Tradeoff Performance of Hybrid Low-Thrust Propulsion System

The employment of low-thrust propulsion systems is an attractive option for space missions requiring large changes in orbital energy. Therefore in this paper, we investigate the performance of a hybrid low-thrust propulsion system, constituted by a solar electric thruster coupled with a solar sail. Loosely speaking, the solar sail may be seen as a propellantless auxiliary system capable of reducing the gravitational force acting on the spacecraft in such a way that the propellant expense for a given mission may be decreased. To quantify this effect, we analyze the problem in terms of optimization of a scalar performance index that takes into account both the mission time and the propellant mass required to reach the target orbit. A weighting parameter is used to trade between these two con flicting requirements. The problem is solved using an indirect approach and the resulting optimal control law is applied to a circle-to-circle rendezvous transfer. Key features of the paper are the use of realistic models for both the solar electric thruster and the solar sail.