Multi-body mission design in the Saturnian system with emphasis on Enceladus accessibility

摘要

Recent discoveries regarding Saturn’s moon, Enceladus, have transformed the small icy moon into one of the most desirable solar system destinations for future robotic reconnaissance. In designing a mission to Enceladus, the insignificant size of Enceladus and its close proximity to Saturn combine to create a remarkably challenging multi-body problem. This investigation offers an overview of three key aspects of the Enceladus transfer problem including: the design of an Enceladus science orbit, the design of Saturnian orbits that permit periodic encounters with Enceladus and additional Saturnian moons, and the design of gravity-assist flyby sequences in the Saturnian system involving five of Saturn’s most massive moons: Enceladus, Tethys, Dione, Rhea, and Titan. Although focused specifically on the design problem associated with supporting a mission in the Saturnian system, the Enceladus transfer problem is analyzed from a multi-body perspective. A substantial portion of this investigation involves the application of the Circular Restricted Three-Body Problem (CR3BP) to the Saturnian system, though the dynamics of the Saturnian system are also investigated using a six-body dynamical model. A technique is introduced to design a sequence of gravity-assist flybys by incorporating multiple gravity fields and applying a scheme that adjusts only one initial variable to yield a trajectory with multiple flybys. The capabilities of the trajectory design algorithm are demonstrated through the design of specific gravity-assist flyby sequences that are used to reduce the orbital energy of a spacecraft in a large Saturnian orbit to an energy level that is closer to the level of Enceladus’ Saturnian orbit.