A Discrete Variational Integrator for Optimal Control Problems on SO

In this paper we study a discrete variational optimal control problem for the rigid body. The cost to be minimized is the external torque applied to move the rigid body from an initial condition to a pre-specified terminal condition. Instead of discretizing the equations of motion, we use the discrete equations obtained from the discrete Lagrange–d’Alembert principle, a process that better approximates the equations of motion. Within the discrete-time setting, these two approaches are not equivalent in general. The kinematics are discretized using a natural Lie-algebraic formulation that guarantees that the flow remains on the Lie group SO(3) and its algebra so(3). We use Lagrange’s method for constrained problems in the calculus of variations to derive the discrete-time necessary conditions. We give a numerical example for a three-dimensional rigid body maneuver. A. Bloch Alexander Ziwet Collegiate Professor of Mathematics and Department Chair Department of Mathematics University of Michigan E-mail: [email protected] I. Hussein Assistant Professor Worcester Polytechnic Institute E-mail: [email protected] M. Leok Hildebrandt Research Assistant Professor Department of Mathematics University of Michigan E-mail: [email protected] A. Sanyal Postdoctoral Research Associate Mechanical and Aerospace Engineering Arizona State University E-mail: [email protected] 2 Bloch, Hussein, Leok and Sanyal