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The design of the Mars Exploration Rover surface impact airbags is described along with a thermal finite differencing model that was created and benchmarked to predict the internal gas temperature and pressure profiles within the airbags. The airbag system deployed on the Mars Exploration Rover missions was part of the landing system of Mars Pathfinder heritage that cushioned the rover's impact landing onto the Mars surface for impact velocities of up to 24 m=s. The model predicted the internal gas temperatures and pressures for both hot and cold mission landing scenarios. These predictions were used to help define the boost grain propellant loading needed within the gas generators in order to produce the necessary internal airbag gas pressure. Predictions of the amount of condensation created within the airbags during and after inflation proved to be the most crucial influence on the internal bag pressure. Final mission predictions for the airbag internal pressures are presented for both hot and cold landing scenarios. Nomenclatureenthalpy of evaporation k l = liquid thermal conductivity L effective = effective length m = mass _ m = mass flow rate Nu = Nusselt number P = pressure P CO2 = CO 2 gas pressure P H2O = H 2 O vapor pressure Pr = Prandtl number Q = heat transfer Re = Reynolds number T sat = saturation temperature T surface = surface temperature t = time u = internal energy v = velocity V bag = airbag volume = difference or change " effective = effective emittance = density = Stefan-Boltzmann const 1 l = liquid viscosity Subscripts amb = ambient GG = gas generator L = based on length ' = liquid = vapor

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