Design of trajectories for continuous polar Earth observation in the Earth-Moon system

This paper investigates orbits and transfer trajectories for continuous polar Earth observation in the Earth-Moon system. The motivation behind this work is to complement the services offered by polar-orbiting spacecraft, which offer high resolution imaging but poor temporal resolution, due to the fact that they can only capture one narrow swath at each polar passage. Conversely, a platform for high-temporal resolution imaging can enable a number of applications, from accurate polar weather forecasting to Aurora study, as well as direct-link telecommunications with high-latitude regions. Such a platform would complement polar orbiters. In this work, we make use of resonant gravity swing-by manoeuvres at the Moon in order to design trajectories that are suitable for quasi-continuous polar observation. In particular, it is shown that the Moon can flip the line of apsides of a highly eccentric, highly inclined orbit from north to south, without the need for thrust. In this way, a spacecraft can alternatively hover for an extended period of time above the two poles. In addition, at the lunar encounter it is possible to change the period of time spent on each pole. In addition, we also show that the lunar swing-by can be exploited for transfer to a so-called pole-sitter orbit, i.e. a spacecraft that constantly hovers above one of the Earth’s poles. It is shown that, by using the Moon’s gravity to change the inclination of the transfer trajectory, the total Δv is less than using a trajectory solely relying on high-thrust or low-thrust, therefore enabling the launchers to inject more mass into the target pole-sitter position.