Ultra-fast missiles designed to strike targets around the globe will be the first technologies to use hypersonic flight, with early prototypes set to begin flight tests this year.

The militaries of the U.S. and Australia are leading the development of the high-speed technology. The recently signed $54 million agreement represents one of the largest collaborations of its kind between the two nations, according to the Air Force Research Laboratory. The U.S. Air Force Research Lab and the Australian Defence Science and Technology Organisation (DSTO) are leading the effort, including coordination of research tasks to be performed with NASA, U.S. industry, the Australian Hypersonics Consortium, and the Hypersonics Research Group at the University of Queensland.

The projects include a test vehicle called the X-51A, run jointly by the U.S. Air Force and the U.S. Defense Advanced Research Projects Agency (DARPA), and a separate DARPA-led vehicle called Falcon.

In addition, a joint U.S.-Australian program called HIFiRE (Hypersonic International Flight Research Experimentation) has just announced plans for 10 test flights over the next five years, to take place beginning late this year on the Woomera range in South Australia.

The HIFiRE program has its roots in, well, practically a glorified science project begun by university students a number of years ago. The students hand-built a small supersonic-combustion scramjet engine and boosted it into the air attached to a model rocket.

"That was the first time confirmed scramjet combustion occurred in flight," Boeing engineer and senior hypersonics specialist Kevin Bowcutt recently told Military.com.

In fact, all of the programs are based on so-called scramjets (supersonic combustion ramjets), a type of reeeeeeheheheheheheally fast jet engine. They are being touted as the next generation of cheap travel, allowing the possibility to launch communications satellites more cheaply or to travel between one side of the planet and the other in a few hours. Rather than carrying oxidizers in their tanks, as do rockets, scramjets inhale oxygen from the atmosphere to burn their fuel. They mix fuel with air and ignite the mixture as it flows through the engine at supersonic speeds. And unlike jet plane engines, which use fans to compress air, they use no moving parts or rotating components — the shape of their air intakes sucks in and compresses air at supersonic speeds.

Pratt and Whitney is building the engine for the X-51A, which uses the gas flow system tested in NASA's X-43A vehicle. The design uses a rectangular intake, which compresses the air and generates a shock wave that pushes the air through the engine vertically.

Boeing is building the vehicle, which will be mounted on a solid rocket booster and fired from a B-52 bomber flying at an altitude of about 10 kilometers. The scramjet will kick in after the rocket reaches Mach 4.5, boosting its speed to nearly Mach 7. The first flight tests are planned for mid- to late 2007.

Because the air flowing through a scramjet must be greater than the speed of sound throughout, a scramjet cannot simply take off from rest. Instead, it requires a staging vehicle — usually a rocket to accelerate the scramjet to a supersonic speed.

The U.S. Air Force and the Australian DSTO are pushing a more advanced, 3-D gas flow system in their $54 million HIFiRe project. The goal is to compress the gas in three dimensions — sideways as well as vertically — using a round intake.

The extra dimension of compression allows "more shock waves and more efficient compression of the flow with lower losses," says Bill Lyons, manager of international research analysis at Boeing Phantom Works. The design should decrease atmospheric drag, allowing the vehicle to increase its range or the weight of its payload.

Boeing, working with the DSTO and The University of Queensland, has already announced that it would run three of the tests, beginning in early 2009, notes The Engineer Online. The program hopes to demonstrate advanced scramjets capable of sustained flight faster than Mach 8.

DARPA's Falcon project is even more ambitious, and plans to reach Mach 15 to 20 — speeds needed to reach and return from orbit. Its first test flights are scheduled for December 2008.

"We're pretty close to the point where we could design a missile, but we're not there. In the longer term, air-breathing hypersonic craft could cut the cost of reaching space," Lyons added in an ANI news report earlier this month.

Several scramjets have been flight-tested around the world, the most well-known of which is the Hyper-X, designed by NASA. The U.S. space agency set the record for hypersonic flight in 2004 with its X-43A test vehicle, which reached 9.6 times the speed of sound, or Mach 9.6. The fastest regular jet engines have only achieved speeds of around Mach 3. However, by then, the agency had already pulled the plug on its planned follow-on vehicle so it could focus on reaching the Moon and Mars.

Practical hypersonic flight remains a long way off, however. New Scientist estimates that the first U.S. Air Force missiles will become operational in 2035, and that unmanned aerial vehicles that could fly as far as 3,000 kilometers are even further off.