Magnetorquer-Only Attitude Control of Small Satellites using Trajectory Optimization

Abstract

This paper presents a magnetorquer-only attitude control technique that utilizes trajectory optimization methods to circumvent the underactuated nature of satellite magnetic field interactions. Given a known orbit and desired attitude state, the method utilizes a nonlinear dynamics model and a fast constrained trajectory optimization solver based on differential dynamic programming to arrive at a nominal torque profile that respects the spacecraft’s actuator limitations. This nominal maneuver is then tracked using a time-varying linear-quadratic regulator (LQR). To demonstrate the effectiveness and robustness of the proposed control technique, closed-loop Monte-Carlo simulations are performed from a variety of orbits and initial conditions. Our method is shown to significantly outperform previous magnetorquer-only control schemes by offering convergence from large initial errors and fast slew rates that exploit the full performance capabilities of the actuators. Computational complexity of the method and future implementation in flight software onboard a CubeSat are also discussed.