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The purpose of this paper is to discuss the selection of a low-temperature coolant used to support Space Station Freedom Active Thermal Control System (SSF ATCS) qualification testing. SSF ATCS testing will use liquid nitrogen (LN2) to reduce the temperature of an intermediate coolant to as low as −78°C; the coolant will then interface with the ATCS working fluid to simulate the heat sink conditions of space. Selection of the intermediate coolant required investigation of the following coolant properties: low freezing point, low viscosity at low temperatures, very low to no toxicity and flammability, and low to moderate vapor pressure at room temperature. Of the four refrigerants that were initially considered, R-124 appeared to be the most attractive. A test was performed to verify the freezing point of R-124. The R-124 test results and a comparison of the four refrigerants are described in detail in this paper.

A liquid fuelled, fuel cell auxiliary power unit (APU) can provide efficient, quiet and low pollution power for a variety of applications including commercial and military vehicles. Truck idling regulation, customer comfort or military “stealth” operation by using electrical power, require a device disconnected from the main diesel engine. The power can be utilized for air conditioning as well as other auxiliary systems found on board commercial trucks for driver comfort. In a military vehicle, this regulated power could be supplied to telecommunication and other computer equipment required for military operations. A system designed to be an add-on or retrofit solution using alternative fuel can have the potential to meet these requirements on the hundreds of thousands of existing vehicles currently in service or as optional equipment on a newly procured vehicle.