Patent ID: 7451022

Claim:
A method for calibration of an attitude reference apparatus, said method comprising the steps of: providing an inertial navigation system for a surface ship, which navigation system provides local reference of the ship's attitude relative to East, North, and UP; providing a star tracker mounted on a platform stabilized by said local reference of the ship's attitude, said star tracker being for comparing the azimuth and elevation angles between the line-of-sight of said star tracker and each of two selected stars, to thereby generate first and second azimuth and elevation differences; controlling said line-of-sight of said star tracker in response to ephemeris of said two selected stars; processing said azimuth and elevation angles to determine first and second vector triads representing ephemeris and the navigation system attitude; processing said first and second triads to determine a coordinate transformation matrix; separating said coordinate transformation matrix into systematic error and reference attitude error; and combining the reference attitude error with the navigation system attitude to generate calibrated navigation system attitude.