Trajectories for Flyby Sample Return at Icy Moons

Abstract

Ballistic trajectories are computed that aim to achieve a sample-return mission to Europa, Enceladus, or Titan without capturing, descending, or landing. The low-cost mission concept uses a free-return trajectory that also involves a close flyby of the icy moon. A broad-search algorithm is developed to construct feasible itineraries, and Venus and Earth gravity-assist sequences are considered. Select solutions from the broad search are then optimized to be continuous using gravity of the full ephemeris. Solution characteristics are examined over a complete 12-year Jupiter period and 30-year Saturn period. For Europa and Titan, the outbound Venus–Earth–Earth gravity assist (VEEGA) option can significantly reduce launch $C_3$ , compared to alternate options. For Europa, various optimized results are computed with $C_3$ as low as $16.0{\mathrm{km}}^2/{\mathrm{s}}^2$ , reentry speeds comparable to the Stardust capsule, and flight times of 9–15 years. Unfortunately, an Enceladus mission requires a flight time of 25 years or more and incurs fairly high relative speeds. Optimized direct and VEEGA missions to Titan are presented, with total flight times of 16 and 25 years, respectively.