Final Design

Functional Requirements

The thermal switch was required to meet the following functional criteria:

Maintain the temperature of the action camera’s battery between 0 ºC and 60 ºC
Be as light as possible for future space travel
Last 10 years or 3000 cycles, whichever comes first
Be clean room compliant
No need for human intervention or electronics to operate
Not contain wax or liquid
Be able to withstand the temperature and pressure ranges of the Moon and Mars

Final Design

With respect to the objective mentioned above, our final design is an argon-filled bellows sealed at both of its ends and directly soldered to an action camera encasement, all of which is encased in an aluminum and polyethylene protective enclosure as shown in Figures 2a and 2b. The aluminum and polyethylene serve to protect the camera from radiation damage, as incident radiation is much greater on the Moon and Mars than on Earth. The polyethylene also serves to insulate the camera during the insulating phase and direct heat transfer during the cooling phase.

The main components of the switch are:

76.2 mm diameter stainless steel bellows filled with 25.2 kPa of argon
Two stainless steel end caps attached to the bellows with 96.5 Sn 3.5 Ag solder
One 316 stainless steel check valve
Aluminum heat sink(s)
Rectangular polyethylene inner encasement
Rectangular aluminum channel outer encasement
Aluminum top and bottom plates
External coating of white paint

Figure 2a: Thermal Switch in Cooling Phase

Figure 2b: Thermal Switch in Insulating Phase

Project Performance

The testing was completed under the following conditions:

Cold test was done inside freezer with ambient temperature of approximately -30 ℃
Hot test was done outside in the sun with a forecasted temperature of 18 ℃
Camera was run at 4k resolution with 60fps for 30 minutes
The control test involved running the camera open to the environment
Bellows were filled with air at approximately 101.325kPa (atmospheric pressure)
Infrared temperature gun was used to measure temperature at the battery compartment

Overall, the thermal switch performed admirably. As seen in the results of the cold test, there was significant improvement in the insulation of the battery compartment as evidenced by the drastic difference in temperature in the control condition and the bellows condition. In the bellows condition, as seen by the 0.7 ºC increase in temperature, the bellows were effective at preventing the heat from dissipating into the environment. With respect to the results of the hot test, it can be seen that though temperatures did increase, they did so with less magnitude in the bellows condition than in the control. This shows that the bellows effectively dissipated the heat of the battery compartment. In all, the results of the testing reveal the presence of two different, effective thermal conductivities as outlined in the project objective. The thermal switch proves the effectiveness of a gas-powered switch that satisfies most assigned performance requirements with the possibility of being scaled for larger use.

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