Optimal attitude scheduling of an imaging satellite

A new result in optimal control is applied to the scheduling of high-resolution imaging of successive ground targets from an orbiting satellite. In low-cost satellite applications, attitude control is accomplished solely through reaction wheels with no thrusting capability. To rapidly acquire a new target, the reaction wheels must be powerful or the satellite moment of inertia must be small. Design tradeoffs for the envisioned system indicate that slew time between targets is not insignificant, reducing the economic value per orbit of the mission. Solving for the optimal solution is complicated by the fact that the attitude control dynamics are nonlinear, there is limited control torque available to the reaction wheels, and there is the need to periodically dump momentum. The objective of this study is to determine time optimal control policies to slew between scheduled views. The multipoint generalization of Pontryagińs Maximum Principle, established in a nearly complete Ph.D. dissertation, is used to find the optimal attitude control policy. The generalization addresses optimizing over a given orbit, not just minimizing slew time from view to view. An example based on design characteristics of a small imaging satellite demostrates the method of solution.