A swift, powerful air strike can be an invaluable tool for U.S. military forces in battle, so long as it gets there fast enough, and the Department of Defense is developing just the aircraft for the job.

The new aircraft is part of DARPA's Force Application and Launch from Continental United States (FALCON) program to build a reusable Hypersonic Cruise Vehicle (HCV) by the year 2025. A simpler and shorter-term version of the craft, dubbed the Small Launch Vehicle (SLV), is expected by 2010.

"Recent military engagement in Bosnia, Afghanistan, and Iraq have underscored both the capabilities and limitations of United States air forces in terms of placing ordnance on military targets," stated a DARPA FALCON draft report on the agency's web site. Despite advancements in target identification and precision, it went on, deficiencies in conducting time-critical missions and defeating high-value or buried targets still remain.

Hypersonic aircraft are expected to surpass the abilities of today's supersonic planes by reaching speeds of Mach 7 or more, over seven times the speed of sound. Current efforts, such as NASA's X-43 program, are designed to use a supersonic combustion ramjet -- or scramjet -- to zoom through the air at up to Mach 10, about 7,381 miles (11,880 kilometers) per hour.

FALCON's requirements call for a hypersonic plane with a range of 9,000 nautical miles (16,668 kilometers) and the ability to fly heavy loads of ordinance or other payload to targets from its home airstrip somewhere in the continental United States.

"This system could become the bomber of the future," said DARPA spokeswoman Jan Walker of FALCON in an e-mail interview

According to DARPA's FALCON report, the hypersonic vehicle should be able to take off from any airstrip in the continental U.S. and carry a 12,000-pound (5,443-kilogram) payload of remote controlled missiles called Common Aero Vehicles. These missiles would basically be hypersonic gliders carrying up to 1,000 pounds (453 kilograms) of bombs or other payload to an intended target that could also be launched via the SLVs.

Although DARPA and the Air Force are just beginning the FALCON project, there are other efforts to build such vehicles as a whole or in part. NASA's Next Generation Launch Technology (NGLT) program is working on the National Aerospace Initiative with the Department of Defense to determine the nation's hypersonic aircraft needs.

"I think everything we're doing is important for this country," NGLT program manager Garry Lyles told SPACE.com. Although the aircraft requirements and their intended missions differ between NASA and the defense department, there is still much crosscutting in the technology for both agencies, he added

Meanwhile, Florida-based Pratt & Whitney Space Propulsion unveiled its Ground Demonstration Engine, GDE-1, scramjet engine developed for the Air Force Research Laboratory's Hypersonic Technology (HyTech) program. Unveiled at the recent International Air and Space Symposium in Dayton, Ohio, the GDE-1 is light enough to fit on an airplane and has been ground-tested up to Mach 6.5. It weighs less than 150 pounds (68 kilograms) and is a slimmer version of Pratt & Whitney's first scramjet engine, a 2,000 pound copper behemoth that will forever stay grounded.

"I think the next major step is to demonstrate this [GDE-1] engine in flight," said Joaquin Castro, manager of hypersonic programs for Pratt & Whitney. In addition to the development of a GDE-2, Castro hopes to assemble a trio of GDE-1 engines to propel NASA's X-43C hypersonic test vehicle, although a final agreement has yet to be made.

The FALCON program is reminiscent of other unmanned aerial vehicles designed for combat such as Predator and Global Hawk that can also attack or reconnoiter targets by remote control. Global Hawk, for one, is a long-range reconnaissance vehicle capable of flying 36 continuous hours with a range of 13,500 nautical miles (25,002 kilometers). But while those vehicles are designed to strike at military targets without risking the lives of pilots, FALCON vehicles have even speedier goals.

"There's not really a tight connection between FALCON and [unmanned aerial vehicles]," Walker explained. "The driving force behind the FALCON's HCV, SLV and Common Aero Vehicle is to provide capabilities which produce a wide range of effects much more rapidly than today's systems."

Those effects include the ability to strike numerous targets around the globe in just a few hours, or launching short-term satellites to bolster communications, remote sensing or navigation abilities in a target region, she added. Predator and other unmanned aircraft could then use those services during their individual missions.

Military applications aside, FALCON's hypersonic cruise vehicle of could lead to an aircraft capable of putting a satellite -- and possibly even humans -- into space. The project's SLV, for example, should be able to loft 2,204-pound (1,000-kilogram) satellites into sun-synchronous orbits, according the FALCON report released by DARPA.

"The technologies implemented by FALCON will lead to capabilities that open the door to a much more robust use of space for the military, civil and commercial sectors," Walker added.

A space shot could be done in stages, allowing a craft to build up enough speed to escape Earth while in flight.

After take-off, a hypersonic craft could use a supersonic turbine engine to reach speeds of Mach 2 or Mach 3, velocities that enable scramjet engines to work by using the plane's speed to compress air for combustion. Once the vehicle reaches its max hypersonic speed, it could then deploy either a separate craft to reach space, as planned for the SLVs, or switch from its air-breathing scramjet engine to some sort of rocket propulsion.

"You can do all this by just staging the vehicle," Lyles said, adding that NASA's X-43C air tests should take flight around 2007. "And I think it's all very exciting."