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The Mars Science Laboratory (MSL) mission to land a large rover on Mars is being prepared for Launch in 2011. A Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) on the rover provides an electrical power of 110 W for use in the rover and the science payload. Unlike the solar arrays, MMRTG provides a constant electrical power during both day and night for all seasons (year around) and latitudes. The MMRTG dissipates about 2000 W of waste heat to produce the desired electrical power. One of the challenges for MSL Rover is the thermal management of the large amount of MMRTG waste heat. During operations on the surface of Mars this heat can be harnessed to maintain the rover and the science payload within their allowable limits during nights and winters without the use of electrical survival heaters. A mechanically pumped fluid loop heat rejection and recovery system (HRS) is used to pick up some of this waste heat and supply it to the rover and payload.

One of the new technologies successfully demonstrated on the recent Mars Pathfinder mission was the active Heat Rejection System (HRS). This system consisted of a mechanically pumped cooling loop, which actively controlled the temperatures of the various parts of the spacecraft. A single phase Refrigerant 11 liquid was mechanically circulated through the lander and cruise electronics box heat exchangers. This liquid transferred the excess heat to an external radiator on the cruise stage. This is the first time in unmanned spacecraft history that an active heat rejection system of this type has been used on a long duration spacecraft mission. Pathfinder was launched in December 1996 and landed on the Martian surface on July 4, 1997. The system functioned flawlessly during the entire seven months of flight from Earth to Mars. A life test set up of the cooling loop was used to verify the life of the system.

Multi Layer Insulation (MLI) is very commonly used in all spacecraft for heat conservation. In most instances one has to deal with MLI facing space or other cold surfaces while protecting the thermally controlled surface at more moderate temperatures than the heat sink. But in some instances, either in steady state or transient modes, one has to deal with the MLI facing the sun. Examples of such situations are during spacecraft turns, deliberate or inadvertent, when the MLI is exposed to solar insolation for short or extended periods. The effective emittance of MLI is commonly used to describe its heat loss behavior in the absence of solar incidence and is well documented in widespread literature based on measurements and rules of thumb from practice. However, when MLI faces the sun, its effective solar absorptance comes into play to determine its effectiveness in controlling the temperature of the object that it was designed to protect thermally.