Hybrid Heat Pipes for High Heat Flux Spacecraft Thermal Control

Grooved aluminum/ammonia Constant Conductance Heat Pipes (CCHPs) are the standard for thermal control in zero-gravity. Unfortunately, they are limited in terms of their heat flux capability, approximately 5W/cm2. Incident heat flux for laser diode applications is on the order of 5-10W/cm2, although this is expected to increase towards 50W/cm2. This is a severe limitation for axial groove (CCHP) as well as loop heat pipes (LHP). Standard CCHPs are also not suitable for Lunar and Martian Landers and Rovers, since they can only operate with a very small adverse elevation, on the order of 0.10 inch. Landers can have tilts of±20<SUP>o</SUP>, while rovers can have tilts of±45<SUP>o</SUP>. As a result, a wick with a higher heat flux capability and pumping capability is required. This program will develop heat pipes with both 1) Sintered wicks, and 2) Hybrid grooved and sintered wicks. Heat pipes with both wick designs will be capable of operating at heat fluxes in the ten's of watts per cm2, and in Lunar or Martian environments at large slopes against gravity. An all-sintered wick will be used when the entire heat pipe must be able to operate against gravity, while a hybrid wick will be used when the condensers will always be gravity aided on the planetary surface.