Titanium-Water Heat Pipe Radiators for Space Fission Power System Thermal Management

Abstract

For future space transportation and planetary exploration mission power applications, NASA Glenn Research Center (GRC) is currently developing a small-scale nuclear fission system (i.e. Kilopower system), which has an operable range of 1 to 10 kWe and a design life of 8 to 15 years. The thermal management system of Kilopower system involves two types of heat pipes: high temperature alkali metal heat pipes that are used to transport thermal energy from the nuclear reactor to the Stirling convertors hot end and titanium water heat pipes that are used to remove the waste heat from the convertors cold end and transport it to the radiators for ultimate rejection. This paper presents the development of the titanium water heat pipes, which are featured with a special wick structure design: it has bi-porous screened evaporator and screen-groove hybrid wick in the adiabatic and condenser sections. This will allow the heat pipe to (1) operate in space with zero gravity (2) operate on planetary surface with gravity-aided orientation (3) be tested on ground with slight adverse gravity orientation and (4) to startup smoothly after being frozen. Under a research and development program, several freeze/thaw tolerant heat pipes were designed, fabricated and experimentally validated. Later, various heat pipe radiators were developed and tested in a thermal vacuum chamber (TVC). Test results successfully demonstrated that the titanium heat pipes with radiator attached are able to transfer the required power at the working temperature of 400 K under space-like testing conditions with a thermal resistance of 0.019 °C/W while the total heat pipe radiator weight is less than 0.73 kg.