DARPA has repeatedly indicated an interest in developing hypersonic aircraft and weapons systems which are capable of Mach-20 speeds and thus able to reach any region of the planet within an hour. To this end, the agency has announced its new Integrated Hypersonics (IH) program, which draws upon previous research and aims to create a hypersonic X-plane (HX) ready for testing by 2016.
In a press release titled "Hypersonics - The New Stealth", DARPA posits the belief that high speed flight will become the next game-changing war technology, much like stealth flight did in previous decades. The finer details of just what form the HX will actually take are still vague at this point, but DARPA did reveal that the aircraft is envisioned as a recoverable next-generation configuration which makes use of rocket-based propulsion in order to facilitate highly maneuverable, long-range hypersonic flight.
Such scant information leaves plenty of room for uncertainty, but we can also assume that the HX will make use of experience gleaned from the Falcon Hypersonic Technology Vehicle (HTV-2) project. However, as evidenced by the fact that both the first and second HTV-2 test flights ended in unplanned crashes into the Pacific Ocean, the IH program will face formidable challenges: a Mach-20 HX will fly at speeds of over 15,000 mph (or 24,000 km/h) while also being required to deal with temperatures which exceed 3,500°F (1,927°C).
This all adds up top the fact that we're still a long way from a Mach-20 HX becoming fully operational. To help bring this technology forward, DARPA is to host a Proposers' Day at the DARPA Conference Center in Ballston, Arlington, on August 14. During this event, the agency will detail the areas for which proposals are being sought, and seek solutions from aerospace manufacturers.
“We do not yet have a complete hypersonic system solution,” said Gregory Hulcher, director of Strategic Warfare, Office of the Under Secretary of Defense for Acquisition, Technology and Logistics. “Programs like Integrated Hypersonics will leverage previous investments in this field and continue to reduce risk, inform development, and advance capabilities.”
Source: DARPA via The Register
Getting the velocity with an air breathing engine however is currently beyond state of the art. It would be nice weather or not your intended destination is on Earth.
The D in DARPA stands for defense. If the military already had it DARPA would not be spending to create it.
Current DARPA projects entail a launch vehicle such as an ICBM to fire off the test lifting body into initial orbit, restricting the size of the test aircraft and forcing it to have a glide phase with as of yet no prospect of powered landing and intact retrieval.
Therefore we are looking at exotic fuels from exotic engines such as the magnetic pinch fusion pulse engine - a Nuclear fueled rocket.