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Theses and Dissertations

Rachel M. Brewer, M.S.

The Impact of Proton-Induced Single Events on Image Classification in a Neuromorphic Computing Architecture

Neuromorphic computing endeavors to imitate the way biological brains process information and problem-solves. Uses for neuromorphic computing span disciplines and include applications in image processing, audio processing, optimization, and more. This work explores the effect of proton-induced single-event upsets on a neuromorphic computing architecture engaged in image recognition. Two main results are found. One, the overall classification accuracy is unchanged although a high number of hidden, tolerable errors occurred. Additionally, single event upsets are found to alter the relative occurrence of false positives and false negatives, which occurred despite the overall classification accuracy remaining unaffected.

| Thesis |

Rebekah A. Austin, Ph.D.

Modeling Radiation Risk Assessment and Mitigation for Spacecraft Electronics

Abstract: Space-based missions are increasingly having to design and test systems with shorter development times and small budgets and teams. These missions additionally have a higher risk tolerance, leading them to choose commercial parts over radiation-hardened parts in their systems. Additionally, over the last decade, improvements to radiation environment models have enabled the quantification of the uncertainty in the predicted environment, allowing for smaller margins in radiation requirements.

In this dissertation, a novel method to calculate the likelihood of radiation-induced destructive faults for silicon carbide power metal-oxide field-effect transistors was developed. The method calculates the probability of failure for destructive single-event burnout and includes environment variability enabled by the PSYCHIC solar heavy-ion environment model. The calculation decouples the part-to-part variability and environment variability. The calculated likelihood can be included with other types of faults and used in system-level probabilistic risk assessment.

Additionally, new guidelines for space-radiation risk assessment and risk management within model-based mission assurance are proposed. The guidelines integrate common modeling languages for systems and mission requirements used in model-based systems engineering with information and activities for radiation hardness assurance. A novel fault propagation model is proposed to enable the evaluation of radiation-induced faults and consequences within traditional model-based systems engineering. These guidelines and fault propagation models were implemented on a free-to-use web-based platform supported by NASA’s Office of Safety and Mission Assurance and demonstrated on a CubeSat radiation effects experiment board and for a single-event burnout radiation requirement.

These additions to the radiation hardness assurance process enable the inclusion of radiation into model-based mission assurance so that constraint-driven systems can maximize limited resources. By leveraging model-based engineering practices, these constraint-driven teams can use these methods to evaluate radiation risks at the system level and estimate probabilities of failure for destructive effects in emerging technologies.
| Dissertation |

A Radiation-Reliability Assurance Case using Goal Structuring Notation for a CubeSat Experiment

Abstract: CubeSats have become an attractive platform for university-based spacecraft designs because they are cheaper and quicker to launch than full-scale satellites. One way of keeping costs for CubeSats low is using commercial off-the-shelf parts (COTS) instead of using space-qualified parts. Space-qualified parts are often costly, larger, and consume more power than their commercial counterparts prohibiting their use within a CubeSat. Given typical power budgets, monetary budgets, and timelines for CubeSat missions, conventional radiation hardness assurance, like the use of hardened parts and radiation testing campaigns of COTS parts, is not possible, requiring a system-level approach to radiation effects mitigation. In this thesis an assurance case for the radiation reliability of a CubeSat experiment is expressed using Goal Structuring Notation (GSN), a graphical argument standard. The case specifically looks at three main mitigation strategies for the radiation environment: total ionizing dose (TID) screening of parts, detection and recovery from single-event latch-ups (SEL) and single-event functional interrupts (SEFI). The graphical assurance case presented makes a qualitative argument for the radiation reliability of the CubeSat experiment using part and system-level mitigation strategies and is supported by functional and system models of the system.
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Ryan F. Keller, M.S.

Total Ionizing Dose Effects in Silicon Bulk FinFETs at Cryogenic Temperatures

Abstract: The icy bodies of the solar system, such as Europa and Titan, are high priority targets for exploratory spacecraft missions by NASA and the world’s space agencies. Such missions would likely involve electronic payloads being subjected to harsh radiation environments while at extremely low temperatures. This work aims to characterize the effects of such an environment on the modern bulk FinFET device geometry in order to determine viability and design optimization. The operation of bulk Silicon FinFET devices at temperatures from room temperature (293 K) to 90 K is explored. The TID responses of bulk FinFET devices irradiated with protons at 89 K are compared to the responses of devices irradiated at 293 K. Experiments show that fin-width is a determining factor in device operation at lower temperatures, and in the radiation response of devices at both room temperature and cryogenic temperatures. Devices irradiated at low temperatures experienced different TID effects due to the changes in material properties at low temperatures. In particular, they experienced greater transconductance degradation and relatively greater subthreshold slope degradation.

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