Title:

Gravity Probe B: Testing General Relativity
N. Jeremy Kasdin
W. W. Hansen Experimental Physics Laboratory, Stanford University

Abstract:

Gravity Probe B (GP-B) is a NASA experiment to test Einstein's General Theory of Relativity. In 1959, Leonard Schiff of the Stanford Physics Department predicted, using General Relativity, that a local, free-falling inertial frame would undergo two orthogonal rotations, the geodetic and frame-dragging, with respect to the universe's inertial (fixed) frame. These drifts are not predicted by Newton's gravity theory. Schiff proposed that the drifts be measured by orbiting near perfect gyroscopes and comparing their spin-axis directions (fixed in the local, free-falling frame) with a distant inertial reference provided by pointing an onboard telescope at a fixed guide star.

GP-B is the culmination of the proposed experiment. Scheduled to be launched in March 2000, GP-B consists of four superconducting, electrostatically suspended gyroscopes housed in a block of fused quartz that is optically contacted to a quartz telescope used for the inertial reference. In order to obtain an uncorrupted measurement of the relativistic effects, it is necessary to free the gyroscope's quartz rotors from all inertially fixed forces and torques, thus reducing the Newtonian drift below the experiment accuracy goal of 0.1 marcsec/year. The talk will describe the various instruments and satellite technologies developed to achieve this unprecedented level of measurement accuracy. As well, a few of the many spin-offs of the GP-B program will be discussed, including a novel method for automatically landing airplanes with the global positioning system.