Reports

Executive Summary

The thermal switch project, sponsored by Professor Carlos F. M. Coimbra and Gregory Specht, studied the effectiveness of a gas-filled expansion switch design. Specifically, the focus of the project was to prove or disprove the possibility of a gas powered thermal switch to be used on rovers in Lunar and Martian missions. 

Thermal switches have been used for decades to regulate the temperature of electronic components in space without the need for human interference, in which the switch being on or off corresponds to cooling or heating the attached component. Historically, the switching mechanism has consisted of a solid or liquid material, such as paraffin wax or bimetallic strips. When the temperature of the environment and component reaches a predetermined temperature, the mechanism switches on or off by utilizing the thermal expansion of the chosen solid or liquid component. Though these types of thermal switches have been successful at maintaining the intended temperature ranges of their respective connected electronic components, the weight of solid materials and the potential for sloshing during launch of liquid materials left a lighter, more stable switch to be desired. One possible solution is a gas-filled device capable of expanding or contracting along with the encased gas to power the switch.

The project motivation was to design and fabricate a gas-based thermal switch designed to keep an action camera in its safe operating temperature range despite the temperature extremes of Mars and the Moon. It was to be tested in a vacuum test chamber and designed to eventually be scaled up for use on a real rover in space. Specifically, the following requirements were suggested: 

• Be as light as possible for future space travel

• Last 10 years or 3000 cycles, whichever comes first

• Be clean room compliant

• Not need human intervention or electronics to operate

• Not contain of wax or liquid

• Be able to withstand the temperature and pressure ranges of the Moon and Mars

The design proposed to meet these requirements was a metal bellows attached directly to the action camera test bed and filled with argon, which drove the expansion and contraction of the bellows through thermal expansion. When expanded, the switch was considered to be on, meaning it pulled heat away from the camera battery by making contact with heat sinks. Conversely, when contracted, the switch was off and designed to provide insulation to the battery. The inner switch mechanism was encapsulated in a combination of aluminum and polyethylene to maximize the on and off modes respectively and to protect the entire switch from the harsh space environments. 

The thermal switch prototype was tested by being placed in a freezer and in the sun in order to determine whether or not it successfully turned on or off at the intended transition temperature and to monitor the switch’s effects on the temperature of the camera battery over a range of temperatures.

Some important results of the project include: