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Gravity Probe B mission
Everitt, Francis Gravity Probe B Project, W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, California.
- Why perform another test of Einstein's theory?
- Experimental design
- Extraordinary technologies
- GP-B flight mission
- Data analysis and preliminary results
- The broader legacy of GP-B
- Related Primary Literature
- Additional Reading
Gravity Probe B (GP-B) is a landmark fundamental physics experiment in space to test Einstein's 1916 general theory of relativity. GP-B uses four spherical gyroscopes and a telescope, housed in a satellite orbiting 642 km (400 mi) above the Earth, to measure, with unprecedented accuracy, two extraordinary effects predicted by the theory: the geodetic effect—the amount by which the Earth warps the local spacetime in which it resides; and the frame-dragging effect—the amount by which the rotating Earth drags spacetime around with it. GP-B tests these two effects by precisely measuring the precession (displacement angles) of the spin axes of the four gyroscopes over the course of a year relative to a distant guide star, and comparing the experimental results with the theoretical predictions. In a polar orbit, the two effects occur at right angles to one another—the geodetic effect in the plane of the spacecraft's orbit, and the frame-dragging effect in the Earth's equatorial plane (Fig. 1). Thus, each gyroscope measures both effects simultaneously.
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