Optimal Radially Accelerated Interplanetary Trajectories

Interplanetary trajectories for a propulsion system providing a continuous outward radial thrust that varies according to the inverse square of heliocentric distance are investigated. This type of radial acceleration regime is realized by sun-facing solar sails and minimagnetospheric plasma propulsion, which allow the acceleration magnitude to be modulated in flight. Formulating the interplanetary trajectories as an optimal control problem, the escape from the solar system is studied, considering the maximization of the terminal orbital energy, while conserving the orbital angular momentum. The achievable hyperbolic excess velocity is studied in terms of the available maximum radial acceleration and the transfer angle. The inclusion of the Earth gravity assist for the escape from the solar system is shown to provide a more efficient means of achieving escape at the expense of flight time. Transfer between circular orbits is similarly realized by a combination of radial acceleration propulsion and planetary gravity assist, in which the radial acceleration acts as a control of the orbital energy and the planetary gravity assist acts as a control of the angular momentum.