Satellite Attitude Estimation with Measurements Available at Random Points in Time.

The state, measurement model, and linear filter for estimating the three small rotation angles between the measured attitude of a spacecraft and the actual attitude of the spacecraft are developed. The measured spacecraft and actual spacecraft have different attitudes due to gyro errors. The measurements available for the small angle estimation are voltage pip time caused by star images crossing slits on the reticles of star sensors rigidly mounted to the spacecraft body. Attitude measurements are generated by comparing one component of the catalogued star vector in the actual spacecraft frame with the same component in the measured spacecraft frame. The pip times for each slit are modeled as a Poisson counting process. This assumption leads to derivation of a suboptimal filter using a gain that is independent of the pip arrival time sequence. Author