This is wrong for a multitude of reasons. 1. Rocket engines have high thrust to weight ratio, typically around 100. Jets can have about 10. Scramjets can be re

This is wrong for a multitude of reasons. 1. Rocket engines have high thrust to weight ratio, typically around 100. Jets can have about 10. Scramjets can be really bad. 2. You can speed up quite quickly since the atmosphere is there for the first 30 km or so only. 3. White Knight Two that launches Spaceshiptwo is subsonic, not supersonic. The air launch is beneficial roughly: - primarily because your rocket engine's expansion ratio can be bigger and you get more thrust for same fuel flow - secondarily because then you can launch flexibly by flying to a location, that for example has less population or air traffic or is easy to launch to the right orbit from - thirdly because you can always glide to a landing if something goes wrong with the engine. With a vertical takeoff there's a time right after takeoff where it's hard to do an engine out abort with something like a parachute. Note all the above advantages are not dependent on carrier aircraft speed. In fact supersonic separation is a hard problem, never mind something at Mach 3. (See D-21) If you look at something like dry mass, rockets will practically always win over air breathers in studies because of the lightness and simplicity of simple tanks and high thrust to weight ratio of rocket engines. This whole scramjet affair is very misguided if you're trying to save something like liquid oxygen which is extremely cheap. Even when it weighs something, it doesn't matter since tanks are light and simple and (did I mention already:) rocket engines have high thrust to weight ratio. I'll choose that any day over a huge scramjet inlet that needs to adjust to variable speeds by having big movable ramps, a big burner and a big exhaust, all experiencing large aerodynamic heating problems, multiple load paths (a rocket has basically only vertical loads).