ExoMars 2020 LHPs: from the concept to the flight models

Loop Heat Pipes (LHPs) have been selected as the cornerstone solution for the ExoMars 2020 Rover Module (RM) thermal control. The RM LHPs include the switch function provided by the Vapor Modulation concept, which guarantees the equipment survival at the extreme Mars environment. This paper describes the concept of the Vapor Modulated Loop heat Pipe (VMLHP) and its implementation to the Flight Models design, manufacturing and testing. The RM LHPs consist of four units, two of them integrated on the Service Module (SVM) and two of them on the Analytical Laboratory Drawer (ALD). Each LHP is designed to transport up to 50 W and operate at temperatures from -50 ºC to +55 ºC at the evaporator level and from -120ºC to +55 ºC at the condenser. The Pressure Regulating Valves, which provide the vapor modulation and switching function, keep the SVM at a temperature higher than 0 ºC and the ALD above -40 ºC, even during the cold Martian night. A detailed thermo-hydraulic model of the LHPs has been developed in EcosimPro and correlated to the test results. The model includes all thermal links representative of the RM and the Martian environment. Operation of each LHPs has been validated through an extensive qualification campaign. Details about the main tests in climatic chamber and in vacuum are presented in the paper. Also, the main lessons learnt during the qualification and their implementation for the flight models are described.