When you're building a jet that exponentially accelerates past Mach 6 -- as one does -- you need to come up with a way to get it off the ground. Scramjets, or Constant Volume Combustion (CVC) engines, use compressed air and a reduced nozzle to accelerate planes, and they're a hot technology in aviation. Problem is, you have to get them to Mach 4 before the magic happens. Traditionally, scramjet tests have involved strapping the craft to supersonic jets
to get the jet up to speed -- not a very cost-effective solution. DARPA
has come up with a hybrid engine design called Vulcan that can power a craft like the Falcon HTV-3X to the magical point with a turbo jet and then switch to the CVC to get the craft to the promised land. They expect to have a working prototype by 2012. Check the concept video after the break.