A geometric approach to near-optimal feedback attitude slewing with directional and actuation constraints

Timely and precise spacecraft reorientation maneuvers are often required, in a variety of mission scenarios. Some of them include specific directional constraints, e.g. the need to avoid bright sources that would damage the optical instrumentation of orbiting telescopes. This research is concerned with feedback attitude control aimed at fast slewing maneuvers. An original, iterative geometric approach is proposed for the real-time feedback control of the attitude maneuver of interest, based on two steps: (i) identification of the minimum-length arc that connects the two points associated with the initial and final pointing direction, with avoidance of forbidden regions, followed by (ii) dynamic time mapping of attitude kinematics along the minimum-length arc. Two different saturation options are considered, corresponding to constraining either the torque magnitude or the torque components. With the intent of identifying the limiting performance of the feedback attitude scheme at hand, an effective (open-loop) direct optimization technique is developed and applied, to determine minimum-time solutions in different scenarios, while assuming ideal actuation. Feedback control is shown to lead to a very limited performance penalty in comparison to the respective (open-loop) minimum-time maneuver. Moreover, two more complex mission scenarios are considered, while modeling actuation through momentum exchange devices, i.e. (a) slewing of a space telescope and (b) agile slewing of a low Earth orbit satellite. The numerical results point out that the geometric feedback technique proposed in this research is both effective and precise in getting the final pointing direction, while satisfying the conic constraints related to forbidden directions. • Spacecraft attitude reorientation with actuation and directional constraints is addressed • Minimum-time reorientation maneuvers are found through direct collocation • A new near-optimal feedback algorithm is introduced, based on two main steps • Near-optimal feedback reorientation is compared to the minimum-time solution • Two scenarios are considered: (a) space telescope and (b) agile LEO satellite