Browsing by Subject "space"
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Item Active Space Debris Removal using Capture and Ejection(2013-04-25) Missel, Jonathan WilliamLow Earth Orbit is over-cluttered with rogue objects that threaten existing technological assets and interfere with allocating new ones. Traditional satellite missions are not efficient enough to collect an appreciable amount of debris due to the high cost of orbit transfers. Many alternate proposals are politically controversial, costly, or dependent on undeveloped technology. This dissertation attempts to solve the problem by introducing a new mission architecture, Space Sweeper, and bespoke hardware, Sling-Sat, that sequentially captures and ejects debris plastically. Resulting momentum exchanges are exploited to aid in subsequent orbit transfers, thus saving fuel. Sling-Sat is a spinning satellite that captures debris at the ends of adjustable-length arms. Arm length controls the angular rate to achieve a desired tangential ejection speed. Timing the release exacts the ejection angle. This process redirects debris to burn up in the atmosphere, or reduce its lifetime, by lowering its perigee. This dissertation establishes feasibility of principles fundamental to the proposed concept. Hardware is conceptualized to accommodate Space Sweeper ?s specialized needs. Mathematical models are built for the purpose of analysis and simulation. A kinematic analysis investigates system demands and long-term behavior resulting from repeated debris interaction. A successful approach to enforce debris capture is established through optimal control techniques. A study of orbital parameters and their response to debris interactions builds an intuition for missions of this nature. Finally, a J2-compliant technique for path optimization is demonstrated. The results strongly support feasibility of the proposed mission.Item Characterizing strain in the proximal rat tibia during electrical muscle stimulation(Texas A&M University, 2007-09-17) Vyvial, Brent AronHindlimb unloading is a widely used model for studying the effects of microgravity on a skeleton. Hindlimb unloading produces a marked loss in bone due to increased osteoclast activity. Electrical muscle stimulation is being investigated as a simulated resistive exercise countermeasure to attenuate this bone loss. I sought to determine the relationship between strain measured at the antero-medial aspect of the proximal diaphysis of tibia and plantar-flexor torque measured at the ankle during electrical muscle stimulation as an exercise countermeasure for hindlimb unloading in rats. A mathematical relationship between strain and torque was established for the exercise during a 28 day period of hindlimb unloading. The strain generated during the exercise protocol is sufficient to attenuate bone loss caused by hindlimb unloading. Twelve six-month old Sprague-Dawley rats were implanted with uni-axial strain gages in vivo on the antero-medial aspect of the proximal diaphysis of the left tibia. Strain and torque were measured during electrical muscle stimulation for three time points during hindlimb unloading (Day 0 (n=3), Day 7 (n=3), Day 21 (n=3)). Peak strain decreased from 1,100 strain at the beginning of the study to 660 strain after 21 days of hindlimb unloading and muscle stimulation. The peak strain rate measured during muscle stimulation was 10,350 strain/second at the beginning and decreased to 6,670 strain/second after 21 days. The changes in strain are not significant, but the underlying trend in strain values may indicate an increase in bone formation due to the electrical muscle stimulation countermeasure. A mathematical model that relates measured strain to peak eccentric torque during muscle stimulation was created to facilitate estimation of strain for future studies of electrical muscle stimulation during hindlimb unloading.Item Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes(2012-12-07) Ebersohn, Frans 1987-Plasma flow physics in magnetic nozzles must be clearly understood for optimal design of plasma propulsion devices. Toward that end, in this thesis we: i) perform an extensive literature survey of magnetic nozzle physics, ii) assess the validity of magnetohydrodynamics for studying magnetic nozzle physics, and iii) illustrate the effects of the Hall term in simple flows as well as in magnetic nozzle configurations through numerical experiments with the Magneto-Gas Kinetic Method (MGKM). The crucial steps necessary for thrust generation in magnetic nozzles are energy conversion, plasma detachment, and momentum transfer. These three physical phenomena must be understood to optimize magnetic nozzle design. The operating dimensionless parameter ranges of six prominent experiments are considered and the corresponding mechanisms are discussed. An order of magnitude analysis of the governing equations reveal: i) most magnetic nozzles under consideration operate at the edge of the continuum regime rendering continuum-based description and computation valid; ii) in the context of MHD framework, the generalized Ohm?s law must be used to capture all of the relevant physics. This work also continues the development of the Magneto Gas Kinetic Method (MGKM) computational tool. Validation of the solver is performed in shock-tube and Hartmann channel flows in the Hall physics regime. Comparison with theory and available data is made whenever possible. Novel numerical experiments of magnetic nozzle plasma jets in the Hall regime are performed, confirming the theoretically predicted azimuthal rotation of the plasma jet due to Hall physics. The primary conclusion from this work is that the addition of the Hall effect generates helical structures in magnetic nozzle plasma flows. Preliminary results are encouraging for future magnetic nozzle studies and further challenges are identified.Item Modulating Peripersonal and Extrapersonal Reach Space: A Developmental Perspective(2012-10-19) Cacola, Priscila MartinsThe primary intent of this study was to gain insight into the developmental nature of spatial perception and representation. More specifically, the work presented here examined 1) the age-related ability to modulate peri- and extrapersonal space via hand and tool use, 2) the adjustment period associated with extending and retracting spaces, and 3) the effect of tool length on modulation of space. Seventy children representing age groups 7-, 9-, 11 years and adults were presented with two experiments using an estimation of reach paradigm involving hand and tool conditions and a switch-block of the opposite condition. Experiment 1 tested Hand and Tool (20cm length) estimation and found a significant effect for Age, Space, and an Age x Space interaction (ps <.05). Both children and adults were less accurate in extrapersonal space, indicating an overestimation bias. Interestingly, the adjustment period during the switch-block condition was immediate and similar across age. Experiment 2 was similar to Experiment 1 with the exception of using a 40cm length tool. Results of 55 participants also revealed a difference in estimation responses between Age groups (p <.05); 7- and 9-year-olds were similar and less accurate than adults, and 11-year-olds were not different from any other age group. There was also a difference in Space (p <.05), revealing that participants underestimated their reaching abilities with higher accuracy in extrapersonal space. Interestingly, whereas participants overall overestimated with the 20cm tool, they tended to underestimate while using the 40cm tool. This finding suggests that participants were less confident when presented with a longer tool, even though the adjustment period with both tool lengths was similar. Considered together, these results hint that: (1) children as young as 6 years of age are capable of re-scaling peripersonal space via tool use in the context of estimation reach, (2) the adjustment period associated with extending and retracting spaces is immediate rather than gradual, and (3) tool length may influence confidence of participants, shifting the general direction of error from overestimation with a 20cm tool to underestimation with a 40cm tool.Item Neither Wholly Public, Nor Wholly Private: Interstitial Spaces in Works by Nineteenth-Century American Women Writers(2010-10-12) Green-Barteet, Miranda A.This project examines the representation of architectural and metaphoric spaces in the works of four nineteenth-century American women writers: Harriet Wilson, Harriet Jacobs, Elizabeth Stuart Phelps, and Edith Wharton. I focus on what I call interstitial spaces: spaces that are neither wholly public nor private but that exist somewhere in between the public and private realms. Interstitial spaces are locations that women writers claim to resist the predominantly private restrictions of the family or the predominantly public conventions of society. Interstitiality becomes a border space that enables women writers?both for themselves and for their fictional characters?to redefine, rearrange, and challenge the expectations of public and private spaces in the nineteenth century. This dissertation investigates how nineteenth-century American women writers create interstitial spaces. Further, it demonstrates how they use such spaces to express their views, manipulate the divisions between the public and private realms, and defy societal and familial conventions. Since the mid-1970s, critics have been analyzing public and private under the assumption that the boundaries between the spheres were more porous than originally thought. This project adds to the critical dialogue concerning the separation of public and private realms as the conceptual framework of criticism shifts from an increased awareness of gender, race, and class. My project responds to the growing trend of analyzing literary works through architectural and spatial theories. While applying such theories, I focus on how race and class affect a writer's ability to create interstitial spaces. I further respond to this trend by considering authors who have not yet been included in this way, namely Wilson and Phelps. By analyzing the physical and rhetorical ways these authors manipulate space, I offer an account of gender, race, and class along with architectural and spatial concepts that juxtaposes authors who have not yet been considered together. My dissertation offers a new critical vocabulary to consider writers' representations of spaces by employing the word interstitial, which no other critic uses. I specifically use interstitial to describe spaces that exist between the public and private realms and describe the transformation in space that occurs through spatial and rhetorical manipulation.