Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1989. / Includes bibliographical references (leaves 81-82). / by Nicolas R. Goulet. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1989. / Includes bibliographical references (leaves 124-126). / by John Joseph Blandino. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 179-182). / In this thesis, I present neutral atmosphere, ionosphere and total delays experienced by GPS signals traveling to space vehicles during launch, orbit and reentry. I calculate these delays for receivers at 0 km to 1700 km altitude by ray-tracing through the Global Reference Atmosphere Model (1999) and the International Reference Ionosphere (2001). These delays are potentially much larger than those experienced by signals traveling to GPS receivers near the surface of the Earth, but are primarily experienced at negative elevation angles, and are therefore most relevant for space vehicles with limited visibility of GPS satellites and during launch and reentry. I compare these signal delays to the delays predicted by three onboard delay models: the Altshuler and NATO neutral atmosphere delay models, and the Klobuchar ionosphere delay model. I find that these models are inadequate when the space vehicle is in orbit. The NATO model will suffice during the final period of reentry, where it predicts the neutral atmosphere delay to within 1 m of the ray-traced value, but it will not suffice when a satellite is rising or setting. I propose a method to extend the NATO model for receivers at higher altitudes. The Klobuchar model will suffice for most satellites during reentry, but will potentially predict ionosphere delays with errors up to 30 m, and will not suffice when a satellite is rising or setting. / by Rachel Neville Thessin. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 56-63). / Alternative fuels have the potential to mitigate transportation's impact on the environment and enhance energy security. In this work, we investigate two alternative fuels: liquefied natural gas (LNG) as an aviation fuel, and middle distillate fuel derived from woody biomass for use in aviation or road transport. The use of LNG as a supplemental aircraft fuel is considered in the context of the Lockheed Martin C- 1 30H and C-130J transport aircraft. We estimate the cost of retrofitting these aircraft to use LNG and the savings from reduced fuel expenses. We evaluate the societal impacts of LNG within a cost-benefit framework, taking into account resource consumption, human health impacts related to air quality, and climate damage. We find that aircraft operators can save up to 14% on fuel expenses (retrofit costs included) by employing LNG retrofits, with a 95% confidence interval of 2-23%. Society can also benefit by 12% (3-20%) from LNG use as a result of improved surface air quality, lower resource consumption, and climate neutrality relative to conventional fuel. These results are highly dependent on fuel prices, the quantity and cost of the LNG retrofits, and the frequency and length of missions. Woody biomass harvested from old-growth forests produces a large carbon debt when used as a feedstock for transportation fuel. Managed forests are an attractive alternative for inexpensive biomass production with the potential to reduce this carbon debt. We study the effect of forest management practices on the carbon debt payback time resulting from harvesting woody biomass from managed forests for middle distillate fuel production. We also calculate the breakeven time in terms of radiative forcing, temperature change, and economic damages. We find that biofuels produced over a period of 30 years have higher CO 2 emissions than fossil fuels for 59 years, higher radiative forcing for 42 years, higher temperature change for 48 years, and higher cumulative discounted (1-2%) economic damages for more than 100 years. These damages never break even at discount rates above 2%. Payback times can be reduced by increasing the age at which biomass is harvested. When biofuel production is sustained indefinitely, greater climate benefits are achieved over the next 100 years by instead producing long-lived wood products like lumber. / by Mitch Russell Withers. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references (p. 127-131). / The new solar system exploration objectives announced in January 2004 have the goal of sending humans back to the Moon by the year 2020 in preparation for human exploration of Mars. Advanced, but cost effective, surface navigation and communication capabilities are required to support these new exploration objectives. In response to this need, a set of three Navigation/Communication architectures have been designed: Minimalist, Simple, and Performance, as well as several augmentation options. The design and refinement of these architectures was performed using numerous models and tools developed for this work. A unique feature of the analysis in this thesis was that the architectures considered combine different navigation assets (onboard, on-surface and on-orbit). The three main Navigation/Communication architectures were then evaluated and compared using several metrics, such as navigation coverage, accuracy and operability, communication metrics, and mass. Based on this analysis we recommend the initial deployment of the Simple architecture for surface exploration of the Moon and Mars with a gradual accretion of assets and possibly transition to the Performance architecture. A specific combination of onboard and vision-based sensors is recommended as the fundamental navigation equipment. In addition to this navigation study, a control-based analysis of formation flying dynamic models around the libration point L₂ of the Sun-Earth system is also presented. The objective of this research was to assess the quality of different dynamical models of the relative motion of two spacecraft in orbit around Sun-Earth L₂. / (cont.) This was done using open-loop simulations to investigate the intrinsic fidelity of each model and closed-loop simulations to evaluate the impact of modeling errors on fuel costs. The conclusion from this analysis is that the more sophisticated models give appreciable better closed-loop performance, and that the difference appears to be sufficient to justify the additional effort required to implement them on-line. / by Thomas Chabot. / S.M.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1940. / Microfiche copy available in Barker. MIT copy bound with: Characteristics of gasoline-alcohol blends / Edgardo N. Accinelli. 1940. / by Paul M. Butman. / B.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 99-100). / by Samuel A. Schweighart. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999. / Includes bibliographical references (p. 145-150). / The pressure ratio of axial compressor stages can be significantly increased by controlling the development of blade and endwall boundary layers in regions of adverse pressure gradient by means of boundary layer suction. This concept is validated and demonstrated through the design and analysis of two unique aspirated compressor stages: a low-speed stage with a design pressure ratio of 1.6 at a tip speed of 750 ft/s, and a high-speed stage with a design pressure ratio of 3.5 at a tip speed of 1500 ft/s. The aspirated compressor stages were designed using a new procedure which is a synthesis of low speed and high speed blade design techniques combined with a flexible inverse design method which enabled precise independent control over the shape of the blade suction and pressure surfaces. Integration of the boundary layer suction calculation into the overall design process is an essential ingredient of the new procedure. The blade design system consists of two axisymmetric through-flow codes coupled with a quasi three-dimensional viscous cascade plane code with inverse design capability. Validation of the completed designs were carried out with three-dimensional Euler and Navier-Stokes calculations. A single spanwise slot on the blade suction surface is used to bleed the boundary layer. The suction mass flow requirement for the low-speed and high-speed stages are 1 % and 4% of the inlet mass flow, respectively. Additional suction between 1-2% is also required on the compressor end walls near shock impingement locations. The rotor is modeled with a tip shroud to eliminate tip clearance effects and to discharge the suction flow radially from the flowpath. Three-dimensional viscous evaluation of the designs showed good agreement with the quasi three-dimensional design intent, except in the endwall regions. The suction requirements predicted by the quasi three-dimensional calculation were confirmed by the three-dimensional viscous calculations. The three-dimensional viscous analysis predicted a peak pressure ratio of 1.59 at an isentropic efficiency of 89% for the low-speed stage, and a peak pressure ratio of 3.68 at an isentropic efficiency of 94% for the high-speed rotor. / by Ali M. Merchant. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 79-81). / A primary goal in compressor design for jet engines is the reduction of size and weight. This can be achieved by increasing the work output per stage, thereby reducing the required number of stages. In this thesis, the aerodynamic design of a high speed compressor that produces a pressure ratio of 9.1:1 in only two stages (rather than the typical six or seven) is presented. This is accomplished by employing blade aspiration in conjunction with rotor counter-rotation. Aspiration has been shown to make feasible significantly increased blade loading and counter-rotation provides a means of taking full advantage of this potential throughout a multistage compressor. The aspirated counter-rotating compressor was designed using a one-dimensional stage analysis program coupled with an axisymmetric throughflow code and a quasi-three- dimensional cascade code for blade design. The design of each stage focused on maximizing pressure ratio within diffusion factor and relative inlet Mach number (i.e. shock loss) constraints. The exit angle of the first stator was optimized to maximize the pressure ratio of the counter-rotating (second) rotor. The blade design code MISES allowed for each feature of the blade sections, including aspiration, to be precisely designed for the predicted conditions. To improve the process of designing blades with MISES, extensive analysis of previously designed high-speed aspirated blades was performed to identify the relationships between various blade features. / by Jody Kirchner. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 47-49). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / In scientific and engineering contexts, physical systems are represented by mathematical models, characterized by a set of parameters. The inverse problem arises when the parameters are unknown and one tries to infer these parameters based on observations. Solving the inverse problem can require many model simulations, which may be expensive for complex models; multiple models of varying fidelity and complexity may be available to describe the physical system. However, inferring the parameters may only be an intermediate step, and what is ultimately desired may be a low-dimensional Quantity of Interest (QoI); we refer to this as the goal-oriented inverse problem. We present a novel algorithm for solving the goal-oriented inverse problem, which allows one to manage the fidelity of modeling choices while solving the inverse problem. We formulate a hierarchy of models, and assume that the QoI obtained by inferring the parameters with the highest-fidelity model is the most accurate QoI. We derive an estimate for the error in the QoI from inferring the parameters using a lower-fidelity model instead of the highest-fidelity model. This estimate can be localized to individual elements of a discretized domain, and this element-wise decomposition can then be used to adaptively form mixed-fidelity models. These mixed-fidelity models can be used to infer the parameters, while controlling the error in the QoI. We demonstrate the method with two pairs of steady-state models in 2D. In one pair, the models differ in the physics included; in the other pair, the models differ in the space to which the parameters belong. In both cases, we are able to obtain a QoI estimate with a small relative error without having to solve the inverse problem with the high-fidelity model. We also demonstrate a case where solving the inverse problem with the high-fidelity model requires a more complex algorithm, but where our method gives a mixed-fidelity model with which we can infer parameters using a simple Newton solver, while achieving a low error in the QoI. / by Harriet Li. / S.M.