SBIR-STTR Award

Our proposed innovation advocates the use of well-known variable conductance heat pipe (VCHP) technology for cryogenic applications where temperature control of sensitive components is also required. IR sensors operating at cryogenic temperatures frequently require temperature control to plus or minus 1.0 degrees C while some applications demand finer control down to pluse or minus 0.1 degrees C. While VCHP's have been used on satellites to control electronic components to narrow temperature bands, despite changes in load and environment that are normally experienced, they have not been developed for cryogenic applications. Our program seeks to evaluate their use by studying the available combinations of working fluids and noncondensible gases that lead to efficient (VCHP) control systems. We propose to use a modified version of a successfully developed monogroove heat pipe as our VCHP baseline design because it has many desirable features in cooling cryogenic IR sensor systems currently being sought by AF and NASA. Having but a single groove, it provides maximum heat transport with minimum fluid charge thereby reducing ambient pipe pressure; it can be configured with flexible sections to provide compliance; it can be configured with multiple evaporators to accommodate multiple sensor/single cooler applications.

Our proposed Phase II program exploits the use of cryogenic variable conductance heat pipe (CVCHP) technology to provide temperature control for two demonstration systems, a 220 K active aperture radar antenna and a 35 K IR sensor, whose feasibility was established in Phase I. To capture the performance benefits of radar operating at these low temperatures, either in space or on the ground, the CVCHP offers improvements in temperature uniformity, lower power consumption and simplicity of operation not found with conventional single phase pumped loops. CVCHPs for 35 K IR sensors also offer attractive benefits of temperature stability, lower power consumption, installation flexibility and lower costs compared to the control provided by mechanical cryocoolers. The working and control fluids for the IR sensor application will be neon and helium, respectively. We have selected a modified monogroove heat pipe as our baseline CVCHP for both applications. This heat pipe provides maximum capacity, minimum fluid charge and the ability to provide flexible/bendable sections, as needed. Our objectives in Phase II are to design, fabricate and test demonstrate these two applications. We expect the results will confirm our Phase I findings and allow CVCHPs to be commercialized for these and other applications.