ASETS-II oscillating heat pipe space flight experiment: The first six months on orbit

Abstract

On September 7th, 2017 the U.S. Air Force Research Laboratory launched the second Advanced Structurally Embedded Thermal Spreader (ASETS-II) flight experiment to space on Orbital Test Vehicle 5. The ASETS-II experiment is made of three low-mass, low-cost oscillating heat pipes (OHPs) and an electronics/experiment control box. The three primary science objectives of the experiment are to measure the initial on-orbit thermal performance, to measure long duration thermal performance, and to assess any lifetime degradation. The three OHPs on ASETS-II are of varying configuration (center heating with single-and double-sided cooling) and working fluids (butane and R-134a) in order to isolate specific performance parameters of interest. OHP #3 was specifically designed in order to explore the operating limits on OHP operation in microgravity without requiring excessive operating temperature or pressure. Data collected during the first 6 months of on-orbit operations are presented in this paper. It is shown that each OHP performed as expected, where on-orbit data for OHPs #1 and #2 mirrored ground-truth performance, and the OHP #3 on-orbit maximum operating evaporator temperature increased from ground-truth. The OHPs experienced no significant hysteresis effects and OHP #1 performed successfully in six-week long continuous operation.