Feasible Trajectory Generation for Underactuated Spacecraft Using Differential Flatness

We consider the problem of feasible trajectory generation of an underactuated axi-symmetric spacecraft subject to two external torques acting on the plane normal to the symmetry axis. We derive the condition that must be satissed by an attitude history in order to be a feasible trajectory. W e then propose a methodology to generate trajectories satisfying this condition. Our approach makes use of the well-known atness of the corresponding diierential equations. We emphasize the importance of being able to generate these trajectories on-line and with minimal oo-line intervention. Feasible trajectories can later be used as reference trajectories for tracking problems for underactuated spacecraft.