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A wide range of environmental exposures, stringent payload interface conditions, a low risk requirement, low allowable heater power, constraints of a fixed price contract and aggressive schedule presented a challenge in developing the FUSE bus (spacecraft) thermal design. The bus provides power, attitude control and telemetry for the satellite, which includes the bus and instrument payload. The thermal design that evolved is remarkably self-regulating. This is attributed to the synergistic effect of a compact structure that allows cross-coupling of radiators with different exposures in addition to the advantages of a large louver. This paper discusses the design approach, key thermal control features, supporting analyses and trade studies, and how predicted results compare with requirements for the design envelope and beyond.

The use of the SINDA/FLUINT computer code (Reference 1) for solving convective cooling problems has proven to be a valuable design and analysis tool. SINDA/FLUINT is used to efficiently support design applications where thermal analysis involving both heat transfer and fluid flow are involved. The program allows for simplification of fluid modeling compared to older versions of SINDA where this could only be done through user-generated logic. Also, SINDA/FLUINT provides a faster and simpler analysis basis over more complex fluid dynamics software programs, which can be an advantage for certain design applications. This paper discusses the utilization and benefits of SINDA/FLUINT for examples of such designs.

The importance of developing test correlated analytical models, of critical or unique spacecraft hardware, is not limited to pre-flight design verification. Such thermal models can also be extremely useful tools in assessing on-orbit operational and temperature anomalies. This paper discusses the application of test correlated thermal models, developed for a complex electro-mechanical system, in support of on-orbit operational replanning in response to unexpected mechanism movement and electronics temperature levels. The modeling effort utilized a recently developed routine for chaining coordinate systems in TRASYS (Thermal Radiation Analysis System). Results from the modeling provided detailed data, which complemented the limited telemetry and supported the operational replanning to ensure acceptable performance would be maintained throughout the mission.

In order to characterize the thermal performance of the spacecraft at attitudes beyond initial constraints and to expand the operational envelope, on-orbit testing was performed. Plans and tradeoffs in preparing for the testing are discussed. Results are presented and compared with analytical predictions. Although the payload and bus sections were only separately thermal vacuum tested prior to flight, results from the on-orbit testing indicate the integrated thermal design is robust. One thermal anomaly was discovered which is attributed to specular reflections from a radiator. The influence of the on-orbit testing results on spacecraft continuing operations is also discussed.