Design of a Programmable Star Tracker-Based Reference System For a Simulated Spacecraft

The main objective of this research effort is to achieve an accuracy level for the SimSat star tracker system comparable to what is reported in current literature by various star tracker manufacturers and researchers. Previous work has provided a spherical star dome that needs to be fully populated with light sources. Programmable organic light emitting diode (OLED) panels were chosen to populate the dome to allow high contrast ratios without backlighting and increase the number of star combinations able to be represented. Noise equivalent angles less than five arcseconds (1 delta ) are achieved about the boresight axis and less than half an arcsecond around the other axes. Absolute accuracy near the center of the star dome is tested to be less than 0.04 degree about each axis. Two different approaches to inertially cataloging the star eld are also investigated, externally referencing each panels coordinates using a coordinate measurement arm and utilizing the camera\u27s known position to catalog the panel\u27s location. The full population of the SimSat star dome and reprogrammable capability of the panels allows many future research endeavors related to star pattern recognition and attitude determination to be undertaken

The Deformable Mirror Demonstration Mission (DeMi) CubeSat: optomechanical design validation and laboratory calibration

Coronagraphs on future space telescopes will require precise wavefront correction to detect Earth-like exoplanets near their host stars. High-actuator count microelectromechanical system (MEMS) deformable mirrors provide wavefront control with low size, weight, and power. The Deformable Mirror Demonstration Mission (DeMi) payload will demonstrate a 140 actuator MEMS deformable mirror (DM) with \SI{5.5}{\micro\meter} maximum stroke. We present the flight optomechanical design, lab tests of the flight wavefront sensor and wavefront reconstructor, and simulations of closed-loop control of wavefront aberrations. We also present the compact flight DM controller, capable of driving up to 192 actuator channels at 0-250V with 14-bit resolution. Two embedded Raspberry Pi 3 compute modules are used for task management and wavefront reconstruction. The spacecraft is a 6U CubeSat (30 cm x 20 cm x 10 cm) and launch is planned for 2019.Comment: 15 pages, 10 figues. Presented at SPIE Astronomical Telescopes + Instrumentation, Austin, Texas, US

Calibration and Testing of the Deformable Mirror Demonstration Mission (DeMi) CubeSat Payload

The Deformable Mirror Demonstration Mission (DeMi) is a 6U CubeSat that will operate and characterize the on-orbit performance of a Microelectromechanical Systems (MEMS) deformable mirror (DM) with both an image plane and a Shack-Hartmann wavefront sensor (SHWFS). Coronagraphs on future space telescopes will require precise wavefront control to detect and characterize Earth-like exoplanets. High-actuator count MEMS deformable mirrors can provide wavefront control with low size, weight, and power. The DeMi payload will characterize the on-orbit performance of a 140 actuator MEMS DM with 5.5 _m maximum stroke, with a goal of measuring individual actuator wavefront displacement contributions to a precision of 12 nm. The payload will be able to measure low order aberrations to l/10 accuracy and l/50 precision, and will correct static and dynamic wavefront phase errors to less than 100 nm RMS. The DeMi team developed miniaturized DM driver boards to fit within the CubeSat form factor, and two cross-strapped Raspberry Pi 3 boards are used as payload computers. We present an overview of the payload design, the assembly, integration and test progress, and the miniaturized DM driver characterization process. Launch is planned for late 2019

Absence of direction-specific cross-modal visual–auditory adaptation in motion-onset event-related potentials

Adaptation to visual or auditory motion affects within-modality motion processing as reflected by visual or auditory free-field motion-onset evoked potentials (VEPs, AEPs). Here, a visual–auditory motion adaptation paradigm was used to investigate the effect of visual motion adaptation on VEPs and AEPs to leftward motion-onset test stimuli. Effects of visual adaptation to (i) scattered light flashes, and motion in the (ii) same or in the (iii) opposite direction of the test stimulus were compared. For the motion-onset VEPs, i.e. the intra-modal adaptation conditions, direction-specific adaptation was observed – the change-N2 (cN2) and change-P2 (cP2) amplitudes were significantly smaller after motion adaptation in the same than in the opposite direction. For the motion-onset AEPs, i.e. the cross-modal adaptation condition, there was an effect of motion history only in the change-P1 (cP1), and this effect was not direction-specific – cP1 was smaller after scatter than after motion adaptation to either direction. No effects were found for later components of motion-onset AEPs. While the VEP results provided clear evidence for the existence of a direction-specific effect of motion adaptation within the visual modality, the AEP findings suggested merely a motion-related, but not a direction-specific effect. In conclusion, the adaptation of veridical auditory motion detectors by visual motion is not reflected by the AEPs of the present study

Large animal models of cardiovascular disease

The human cardiovascular system is a complex arrangement of specialized structures with distinct functions. The molecular landscape, including the genome, transcriptome and proteome, is pivotal to the biological complexity of both normal and abnormal mammalian processes. Despite our advancing knowledge and understanding of cardiovascular disease (CVD) through the principal use of rodent models, this continues to be an increasing issue in today's world. For instance, as the ageing population increases, so does the incidence of heart valve dysfunction. This may be because of changes in molecular composition and structure of the extracellular matrix, or from the pathological process of vascular calcification in which bone-formation related factors cause ectopic mineralization. However, significant differences between mice and men exist in terms of cardiovascular anatomy, physiology and pathology. In contrast, large animal models can show considerably greater similarity to humans. Furthermore, precise and efficient genome editing techniques enable the generation of tailored models for translational research. These novel systems provide a huge potential for large animal models to investigate the regulatory factors and molecular pathways that contribute to CVD in vivo. In turn, this will help bridge the gap between basic science and clinical applications by facilitating the refinement of therapies for cardiovascular disease. Copyright (c) 2016 John Wiley & Sons, Ltd

Decentralized on-board planning and scheduling for crosslink-enabled Earth-observing constellations

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 151-156).Small satellites have improved in capability, nearing a future where high data-rate payloads and crosslinks can provide improved geospatial and temporal coverage, while at a fraction of the cost. Planning and scheduling for efficient bulk data routing with discrete crosslink windows in a dynamic network is a difficult combinatorial optimization problem [30]. As problem size grows, quickly solving the planning and scheduling problem involves implementing algorithms that can leverage parallelization. Decentralized algorithms are inherently parallelizable and can be implemented on-orbit by individual satellites. This thesis investigates a decentralized approach that builds upon the Coupled Constraints Consensus Based Bundle Algorithm (CCBBA) with enhancements to address maximum flow problems.Maximum flow problems occur when moving some resource from sources to sinks across a network, such as a satellite constellation observing targets (sources), moving data between satellites with crosslinks, and down-linking to ground stations (sinks). The CCBBA enhancements include task forking, task outflow coupling, and dynamic task creation based on satellite flow direction preferences. These enhancements increase the total data throughput and decrease required runtime. When implemented on each satellite, this decentralized auction-based approach, named Iterative-CCBBA for Maximum Flow problems (ICMF), provides the following benefits: 1) has robustness in convergence to differences in agent situational awareness, 2) decouples operations from ground station planning resources, and 3) provides an inherently parallelizable algorithm, if implemented on the ground instead of each satellite.ICMF is compared to a state of the art Centralized Global Planner (CGP) in six test cases, with two different inclinations and three different numbers of total satellites. Across all six unique use cases, ICMF has linear scaling in number of consensus rounds and, on average, runs in 94% less time than the CGP, with a 4% improvement in total data volume delivered. ICMF is an effective planner for satellite constellations that value total data throughput and runtime efficiency. The CGP performs better on median latency for observations and median average target age of information, performing better by 58% and 23%, respectively. Future work options for incorporating additional data routing information that could help close the latency and target age of information gap while still using a decentralized approach are presented.by Warren Grunwald.S.M.S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautic