ESA GNC Conference Papers Repository

The Attitude and Orbit Control System (AOCS) software is at the heart of the intelligence of the PROBA-1 and PROBA-2 spacecraft and is crucial to their high level of on-board autonomy. Following the success of these two missions, the microsatellite PROBA-V, for PROBA-Vegetation, was successfully launched in May 2013 to start its mission on the study of the Earth’s vegetation. The PROBA-V AOCS software includes several novelties compared to PROBA-1 and PROBA-2 among which is a novel technique for the autonomous avoidance of forbidden directions during large-angle manoeuvres. The objective of this technique is to prevent, during autonomous large-angle manoeuvres, the pointing of the sensitive elements of the payload instruments in directions (e.g. the Sun, the Moon) that might blind or destroy them. At the same time, in order to maintain the operability of the AOCS, the manoeuvres must also avoid trajectories that would result in the blinding of sensors (e.g. star sensors) by celestial objects (Earth, Sun). Methods for forbidden attitude avoidance based on the potential function have been presented by McInnes [10] in the past. The innovation presented here extends this method to enable the simultaneous avoidance of forbidden directions for two sensitive lines of sight instead of only one. In addition, instead of the controller proposed in [10], the algorithm presented here is based on the PROBA-1 and PROBA-2 sliding-mode controller. The basic concept for this algorithm was introduced in previous papers [8][9]. The present paper first provides an overview of the PROBA-V AOCS software nominal operation flight results. Then, the implementation of the forbidden attitude avoidance algorithm as an experiment on-board the PROBA-V AOCS software and the results of its in-flight demonstration are presented.