Sliding mode control using modified Rodrigues parameters

Introduction Spacecraft pointing poses a complex problem involving nonlinear dynamics with either linear and/or nonlinear control laws. Primary control actuators usually include thrusters for rapid and coarse attitude maneuvers, and reaction wheels for slow and precise attitude maneuvers. Other types of control mechanisms include gravity-gradient stabilization and magnetic torquer assemblies. Control algorithms can be divided into open-loop systems and closed-loop (feedback) systems. Open-loop systems usually require a pre-determined pointing maneuver, and are typically determined using optimal control techniques which involve the solution of a twopoint-boundary-problem. An example of open-loop control is the time-optimal attitude maneuver (e.g., see the excellent survey paper by Scrivener and Thompson 1). Closed-loop systems can provide robustness with respect to spacecraft modeling uncertainties and unexpected disturbances.