Spacecraft guidance strategies for proximity maneuvering and close approach with a tumbling object

Abstract

A six degree of freedom, 20-state model of two spacecraft rendezvous is developed, one of which was controlled and the other considered to be passively tumbling. Solutions that minimize a series of performance indices are obtained for the problem of close approach, up to the point of contact, using a direct optimal control method. The solution is then verified as optimal by way of an indirect method based on the Minimum Principle. Next, a trajectory generation method for spacecraft reorientation is developed, based on a quaternion construction of Inverse Dynamics in the Virtual Domain. This new construction enables development of an Inverse Dynamics in the Virtual Domain rapid-trajectory generation method that exploits the concept of decoupling space and time, for the problem of a spacecraft performing a close approach maneuver to a tumbling object. Finally, the advantages of the new method are demonstrated through simulated scenarios that employ two distinct concepts of closedloop feedback. The benefits seen by Inverse Dynamics in the Virtual Domain methods include the rapid computational time that allows a feasible solution to be generated, potentially onboard a spacecraft and in closed-loop. Although the Inverse Dynamics in the Virtual Domain method cannot match the true optimal solution, it has several advantages. Rapid computational time and the ability to reshape itself when provided updated state variable information reinforce the overall robustness of the method for safe trajectory planning. The novel trajectory generation method developed is tested using Monte Carlo methods to demonstrate its ability to handle realistic situations with varying initial conditions.