Controllability of solar-sail orbits in the Earth-Moon system

Abstract

The propellantless nature of solar-sail propulsion allows researchers to design completely new sets of orbits unreachable or not-maintainable by means of conventional propulsion. The advantage of this somewhat new type of low-thrust propulsion system becomes more evident for long-duration missions where chemical or electrical rocket engines would run out of onboard reaction mass. Solar sails happen to be particularly well-suited for polar observation missions. One can find several works concerning solar-sail orbits to establish a permanent communication link between a settlement on the lunar South Pole and the Earth. In addition, the literature also encourages the usage of solar sails to monitor the melting of the polar ice caps. However, these solutions employ either complicated steering laws or more than one sailcraft. In addition, little is known about how to perform necessary station-keeping maneuvers to keep the sailcraft bounded to the reference orbits under the effect of dynamic perturbations.

This thesis focuses on the orbit control of three types of solar-sail periodic orbits within the Earth-Moon system that have been shown potential for polar observation of either body. One of these orbit types, coined the distant-circular family, is newly introduced in this thesis together with transfers
between orbits within the family; its remote orbits can achieve continuous coverage of both the Earth's North Pole and the lunar South Pole with just a single sailcraft. Developed mainly under the simplified, but non-autonomous, dynamics of the solar-sail circular restricted three-body problem, the studied orbits are all unstable and require an active control strategy for station-keeping. By slowly migrating the dynamics to a higher fidelity model, we introduce several disturbances, namely those associated with the eccentricity of the Moon's orbit, the plane offset between the ecliptic and the Earth-Moon orbital plane, the Sun's gravity, and the heliocentric eccentricity of the system's barycenter. Two solar-sail architectures, a fixed-shape and heliogyro sails, are compared with respect to the objective of tracking the ideal reference orbits that all use a simple Sun-sail steering law as reference control. To do so, we develop a methodology based on multiple shooting differential correction, weighted least squares, particle swarm optimization (quantitative analysis) and acceleration bubble visualisation (qualitative analysis).

We find that the effect of the eccentricity of the Moon's orbit is too large to be considered a perturbation and should be included in the design of the reference orbits. Then, we show that other perturbations can be completely counteracted by the heliogyro, which suggests that pure solar-sail quasi-periodic orbits are maintainable.