Description: NASA Glenn Research Center (GRC) is developing fission power system technology for future space transportation and surface power applications. The early systems are envisioned in the 10 to 100kWe range and have an anticipated design life of 8 to 15 years with no maintenance. A non-nuclear system ground test in thermal-vacuum is planned by NASA GRC to validate technologies required to transfer reactor heat, convert the heat into electricity, reject waste heat, process the electrical output, and demonstrate overall system performance. This SBIR project by ACT will develop a single-facesheet Variable Conductance Heat Pipe (VCHP) radiator, operating near 450K, to support the Technology Demonstration Unit (TDU) for surface power and 100kW-class electric vehicles. ACT will utilize the experience gained during previous Phase I and Phase II VCHP radiator programs for NASA GRC to increase the specific power of the radiator and reduce the overall cost. A trade study will be conducted to compare single-facesheet and dual-facesheet VCHP radiator designs and the ability to directly bond a GFRC facesheet to a titanium heat pipe will be demonstrated. A complete preliminary design for a single-facesheet VCHP radiator for the non-nuclear system will be developed at the end of the Phase I program.

Benefits: The low cost VCHP radiator developed under this Phase I and Phase II program would provide the waste heat rejection system necessary for the non-nuclear TDU to be tested at NASA GRC. Additional, longer term NASA candidate missions that the low cost VCHP radiator would support are initial power sources for human outposts on the Moon or Mars and nuclear electric propulsion systems (NEP) for Mars cargo transport. A secondary application would be for lunar and Martian radiators that can passively accommodate the large swings in environmental conditions between lunar (or Martian) day and night, including long periods at very low temperatures. In addition, the VCHP can passively accommodate large changes in thermal load, and avoid damage during periods of low thermal load. The non-condensable gas in the VCHP will also help with start-up during sudden increases in thermal load.

There is a commercial application for high temperature VCHP heat exchangers in fuel cell reformers. In a fuel cell reformer, steam, air and diesel fuel react in a High Temperature Shift (HTS) and a Low Temperature Shift (LTS) reactor to produce as much hydrogen as possible. Feed streams to and from the reactors must be maintained under tight temperature control, typically within 30�C despite a turndown ratio of 5:1 in reactant flow rate. ACT believes that VCHP heat exchangers can replace the current heat exchanger and control system with a passive system. The VCHP heat pipes passively adjust the heat removed, to maintain the output stream at a constant temperature.