Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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.
Browse
3 results
Search Results
Item Thermal Drilling and Anchoring on Icy Planetary Bodies(2020) Halperin, Adam Hugh; Sedwick, Raymond J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Europa is of scientific interest because it is made primarily of water, may have subsurface liquid oceans, and has active cryovolcanoes. Despite the cryogenic surface temperatures, ambient vacuum pressure, and high levels of radiation, potential missions to its surface or its subsurface oceans are topics of current research. Exploring Europa’s surface poses an interesting challenge because of these ambient conditions. Furthermore, any regions of crevasses, ridges, penitentes, cryovolcano formations, and other extreme terrains would be inaccessible to existing rover designs. The “thermal pick” proposed here is a novel system to enable a rover to traverse even the most extreme Europan terrains. It is a dual-function system that first uses a thermal drilling process to burrow into Europa’s surface ice and then serves as an anchor, supporting the mobility of the rover to which it is attached. Thermal drilling provides high reliability but can be energetically costly. An intermittent thermal drilling approach was developed that dramatically reduces the primary drivers of energy cost for thermal drilling in cryogenic ices. Since thermal drilling can cause thermally induced ice fracturing, operational conditions that minimize the likelihood of ice failure modes were established. Three test rigs, two end effectors, and over ten thermal picks were prototyped and tested. Testing with dry ice at atmospheric pressure and testing with cryogenic water ice in a vacuum chamber provided an understanding of thermal drilling in the sublimation and melting regimes, respectively. This testing demonstrated efficiencies of up to 90% relative to ideal sublimation with dry ice and efficiencies of up to 50% relative to melting with cryogenic water ice under vacuum. For safe mobility in the toughest icy terrains, a single anchor should be capable of supporting an entire rover’s weight. Anchoring strengths in excess of 130N were demonstrated, which is the full weight of 100kg on Europa. This 130N anchoring force was supported by even the weakest anchor tested, suggesting potentially greater anchoring loads can be supported.Item TECTONICS OF ICY SATELLITES DRIVEN BY MELTING AND CRYSTALLIZATION OF WATER BODIES INSIDE THEIR ICE SHELLS(2015) Johnston, Stephanie Ann; Montési, Laurent; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Enceladus and Europa are icy satellites that currently support bodies of liquid water in the outer solar system Additionally, they show signs of being geologically active. Developing numerical models informed by observations of these icy satellites allows for the development of additional constraints and an improved understanding of the tectonics and evolution of icy satellites. The formation mechanisms for both chaos and ridges on Europa are thought to involve water as albedo changes observed in association with them imply the deposition of salt-rich water near these features. Ridges are the most ubiquitous feature on Europa and are described as central troughs flanked by two raised edifices, range in height from tens to hundreds of meters. Europan ridges can extend hundreds of km continuously along strike but are only about 2 km across. A model of a crystallizing dike–like water intrusion is able to match the overall morphology of ridges, and is consistent the long continuous strike. However, the intrusion of a large volume of water is required to match the most common heights of the ridges. Chaos on Europa is defined as a large area of disrupted ice that contain blocks of pre-existing material separated by a hummocky matrix. A proposed mechanism for the formation of Chaos is that a region of heterogeneous ice within the shell is melted and then recrystallizes. Comparing the model results with the geology of Thera Macula, a region where it has been proposed that Chaos is currently forming, suggests that additional processes may be needed to fully understand the development of Chaos. Water-rich plumes erupt from the south pole of Enceladus, suggesting the presence of a pressurized water reservoir. If a pressurized sea is located beneath the south polar terrain, its geometry and size in the ice shell would contribute to the stress state in the ice shell. The geometry and location of such an ocean, as well as the boundary conditions and thickness of an ice shell have important implications for the faulting and tectonic deformation anticipated at the surface.Item Two dimensional mapping of the sodium emission in Europa's exosphere(2007-01-19) Fraga-Encinas, Raquel; Killen, Rosemary M.; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present results of the mapping of Europa's sodium exosphere in two dimensions and through a period of time. We base this research on several observations taken in 2001 and 2002 with the McMath-Pierce Solar Telescope at Kitt Peak, Arizona. We have created sodium emission intensity maps and line of sight column abundance maps of Europa's exosphere in all directions. We include calculations of vertical and tangential column abundances as well as surface densities of sodium relative to the position of Europa and to the Io plasma torus. We find that the sodium exosphere is weakly bound or escaping along the East-West direction, but not to be escaping along the North-South direction. Additionally, we find that the sodium exosphere is energetic enough to extend to a distance of roughly 40,000 km away from the surface of Europa.