The thermal subsystem is tasked with maintaining temperatures in the satellite within operational temperature limits. Each component on the satellite has a hot and cold operating temperature. For example, the CPU on USUSAT II has a cold temperature constraint of -40°C and a hot temperature constraint of 80°C. If the temperature of the CPU is ever outside of this range it will cease to function.

The thermal subsystem controls the temperatures of the satellite using conductive and radiative modes of heat transfer. Internally, the spacecraft transports heat mainly by conduction through the structural panels. Externally, the spacecraft is in balance with the space environment. Energy is absorbed from the sun and the earth and radiated out to the cold of deep space.

USUSAT II uses a passive strategy to control the temperatures. The absorptive properties of the exterior of the spacecraft are balanced with the radiative properties. Using this method it is possible to keep the satellite near room temperature. The passive approach is not sufficient for temperature sensitive components like the nickel-cadmium battery. Heaters have been added in order to keep sensitive components within limits.

A full analysis of the USUSAT II bus has been completed in SINDA via C&R Technologies' Thermal Desktop package. Simulation and design have been completed for hot and cold cases at altitudes of 185, 380, and 1000 km circular orbits.



The thermal subsystem of USUSAT II is capable of meeting temperature constraints in all low earth orbits, from 185 to 1000 km altitude, and all inclinations. The thermal subsystem is robust enough to maintain acceptable temperatures even in GTO.

- Copyright© 2005 Utah State University USU Nanosat Program
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