Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000. / Includes bibliographical references (p. 253-255). / The development of high aspect-ratio, high precision micromachining in silicon or silicon carbide suggests the feasibility of rnicrofabricated, high chamber pressure chemical rocket engines. Such an engine, approximately 20x15x3 mm in size, would produce about three pounds of thrust using 300 sec I sp propellants. As part of the present work, the feasibility of these engines has been investigated and a liquid-cooled, pressure-fed thrust chamber has been designed, fabricated, and tested to evaluate the feasibility of the concept. The results of the tests to date using oxygen and methane as propellants support the feasibility of the concept, producing a maximum thrust of 1 N at a chamber pressure of 12 atm. Given the 1.2 gram mass of the thrust chamber, this corresponds to a thrust-to-weight ratio of 85:1. The characteristic exhaust velocity, c*, a measure of combustion effectiveness, appears to be nearly independent of chamber pressure, indicating that chemical reaction rates are not limiting the combustion. Additionally, when effects of chamber heat loss are included, c* appears to approach its predicted ideal value, indicating that the transport and mixing of propellants in the combustion chamber is of the right order to provide for complete combustion. The thrust chamber was fabricated by etching the required patterns into each side of six 0.5 mm thick silicon wafers, and then diffusion bonding the six wafers together to create the one-piece thrust chamber. A packaging technique is presented to interface high pressure and high temperature fluids to the silicon rocket engine chip. Additionally, initial modelling work has lead to the development of a methodology for mapping the feasible design space of microrocket engines, and for optimizing the performance of such systems given current limitations in microfabrication technology. / by Adam Pollok London. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 85). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / The theoretical and numerical evaluation of synergistic diffusing heat-exchanger design is presented. Motivation for this development is based on current diffuser and heat-exchange technologies in cogeneration plants, which require a large geometric footprint to generate steam using gas-turbine exhaust. A compact design is hypothesized to replace these technologies using synergistic design concepts. An investigation into the feasibility of such design concepts are conducted, providing pressure-recovery, viscous losses and thermal energy extraction sensitivities to cooling and annular blade geometry variations. Results show promising diffusion and heat-transfer capabilities that match or surpass current design performance. Proposed configurations are outlined based on these results that compare favorably to a baseline industrial cogeneration application. / by David S. Lazzara. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. / Includes bibliographical references (p. 161-164). / Measured differences between human and primate VOR may derive from disparate experiences with psychophysical motion stimuli. To test this hypothesis, horizontal and torsional eye movements, as well as roll tilt perception, were measured in both "naive" and "experienced" human subjects during 0.5 Hz sinusoidal roll motion. Between these measurement sessions, subjects experienced pseudo-random roll tilt adaptation sessions. For half of the subjects, these adaptation sessions occurred in the light. Subjects participated in 12 measurement sessions and 9 adaptation sessions over the course of three days. (1) The presence of visual cues did not significantly affect horizontal or torsional VOR, but did adversely influence perception of roll tilt as measured using a somatosensory bar. (2) Torsional VOR followed a pattern of habituation and/or adaptation for naive and dark-adapted subjects. (3) Experienced subjects made horizontal eye movements of significantly larger amplitude than those made by naive subjects. (4) The motion paradigm yielded a significant decrease in torsional amplitude without a corresponding decrease in horizontal amplitude. These last two findings suggest experience does not affect the horizontal VOR. Consequently, the hypothesis that human/primate horizontal VOR differences stem from dissimilar motion experience is not supported. Primate and human VOR must continue to be studied separately. / by Robert P. Ocampo. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 81-85). / This thesis presents the development of and the findings from the design and evaluation of a hidden semi- Markov model (HSMM)-based operator state monitoring display. This operator state monitoring display is designed to function as a decision support tool (DST) for the supervisor of a small team of operators (between 2 and 4 team members) that are each monitoring and controlling multiple highly autonomous heterogeneous unmanned vehicles (UVs). Such displays are important in real-time, mission-critical complex systems because both operator and vehicle state monitoring are difficult, and failure to appropriately handle emerging situations could have life or mission-critical consequences. Recent research has shown that HSMM-based models can be used to model the time-sensitive behavior of operators controlling multiple heterogeneous UVs. Because this method requires substantial knowledge in probability theory to understand, the difficulty lies in the accurate, useful display of the HSMM information to a team commander in the field. It must be assumed that the team commander generally does not have the required background in stochastic processes to understand the method and may be biased in interpreting probabilistic functions. This further increases the difficulty of the proposed method. In this thesis, a cognitive task analysis (CTA) was performed to determine the functional and information requirements of the DST, and a human systems engineering design process was used to develop a prototype display. A human subject experiment was then conducted to test the effectiveness of the DST. The DST was shown to improve team supervisor performance in terms of increased decision accuracy, decreased incorrect interventions, and decreased response times in single alert scenarios. The DST was also shown to decrease the number of incorrect interventions, while having no affect on decision accuracy and total response time scenarios when the supervisor faced multiple simultaneous alerts. Additionally, the DST was not shown to increase operator mental workload, as measured by a secondary task, for any of the scenarios. Overall, the results suggest that HSMM-based operator state modeling can be effectively utilized in a real-time DST for team supervisors. While this research was focused on a team supervisor of multiple operators each independently controlling multiple heterogeneous UVs, the results are generalizable, and any research in time-critical team HSC domains may benefit from this work. / by Ryan W. Castonia. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 399-410). / Prior studies have estimated that there are over 100 potential target objects near the Geostationary Orbit belt that are spinning at rates of over 20 rotations per minute. For a number of reasons, it may be desirable to operate in close proximity to these objects for the purposes of inspection, docking and repair. Many of them have an unknown geometric appearance, are uncooperative and non-communicative. These types of characteristics are also shared by a number of asteroid rendezvous missions. In order to safely operate in close proximity to an object in space, it is important to know the target object's position and orientation relative to the inspector satellite, as well as to build a three-dimensional geometric map of the object for relative navigation in future stages of the mission. This type of problem can be solved with many of the typical Simultaneous Localization and Mapping (SLAM) algorithms that are found in the literature. However, if the target object is spinning with signicant angular velocity, it is also important to know the linear and angular velocity of the target object as well as its center of mass, principal axes of inertia and its inertia matrix. This information is essential to being able to propagate the state of the target object to a future time, which is a key capability for any type of proximity operations mission. Most of the typical SLAM algorithms cannot easily provide these types of estimates for high-speed spinning objects. This thesis describes a new approach to solving a SLAM problem for unknown and uncooperative objects that are spinning about an arbitrary axis. It is capable of estimating a geometric map of the target object, as well as its position, orientation, linear velocity, angular velocity, center of mass, principal axes and ratios of inertia. This allows the state of the target object to be propagated to a future time step using Newton's Second Law and Euler's Equation of Rotational Motion, and thereby allowing this future state to be used by the planning and control algorithms for the target spacecraft. In order to properly evaluate this new approach, it is necessary to gather experi / by Brent Edward Tweddle. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 167-182). / Maps used for navigation often include a database of location descriptions for place-recognition (to enable localization or loop-closing), which permits bounded-error navigation performance. A standard localization system must describe the entire operational environment in its place-recognition database. A standard pose-graph-based simultaneous localization and mapping (SLAM) system adds a new place-recognition database entry for every new vehicle pose, which grows linearly and unbounded in time and thus becomes unsustainable. To address these issues, this thesis proposes a new map-reduction approach that pre-constructs a fixed-size place-recognition database amenable to the limited storage and processing resources of the vehicle by exploiting the high-level structure of the environment and vehicle motion. In particular, the thesis introduces the concept of location utility - which encapsulates the visitation probability of a location and its spatial distribution relative to nearby locations in the database - as a measure of the value of potential localization or loop-closure events to occur at that location. While finding the optimal reduced location database is NP-hard, an efficient greedy algorithm is developed to sort all the locations in a map based on their relative utility without access to sensor measurements or the vehicle trajectory. This enables predetermination of a generic, limited-size place-recognition database containing the N best locations in the environment. A street-map simulator using city-map data and a terrain relative navigation simulator using terrestrial rocket flight data are used to validate the approach and show that an accurate map and trajectory reconstruction (pose-graph) can be attained even when using a place-recognition database with only 1% of the entries of the corresponding full database. / by Theodore J. Steiner III. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 129-139). / Breakthroughs in sensing technology in the past decade have greatly improved the capability of robots to sense complicated, partially-known environments. For example, RGB-D cameras and Velodyne scanners allow for the collection of massive amounts of sensor data in real time. These new technologies enable many new possibilities for mobile robots, such as driverless cars, drones, delivery robots, and autonomous marines vehicles. While advances in sensing technology have enabled robots to obtain data quickly and cheaply, robots are typically resource-constrained in storing and processing all the of the data. New algorithmic challenges arise that how to process data selectively to be directly useful for the robot tasks, and use sparse models to meet resource constraints. In many of the applications, a fundamental problem for autonomous systems is the ability to simultaneously map the environment and localize within, especially when there is no global reference. This problem is often referred to as Simultaneous Localization and Mapping (SLAM). This thesis particularly studies three related key technologies in SLAM, sparse mapping, autonomous path planning and interacting with natural objects, but in the content of being task-driven and resource-constrained. In part one, given a pre-collected dataset, only a subset of landmarks and measurements of landmarks are carefully selected to build a sparse map, such that the robot still achieves good navigation performance (minimal collision) with this sparse map. Part two extends the robot's capability to plan its own trajectories while autonomously exploring an unknown environment to build maps. A Topological Feature Graph is developed to maintain sparsity of the map but still enable collision check for path planning. The new approach uses a .unified information metric to explicitly balance exploration of new environment and exploitation of mapped environments. Part three uses deep neural networks to detect real-world objects as landmarks for map building. The new algorithm explicitly takes into account false positives in object detection, and performs object data association and SLAM simultaneously. The proposed approaches are compared with existing methods using both detailed simulations as well as real-world experiments. The results show that the new approaches have good navigation and mapping performance with significantly less memory and computation resources. / by Beipeng Mu. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1987. / Bibliography: v. 2, leaves 309-311. / by Rick Harper. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 129-134). / This thesis investigates the use of Carrier-phase Differential GPS (CDGPS) in relative navigation filters for formation flying spacecraft. This work analyzes the relationship between the Extended Kalman Filter (EKF) design parameters and the resulting estimation accuracies, and in particular, the effect of the process and measurement noises on the semimajor axis error. This analysis clearly demonstrates that CDGPS-based relative navigation Kalman filters yield good estimation performance without satisfying the strong correlation property that previous work had associated with "good" navigation filters. Several examples are presented to show that the Kalman filter can be forced to create solutions with stronger correlations, but these always result in larger semimajor axis errors. These linear and nonlinear simulations also demonstrated the crucial role of the process noise in determining the semimajor axis knowledge. More sophisticated nonlinear models were included to reduce the propagation error in the estimator, but for long time steps and large separations, the EKF, which only uses a linearized covariance propagation, yielded very poor performance. In contrast, the CDGPS-based Unscented Kalman relative navigation Filter (UKF) handled the dynamic and measurement nonlinearities much better and yielded far superior performance than the EKF. The UKF produced good estimates for scenarios with long baselines and time steps for which the EKF would diverge rapidly. A hardware-in-the-loop testbed that is compatible with the Spirent Simulator at NASA GSFC was developed to provide a very flexible and robust capability for demonstrating CDGPS technologies in closed-loop. / (cont.) This extended previous work to implement the decentralized relative navigation algorithms in real time. / by Megan Leigh Mitchell. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references (p. 170-173). / Recent updates to the IPCC estimates of radiative forcing contributions from aircraft have raised concerns about the impacts of contrails and aviation-induced cirrus on climate. Increasing demand for aviation will further increase contrail formation. This thesis provides a model to assess operational options for reducing contrail coverage. This model couples realistic flight performance and best-available global meteorological data assimilations. Comparisons were made between satellite-identified contrails and contrail persistence estimates from flight data for 53,844 U.S. continental flights performed during the week of November 11/12-18, 2001. The satellite data were processed by NASA Langley Research Center using methods for identifying contrails as described by Mannstein [28]. Given detailed knowledge of the aircraft types and radar-based trajectory data, simulated contrails did not match contrails observed in the satellite images. First, striated cirrus cloud formations were misidentified as contrail pixels. This resulted in the "contrails" typically aligning N-S, while most aircraft routes are aligned E-W. Perhaps 40-50% of the contrail pixels were misidentified. Second, a total of 60-90% of the contrail pixels (all demonstrated to be either contrails or clouds) occurred in areas where the assimilated meteorological fields showed RHi < 100%. This demonstrates that the RHi fields, although representative, do not accurately portray the true RHi fields on a given day in 2001. Finally, the typical length of the estimated contrails (several degrees) was longer than the typical length of the observed contrails (one degree). / (cont.) This may reflect a limitation of the satellite sensing of the contrails, but it also implies that the chord lengths used within aviation system model need to be shortened so that they are consistent with length-scales observed in the RHi data. Despite the inability to replicate satellite data, the model was used to develop preliminary estimates of the costs and benefits of operational strategies for contrail and aviation-induced cirrus mitigation. Custom reroutes which minimized fuel burn were created reflecting different options for flying above, below, and around regions of high relative humidity. These options were all consistent with standard reroute procedures employed by the airlines and the Federal Aviation Administration. Using these custom reroutes, analyses were completed for 581 continental flights between 14 city pairs, and 628 international flights over the North Atlantic between 15 city pairs. Given perfect knowledge of meteorological data and no air traffic controls, if aircraft were individually rerouted, it was possible to mitigate 65%-80% of persistent contrails and simultaneously achieve an average decrease of 5%-7% of the total operating cost for the week in November 2001 for which this analysis was carried out. These reductions are relative to the actual routes flown by the aircraft during this week, reflecting the impact of non-optimal routing not only on contrail formation, but also on fuel bum and operating costs in general. Significant contrail reduction may also be achieved if aircraft are rerouted in weekly increments. For the time period that was analyzed it was possible to mitigate 40%-75% of persistent contrails for a change of -10% to +5% of the total operating cost. / (cont.) An assessment was also made of the cost for mitigating contrails compared to the custom reroute that minimized fuel bum. In this case, 55%-85% of the contrails could be mitigated, for roughly a 0.5-1% increase in time and 2.5-3.5% increase in fuel bum (or 1-2% increase in total operating cost). In general, contrail persistence can be mitigated by altering latitude/longitude trajectory, flying at an altitude much lower or much higher than the tropopause, flying a route that minimizes fuel bum, and choosing more northerly routes over the Atlantic Ocean. Key areas of uncertainty that may impact these results include the validity of the contrail identification methods, the validity/range/resolution of the RHi estimates obtained from the assimilated meteorological data, the advection of contrails over time, the chord lengths in the aviation system model, the value of RHi assumed as the contrail persistence threshold, the validity of the engine modeling methods, the database of flights examined, and the construction of the custom reroutes. Further, contrail formation is a strong function of latitude and time of year. Therefore, the results cannot be generalized beyond the global regions and times of year that were analyzed. / by Kelly Klima. / S.M.