Gravity Probe B. or GPB. was a mission designed to test two predictions of Einstein's general theory of relativity.
GPB. containing the world's most precise gyroscopes. spent 17 months collecting data while in orbit around the Earth.
Unlike most NASA science missions that seek to make new observational discoveries. GPB was conducted to verify
fundamental assumptions in physics. which have implications for all of space exploration.
The GPB spacecraft launched from Vandenberg Air Force Base. California.
atop a Boeing Delta II rocket at 9:57 a.m. Pacific Time on April 20. 2004.
The solar arrays deployed on schedule. and the Boeing Delta II launch vehicle second stage released the spacecraft
in a circular polar orbit so precise. that no orbit trim or correction was required.
Scientists have analyzed the data since October 2005. and expect to report findings in 2011.
After completing operations. Gravity Probe B was successfully decommissioned on Dec. 8. 2010.
The spacecraft will continue to circle the Earth in a polar orbit at an altitude of 400 miles.