| Summary: | Throughout the history of spaceflight, new missions and capabilities have been enabled by the development of increasingly efficient and powerful propulsion systems. However, all of these systems, from the earliest chemical engines to modern electric thrusters, require propellant, thereby reducing the mass budget available for a payload. By harnessing the momentum of reflected photons of sunlight, solar sails offer a propellant-free alternative but are limited by attitude restrictions and their low thrust. Their improvement has also been inhibited by current knowledge of both materials science and structural engineering. In this dissertation, an assessment of a hybrid propulsion system is presented that maximizes the positive traits of its two constituent subsystems. By augmenting solar electric propulsion (SEP) with a solar sail, a spacecraft may be created with lower propellant consumption than SEP alone and greater thrust than a pure sailcraft, while not necessitating the technical development of the most ambitious proposed solar sails. To conduct this study, trajectories are generated to potential heliophysics and smallbody targets: high-inclination, heliocentric orbits and interstellar objects (ISOs). For the former, detailed mass budgets are created and a trade study of subsystem size versus mass is conducted to identify the performance necessary to produce a net positive change in launch mass. For the latter, six spacecraft propulsion systems and four launch vehicles are considered in a broad study of mission viability using two separate databases of synthetic target ISOs. The ability of the hybrid low-thrust propulsion configuration to produce lower mean arrival velocities than more conventional alternatives is then determined. In both cases, nonidealized power and propulsion models are used to improve upon the preexisting literature and make a more accurate assessment of the technology.
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