Design of Science Orbits About Planetary Satellites: Application to Europa

Abstract

Low-altitude, near-polar orbits are very desirable as science orbits for missions to planetary satellites, such as Jupiter’s moon Europa. However, previous research has shown that a spacecraft in such a low-altitude, near-polar orbit about Europa will impact relatively quickly. To remedy this we study the underlying dynamics governing motion in the vicinity of Europa using a model that includes the tidal force from Jupiter and the J2, C22, and J3 gravity coefficients of Europa. Averaging is applied twice to reduce the original 3-degree-of-freedom system to an integrable 1-degree-of-freedom system. By studying this simplified 1-degree-of-freedom systemwe can identify paths that yield long lifetime trajectories. In order for a spacecraft in the original 3-degree-of-freedom system to follow one of these paths, initial conditionsmust be computed such that the trajectory in the 3-degree-of-freedom system follows the trajectory in the 1-degree-of-freedom system on average. To ensure this we develop a technique that allows us to systematically compute the necessary initial conditions in the 3-degree-of-freedom system to maximize the orbit lifetime. The resulting orbits have lifetimes on the order of 150 days, compared with lifetimes on the order of 40 days for randomly chosen initial conditions.