The fast-growing space industry results in increasing demand for thermal control systems. Loop heat pipes (LHPs) are a commonly utilized device for spacecraft due to high efficiency and flexibility (ability to integrate with deployable radiator, thermal control valve, etc.). However, they are currently too costly to manufacture to make them viable for most cost-sensitive applications such as CubeSats and SmallSats. Conventional loop heat pipe manufacturing method involves multiple labor-intensive steps including a knife edge seal process to ensure no back leak of vapor that affects the thermal transport capability. Unfortunately, the steps to manufacture the wick, insert it in the LHP evaporator, and seal with a knife edge results in very high manufacturing costs. Advanced Cooling Technologies, Inc. (ACT) has developed a low-cost LHP evaporator using a technique called Direct Metal Laser Sintering (DMLS), otherwise known as 3D printing. With the capability of building a porous wick structure together with a solid wall via additive manufacturing, 3D printed LHP eliminates the knife edge seal as well as many wick manufacturing and testing steps. The 3D printed LHP reduces the fabrication cost by an order of magnitude, which enables the use of LHPs in many emerging space applications, including CubeSats and SmallSats.
While the developed 3D printed loop heat pipe shows significant cost benefit compared to the loop heat pipe made by conventional fabrication process, the pore size of 3D printed primary is around 5~7 μm, much larger than the 1 μm pore size made by sintering process. In addition, the porosity of the 3D printed primary wick is lower than sintering wick (31% vs. > 40%). In order to apply this emerging technology to higher power, large satellite applications, which are the current main loop heat pipe market, further pore size reductions and increased porosity are needed.
NASA is interested in using loop heat pipes for various applications, including SamllSat, CubeSat, Large Satellite, as well as Lunar Rovers and Landers. The proposed technology provides a low cost manufacturing method for loop heat pipe, which addresses the main drawback (high cost) of this technology. In addition, by eliminating the knife edge seal, the 3D printed loop heat pipe can be more robust.
In addition to NASA, DOD have similar demands for the space thermal control and can benefit from the developed low-cost 3D printed loop heat pipe technology. More important, there are an increasing number of cost-sensitive commercial satellites, including satellite swarms. The developed 3D printed LHP provides a low cost solution to address this increasing demand.