[Final Authority]

Both refractory metal and graphite burn in air. Bad solution even if one could. Besides, refractory metal is too heavy (dense) to be used as a heat shield or airframe in an aircraft. If one was to use regenerative cooling one would always have to have a reserve to keep the craft cool even after the boost phase of a mission. Not efficient at all. I have worked on oxidation resistant Carbon-carbon composites for years and have yet to meet all of the design goals. There are no solutions on the horizon quite yet for making a ship reliable enough for manned flight at hypersonic speeds in the atmosphere.

[orionblamblam]

> refractory metal is too heavy (dense) to be used as a heat shield or airframe in an aircraft.

Depends on your limits of definition of "aircraft." The X-20 and X-33 were to have refractory metal heat shields, but of course were not going to spend an hour plowign through re-entry.

> If one was to use regenerative cooling one would always have to have a reserve to keep the craft cool even after the boost phase of a mission.

For airbreathing hypersonic transport aircraft, there is no "boost phase." The engine is on the whole time. Only exoatmospheric craft have "boost phases," and if you're leaving the atmosphere, scramjets are a sucko way of going about it. Rockets rule.