Optimal Intermediate-Thrust Arcs in a Gravitational Field

Optimal Intermediate-Thrust Arcs in a Gravitational Field. An earlier general theory of optimal rocket trajectories is extended to allow for the possibility that powered arcs, over which the motor thrust is not a maximum, may be included in the trajectory. The spiral form taken by such arcs in the field due to a single centre of inverse square law attraction is examined in detail and the question of whether a transfer between two Keplerian orbits via such a spiral can ever be more economical than a two-impulse transfer is considered but not finally resolved.