Larry J said the following:

>Mach 10 is roughly 6500 MPH, or roughly 37%
>of orbital velocity. Getting something moving
>Mach 10 at 100,000+ feet altitude, then fire a
>rocket to take it the rest of the way to orbit
>might be a lot easier than building a faster
>scramjet based on LH.

Unfortunately a scramjet will not light up until it is at Mach 6. That means you have to use a rocket or turbojet/ramjet variable cycle engine to get from zero to Mach 6. If you use a turbojet, then you have to haul it into the fuselage once the scramjet lights up and carrying around its dead weight. The scramjet only gets you from Mach 6 to Mach 10 and will only work in the lower atmosphere. Because you're in the lower atmosphere, you have to carry around lots of extra thermal protection. When you add up all the extra mass required for the scramjet, you find out that there was no advantage to air breathing. I'm an ex-believer of using scramjets for cheap access to LEO. I think scramjets are neat in terms of their physics (they're useful as weapons or Mach 9 cruise propulsion systems) but unfortunately they are not the solution for cheap access to space. For near term cheap access, we should use kerosene fuelled turbopumped rocket engines on a TSTO airframe. A KISS (Keep It Simple Stupid) approach is best for desigining near term cheap access to space.

Gary