Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 81-91). / Simulation of high speed flows where shock waves play a significant role is still an area of development in computational fluid dynamics. Numerical simulation of discontinuities such as shock waves often suffer from nonphysical oscillations which can pollute the solution accuracy. Grid adaptation, along with shock-capturing methods such as artificial viscosity, can be used to resolve the shock by targeting the key flow features for grid refinement. This is a powerful tool, but cannot proceed without first converging on an initially coarse, unrefined mesh. These coarse meshes suffer the most from nonphysical oscillations, and many algorithms abort the solve process when detecting nonphysical values. In order to improve the robustness of grid adaptation on initially coarse meshes, this thesis presents methods to converge solutions in the presence of nonphysical oscillations. A high order discontinuous Galerkin (DG) framework is used to discretize Burgers' equation and the Euler equations. Dissipation-based globalization methods are investigated using both a pre-defined continuation schedule and a variable continuation schedule based on homotopy methods, and Burgers' equation is used as a test bed for comparing these continuation methods. For the Euler equations, a set of surrogate variables based on the primitive variables (density, velocity, and temperature) are developed to allow the convergence of solutions with nonphysical oscillations. The surrogate variables are applied to a flow with a strong shock feature, with and without continuation methods, to demonstrate their robustness in comparison to the primitive variables using physicality checks and pseudo-time continuation. / by Carlee F. Wagner. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995. / Includes bibliographical references (p. 199-200). / by Jason R. Schott. / M.S.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1987. / Bibliography: leaves 180-183. / by Kenneth Charles Hall. / Sc.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990. / Title as it appeared in MIT Graduate list, June 1990: Simulation of hypersonic flows over a blunt delta wing. / Includes bibliographical references (leaves 134-136). / by Kuok-Ming Lee. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2002. / Includes bibliographical references (leaves 173-181). / One of the most important steps in hazard analysis is determining whether a particular design can reach a hazardous state and, if it could, how to change the design to ensure that it does not. In most cases, this is done through testing or simulation or even less rigorous processes--none of which provide much confidence for complex systems. Because state spaces for software can be enormous (which is why testing is not an effective way to accomplish the goal), the innovative Hazard Automaton Reduction Algorithm (HARA) involves starting at a hypothetical unsafe state and using backwards reachability techniques to obtain enough information to determine how to design in order to ensure that state cannot be reached. State machine models are very powerful, but also present greater challenges in terms of reachability, including the backwards reachability needed to implement the Hazard Automaton Reduction Algorithm. The key to solving the backwards reachability problem lies in converting the state machine model into a controls state space formulation and creating a state transition matrix. Each successive step backward from the hazardous state then involves only one n by n matrix manipulation. Therefore, only a finite number of matrix manipulations is necessary to determine whether or not a state is reachable from another state, thus providing the same information that could be obtained from a complete backwards reachability graph of the state machine model. Unlike model checking, the computational cost does not increase as greatly with the number of backward states that need to be visited to obtain the information necessary to ensure that the design is safe or to redesign it to be safe. The functionality and optimality of this approach is proved in both discrete and hybrid cases. / (cont.) The new approach of the Hazard Automaton Reduction Algorithm combined with backwards reachability controls techniques was demonstrated on a blackbox model of a real aircraft altitude switch. The algorithm is being implemented in a commercial specification language (SpecTRM-RL). SpecTRM-RL is formally extended to include continuous and hybrid models. An analysis of the safety of a medium term conflict detection algorithm (MTCD) for aircraft, that is being developed and tested by Eurocontrol for use in European Air Traffic Control, is performed. Attempts to validate such conflict detection algorithms is currently challenging researchers world wide. Model checking is unsatisfactory in general for this problem because of the lack of a termination guarantee in backwards reachability using model checking. The new state-space controls approach does not encounter this problem. / by Natasha Anita Neogi. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 113-115). / Electromagnetic Formation Flight (EMFF) consists of using electromagnetic forces to position or orient satellites in a relative target location or attitude and achieve a certain target formation on orbit. This thesis introduces the fundamental equations of EMFF and the design of the Resonant Inductive Near-Field Generation System (RINGS). RINGS is a testbed composed of two vehicles that are used to demonstrate EMFF in a 6 DoF environment. In this thesis, a RMS current level controller is modeled and implemented in RINGS to give the system electromagnetic actuation capability. Subsequently, a simulation of RINGS that incorporates an EM dynamics model applicable to two RINGS vehicles operating in close proximity is developed. This model was validated using a set of open-loop maneuvers by comparing it with data obtained from experiments using the RINGS aboard the International Space Station (ISS). Finally, this simulation was used to test linear controllers that incorporate an 'Adaptive Control' approach to achieve system stability for a specific configuration and range of disturbances. / by Bruno Alvisio. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 273-292). / Communications satellite operators maintain archives of component telemetry to monitor system function. Operators generally do not typically use the telemetry data for scientific analysis of the space radiation environment effects on component anomalies or performance. We partnered with four geostationary (GEO) operators, acquired >1 million hours of telemetry, and combined these data with space weather observations to investigate relationships between space weather and hardware performance. We focused on the effects of space weather on two component types: solar cells and high power amplifiers. For solar cells, by augmenting >20 years of GEO telemetry with separate GEO space weather measurements, we calculated both on-orbit degradation of Si and GaAs solar cells in an annual average sense, and also quantified the degradation of cells during severe solar proton events (SPEs) of 10 MeV protons > 10,000 pfu. A functional relationship between the amount of degradation and proton fluence is also considered. We used the calculated degradation to evaluate several combinations of space weather environment models with solar cell degradation models and found that predicted performance is within 1% of the observed degradation. These models had not previously been validated using multiple on-orbit GEO datasets. We did not find a model pairing that consistently outperformed the others over all of the datasets. For high power amplifiers, through the use of statistical analysis, simulations, and electron beam experiments we conducted a root-cause analysis of solid state power amplifier (SSPA) anomalies on-board eight GEO satellites. From the statistical analysis, we identified that the occurrence of anomalies was not random with respect to the space weather environment, but that there appeared to be a relationship to high-energy electron fluence for periods of time between 10 - 21 days before the anomalies. From the simulations and electron beam lab tests, we demonstrated that internal charging occurs in the amplifier chain, potentially identifying a cause for the observed anomalies. We substantiated an approach toward understanding space weather effects on space components by obtaining and using long-duration archives of standard commercial telemetry for scientific analysis. The analysis of large telemetry data sets of similar components over long periods of time improves our ability to assess the role of different types of space weather events in causing anomalies and helps to validate models. The findings in this work that relate deep dielectric charging to component anomalies and solar proton events to solar cell degradation make use of only a small fraction of the potentially available commercial geostationary satellite telemetry. Expansion of this work would provide additional insights on the role of space weather to the science community and to the satellite design and operator community. / by Whitney Quinne Lohmeyer. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995. / Includes bibliographical references (p. 274-283). / by James D. Soldi, Jr. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 225-230). / The future of Mars exploration is challenging from multiple points of view. To enhance their science return, future surface probes will most likely be equipped with complex Sample Preparation And Transfer (SPAT) facilities. Future rovers will need to be able to perform longer traverses and delicate sample acquisition operations. Mars return missions would benefit from a new propulsion system, with better fuel and travel time efficiencies than chemical and electric propulsions, respectively. A model was developed that optimizes SPAT facilities in terms of productivity and system mass. The SPAT model especially investigates two trade-offs: shared versus specific preparation, and warm versus cold redundancy for SPAT elements. A Mars Surface Exploration (MSE) framework was created to help designers perform preliminary studies on rover missions. MSE applies multidisciplinary design optimization techniques for the analysis of design trade-offs relevant to the rover design community. The Propellant Production In Mars Orbit (PPIMO) is presented as a promising solution for performing return travels to Mars. PPIMO uses the concept of regenerative aerobraking to produce fuel in-situ. The SPAT model shows that warm redundancy improves productivity by both reducing risk and removing sample throughput bottlenecks. A method is presented for determining the economy of scale the shared preparation architecture must exhibit for it to be competitive in comparison to the distributed architecture. MSE is used to budget the future development costs of rover autonomy, in addition to assessing: the benefits of oversized suspensions, the practicality of solar versus nuclear power for future missions, and the advantages of multi-rover missions. When compared / (cont.) to chemical and electric propulsions, PPIMO propulsion shows a better performance in terms of transportation ratio for payloads larger than 1000 kilograms. / by Julien-Alexandre Lamamy. / S.M.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1972. / Part of the pages are numbered as leaves. / Includes bibliographical references. / Sc.D.