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The Gravity Probe B spacecraft, developed, integrated, and tested by Lockheed Missiles & Space Company and later Lockheed Martin Corporation, consisted of structures, mechanisms, command and data handling, attitude and translation control, electrical power, thermal control, flight software, and communications. When integrated with the payload elements, the integrated system became the space vehicle. Key requirements shaping the design of the spacecraft were: (1) the tight mission timeline (17 months, 9 days of on-orbit operation), (2) precise attitude and translational control, (3) thermal protection of science hardware, (4) minimizing aerodynamic, magnetic, and eddy current effects, and (5) the need to provide a robust, low risk spacecraft. The spacecraft met all mission requirements, as demonstrated by dewar lifetime meeting specification, positive power and thermal margins, precision attitude control and drag-free performance, reliable communications, and the collection of more than 97% of the available science data.

Gravity Probe-B (GP-B) is a space mission that was launched in April 2004 that is intended to measure the prediction by General Relativity Theory that a rotating gravitational field, namely the Earth's, "drags" the space-time continuum by a definite amount. GP-B utilizes a telescope with silicon photodiode detectors. Light from a distant reference frame, namely, a star designated as IM Peg, is used to reference the orbital motion of the spacecraft about the Earth and Sun to within 200 milliarcseconds at a frequency of 10 Hz. Fine angular control of the spacecraft orientation uses the signals from the telescope detectors during the 55 minute portion of the orbit during which the star is visible. The performance of the detectors and the control system's resultant pointing are discussed.