Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / Includes bibliographical references (p. 97-101). / NASA's human lunar and Mars exploration program requires a new transportation system between Earth and the Moon or Mars. In recent years, unfortunately, human space exploration programs have faced myriad political, technical, and financial difficulties. In order to avoid such problems, future human space exploration programs should be designed from the start for affordability. This thesis addresses one aspect of affordable exploration programs by tackling the issue of high costs for access to space. While launch vehicle trades for exploration programs are relatively well understood, on-orbit assembly has been given much less attention, but is an equally important component of the infrastructure enabling human access to space. Two separate but related perspectives on in-space assembly of modular spacecraft are provided: first, the coupling between launch vehicle selection, vehicle design, and on-orbit assembly is explored to provide a quantitative understanding of this combined tradespace; and second, a number of on-orbit assembly methods are analyzed in order to understand the potential value of a reusable assembly support infrastructure. / (cont.) Within the first topic, a quantitative enumeration of the launcher-assembly tradespace (in terms of both cost and risk) is provided based on a generalizable process for generating spacecraft modules and launch manifests from a transportation architecture. An optimal module size and launcher capability is found for a sample architecture at 82 metric tons; a 28-mt EELV emerges as another good option. The results show that the spacecraft design, assembly planning, and launcher selection are highly coupled and should be considered together, rather than separately. Within the second topic, four separate assembly strategies involving module self-assembly, tug-based assembly, and in-space refueling are modeled and compared in terms of mass-to-orbit requirements for various on-orbit assembly tasks. Results show that the assembly strategy has a significant impact on overall launch mass, and reusable space tugs with in-space refueling can significantly reduce the required launch mass for on-orbit assembly. This thesis thus examines a broad but focused set of issues associated with on-orbit assembly of next-generation modular spacecraft. / by Erica Lynn Gralla. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2010. / "September 2009." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 135-143). / To improve capacity and efficiency of the air transportation system, a number of new systems-level changes have been proposed. Key aspects of the proposed changes are combined functionality across technology and procedures and large physical scale of deployment. The objective of this work is to examine the current safety assessment processes for systems-level changes and to develop an understanding of key challenges and implications for the assessment and approval of future systems-level changes. From an investigation of current U.S. and international safety regulatory policies and processes, a general model was created describing key processes supporting operational approval. Within this model, a framework defined as an influence matrix was developed to analyze key decisions regarding the required scope of analysis in safety assessment. The influence matrix represents the expected change in levels of risk due to changes in behavior of elements of a system. It is used to evaluate the appropriate scope of analysis in safety assessment. Three approaches to performing safety assessment of systems-level changes were analyzed using the framework: the risk matrix approach, target level of safety approach, and performance-based approach. Case studies were performed using eight implemented and pending systems-level changes. In this work, challenges expected in safety assessment of future systems-level changes were identified. Challenges include the large scope of proposed changes, which drives a need for a broad and deep scope of analysis, including the multiple hazards and conditions and complex interactions between components of a change and the external system. In addition, it can be expected that high safety expectations will increase the required accuracy of models and underlying data used in safety assessment. Fundamentally new operational concepts are also expected to expand the required scope of safety assessment, and a need to interface with legacy systems will limit achievable operations. The large scope of analysis expected for future changes will require new methods to manage scope of safety assessment, and insights into potential approaches are discussed. / by Roland Everett Weibel. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 195-200). / A body-force-based fan model for the prediction of multiple-pure-tone noise generation is developed in this thesis. The model eliminates the need for a full-wheel, three-dimensional unsteady RANS simulation of the fan blade row, allowing Euler calculations to be used to capture the phenomena of interest. The Euler calculations reduce numerical wave dissipation and enable the simultaneous computation of source noise generation and propagation through the engine inlet to the far-field in non-uniform flow. The generated shock Mach numbers are in good agreement with experimental results, with the peak values predicted within 6%. An assessment of the far-field acoustics against experimental data showed agreement of 8 dB on average for the blade-passing tone. In a first-of-its-kind comparison, noise generation and propagation are computed for a fan installed in a conventional inlet and in a boundary-layer-ingesting serpentine inlet for a free-stream Mach number of 0.1. The key effect of boundary layer ingestion is the creation of streamwise vorticity which is ingested into the inlet, resulting in co- and counter-rotating streamwise vortices in the inlet. The fan sound power level increases by 38 dB due to this distortion, while the vortex whose circulation is in the same direction as the fan rotation enhances the sound power attenuation within the inlet duct such that the far-field overall sound pressure levels are increased by only 7 dB on average. The far-field spectra are altered in the following manner due to inlet distortion: (1) tones at up to 3 times the blade-passing frequency are amplified; and (2) tones above one-half of the blade-passing frequency are attenuated and appear to be cut-off. To quantify the effects of serpentine inlet duct geometry on the generation and propagation of multiple-pure-tone noise, a parametric study of inlets is conducted. The conclusions are that (1) the ingestion of streamwise vorticity alters multiple-pure-tone noise more than changes in inlet area ratio or offset ratio do; and (2) changes in the far-field spectra relative to the conventional inlet results are only weakly affected by the duct geometry changes investigated and are instead predominantly caused by flow non-uniformities. A response-surface correlation for the effects of inlet geometry on far-field noise is also developed. / by Jeff Defoe. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 113-116). / by John Saunders Bellingham. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 99-100). / by Jareb D. Mirczak. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 127-129). / Accurate estimates of multistage axial compressor performance at off-design operating conditions are essential to the determination of key performance metrics of aircraft gas turbine engines, such as fuel burn, thrust output, and stable operating range. However, conventional RANS based CFD calculations of multistage axial compressors diverge at off-design operating conditions where large separation occurs and the stages are mismatched. This thesis demonstrates the feasibility of a body force based approach to capturing the three-dimensional flow field through a turbomachinery blade row at off-design conditions. A first principles based blade passage model is introduced which addresses the limitations of previous approaches. The inputs to the improved blade passage model are determined from three-dimensional, steady, single-passage RANS CFD calculations. In a first step towards modeling multistage configurations, the improved blade passage model is validated using a fan rotor test case. At the design operating conditions, the stagnation pressure rise coefficient and the work coefficient are both estimated within 5%, and the adiabatic efficiency is estimated within 1 percentage point over most of the span relative to single-passage RANS CFD simulations. At low mass flow operating conditions, where the single-passage RANS CFD diverges, the blade passage model and related body force representation are capable of computing the three-dimensional throughflow with separation and reversed flow. These results pave the way for future unsteady calculations to assess compressor stability and for multistage compressor simulations at off-design conditions. / by Maximilian Lewis Brand. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1972. / Bibliography: p. 173-177. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992. / Includes bibliographical references (p. 134-137). / by Bruno Marco Quadrelli. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Pages 129-130 blank. Cataloged from student submitted PDF version of thesis. / Includes bibliographical references (p. 115-119). / The greatest discoveries in astronomy have come with advancements in ground-based observatories and space telescopes. Latest trends in ground-based observatories have been ever increasing size of the primary mirror, providing much higher apertures for more powerful image captures. The same trend can be envisioned for space telescopes. In fact, concepts for ultra-large space telescopes (ULST) on the order of hundreds of meters in size have been emerging since the late 1990's and early 2000's. Currently, James Webb Space Telescope (JWST) scheduled to be launched in 2014 only has primary mirror diameter of 6.5 m. An important issue in the ULST is correcting for optical errors caused by large thermal deformations expected due to exposure to radiation in orbit. As of now, there are no methods for solving technical complexities involved in correcting for such deformations. Furthermore, the costs associated with weight, deployability, and maintenance hinder advancements in large space telescopes. This thesis explores the idea of using binary actuators coupled with elastic elements to offer solutions to these problems. The feasibility of using binary actuators with elastic elements for correcting the focus of the deformed structure is investigated. The investigation begins with simple representations of the primary mirror structure in one-dimensional study, then in two-dimensional study for planar analysis. The analysis includes exploration of the workspace, demonstration of deterioration of superposition, and performance measured in precision of focus correction. In general, the number of actuators required for an acceptable level of correction is about three times the number of degrees-of-freedom in the system. Ultimately, it is concluded that in the planar domain it is feasible to use binary actuators in the control of primary mirror structure for large space telescopes. / by Seung Jae Lee. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 239-252). / High power nuclear electric propulsion systems have the capability to enable many next-generation space exploration applications. To date, use of electric primary propulsion in flight systems has been limited to low-power, solar electric missions. There is a need for a large-scale research and development effort to field systems capable of meeting the demands of future high-power electric propulsion missions, especially missions utilizing nuclear power plants to power electric propulsion systems. In formulating such an effort, it is first important to identify the likely requirements around which such a system might be designed. These requirements can be effectively cast in terms of required thruster lifetime, thrust, specific impulse, output power, and power plant specific power. Projected requirements can be derived based on the mass characteristics of space-borne nuclear power plants, and the optimized trajectories of spacecraft missions enabled by the use of megawatt-level nuclear electric power systems. Detailed mass modeling of space-based Rankine cycle nuclear power plants is conducted to evaluate the achievable specific power of these systems. Based on the figures for specific power so obtained, mission modeling is next conducted using the Mission Analysis Low-Thrust Optimization software package. Optimized thrust, specific impulse and lifetime figures are derived for several missions of interest. A survey of available electric propulsion thrusters is conducted and thruster configurations presenting the lowest developmental risks in migrating to high thruster output power are identified. Design evolutions are presented for three thrusters that would enhance or enable operation at the megawatt level. First, evaluation of projected lifetime for dual-stage gridded ion thrusters is conducted using the CEX2D simulation tool to evaluate the utility of multi-stage gridded ion engines in obtaining the required thruster lifetime for operation at high specific impulse. Next, to evaluate the utility of Hall thrusters operating at high propellant mass flow rate, a numerical thruster model is developed that incorporates the effects of the neutral fluid in predicting thruster performance. Using this code, numerical simulations are conducted to investigate the effects of variations in propellant mass flow rate, magnetic field topology, and thruster channel geometry on achievable performance. Finally, the effects of variations in the channel contour of magnetoplasmadynamic thrusters on performance and efficiency are evaluated using the MACH2 software package. Incremental variations in thruster channel contour are implemented, and the effects of these variations on the performance onset condition, and electrode current distributions are observed. Conclusions regarding the utility of each of these three design evolutions in developing thrusters for multi-megawatt electric propulsion systems are discussed. Contributions stemming from this research include, first, the establishment of an appropriate requirements space for the design of advanced highpower electric power and propulsion systems. This design space is comprised of projected requirements for power plant specific power, derived from power plant mass modeling, and thruster output power, specific impulse and lifetime derived from mission modeling. Additionally, this work provides evaluation, using state-of-the-art simulation suites, of several electric thruster design evolutions of potential utility in developing electric propulsion systems designed to operate at the megawatt level. / by Daniel B. White. / Ph.D.