Lyapunov-based Spacecraft Rendezvous Maneuvers using Differential Drag

Abstract

This work presents a Lyapunov-based control strategy to perform spacecraft rendezvous maneuvers exploiting differential drag forces. The differential drag is a virtually propellantfree alternative to thrusters for generating control forces at low Earth orbits, by varying the aerodynamic drag experienced by different spacecraft, thus generating differential accelerations between the vehicles. The variation in the drag can be induced, for example, by closing or opening flat panels attached to the spacecraft, hence effectively modifying their cross- sectional area. In a first approximation, the relative control forces can be assumed to be of bang-off-bang nature. The proposed approach controls the nonlinear dynamics of spacecraft relative motion using differential drag on-off control, and by introducing a linear model. A control law, designed using Lyapunov principles, forces the spacecraft to track the given guidance. The interest towards this methodology comes from the decisive role that efficient and autonomous spacecraft rendezvous maneuvering will have in future space missions. In order to increase the efficiency and economic viability of such maneuvers, propellant consumption must be optimized. Employing the differential drag based methodology allows for virtually propellant-free control of the relative orbits, since the motion of the panels can be powered by solar energy. The results here presented represent a breakthrough with respect to previous achievements in differential drag based rendezvous.