Mars gravity assist to improve missions towards main-belt asteroids

An indirect optimization method is applied to find rendezvous trajectories to reach asteroids of the main belt using solar electric propulsion. Direct trajectories and missions that receive gravity assist from Man en route to the target are presented and compared in terms of final mass. Numerical results prove that missions with gravity assist surely perform better, if the trip tune exceeds five years. Faster flyby missions are superior to direct trajectories if simple guidelines concerning the asteroid's orbital parameters are used to select the target and to take the greatest benefit from the Mars gravity assist. A direct mission can be carried out with a similar performance at time intervals which correspond to the Earth/asteroid synodic period. Gravity assist missions require the correct angular phasing of the three relevant bodies and mission opportunities are less frequent, a shortcoming which is overwhelmed by the large number of potential targets. Actual mission opportunities for a rendezvous in the next decade are found and presented for a small number of interesting asteroids.