Imagine flying faster than Mach 5. Such speeds would cut the long flight times to distant cities. On the other hand, the same technology in a terrorist’s missile could spell disaster. No wonder the race is on to master scramjet engines.

Called hypersonic flight, the technology is proven but not scalable for manned flights — yet. Though, some people feel that hypersonic flight will elude us. These folks note that “the only piloted hypersonic vehicles (X-15, Space Shuttle and a variety of space capsules) have all been rocket powered,” says NASA.

With hypersonic flight, NASA explains that the temperature of the flow around the aircraft reaches so high that the chemistry of the gas must be considered. At low hypersonic speeds, the molecular bonds vibrate, which changes the magnitude of the forces generated by the air on the aircraft.

At higher hypersonic speeds, the molecules break apart producing electrically charged plasma around the aircraft. Besides understanding and accommodating these phenomena through special materials and designs, the engines need to create a huge amount of thrust.

These challenges seem increasingly less daunting to some, however, as recent breakthroughs in scramjet engines are making the race to develop them as fierce as ever, despite a recent test failure.

"An innovative hypersonics program has suffered a failure, with a prototype supersonic-combustion-ramjet (scramjet) missile failing to perform properly and crashing into the Pacific after less than a minute in the air," UK's The Register reports.

Rather than use hydrogen, though, the HyFly ("Hypersonic Flight Demonstration") test relied on JP-10 hydrocarbon fuel and a dual-combustion ramjet. The U.S. military, which sponsored the HyFly prototype missile construction, wanted to eliminate liquid hydrogen’s drawbacks: difficult storage and bulkiness. Scramjets usually use hydrogen because it burns particularly quickly and easily, which offers a decent chance of maintaining combustion even when air is flowing through the engine supersonically. Normal ramjets slow the air down to subsonic speed, but the resulting drag limits them to the Mach 3-4 range.

In Oxfordshire, U.K., a company called Reaction Engines has plans to build a commercial 470-foot-long aircraft “roughly twice as long as the Airbus A380 jumbo jet, though with about half the wingspan,” says CNET. This aircraft, called the A2, would rely on hydrogen, making it better for the environment but limiting the number of passengers to 300 because of the volume needed for hydrogen storage.

Nicknamed the LAPCAT (Long-Term Advanced Propulsion Concepts and Technologies), the A2 is being backed by the European Space Agency. If all goes as planned, the A2 will begin commercial flights within 25 years.

With this ambition stated, some Americans are proposing spending $750 million to fund a prototype hypersonic aircraft called Blackswift, reports Inside Defense (via Wired's Danger Zone blog). As envisioned, the Defense Advanced Research Projects Agency (DARPA) and the U.S. Air Force would manage the Blackswift program, having signed a memorandum of understanding on Blackswift last year. The U.S. Congress will decide if or how much money might go to fund this project. The military will not offer details about the project before the release of the fiscal-year 2009 budget.

Despite the lack of details from inside the beltway, engineers at Purdue University have conducted experiments using the only wind tunnel capable of running quietly at "hypersonic" speeds. The results could help designers of an advanced aircraft called the X-51A. A scramjet would power this test vehicle, and it is expected to evolve into missiles “capable of flying at Mach 6 enabling them to hit mobile ‘time-critical’ targets,” says Purdue University News.

“The X-51 project is led by the Air Force Research Laboratory and DARPA, and the vehicle is being built by Pratt & Whitney and the Boeing Co.,” adds the university press room.

In 2004, data from NASA's scramjet X-43A research vehicle show its engine worked successfully at nearly Mach 9.8 or 7,000 mph. Scramjets promise more airplane-like operations for increased affordability, flexibility and safety in ultra high-speed flights within the atmosphere and for the first stage to Earth orbit. The scramjet advantage is once it is accelerated by a conventional jet engine or booster rocket, it can fly at hypersonic speeds, possibly as fast as Mach 15, without carrying heavy oxygen tanks (as rockets must).

On the other hand, governments that are struggling to keep their citizens' lifestyles as high as possible despite high energy and materials costs may not be inclined to spend the money needed for research to fund the technologies needed for taking hypersonic flight to the next level for those who can pay for airfare.

Are recent breakthroughs bringing us closer to viable hypersonic transport? Or is it as Wired.com's Danger Room blog notes of the technology: "It's the future of aerospace ... and always will be."

Earlier: Australia-U.S. Collaboration Explores Hypersonic Flight

Resources

Ordinary-Fuel Scramjet Prototype Suffers Test Failure
by Lewis Page
The Register, Feb. 7, 2008

Blackswift Swoops in for $750 Million
by Sharon Weinberger
Wired.com Danger Zone, Jan. 24, 2008

Images: High-speed hopes for the hypersonic A2
CNET.com, Feb. 5, 2008

Hypersonic Jet Photo Creates Buzz: Five Hours From Europe to Australia
by Jim Roberts
National Ledger, Feb 7, 2008

Purdue Wind Tunnel Key for ‘Hypersonic Vehicles,’ Future Space Planes
by Emil Venere
Purdue News Service, Jan. 2, 2008

NASA’s X-43A Scramjet Breaks Speed Record
NASA, Nov. 16, 2004