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Would it be feasible to use ice as a sacrificial heat shield in space?

ESA’s AST (space tug) is disposable!? Would it be feasible to use ice as a sacrificial heat shield? Conditions in space are ideal for ice creation and this particular material melts at a predictable rate and is a non-pollutant.
Frank Purcell from Swansea (Age: 45-54)

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2 Responses

  1. I don’t see any advantage to using ice as a heat shield during reentry. The heat absorbed by melting the ice will be much less than that absorbed when the resulting water vaporises. So any material that vaporises at a low enough temperature would be as good as water. The problem with a sacrificial heat shield is the weight it would add to the spacecraft, making it much more expensive to launch.

    In fact most of the energy of a returning space vehicle is lost by transfer to the air molecules it encounters during reentry. If the heat shield does have an outer layer that vaporises, the purpose of this is to create a thin layer of cooler gas between the shield and the very hot air created by the shock wave in front of the vehicle.

  2. A quick calculation confirms the above answer, For every 1kg at a height of 100km to remove its potential energy in returning to earth it would require approximately 4 kg of ice at -100C. Assuming the heat shield is purely sacrificial. Which is too much weight and not much margin of error.

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