An Interesting Solution to Heating in High Speed Flight

Germany's aerospace research center, DLR, is looking at a capillary system using water for cooling on a civilian high speed sub orbital transport

Obviously, you have the weight of the water to deal with, but with the specific heat of water being more than double that of kerosene (4.19 vs 2.01 ^kJ/_{kg K}), the greater density of water ( 1000 vs. 817.15 ^kg/_m³), and the much greater heat of vaporization (2257 vs 108 ^kJ/_kg), there are weight savings with the associated pumps, tankage, and tubing:

An orbiter sub-scale wing leading edge section made of carbonfibre-reinforced carbon (known as carbon-carbon and developed for use in the nose cones of intercontinental ballistic missiles, as well as Space Shuttle leading edges) will be water cooled. In theory the temperature of the orbiter's wing leading edges could reach up to 2,500 Kelvin (2,227°C).

"With water you can use small amounts because it takes so much energy for a phase state change [from liquid to gas]. The leading edge will cool to the temperature of the boiling water and natural capillary action will constantly draw the fluid through the material to the surface at the rate we need," says DLR space launcher systems analysis group research engineer Arnold Van Foreest.

Of course, the real problem here is not cooling, it's the economics of such a transport, where the costs of transporting payload/passengers will likely be in excess of €10/_kg in a best case situation, mitigate against this becoming reality.