Solution of a Hard Flight Path Optimization Problem by Different Optimization Codes

Solar electric propulsion is the key technology to reduce propellant consumption for interplanetary missions. A number of studies of interplanetary and lunar missions are currently performed by the European Space Agency (ESA), which exploit the benefits of solar electric propulsion (e.g., [11,8]). Although solar electric propulsion has the disadvantage of low-thrust levels the high specific impulse leads to considerable reduction of propellant mass and therefore to an increase in payload mass. Trajectory optimization problems with solar electric propulsion are known to be extremly difficult (e.g., [3]). They have in the past been successfully solved by indirect methods while direct methods usually failed. Nevertheless the sophistication of direct solution methods has also permanently increasedThe interesting question is: Can low-thrust missions be solved today by direct methods? How precise are these solutions compared with an indirect solution? What time and requirements does it take for a successful solution?A detailed numerical comparison of the direct solution code NUDOCCCS (Büskens [11]) and the indirect multiple shooting code MUMUS (Hiltmann [7]) is presented for a reference problem (a low thrust orbital transfer problem of a LISA spacecraft with constraints on the solar aspect angle) from [11]