Advanced Passive Thermal eXperiment (APTx) for Warm Reservior Hybrid Wick Variable Conductance Heat Pipes on the International Space Station

As NASA prepares to further expand human and robotic presence in space, it is well known that spacecraft architectures will be impacted by unprecedented power requirements and thermal environments in deep space. In addition, there is a need to extend the duration of the missions in both cold and hot environments, including cis-lunar and planetary surface excursions. The heat rejection turn–down ratio of the increased thermal loads in the above-mentioned conditions is crucial for minimizing vehicle power needs. Therefore, future exploration activities will have the need of thermal management systems that can provide higher reliability and performance, and power and mass reduction. In an effort to start addressing the current technical gaps in thermal management systems, novel new passive thermal technologies have been selected and tested on the board of the International Space Station (ISS). This testing was performed under the Advanced Passive Thermal eXperiment (APTx) project that is a collaboration between the Johnson Space Center (JSC), Marshall Space Flight Center (MSFC), University of Texas, and Advanced Cooling Technologies, Inc. (ACT) with funding from ISS Technology Demonstration Office at JSC as well as NASA’s Small Business Innovative Research Program. A hybrid-wick copper-Monel-water Variable Conductance Heat Pipe (VCHP) with warm reservoir design that consists of a copper evaporator (with sintered wick), a monel adiabatic section and a condenser both with grooved wick inside was developed and tested successfully on ground. The VCHP worked on the board of the ISS, but at higher temperatures than expected. Hence, a new flight VCHP design is currently under development to mitigate the shortcomings encountered in microgravity. The final paper will include some results and conclusions from the original flight testing and the ground test results for the improved VCHP.