Pierce Nichols wrote:
Yes, but if I understand Michael's point correctly, he seems to be pointing out that water and peroxide are somewhat similar, and so may absorb somewhat as much heat as water, by passing the peroxide through the skin of the vehicle and then decomposing the peroxide through the engine and therefore using it as a barrier to the reentry gases, and you may already have most of the plumbing, tanks and so on, that and your vehicle is simpler; simpler reduces costs.
Actually, I've managed to convince myself that transpiration cooling is not intrinsically heavier than ablative, all other things being equal. Both function by the same mechanism, i.e. absorbing and carrying off the heat by evaporating an expendable coolant. Water will absorb more heat per kg than anything else I know of, due to its extremely high specific heat and latent heat of vaporization.
However, with water, certainly the amount of water needed isn't typically outrageous, but then again the water comes out of your payload; so using somewhat more mass of peroxide may not be desirable.
So, whilst I'm sure it can work, I'm not sure that peroxide works well enough; one issue is the decomposed peroxide is fairly hot in its own right, whereas steam keeps sucking heat in even after boiling, so the thermal balance is worse; and the other is that designs for transpirational cooling systems have small holes every centimeter or so; so it is unclear whether reentering into your own exhaust gases can be anywhere as even. Still, in the absence of any clear experimental evidence and further investigation I certainly reserve my judgement.
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