[Final Authority]

How does one cool the hot parts of the engine? Even the cold parts are hotter than the hot parts of a conventional jet engine of today. I have had the privilege of working on programs since 1983 investigating technology designed to answer such questions. It isn't easy and we are still quite far from solving all of the problems. Active cooling is effective but it is not fuel efficient so it isn't useful load efficient and it isn't cost effective.

The concept of ram jet, later scram jets, was developed in the '50s for missile defense where the flight was one way only. Now, these flights are experimental to develop combustion models and test materials for reusable flights. As I said, we are a long way off.

[orionblamblam]

> Active cooling is effective but it is not fuel efficient so it isn't useful load efficient and it isn't cost effective.


Depends on the method of active cooling. If you use transpiration cooling... yeah, yer throwing fuel overboard. If you use regenerative cooling, what you're doing is actually *improving* combustion efficiency by pre-vaporizign the fuel.

None of this is meant to suggest that this sort of thing is *easy.* jsut better than tryign to carve an HST out of a block of refractory metal of pyrolitic graphite.

> As I said, we are a long way off.

No disagreement there.

[Ichneumon]

The concept of ram jet, later scram jets, was developed in the '50s for missile defense where the flight was one way only.

Wasn't the German "buzz bomb" of the 40's considered a ramjet? In any case it was the first "cruise missile".