Loop Heat Pipe with Thermal Control Valve for Variable Thermal Conductance Link of Lunar Landers and Rovers

Abstract

A number of proposed Lunar landers and rovers have a Warm Electronics Box (WEB) and a battery, both of which must be maintained in a fairly narrow temperature range using a variable thermal conductance link. During the Lunar day, heat must be transferred from the WEB to a radiator as efficiently as possible. During the night, heat transfer from the WEB must be minimized to keep the electronics and batteries warm with minimal power, even with a very low (100 K) heat sink. A mini-LHP has the highest Technology Readiness Level, but requires electrical power to shut-down during the 14-day Lunar night, with a significant penalty in battery mass: 1 watt of electrical power translates into 5kg of battery and solar cell mass. A mini-LHP with a Thermal Control Valve (TCV) was developed to shut down without electrical power. An aluminum/ammonia LHP which included a TCV in the vapor exit line from the evaporator was designed, fabricated and tested. The TCV could route vapor to the condenser, or bypass the condenser and route vapor directly back to the compensation chamber, depending upon the temperature conditions. During testing, the LHP condenser temperature was decreased to -60oC and the power input was decreased to near zero power: the evaporator remained above 0oC. This paper will describe the LHP and TCV design, fabrication and testing details.