http://hdl.handle.net/1721.1/7767 Tue, 18 Jun 2013 23:31:23 GMT 2013-06-18T23:31:23Z http://hdl.handle.net/1721.1/79336 Continuous relaxation to over-constrained temporal plans Yu, Peng, S.M. Massachusetts Institute of Technology When humans fail to understand the capabilities of an autonomous system or its environmental limitations, they can jeopardize their objectives and the system by asking for unrealistic goals. The objective of this thesis is to enable consensus between human and autonomous system, by giving autonomous systems the ability to communicate to the user the reasons for goal failure and the relaxations to goals that archive feasibility. We represent our problem in the context of temporal plans, a set of timed activities that can represent the goals and constraints proposed by users. Over-constrained temporal plans are commonly encountered while operating autonomous and decision support systems, when user objectives are in conflict with the environment. Over constrained plans are addressed by relaxing goals and or constraints, such as delaying the arrival time of a trip, with some candidate relaxations being preferable to others. In this thesis we present Uhura, a temporal plan diagnosis and relaxation algorithm that is designed to take over-constrained input plans with temporal flexibility and contingencies, and generate temporal relaxations that make the input plan executable. We introduce two innovative approaches within Uhura: collaborative plan diagnosis and continuous relaxation. Uhura focuses on novel ways of satisfying three goals to make the plan relaxation process more convenient for the users: small perturbation, quick response and simple interaction. First, to achieve small perturbation, Uhura resolves over-constrained temporal plans through partial relaxation of goals, more specifically, through the relaxation of schedules. Prior work on temporal relaxations takes an all-or-nothing approach in which timing constraints on goals, such as arrival times to destinations, are completely relaxed in the relaxations. The Continuous Temporal Relaxation method used by Uhura adjusts the temporal bounds of temporal constraints to minimizes the perturbation caused by the relaxations to the goals in the original plan. Second, to achieve quick responses, Uhura introduces Best-first Conflict-directed Relaxation, a new method that efficiently enumerates alternative options in best-first order. The search space of alternative options to temporal planning problems is very large and finding the best one is a NP-hard problem. Uhura empirically demonstrates fast enumeration by unifying methods from minimal relaxation and conflict-directed enumeration methods, first developed for model based diagnosis. Uhura achieves two orders of magnitude improvement in run-time performance relative to state-of-the-art approaches, making it applicable to a larger group of real-world scenarios with complex temporal plans. Finally, to achieve simple interactions, Uhura presents to the user a small set of preferred relaxations in best-first order based on user preference models. By using minimal relaxations to represent alternative options, Uhura simplifies the options presented to the user and reduces the size of its results and improves their expressiveness. Previous work either generates minimal relaxations or full relaxations based on preference, but not minimal relaxations based on preference. Preferred minimal relaxations simplify the interaction in that the users do not have to consider any irrelevant information, and may reach an agreement with the autonomous system faster. Therefore it makes communication between robots and users more convenient and precise. We have incorporated Uhura within an autonomous executive that collaborates with human operators to resolve over-constrained temporal plans. Its effectiveness has been demonstrated both in simulation and in hardware on a Personal Transportation System concept. The average runtime of Uhura on large problems with 200 activities is two order of magnitude lower compared to current approaches. In addition, Uhura has also been used in a driving assistant system to resolve conflicts in driving plans. We believe that Uhura's collaborative temporal plan diagnosis capability can benefit a wide range of applications, both within industrial applications and in our daily lives. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 165-168). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79336 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79335 Development of a rapid global aircraft emissions estimation tool with uncertainty quantification Simone, Nicholas W. (Nicholas William) Aircraft emissions impact the environment by changing the radiative balance of the atmosphere and impact human health by adversely affecting air quality. Many tools used to quantify aircraft emissions are not open source and in most cases are computationally expensive. This limits their usefulness for studies that require rapid simulation, such as uncertainty quantification and assessment of many policy options. We describe the methods used to develop the open source Aviation Emissions Inventory Code (AEIC) and produce a global emissions inventory for the year 2005 from scheduled civil aviation, with quantified uncertainty. This is the most up-to-date openly available inventory for use in atmospheric modeling studies. We estimate that in 2005, scheduled civil aviation was responsible for 180.6 Tg (90% CI: 136.1-232.9 Tg) of fuel burn, equating to 155.5 Tg of CO2 as C (90% CI: 117.3-200.7 Tg) and 0.108 Tg of SOx as S (90% CI: 0.080-0.142 Tg) emissions. 2.689 Tg of NOx as NO2 (90% CI: 1.761-3.804 Tg), 0.749 Tg of CO (90% CI: 0.422-1.145 Tg), and 0.201 Tg of HC as CH4 (90% CI: 0.072-0.362 Tg) were also emitted. 92% of fuel burn took place in the northern hemisphere. Landing and takeoff operations were responsible for 9.1% of total global fuel burn, while 70.6% of fuel burn occurred above 8 km. Our total fuel burn estimate agrees within 4% of other published emissions inventories for the years 2004 and 2006, which is within the uncertainty range of the analysis. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 44-47). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79335 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79334 High-temperature superconductors as electromagnetic deployment and support structures in spacecraft Gettliffe, Gwendolyn Vines In this thesis, we investigate a new structural and mechanical technique aimed at reducing the mass and increasing the stowed-to-deployed ratio of spacecraft systems. This technique uses the magnetic fields generated by high-temperature superconductors (HTSs) to support spacecraft structures and deploy them to operational configurations from stowed positions inside a launch vehicle fairing. The chief limiting factor in spacecraft design today is the prohibitively large launch cost per unit mass. Therefore, the reduction of spacecraft mass has been a primary design driver for the last several decades. Traditionally, spacecraft mass reduction occurs through the use of isogrid panels, aluminum or composites, and inflatable beams all reduce the mass of material necessary to build a truss or apply surface forces to a spacecraft structure. We instead look at using electromagnetic body forces generated by HTSs to reduce the need for material, load bearing support, and standoffs on spacecraft by maintaining spacing, stability, and position of elements with respect to one another. The objective of this thesis is to conduct an initial feasibility study for the use of HTS coils as deployment and support elements in spacecraft structures. To accomplish this objective, we have developed the equations of motion for coils responding to electromagnetic forces while under the influence of constraining elements (i.e. tethers and hinged panels) and validated numerical models of these equations against known analytical solutions. By nondimensionalizing the equations of motion, we have been able to reduce our design variable space through the introduction of lumped dimensionless parameters. This enables simpler trade analysis with regards to structure deployment time and equilibrium configuration, the results of which are also presented and discussed. On the basis of these analyses, we provide suggestions for the selection of design values to achieve desired structural characteristics. Finally, we have introduced, and discussed on the basis of our modeling results, the viability of HTS structures in the context of trade analyses. Trades were described at the mission level, the structural subsystem level, and the component level against traditional and more recently developed alternative structural technologies. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 128-130). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79334 2013-01-01T00:00:00Z http://hdl.handle.net/1721.1/79333 Data management of geostationary communication satellite telemetry and correlation to space weather observations Lohmeyer, Whitney Quinne To understand and mitigate the effects of space weather on the performance of geostationary communications satellites, we analyze sixteen years of archived telemetry data from Inmarsat, the UK-based telecommunications company, and compare on-orbit anomalies with space weather observations. Data from multiple space weather sources, such as the Geostationary Operational Environmental Satellites (GOES), are compared with Inmarsat anomalies from 1996 to 2012. The Inmarsat anomalies include 26 solid-state power amplifier (SSPA) anomalies and 226 single event upsets (SEUs). We first compare SSPA anomalies to the solar and geomagnetic cycle. We find most SSPA anomalies occur as solar activity declines, and when geomagnetic activity is low. We compare GOES 2 MeV electron flux and SSPA current for two weeks surrounding each anomaly. Seventeen of the 26 SSPA anomalies occur within two weeks after a severe space weather event. Fifteen of these 17 occur after relativistic electron events. For these fifteen, peak electron flux occurs a mean of 8 days and standard deviation of 4.7 days before the anomaly. Next, we examine SEUs, which are unexpected changes in a satellite's electronics, such as memory changes or trips in power supplies. Previous research has suggested that solar energetic protons (SEPs) cause SEUs. However, we find that SEUs for one generation of satellites are uniformly distributed across the solar cycle. SEUs for a second generation of satellites, for which we currently have only half a solar cycle of data, occur over an order of magnitude more often than the first, even during solar minimum. This suggests that SEPs are not the primary cause of SEUs, and that occurrence rates differ substantially for different satellite hardware platforms with similar functionality in the same environment. These results will guide design improvements and provide insight on operation of geostationary communications satellites during space weather events. Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.; This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from department-submitted PDF version of thesis.; Includes bibliographical references (p. 86-89). Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/1721.1/79333 2013-01-01T00:00:00Z