Regulative Characteristic of Methanol–Copper Heat Pipes for Asteroid Lander "MASCOT"

Abstract

Variable conductance heat pipes (VCHPs) are the main part of MASCOT (Mobile Asteroid surface SCOuT) lander thermal control system (TCS). They provide variable conductivity by utilizing the heat transfer limitations. This allows the heat pipes to act as thermal switches without additional constructive elements. The advantage is simplicity and compactness of conventional heat pipe design. Two cylindrical copper-methanol heat pipes with shell length of 0.482 m and 0.438 m and external diameter of 0.006 m, having copper discrete metal fiber wick and copper shell were constructed and verified in the temperature range between −75 and +60 °C. The purpose is to apply this design into the MASCOT thermal control system and to investigate their regulative characteristics and heat transfer limitations. VCHPs show a change of thermal resistivity from 70 K/W, at a heat sink temperature of −60 °C, to 0.8 K/W at a heat sink temperature of +60 °C; with a obtained maximal heat transfer rate of 5 W and 16 W, respectively. It is found, that the switching effect of the heat pipes is governed by the sonic velocity limitation, the saturation vapor pressure of the working fluid and the maximal capillary pressure of the wick. Operation of heat pipes as the part of TCS has confirmed their variable thermal properties.