Generation of Optimal Trajectories for Earth Hybrid Pole Sitters

摘要

A pole-sitter orbit is a closed path that is constantly above one of the Earth's poles by means of continuous low thrust. This work proposes to hybridize solar sail propulsion and solar electric propulsion on the same spacecraft to enable such a pole-sitter orbit. Locally optimal control laws are found with a semianalytical inverse method, starting from a trajectory that satisfies the pole-sitter condition in the sun-Earth circular restricted three-body problem. These solutions are subsequently used as a first guess to find optimal orbits, using a direct method based on pseudospectral transcription. The orbital dynamics of both the pure solar electric propulsion case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions, a hybrid pole sitter, based on midterm technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure solar electric propulsion spacecraft.