A study on station-keeping over irregularly shaped asteroids with different sized solar sails
Asteroid reconnaissance missions offer great contributions to a better understanding of the origins of our Solar System and planetary defense from hazardous objects. The employment of solar sails enable a greater number of missions and target asteroids, given it is a cheaper propulsion method. However, modeling the dynamics of solar sails orbiting irregular gravitational fields is a challenge. And since asteroids have a wide variety of shapes and sizes, it is important to make use of a robust optimization method that allows fast adjustments to this dynamics. This study examines the use of different solar sails and asteroid sizes for station-keeping a spacecraft orbiting an irregularly shaped asteroid. To achieve this goal, a rational agent was developed to act as an attitude guidance system. It calculates the necessary sail orientation to keep the spacecraft near its initial orbit. The agent uses a direct optimization strategy based on a decision tree algorithm in order to account for a solar sail with non-ideal reflective properties and the non-uniform gravitational field of the asteroid. By testing multiple sail sizes, this study evaluates how long the agent may maintain the same sail orientation while still being successful at its station keeping mission. This analysis is done for different asteroid sizes and a relation between different sail and asteroid sizes is established. Results reveal a relation between sail and asteroid sizes and the attitude change frequency. Smaller sails can sustain station-keeping with fewer attitude changes. However, they are not able to achieve this goal on larger asteroids. For sufficiently small asteroids, sails smaller than those used on recent missions may be more appropriate for station-keeping. These findings suggest that current solar sail technology is already capable of enabling successful asteroid reconnaissance missions.