A demonstrator for a Heat Switch for Mars Rover: 1 year of ground testing activities

Abstract

An Heat Switch, capable of self-regulation of its thermal conductance, has been developed for use on Planetary Exploration Rovers. Based on LHP technology, the Heat Switch includes a completely passive bypass valve, which can regulate the working fluid (propylene) vapour flow to the condenser, in order to prevent the evaporator temperature from falling below a given temperature set point. This allows the heat switch to cope with extremely high external temperature excursions of the outer environment and large internal power dissipation variations, still keeping a remarkable temperature stability on the controlled items and preventing their overcooling. An Heat Switch breadboard has been designed, manufactured and tested in the framework of an European Space Agency technological research programme. The activities have been successfully concluded in August 2008. The Heat Switch design and test results have been described in previous papers. This paper contains the results of the continuation of the thermal test campaign on the breadboard, which has been carried out at Carlo Gavazzi Space for more than one year in the timeframe 2008-2009. Tests have been performed both in the laboratory, at ambient temperature, and in a climatic chamber. Tests focus on those Heat Switch features which had been identified worth to be further investigated in the previous test campaign, namely the startup event and the gravity effects. Also related to the gravity effects, the valve oscillations have been investigated in detail. A large number (hundreds) of startup events has been collected, to analyze them on a statistical basis. Additional important results are the long term stability of the thermal performance parameters, the temperature control capabilities through compensation chamber heater actuation, and the detailed characterization of the condenser temperature profile at different combinations of heat loads and environmental temperatures.