Autonomous gyro scale factor and misalignment calibration

A method of estimating the attitude of a spacecraft, the method comprising the steps of:

• receiving inertial information from three inertial sensors;
• correcting the inertial information using a first time varying matrix having corrective data associated with scale factor and misalignment errors in the inertial information computed by a digital filter;
• propagating a three axis attitude using the corrected inertial information to produce a propagated attitude estimate;
• and
• correcting the propagated attitude estimate for attitude errors to produce a final output attitude estimate, the correction being made using a second time varying matrix computed by the digital filter.

A system for estimating the attitude of a spacecraft comprising:

• a first sensor that acquires three axis inertial data;
• a second sensor that acquires star position data;
• a first processor that processes the three axis inertial data to produce a first estimate of spacecraft attitude;
• a second processor that processes the star position data to produce a second estimate of spacecraft attitude;
• a digital filter that compares the first and second estimates of spacecraft attitude, and therefrom produces at least a first time varying matrix having corrective data associated with scale factor and misalignment errors in the three axis inertial data;
• and
• the first processor further adapted to apply the corrective data to the first estimate of spacecraft attitude.