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The future Mars rover thermal design presents a unique challenge to the thermal engineers: the need arises for a thermal control system able to keep rover elements within their operational and non-operational temperature ranges in the face of extreme environmental conditions, characterized by broad day/night temperature excursions, cold biased conditions and long periods in standby modes induced by dust storms. A thermal device is needed, which allows the removal of excess heat from dissipating units during the Martian day and to keep them above their minimum operational/survival temperature during night. Moreover the scientific goals introduce strict requirements in terms of allowable internal components temperature ranges and thermal stability, which the candidate device has to fulfill against wide-ranging power dissipation modes. Such a device has been called Variable Thermal Conductance Device, or ‘Heat Switch’.

A Heat Switch has been developed, namely a device able to autonomously regulate its own thermal conductance in function of the equipment dissipation and environmental heat sink conditions. It is based on a Loop Heat Pipe (LHP) technology, with a passive bypass valve which diverts the flow to the Compensation Chamber when needed for regulation purposes. The target application is the potential use on a Mars Rover thermal control system. The paper recalls the Heat Switch design, and reports the results of an extensive test campaign on the ground demonstrator. The performance of the device was found extremely satisfying, and often exceeded the system requirements.

Improvements on the thermal analysis for system perturbed by micro-thermal fluctuations are presented: the method applies to any kind of (small) perturbation, in particular to the random ones. Opposite to time domain conventional transient analysis, this method answers the need for frequency domain thermal analysis dictated by the newest scientific missions, with tight temperature stability requirements (expressed in the frequency domain). The small temperature fluctuations allow for assuming any thermal systems a linear one; hence linear system theory holds, and powerful tools to calculate key parameters like frequency response can be successfully employed. MIMO (Multi-Input-Multi-Output) systems theory is applied, the inputs being perturbations to the thermal system (boundary temperatures oscillations and power sources ripple of any shape: pulse, step, periodic, random, …), while the outputs are the temperatures of the sensible parts.