Calibration of the Gravity Probe B Scientific Instrument Prior to Launch

Details Calibration of the Gravity Probe B Scientific Instrument Prior to Launch Calibration of the Gravity Probe B Scientific Instrument Prior to Launch

Apr 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..aprs12006k&link_type=abstract

American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As

Astronomy and Astrophysics

Astrophysics

Scientific paper

The Gravity Probe B satellite is designed to measure the precession of the local inertial reference frame in a satellite in a 640 km polar orbit relative to a distant inertial reference frame defined by extragalactic reference sources. The General Theory of Relativity predicts that the spin axis of a perfect gyroscope in this reference frame will precess 6.6 arc sec/year about a direction perpendicular to the plane of the orbit and 0.042 arc sec/year about a direction parallel to the direction of the earth's rotation axis. Measurement of these two precession rates to an accuracy of better than 0.0005 arc sec/year will not only confirm the existence of these two effects but will also provide the most accurate non-null experimental test of General Relativity. The Gravity Probe B cryogenic scientific instrument consists of four electrostatically supported gyroscopes with superconducting readouts housed in a quartz block, which is bonded to a telescope that measures the direction to the reference star, HR 8703. The gyroscope and telescope electronic readout systems, as well as the gyroscope electrostatic suspension systems, operate at the ambient satellite temperature and are mounted close to the warm end of the cyrogenic probe but within a passive shield. This talk summarizes the work that has been done to calibrate the scientific instrument and the electronic readout systems. The mechanical properties of the gyroscopes, the optical properties of the telescope, the thermal sensitivity of the readout systems, and the sensitivity of the readout systems to energetic particles and the earth's magnetic field have all been measured. The timing of the measured gyroscope and telescope readout signals and the sensors to measure the on-board environment, relative to one another and also relative to UTC time, has also been measured. These measurements, when combined with the anticipated on-orbit environment, demonstrate that the drift rate of each gyroscopes due to classical torques will be less than 0.10 milli-arc-sec/year and that the systematic errors in the gyroscope and telescope readout systems will be less than 0.15 milli-arc-sec/year. When combined with the measured on-orbit environment, they may also permit a modest improvement in the overall accuracy of the experiment.

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