: 1-2 years
Primary Applications: relativity experiment
Primary Applications: precision orbit determination
COSPAR ID: 0401401
SIC Code: 8603
Satellite Catalog (NORAD) Number: 28230
Launch Date: 20-Apr-2004
RRA Diameter: to be determined
RRA Shape: Hemisphere
Reflectors: 9 corner cubes
Orbit: polar
Inclination: 90
Eccentricity: 0.0014
Perigee: 650 km
Period: 48.75 min.
Weight: 3334 kg

Additional Information: