Gyroless angular rate determination based on star sensor images

The knowledge of spacecrafts’ angular rate is required for attitude control and determination, generally obtained from gyros. However, gyros tend to degrade or fail in orbit and cannot be found in some small spacecraft designs. In such scenarios, there is always the need to estimate angular rate and a fully gyroless solution offers the benefit of significant cost savings combined with the advantages of a simplified AOCS architecture. The paper focuses on the problem of determining spacecraft body angular rates from star-tracker measurements only without impacting the star tracking functions and regardless of the magnitude of body angular rates and the update rate of the star tracker. The considered approach is based on the processing and comparison of consecutive images for noises filtering while allowing the continuity of star tracking function without stars identification. The angular velocity estimate is based on the Wahba problem and relies upon a differentiation approach without a spacecraft dynamics model. An Extended Kalman Filter (EKF) filters out spikes due to uncertainties in the centroids’ measurements, especially at high angular rates. The proposed algorithm is tested using a High-Fidelity Star Tracker Simulator and results obtained from simulations will be shown to assess the algorithm performances.