Abstract: To satisfy the requirement of long-term on-orbit displaced spacecraft for specific tasks, a hybrid propulsion technology, consisting of solar electric propulsion (SEP) and solar sail, was studied for the displaced geostationary orbit. The relation between the sail attitude angles and the SEP acceleration for hybrid propulsion system was firstly deduced. A single variable extremum problem obtained from the first-order optimality condition was solved to minimize the SEP acceleration and acquire the control law of solar sail attitude angles. Numerical simulations show that the hybrid propulsion approach can save about 57% of fuel consumption per year compared with the SEP method. The hybrid propulsion approach achieves the goal of improving the lifetime of spacecraft and meets the requirements of the displaced geostationary orbits.

Key words: Displaced orbits, Hybrid propulsion strategy, Trajectory optimization, Solar electric propulsion, Solar sail