Exploration and optimization of low-energy capture options at Jovian moons
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A key trade-off for planetary system exploration is the fuel cost required versus science data obtained. Historically, planetary systems have been explored utilizing multiple flybys, such as Galileo, Cassini's complex Saturnian tour, as well as the trajectory for the proposed Europa Clipper mission. While this approach eliminates the need for expensive capture maneuvers, it can require days to weeks between observations, limiting available science data. An alternative that seeks to maximize science return is to capture about each moon of interest. Investigations of low-energy dynamics have shown the existence of relatively inexpensive transfers between halo orbits at different moons. Chaining these transfers in a moon-hopping tour allows one spacecraft to visit multiple moons. The next step for a multi-moon mission is to connect the inter-moon transfers to science orbits at specific moons. Two capture orbit scenarios are considered for comparison: 1) traditional, tightly captured low-altitude orbits and 2) low-energy, loosely captured high-altitude orbits. Near-global grid search methods are developed to generate initial capture trajectories from staging halo orbits. To help determine which solutions are near optimal, an analytical expression for the predicted floor cost is derived. Low cost captures are identified and optimized using impulsive primer vector theory to determine the ideal number and location of impulses. The trajectory is then extended to include the last resonant-orbit of the inter-moon transfer, using the halo orbit as a patch point to connect the phases. A new three-dimensional periodic orbit that naturally transfers between the resonant and halo orbits is generated to facilitate the connection. The resulting resonant-to-capture transfers are again optimized with primer vector theory, resulting in several optimized options for comparison. As an additional mission design option, the possibilities of advanced exploration using an electrodynamic tether are investigated. An approximation to the tether-perturbed dynamics is derived that allows for an integral of motion, enabling useful analytical techniques. New periodic orbit families are generated as a function of tether length, using continuation from non-perturbed Lyapunov orbits. The new orbits are analyzed in terms of stability and utility for future use in mission design.