A Feasibility Study of Micro-Satellites for Earth Observation

There is a continuing desire to minimize the fabrication, launch, and operational costs of Earth-observing satellites, while still maintaining their high-resolution capabilities. Micro-satellites have been suggested as a method for obtaining these results using several different configurations; such as conventional filled aperture optics, distributed aperture systems, constellations and tethers. The ability of the different spacecraft types to achieve images of a specified resolution and quality are examined, as are their affects on the mass and size of the spacecraft. However, first a minimum spacecraft size is discussed and formulated for missions of this and similar types. This is used as a first order analysis to determine when micro-satellites may be applicable to a specific mission. These results, and those from the analysis of the different spacecraft types are then used to determine when, and if, it is beneficial to use a micro-satellite over a more conventional spacecraft design. It will be demonstrated that distributed aperture systems and deployable primary mirrors are generally the best approaches for highresolution- imaging micro-satellites, but that distributed aperture systems are useful when replacing very large primary mirrors

Strategy for Mitigating Collision Between Landsat-5 and the Afternoon Constellation

The NASA Goddard Space Flight Center Earth Science Mission Operations project, the French space agency Centre National d tudes Spatiales, the Argentinian space agency Comisi n Nacional de Actividades Espaciales, and the United States Geological Survey all operate spacecraft in sun-synchronous frozen orbits. The orbits are planned to not place any of the spacecraft at risk of colliding with another. However, evolution of these orbits over time has com-promised the safe interaction between Landsat-5 and the Afternoon Constella-tion. This paper analyzes the interactions between the Landsat-5 spacecraft and the Afternoon Constellation members over a period of 6 years, describing the current risk and plan to mitigate collisions in the future

Recycled polycarbonate and polycarbonate/acrylonitrile butadiene styrene feedstocks for circular economy product applications with fused granular fabrication-based additive manufacturing

Distributed recycling and additive manufacturing (DRAM) holds enormous promise for enabling a circular economy. Most DRAM studies have focused on single thermoplastic waste stream. This study takes three paths forward from the previous literature: 1) expanding DRAM into high-performance polycarbonate/ acrylonitrile butadiene styrene (PC/ABS) blends, 2) extending PC/ABS blend research into both recycled materials and into direct fused granular fabrication (FGF) 3-D printing and 3) demonstrating the potential of using recycled PC/ABS feedstocks for new applications in circular economy contexts. A commercial open source large-format FGF 3-D printer was modified and used to assess the different printability and accuracy of recycled PC and PC/ABS. The mechanical properties (tensile and impact) following the ASTM D638 and D6110–18 standards were quantified. A weather simulation test (ASTM D5071–06) was performed to assess outdoor performance. Finally, two applications in sporting goods and furniture were demonstrated. In general, better printability was achieved with recycled PC/ABS compared to recycled PC, as well as good dimensional accuracy at printing speeds of 30 and 40 mm/s. Minimal qualitative differences and discoloration were visible on the samples after accelerated weather exposure, with results in accordance with the state-of-the-art. The rPC/ABS results from tensile tests show similar values to those of rPC for elastic modulus (2.1 ± 0.1 GPa), tensile strength (41.6 ± 6.3 MPA), and elongation at break (2.8 ± 0.9%), which are also comparable with previous studied virgin 3-D printed filaments. Similarly, impact energy (115.78 ± 24.40 kJ/m2) and resistance values (810.36 ± 165.77 J/m) are comparable in the two tested formulations, reaching similar results compared to FFF 3-D printed filaments, as well as virgin materials for injection molding. Finally, the two demonstration products in the sporting goods and furniture sectors were successfully fabricated with rPC/ABS, achieving complex patterns and good printing speeds for recycled feedstocks. It is concluded rPC/ABS blends represent a potential high-performance feedstock for DRAM, validating its use in direct FGF 3-D printing systems and potential applications for a circular economy

Airport access via rail transit : what works and what doesn't

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1999.Includes bibliographical references (p. 139-140).Despite their potential for providing efficient and reliable airport access, rail connections to U.S. airports have consistently had trouble attracting a significant percentage of airport passengers. This thesis attempts find out which characteristics of airport rail links most strongly influence mode share so that future rail link plans can be assessed. These findings are then applied to the current plans for an airport rail link in San Juan, Puerto Rico. The thesis begins by examining current airport rail links in the U.S. Detailed case studies are performed for the following airports: John F. Kennedy, Philadelphia, Boston Logan, Washington National, Chicago O'Hare, Chicago Midway, and San Jose. Smaller case studies are performed for Atlanta, Cleveland, St Louis, Baltimore-Washington, Miami, and Oakland. The data collected for these airports is compared by looking for relationships between characteristics of the rail links and their mode shares. Two variables, rail travel time and the difference between rail and auto travel time, are apparently related to rail link mode share. Several propositions are advanced about the characteristics of airport rail links that affect mode share, and the way in which they affect mode share. The strongest of these propositions are that the lower the travel time difference between rail and auto the greater the rail mode share, that on-airport rail stations are likely to increase mode share, and that effectively serving population and employment centers is likely to increase airport rail link mode share. Some further analysis is then performed on two of the propositions advanced. First, the relevance of the airport rail station location is tested by looking at the effect on mode share at Washington National when the rail station was, in effect, moved closer to the airport terminal. This analysis indicates that it is likely that the location of an airport rail station is related to mode share. Second, an analysis of population and employment around airport rail link stations is performed for Boston, New York City, and Chicago. This analysis indicates that the rail links examined serve a very small percentage of the population and jobs in their respective metro areas. This makes sense since rail links in these cities all have relatively low mode shares. Finally, a case study of San Juan is presented. This case study is different than the previous ones since the San Juan link is in the planning stages. After the San Juan plan is presented, each proposition developed earlier is applied to the San Juan case to determine the potential effect of that proposition on mode share for the San Juan link. This analysis and a model for calculating mode share based on rail/auto time difference help to predict mode share for San Juan. The mode share for San Juan is likely to be between 2% and 5%. The thesis concludes with potential changes to the plan that might help increase that figure.by Joshua Schank.M.C.P

Process and design of a once-through dimethyl ether process using aveva process simulation

In this project, an optimization and preliminary economic analysis based on the lowest rent and utility cost was performed on a dimethyl ether process plant. This process model was performed with AVEVA Process Simulation software. Basic chemical engineering design principles as well as 3D response surface modeling and the native AVEVA optimization tool were used to select the most cost-effective equipment by varying process specifications to minimize utility cost, finding the least expensive equipment combinations possible, and selecting the feed tray location. The rental prices were fixed, so only utility and limited process specifications such as feed tray location could be varied to find the minimum equivalent annual operating cost. It was found that dimethyl ether process has the ability to be profitable with an economic potential of $6.8 million annually and the rent and utility cost being about$642,000 annually. It is recommended based on the economic potential to continue the analysis of the project as outlined in this thesis

Metabolic engineering of \u3ci\u3eEscherichia coli\u3c/i\u3e for the \u3ci\u3ede novo\u3c/i\u3e stereospecific biosynthesis of 1,2-propanediol through lactic acid

1,2-propanediol (1,2-PDO) is an industrial chemical with a broad range of applications, such as the production of alkyd and unsaturated polyester resins. It is currently produced as a racemic mixture from nonrenewable petroleum-based feedstocks. We have reported a novel artificial pathway for the biosynthesis of 1,2-PDO via lactic acid isomers as the intermediates. The pathway circumvents the cytotoxicity issue caused by methylglyoxal intermediate in the naturally existing pathway. Successful E. coli bioconversion of lactic acid to 1,2-PDO was shown in previous report. Here, we demonstrated the engineering of E. coli host strains for the de novo biosynthesis of 1,2-PDO through this pathway. Under fermenter-controlled conditions, the R-1,2-PDO was produced at 17.3 g/L with a molar yield of 42.2% from glucose, while the S-isomer was produced at 9.3 g/L with a molar yield of 23.2%. The optical purities of the two isomers were 97.5% ee (R) and 99.3% ee (S), respectively. To the best of our knowledge, these are the highest titers of 1,2-PDO biosynthesized by either natural producer or engineered microbial strains that are published in peer-reviewed journals

Bringing computational thinking to K-12 and higher education

Doctor of PhilosophyDepartment of Computer ScienceWilliam H. HsuSince the introduction of new curriculum standards at K-12 schools, computational thinking has become a major research area. Creating and delivering content to enhance these skills, as well as evaluation, remain open problems. This work describes different interventions based on the Scratch programming language aimed toward improving student self-efficacy in computer science and computational thinking. These interventions were applied at a STEM outreach program for 5th-9th grade students. Previous experience in STEM-related activities and subjects, as well as student self-efficacy, were surveyed using a developed pre- and post-survey. The impact of these interventions on student performance and confidence, as well as the validity of the instrument are discussed. To complement attitude surveys, a translation of Scratch to Blockly is proposed. This will record student programming behaviors for quantitative analysis of computational thinking in support of student self-efficacy. Outreach work with Kansas Starbase, as well as the Girl Scouts of the USA, is also described and evaluated. A key goal for computational thinking in the past 10 years has been to bring computer science to other disciplines. To test the gap from computer science to STEM, computational thinking exercises were embedded in an electromagnetic fields course. Integrating computation into theory courses in physics has been a curricular need, yet there are many difficulties and obstacles to overcome in integrating with existing curricula and programs. Recommendations from this experimental study are given towards integrating CT into physics a reality. As part of a continuing collaboration with physics, a comprehensive system for automated extraction of assessment data for descriptive analytics and visualization is also described