The Orion Crew Module has a pressurized cabin of approximately 20 m3 in volume. There are a number of cold plates within the Crew Module for thermal management. An optical communication type of payload consists of electronics boxes and modems that dissipate a significant amount of heat during science operation. Generally, such payloads operate for a short term (e.g., up to one hour). If these heat-dissipating components are flown inside the Crew Module, they require heat rejection to the cold plates in the Crew Module. The waste heat is transported from the cold plate to thermal radiators located outside the Orion spacecraft. This makes such a payload thermally dependent on the Crew Module cold plates.
A concept of using paraffin phase change material with a melting point of 28 °C to make optical communication-type payloads thermally self-sufficient for operation in the Orion Crew Module is presented. It stores the waste heat of the payload and permits it to operate for up to about one hour by maintaining its temperature within the maximum operating limit. It overcomes the problem of relying on the availability of a cold plate heat sink in the Orion Crew Module.
These components can be attached to paraffin panels that contain Octadecane (C18H38) with a 28 °C melting point. It requires a thermal interface environment of colder than 28 °C to prevent the paraffin from melting prior to payload operation. During science operation, waste heat from the payload melts the paraffin at a constant temperature of 28 °C. When powered off for an extended period of time, the paraffin freezes at a constant temperature of 28 °C because components lose heat to the pressurized cabin. Generally, the maximum operating temperature limit for electronics boxes and modem is 30 to 40 °C. The 28 °C melting point of Octadecane allows these components to operate within the maximum temperature limits.
To store 100 W of payload waste heat for one hour requires approximately 1.4 kg of paraffin phase change material and 0.7 kg of aluminum shell. These can be scaled linearly for other power dissipation or science operation time.
This work was done by Michael Choi of Goddard Space Flight Center. GSC-17217-1