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In this paper we present an implementation of the two-stage time-integration technique for solving semi-discrete systems of elastodynamics problems. This numerical approach effectively suppress the spurious high-frequency oscillations without affecting the accuracy of low modes, especially for long-term integration. At the stage of basic computations zero-dissipative Runge-Kutta methods are applied which yield no error accumulation due to numerical dissipation in the obtained solutions. Then for the suppression of spurious high-frequency oscillations, the filtering stage including pre- or/and post-processing are proceeded by using time integration methods with large numerical dissipation. Therein, the minimum necessary amount of numerical dissipation for filtering the spurious oscillations are determined by using a calibration procedure in which the amplitudes of spurious oscillations occurring the solution profile are minimized by varying stepsizes. The two-stage time integration technique is implemented...

NASA is currently funding an effort involving the Department of Energy (DOE), Lockheed Martin (LM), Glenn Research Center (GRC), and Sunpower (SP), Inc. to develop a high specific power Advanced Stirling Radioisotope Generator (ASRG). GRC and SP are responsible for providing the Stirling convertor, while LM is responsible for the generator housing, controller, and system integration. GRC also provides supporting technologies for various components as well as extended operation testing, both in air and in a thermal vacuum environment. Because of the 17‐year life requirement of the ASRG, reliability considerations are the main design driver. Components such as the heater head, fasteners, magnets, and planar spring have been studied to ensure high reliability. To encompass unique design features, long lifetimes and extreme environmental conditions, both reliability analyses and qualification tests are used to support the design process. This paper presents an overview of the ASRG reliability approach and the impact of the Reliability Working Group (RWG) on the recently finished design effort. It also provides a summary of current and planned extended operation tests, specifically targeted to demonstrate long‐life capability and to support further reliability assessment. In the event of no, or minimal failures during these extended tests, a Weibayes approach will be used to create a trend of improving reliability predictions.

The nuclear risk analysis of the Cassini mission is one of the most comprehensive risk analyses ever conducted for a space nuclear mission. The complexity of postulated accident scenarios and source term definitions, from launch to Earth swingby, has necessitated an extensive series of analyses in order to provide best-estimates of potential consequence results and bounding uncertainty intervals. The Space Accident Radiological Release and Consequence (SPARRC) family of codes, developed by Lockheed Martin to analyze polydispersed source terms and a combination of different atmospheric transport patterns, have been used for the Cassini Final Safety Analysis Report (FSAR). By identifying dominant contributors, the nuclear risk of each mission segment is understood with a high level of confidence. This paper provides the overall analysis process and insights developed from the risk analysis.

This paper shows that the exceptionally wide range and complexity of physical phenomena involved in transport of released radioisotopes following postulated space nuclear accidents must be adequately modeled to realistically assess the radiological consequences. In particular the role of the wide range of particle sizes (at least 12 orders of magnitude) is emphasized. Results from the SPARRC space accident radioisotope transport code system are used to demonstrate this point. The results show that particle size, 3‐D wind fields, and interaction of process time constants produce complex patterns of radiological exposure in space and time. These aspects must be modeled in detail to have a transport methodology that can be applied to the variety of scenarios encountered in space missions.

The nuclear assembly and test site for the SP‐100 test article will be designed to allow it to be safely assembled, operated, disassembled, and disposed. Such safety provisions are discussed.(AIP)