Gravity Probe B – Testing Einstein at the Limits of Engineering

The Gravity Probe B experiment was developed to test two predictions of General Relativity; the Geodetic and the frame-dragging precessions of a mechanical gyroscope due to the gravitational field of the Earth. This space-based, cryogenic experiment was carried into orbit on 20 April 2004 atop a Boeing Delta II rocket. On-orbit operations consisted of 4.3 months of experiment setup, 11.6 months of science data collection, and 1.4 months of post-science calibrations. Analysis of the science data is now in progress, scheduled to complete in 2007.