Dynamic programming applied to electromagnetic satellite actuation

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."June 2013." Cataloged from department-submitted PDF version of thesisIncludes bibliographical references (p. 135-140).Electromagnetic formation flight (EMFF) is an enabling technology for a number of space mission architectures. While much work has been done for EMFF control for large separation distances, little work has been done for close-proximity EMFF control, where the system dynamics are quite complex. Dynamic programming has been heavily used in the optimization world, but not on embedded systems. In this thesis, dynamic programming is applied to satellite control, using close-proximity EMFF control as a case study. The concepts of dynamic programming and approximate dynamic programming are discussed. Several versions of the close-proximity EMFF control problem are formulated as a dynamic programming problems. One of the formulations is used as a case study for developing and examining the cost-to-go. Methods for implementing an approximate dynamic programming controller on a satellite are discussed. Methods for resolving physical states and dynamic programming states are presented. Because the success of dynamic programming depends on the system model, a novel method for finding the mass properties of a satellite, which would likely be used in the dynamic programming model, is introduced. This method is used to characterize the mass properties of three satellite systems: SPHERES, VERTIGO, and RINGS. Finally, a method for position and attitude estimation for systems that use line-of-sight measurements that does not require the use of a model is developed. This method is useful for model validation of the models used in the dynamic programming formulation.by Gregory John Eslinger.S.M

Bilingualism, social cognition and executive functions:A tale of chickens and eggs

AbstractThe influence of bilingualism on cognitive functioning is currently a topic of intense scientific debate. The strongest evidence for a cognitive benefit of bilingualism has been demonstrated in executive functions. However, the causal direction of the relationship remains unclear: does learning other languages improve executive functions or are people with better executive abilities more likely to become bilingual?To address this, we examined 90 male participants of the Lothian Birth Cohort 1936; 26 were bilingual, 64 monolingual. All participants underwent an intelligence test at age 11 years and were assessed on a wide range of executive and social cognition tasks at age 74. The only notable differences between both groups were found for the Simon Effect (which indexes stimulus-response conflict resolution; β=−.518, p=0.025) and a trend effect for the Faux Pas task (a measure of complex theory of mind; ToM, β=0.432, p=0.060). Controlling for the influence of childhood intelligence, parental and own social class significantly attenuated the bilingual advantage on the Faux Pas test (β=0.058, p=0.816), whereas the Simon task advantage remained (β=−.589, p=0.049).We find some weak evidence that the relationship between bilingualism and cognitive functions may be selective and bi-directional. Pre-existing cognitive and social class differences from childhood may influence both ToM ability in older age and the likelihood of learning another language; yet, bilingualism does not appear to independently contribute to Faux Pas score. Conversely, learning a second language is related to better conflict processing, irrespective of initial childhood ability or social class

Demonstration of electromagnetic formation flight and wireless power transfer

The Resonant Inductive Near-Field Generation System uses a single set of hardware to perform both electromagnetic formation flight and wireless power transfer operations in a six-degree-of-freedom microgravity environment. The system serves primarily as a test bed for control algorithms, and operation onboard the International Space Station allows for more complicated and realistic algorithms to be tested. This offers an advantage compared with the restrictive, dynamic environment of flat floor facilities on the ground or the limited duration of reduced-gravity flights. The hardware attaches to the formation flight-test facility inside the International Space Station referred to as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites. Design and development of the support hardware and electronics, as well as some test results from ground testing, a parabolic flight campaign, and preliminary test sessions on the International Space Station are presented. Ground tests and the parabolic flight campaign results include preliminary inertia and thruster characterization of the combined Resonant Inductive Near-field Generation System/Synchronized Position Hold, Engage, Reorient, Experimental Satellites assembly. Preliminary on-orbit test results include data demonstrating wireless power transfer of approximately 30% and qualitative observations of electromagnetic formation flight with one Resonant Inductive Near-Field Generation System unit restrained and the other unit free floating.Peer ReviewedPostprint (published version

Demonstration of electromagnetic formation flight and wireless power transfer

The Resonant Inductive Near-Field Generation System uses a single set of hardware to perform both electromagnetic formation flight and wireless power transfer operations in a six-degree-of-freedom microgravity environment. The system serves primarily as a test bed for control algorithms, and operation onboard the International Space Station allows for more complicated and realistic algorithms to be tested. This offers an advantage compared with the restrictive, dynamic environment of flat floor facilities on the ground or the limited duration of reduced-gravity flights. The hardware attaches to the formation flight-test facility inside the International Space Station referred to as the Synchronized Position Hold, Engage, Reorient, Experimental Satellites. Design and development of the support hardware and electronics, as well as some test results from ground testing, a parabolic flight campaign, and preliminary test sessions on the International Space Station are presented. Ground tests and the parabolic flight campaign results include preliminary inertia and thruster characterization of the combined Resonant Inductive Near-field Generation System/Synchronized Position Hold, Engage, Reorient, Experimental Satellites assembly. Preliminary on-orbit test results include data demonstrating wireless power transfer of approximately 30% and qualitative observations of electromagnetic formation flight with one Resonant Inductive Near-Field Generation System unit restrained and the other unit free floating.Peer Reviewe

Ventromedial-frontopolar prefrontal cortex atrophy correlates with insight loss in frontotemporal dementia and Alzheimer's disease

Loss in insight is a major feature of frontotemporal dementia (FTD) but has been investigated relatively little. More importantly, the neural basis of insight loss is still poorly understood. The current study investigated insight deficit profiles across a large cohort of neurodegenerative patients (n = 81), including FTD and Alzheimer's disease (AD) patients. We employed a novel insight questionnaire, which tapped into changes across different domains: social interaction, emotion, diagnosis/treatment, language, and motivation. FTD subtypes varied considerably for insight loss, with the behavioral variant worst and the progressive non-fluent variant least affected. All other subtypes and AD showed milder but consistent insight loss. Voxel-based morphometry analysis revealed that overall insight loss correlated with ventromedial and frontopolar prefrontal atrophy, with exception of social interaction and emotion insight loss, which additionally correlated with lateral temporal and amygdala atrophy, respectively. Our results show that patients with neurodegenerative conditions show variable loss of insight, with ventromedial and frontopolar cortex regions appearing to be particularly important for insight. Hum Brain Mapp 35:616-626, 2014

Selective impairment of reasoning about social exchange in a patient with bilateral limbic system damage

Social exchange is a pervasive feature of human social life. Models in evolutionary biology predict that for social exchange to evolve in a species, individuals must be able to detect cheaters (nonreciprocators). Previous research suggests that humans have a cognitive mechanism specialized for detecting cheaters. Here we provide neurological evidence indicating that social exchange reasoning can be selectively impaired while reasoning about other domains is left intact. The patient, R.M., had extensive bilateral limbic system damage, affecting orbitofrontal cortex, temporal pole, and amygdala. We compared his performance on two types of reasoning problem that were closely matched in form and equally difficult for control subjects: social contract rules (of the form, “If you take the benefit, then you must satisfy the requirement”) and precaution rules (of the form, “If you engage in hazardous activity X, then you must take precaution Y”). R.M. performed significantly worse in social contract reasoning than in precaution reasoning, when compared both with normal controls and with other brain-damaged subjects. This dissociation in reasoning performance provides evidence that reasoning about social exchange is a specialized and separable component of human social intelligence, and is consistent with other research indicating that the brain processes information about the social world differently from other types of information