Advances in Constrained Spacecraft Relative Motion Planning

This dissertation considers Spacecraft Relative Motion Planning (SRMP), where maneuvers are planned for one or more spacecraft to execute in close proximity to obstacles or to each other. The need for this type of maneuver planning has grown in recent years as the space environment becomes more cluttered, and the focus on space situational awareness increases. In SRMP, maneuvers must accommodate non-linear and non-convex constraints, be robust to disturbances, and be implementable on-board spacecraft with limited computational capabilities. Consequently, many standard optimization or path planning techniques cannot be directly applied to SRMP. In this dissertation, three novel SRMP techniques are developed and simulations are presented to illustrate the implementation of each method. Firstly, an invariance-based SRMP technique is proposed. Maneuvers are planned to transition a spacecraft between specified natural motion trajectories, which require no control to follow, while avoiding obstacles and accommodating minimum and maximum actuation limits. The method is based on a graph search applied to a ``virtual net'' with nodes corresponding to natural motion trajectories. Adjacency rules in the virtual net are based on safe positively invariant tubes built around each natural motion trajectory. These rules guarantee safe transitions between adjacent natural motion trajectories, even when set-bounded disturbances are present. Procedures to construct the safe positively invariant tubes and the virtual net are developed. Methods to reduce calculations are proposed and shown to significantly reduce computation time, with tradeoffs related to maneuver planning flexibility. Secondly, a SRMP technique is developed for the specific problem of satellite inspection. In this setting, an inspector spacecraft maneuvers to gather information about a target spacecraft. An information collection model is developed and used to construct a rapidly computable analytical control law based on the local gradient of the information rate. This control law drives the inspector spacecraft on a path along which the rate of information collection is strictly increasing. To ensure constraint satisfaction, the local gradient control law is combined with a state feedback control law, and rules are developed to govern switches between the two controllers. The method is shown to be effective in generating trajectories to gather information about a specified target point while accommodating disturbances. Finally, a control strategy is proposed to generate a formation containing an arbitrary number of vehicles. This strategy is based on an add-on predictive control mechanism known as a parameter governor. Parameter governors work by modifying parameters, such as gains or offsets, in a nominal closed-loop system to enforce constraints and improve performance. The parameter governor is first developed in a general setting, using generic non-linear system dynamics and an arbitrary formation design. Required calculations are minimized, and non-convex constraints are accommodated through use of a parameter update strategy based on graph colorability theory, and by limiting parameter values to a discrete set. A convergence analysis is presented, proving that under reasonable assumptions, the parameter governor is guaranteed to generate the desired formation. Two specific parameter governors, referred to as the Scale Shift Governor and Time Shift Governor, are proposed and applied to generate formations of spacecraft. These parameter governors enforce constraints by modifying either scale- or time-shifts applied to the target trajectory provided to each spacecraft in formation. Simulation case studies show the effectiveness of each method and demonstrate robustness to disturbances.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145795/1/gfrey_1.pd

KAM Torus Frequency Generation from Two-Line Element Sets

The Kolmogorov Arnold and Moser (KAM) theorem states that a lightly perturbed Hamiltonian system will have solutions which lie on a torus. Earlier work by the second author has shown that most Earth satellite orbits perturbed by the geopotential lie on KAM tori. The problem then arises as to how to convert the current satellite tracking orbits to KAM tori. A KAM torus is characterized by three frequencies and three phase angles. The frequencies are essentially the rates of change of the mean anomaly, the longitude of the ascending node, and the argument of perigee. In this paper we explore the determination of these three rates from the fitting of SGP4 two line element sets (TLEs), and then constructing KAM tori with the specified frequencies. The success of this process, and an idea of the residual errors, can then be obtained by comparing the SGP4 predictions with the KAM torus predictions. Second order polynomials are fit to data from TLEs over 18 months using a least squares technique. The first order coefficients are used as the torus basis frequencies while the second order terms are used to account for perturbations to the satellite\u27s orbit such as air drag. Four cases are attempted using the Hubble Space Telescope and three rocket bodies as test subjects. A KAM torus with the desired basis frequencies is constructed and used to predict satellite position. For the final test case, this shows an oscillatory error with an amplitude of less than 80 km over a period of almost two years. The authors speculate that this is caused by periodic lunar and solar perturbations, masked in the SGP4 fits by frequent updates

Digging Digitally: Creating a More Dynamic Archaeological Field Journal Archive

As the daily record of observations, the field journal always has been central to the archaeological process. Yet in recent decades, these important texts have been ignored in the rush to create digital artifact archives. This project, which builds upon software designed to manage the field books at the Ohio State University Excavations at Isthmia, will correct this oversight by enabling a community of scholars to use scans of the hand written texts to link electronically the disparate forms of evidence that make up the archaeological record. Also, this project will determine the best equipment and practices to allow archaeologists to utilize a digital notebook archive in their research. The result will be an inexpensive, multi-platform, and open source system that can be adapted by other scholars to simplify and enhance research in any field of humanities research that depends upon hand written documents as a primary source of evidence

RNA-mediated interaction of Cajal bodies and U2 snRNA genes

Cajal bodies (CBs) are nuclear structures involved in RNA metabolism that accumulate high concentrations of small nuclear ribonucleoproteins (snRNPs). Notably, CBs preferentially associate with specific genomic loci in interphase human cells, including several snRNA and histone gene clusters. To uncover functional elements involved in the interaction of genes and CBs, we analyzed the expression and subcellular localization of stably transfected artificial arrays of U2 snRNA genes. Although promoter substitution arrays colocalized with CBs, constructs containing intragenic deletions did not. Additional experiments identified factors within CBs that are important for association with the native U2 genes. Inhibition of nuclear export or targeted degradation of U2 snRNPs caused a marked decrease in the levels of U2 snRNA in CBs and strongly disrupted the interaction with U2 genes. Together, the results illustrate a specific requirement for both the snRNA transcripts as well as the presence of snRNPs (or snRNP proteins) within CBs. Our data thus provide significant insight into the mechanism of CB interaction with snRNA loci, strengthening the putative role for this nuclear suborganelle in snRNP biogenesis

Design of a Low-Cost Autoclave for Developing World Health Clinics

Incidence of surgical site infection is 2–5 times higher in developing nations as compared to developed nations. A low-cost, easy to use autoclave was designed to address the unique technical, behavioral, and market challenges present in rural, health posts of the developing world. A thorough stakeholder analysis was performed very early in the design process to address non-technical needs for sustained user adoption as well as manufacturability and scalability. Twelve partnering clinics in Nepal trialed these autoclaves from July until December 2012. Usage statistics and follow-up observations highlight important factors for successful adoption. These findings were used to improve the autoclave design. The goal of this paper is to detail a case study and methodology to incorporate multiple stakeholder needs into the early design process.MIT IDEAS Global ChallengeMassachusetts Institute of Technology. Priscilla King Gray Public Service CenterMIT International Development Initiativ

Association of snRNA genes with coiled bodies is mediated by nascent snRNA transcripts

AbstractBackground: Coiled bodies are nuclear organelles that are highly enriched in small nuclear ribonucleoproteins (snRNPs) and certain basal transcription factors. Surprisingly, coiled bodies not only contain mature U snRNPs but also associate with specific chromosomal loci, including gene clusters that encode U snRNAs and histone messenger RNAs. The mechanism(s) by which coiled bodies associate with these genes is completely unknown.Results: Using stable cell lines, we show that artificial tandem arrays of human U1 and U2 snRNA genes colocalize with coiled bodies and that the frequency of the colocalization depends directly on the transcriptional activity of the array. Association of the genes with coiled bodies was abolished when the artificial U2 arrays contained promoter mutations that prevent transcription or when RNA polymerase II transcription was globally inhibited by α-amanitin. Remarkably, the association was also abolished when the U2 snRNA coding regions were replaced by heterologous sequences.Conclusions: The requirement for the U2 snRNA coding region indicates that association of snRNA genes with coiled bodies is mediated by the nascent U2 RNA itself, not by DNA or DNA-bound proteins. Our data provide the first evidence that association of genes with a nuclear organelle can be directed by an RNA and suggest an autogenous feedback regulation model

Constrained Spacecraft Relative Motion Planning Exploiting Periodic Natural Motion Trajectories and Invariance

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143124/1/1.G002914.pd

Microalbuminuria and hyperfiltration in subjects with nephro-urological disorders

Background Microalbuminuria (MA) has been shown to be an early biomarker of renal damage. It is postulated that MA is the early result of hyperfiltration, which could evolve into glomerular sclerosis and renal failure if hyperfiltration is left untreated. We hypothesized that MA is a good indicator of hyperfiltration in children with kidney disorders, obviating the need to calculate the filtration fraction (FF). Methods A total of 155 children or young adults were prospectively included [42 single kidney (SK), 61 vesico-ureteral reflux, 23 obstructive uropathies, 29 other kidney diseases]. We measured inulin, para-aminohippuric acid clearances, FF and MA. Prediction of hyperfiltration was explored by studying the association between the FF and other variables such as urinary albumin (Alb), urinary albumin-creatinine ratio (ACR) and creatinine clearance. Results A significant but weak association between urinary Alb or ACR and FF was found in subjects with an SK (Spearman correlation coefficients 0.32 and 0.19, respectively). Multivariate analysis also showed that urinary Alb and ACR significantly predict FF only in subjects with an SK (r2 = 0.17, P = 0.01 and r2 = 0.13, P = 0.02, respectively). This holds true only in subjects with an SK and inulin clearance >90 mL/min/1.73 m2 (r2 = 0.41, P < 0.001). There was no association between creatinine clearance and FF. Conclusions MA is not associated with FF in our subjects with nephro-urological disorders, except in those with an SK, where the association is weak, indicating that MA is due to other mechanisms than high FF and cannot predict hyperfiltration in such group

Challenges and opportunities for agroforestry practitioners to participate in state preferential property tax programs for agriculture and forestry

All 50 states offer preferential property tax programs that lower the taxes paid on enrolled agricultural and/or forest lands. While agroforestry is a land-use that combines elements of both agriculture and forestry, eligibility criteria and other rules and regulations may prevent landowners from enrolling agroforestry practices in one or more of the agricultural and forestry tax programs. This pilot-scale study developed conceptual and methodological frameworks to identify the current barriers to and opportunities in preferential tax policies applicable to agroforestry practices. We conducted an extensive review of state preferential property tax programs relevant for agroforestry practices, following focus group discussions with regional experts in five selected states across the United States: North Carolina, Nebraska, Wisconsin, New York, and Oregon. Based on a systematic review of statutes and their supporting documents, we developed a database of programs, which support or create barriers to enrollment of agroforestry practitioners into the programs. We found that agricultural tax assessments were more likely to favor multi-use agriculture and forestry systems than the preferential tax assessments of forestlands in the five states. Forest farming and silvopasture, followed by alley cropping, windbreaks, and riparian forest buffers, were found to be the most common agroforestry practices allowed under preferential tax classifications in the study states. This study provides a framework for cataloging and analyzing preferential property tax-programs to document barriers and facilitators to agroforestry practices in the United States

Comparing silvopastoral systems and prospects in six regions of the world

Paper presented at the 12th North American Agroforesty Conference, which was held June 4-9, 2011 in Athens, Georgia.In Ashton, S. F., S.W. Workman, W.G. Hubbard and D.J. Moorhead, eds. Agroforestry: A Profitable Land Use. Proceedings, 12th North American Agroforestry Conference, Athens, GA, June 4-9, 2011.Silvopasture systems combine trees, forage and livestock in a variety of different species and management regimes, depending on the biophysical, economic, and social factors in a region. In some regions, culture and tradition cause producers to primarily focus on management of either the livestock and forage or the trees, while in other regions, the focus is on joint production. We describe and compare silvopastoral systems in six regions within five countries of the world: Misiones and Corrientes provinces, Argentina, La Pampa province, Argentina, the Southeast United States, the North Island of New Zealand, Paraguay and Uruguay. This summarizes the biological and social factors that have led to their adoption by farmers and the current status of these systems in each country.Frederick Cubbage (1), Gustavo Balmelli (2), Adriana Bussoni (3), Elke Noellemeyer (4), A. Pachas (5), Hugo Fassola (5), Luis Colcombet (5), Bel�n Rossner (5), Gregory Frey (6), Hayley Stevenson (1), James Hamilton (7) and William Hubbard (8) ; 1. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, USA. 2. Instituto Nacional de Investigaci�n Agropecuaria, Tacuaremb�, Uruguay. 3. Universidad de la Rep�blica, Montevideo, Uruguay. 4. Universidad Nacional de La Pampa, Santa Rosa, La Pampa, Argentina. 5. INTA EEA Montecarlo, Montecarlo. Misiones, Argentina. 6. World Bank, Washington, D.C. 7. NC Cooperative Extension Service, Watauga County, Boone, North Carolina, USA. 8. Southern Regional Extension Forester, University of Georgia, Athens, Georgia, USA.Includes bibliographical references