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Abstract

The Gravity Probe B Experiment: Data Analysis Journey

Gravity Probe B (GP-B), launched on 20 April 2004, is a landmark physics experiment that uses the world’s most precise (cryogenic) gyroscopes to test two fundamental GR predictions: the geodetic and frame-dragging effects. Data collection began in August of 2004 and science operations were completed in September of 2005. The simple pre-flight data analysis has proven to be more challenging than expected and has evolved in the elaborate multi-level structure after the discovery of the complex polhode motion and the patch effect Newtonian torques. We present a cascade of estimators (filters) that reduce the science data (SQUID and telescope signals) to the estimates of the relativistic drift rates. These filters are based on the polhode-related models for the readout scale factor and patch effect torques. Full torque modeling together with the Trapped Flux Mapping (analysis of the high frequency gyro readout information to precisely estimate the gyroscope polhode motion) provides a successful compensation of the torque contributions, and leads to consistent estimates of the relativistic drift rates.

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