Originally Posted by tdracer
"My personal vision has long been for a two stage shuttle - horizontal takeoff, the first stage being air breathing using hydrocarbon liquid fuel and some combination of turbojets/ramjets/scramjets, and a pure rocket H2/O2 orbiter. Of course it would cost a large fortune to develop, but per launch costs would basically be fuel and maintenance."
Winged HTOL air breathing shuttles (esp SSTO) have long been the ultimate dream. Superficially it's an alluring concept: just make it like an airliner. The U.S. spent billions of $ on the National Aerospace Plane (NASP) with this goal, and the UK is still backing Skylon.
Unfortunately the ugly reality is orbital velocity requires gigantically higher kinetic energy -- KE = 1/2*m*v^2, and every element in the design hinges on this. An air breathing first stage doesn't provide much performance advantage, yet entails huge financial cost and development risk.
When you calculate what kind of mothership is needed to launch an orbiter having a meaningful useful payload, it's something like a ramjet-powered XB-70 with 4x the gross weight. Then on top of that you need a self-powered orbiter capable of accelerating from Mach 5 to Mach 25.
NASP required multiple breakthroughs on many levels -- unobtanium materials, active cooling of the structure, scramjet propulsion which no wind tunnel can test, etc. A detailed account of this development is in the on-line publication "The Hypersonic Revolution":
http://tinyurl.com/h8advzk
Getting into orbit via airbreathing propulsion has been called "getting to space the hard way". Unlike the casino game of craps, you don't get extra payoff for getting there "the hard way". Rather you want to get there the easiest, simplest way possible. Given current technology, that's probably some kind of a rocket.