Gyroscopic calibration methods for spacecraft

Abstract

Spacecraft cost, volume and weight are reduced with gyroscope calibration methods that can be effected with structures (e.g., a single-axis Sun sensor and a wheel system) which are typically carried by spacecraft for other purposes. In a method embodiment, these methods include an initial step 1) of calibrating a selected gyroscope and subsequent steps for each uncalibrated gyroscope of: 2) slewing the spacecraft by a slew angle and controlling attitude with the uncalibrated gyroscope for a selected time period to thereby couple its drift into the inertial axis of a calibrated gyroscope, 3) backslewing the spacecraft to return the calibrated gyroscope to its inertial axis, and 4) measuring an error angle generated by the uncalibrated gyroscope during the selected time period (e.g., with a Sun sensor or with the calibrated gyroscope). In another embodiment, steps 2-4 are replaced by steps of: 5) orienting a momentum vector to inhibit spacecraft rotation about an uncalibrated gyroscope's respective axis, and 6) calibrating the uncalibrated gyroscope from its output signal. Another method embodiment retains steps 5 and 6 but replaces the initial step 1) by repeating steps 5 and 6 with a different momentum vector. Drift components are thus sensed in two different spacecraft planes and these components are mathematically resolved to find gyroscope drifts.