Optimal Trajectory Design for SIMONE Mission Study

This paper deals with the trajectory optimization, through a direct method, for the SIMONE mission study. The mission consists of six identical microsatellites, each targeting a rendezvous with a different type of NEO using low-thrust propulsion both for deep space navigation and for Earth escape phase, departing from an Earth orbit. The direct method used consists of a transcription using polynomial base functions in which trajectory and control laws are reduced to a finite set of unknown states and controls, then a parametric optimization is carried out on these unknowns with an NLP technique. Finally, the optimal trajectory is recovered from these unknown states and controls by a polynomial interpolation. The mission has been conceptually divided in two segments inside the Earth sphere of influence, dealing with the perigee rising and with the escape from Earth gravity field through a Moon gravity assist, and an interplanetary segment, dealing with the transfer to each of the six selected targets. Two different cases were analyzed for each trajectory, one which considers the engine characteristics fixed for the entire mission, and the second which instead considers maximum thrust level and specific impulse dependent on the distance from Sun.