The Gravity Probe B Data Analysis Filtering Approach

A simple pre-flight strategy of the Gravity Probe B (GP-B) data analysis has evolved in the elaborate multi-level structure after the discovery of the complex polhode motion, and of the patch effect torques. We describe a cascade of estimators (filters) that reduce the science data (SQUID and telescope signals) to the estimates of the relativistic drift rates. Those estimators, structured in two "floors", are based on the polhode-related models for the readout scale factor and patch effect torque. Results of the 1(st) Floor processing-gyro orientation profiles-manifest clearly the strong geodetic effect but also the presence of classical torque. Modeling of the patch effect torque at the 2(nd) Floor provides a successful compensation of the torque contributions, and leads to consistent estimates of the relativistic drift rates.