Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Departure Phase Aborts for Manned Mars Missions(2007-04-20) Dissel, Adam Frederik; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)NASA goals are set on resumption of human activity on the Moon and extending manned missions to Mars. Abort options are key elements of any system designed to safeguard human lives and stated requirements stipulate the provision of an abort capability throughout the mission. The present investigation will focus on the formulation and analysis of possible abort modes during the Earth departure phase of manned Mars interplanetary transfers. Though of short duration, the departure phase encompasses a mission timeline where failures have frequently become manifest in historical manned spacecraft necessitating the inclusion of a departure phase abort capability. Investigated abort modes included aborts to atmospheric entry, and to Earth or Moon orbit. Considered interplanetary trajectory types included conjunction, opposition, and free-return trajectory classes. All abort modes were analyzed for aborts initiated at multiple points along each of these possible departure trajectories across all launch opportunities of the fifteen-year Earth-Mars inertial period. The consistently low departure velocities of the conjunction trajectories facilitated the greatest abort capability. An analysis of Mars transportation architectures was performed to determine the amount of available delta V inherent in each candidate architecture for executing departure aborts. Results indicate that a delta V of at least 4 km/s is required to achieve a continuous departure phase entry abort capability with abort flights less than three weeks duration for all transfer opportunity years. Less demanding transfer years have a corresponding increase in capability. The Earth orbit abort mode does not become widely achievable until more than 6 km/s delta V is provided; a capacity not manifest in any considered architecture. Optimization of the Moon abort mode resulted in slight departure date shifts to achieve improved lunar alignments. The Moon abort mode is only widely achievable for conjunction transfers during the optimum transfer years and delta V values greater than 4 km/s. A lesser delta V potential of 3 km/s is sufficient to enable entry aborts during the least demanding transfer opportunity years. Extensive abort capability is achievable for high delta V capable Mars architectures. Less propulsively capable architectures achieve moderate abort capability during favorable opportunity years.Item Comparative System Analysis of Reusable Rocket and Air-Breathing Launch Vehicles(2005-08-03) Dissel, Adam Frederik; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A conceptual system design study was performed to assess and compare the parameters of single- and two-stage reusable air-breathing and rocket launch vehicles to identify configurations which improve space access and merit further developmental emphasis. Investigated air-breathing configurations included both two-dimensional and inward-turning inlet geometries and horizontal and vertical takeoff modes utilizing rocket or turbine engines. The baseline payload requirement was 20,000 lb to low-Earth orbit. The vehicles were evaluated utilizing several figures of merit including empty weight, wetted area, and maintenance hours. A further weight growth assessment ascertained the growth factor which characterizes each system's design risk and growth response to technological uncertainty. An additional trade study investigated payloads up to 70,000 lb. The two-stage rocket results showed strong performance in applied metrics. Horizontal takeoff single- and two-stage air-breathers trailed far behind, while the vertical takeoff air-breathers were very competitive and merit further attention.