Fuel-Optimal, Power-Limited Rendezvous with Variable Thruster Efficiency

The problem of minimum-fuel, time-fixed, three-dimensional rendezvous for a solar electric propulsion spacecraft discussed. The problem is solved via an indirect approach. The formulation takes into account both a bounded specific impulse and a variable thruster efficiency and permits us to manage solutions with coast . The thruster efficiency is assumed to vary with the specific impulse through a polynomial approximation. The specific impulse control law is found to depend on the instantaneous values of the primer vector modulus, the spacecraft mass, the mass costate, and the thruster model. Optimal interplanetary trajectories toward Mars are discussed. It is shown that the inclusion of a variable efficiency thruster model has important effects on fuel . In particular, the classic constant efficiency thruster model overestimates the final spacecraft mass.