Innovative Gyroless Attitude Estimation Method

Abstract: A key aspect in Attitude and Orbital Control Systems (AOCS) is the ability to estimateaccurately a spacecraft’s attitude and angular rate. While a classic gyrometer and star-trackerhybridization features high performances, gyroless solutions using only star-trackers as attitudesensors are often chosen to reduce the mission’s cost, when possible. Such an estimation is improvedusing the knowledge of the torque commanded by the spacecraft’s reaction wheels. The torqueestimate is however imperfect, mostly due to friction occurring on the wheels’ shafts. This paperpresents the research undertaken to improve this knowledge by adding a secondary torqueestimator to an existing gyroless estimator. An additional filter is developed for that matter, tuned,and the global AOCS performance is tested in diverse operating conditions to assess the newmethod’s benefits. While converged state performances are not improved, this solution is shown tomake the estimator more robust to friction torque spikes occurring on some reaction wheels, and toimprove settling performances after spacecraft manoeuvers.