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Last Updated: Sunday, 28 March, 2004, 02:22 GMT 03:22 UK
Nasa's Mach 7 technology
X-43A, Nasa
The small X-43A separates from its booster at high altitude
The US space agency's experimental hypersonic research aircraft, the X-43A, could one day revolutionise long-distance travel and space launches.

The unpiloted 3.7m-long vehicle uses a scramjet to reach a design speed in excess of Mach 7, about 8,000 km/h (5,000 mph).

Scramjets burn hydrogen but take their oxygen from the air which is forced into the engine at very high speed.

A scramjet operates by the supersonic combustion of fuel in a stream of air compressed by the high forward speed of the aircraft, as opposed to a normal jet engine, in which fan blades compress the air.

Scramjets, BBC

But scramjets only start to work at about Mach 6, or six times the speed of sound. And this means they first have to be boosted to their operational velocity.

In the case of the X-43A, this was done by a modified Pegasus rocket released from under the wing of a B-52 bomber.

The 1,300kg wedge-shaped research craft separated from its booster and accelerated away with the power from its scramjet.

The engine operated for just 10 seconds, after which the X-43A glided through the atmosphere conducting a series of aerodynamic manoeuvres for six minutes on its way to splashdown.

Saturday's test marked the first time a non-rocket, air-breathing scramjet engine has powered a vehicle in flight at hypersonic speeds.

Engineering challenge

Scramjet technology was first proposed in the 1950s and 60s. Because they take their oxidant from the atmosphere, the weight of any aircraft is therefore substantially reduced.

Those weight savings could be used to increase payload capacity, increase range or reduce vehicle size for the same payload.

Concorde: 1350mph (2173km/h)
Japan's bullet train: Record: 277mph (446km/h); scheduled service: 186mph (300km/h)
French TGV: World record (1990): 515.3km/h (320.3mph); scheduled service: 300km/h (186 mph)
The scramjet attraction is obvious. If the many engineering challenges can be overcome, this propulsion technology could make it possible to fly, for example, from London to Sydney in just a couple of hours.

More likely in the first instance, they will find applications in the space delivery business - launching small payloads, such as communications satellites, into orbit.

The first-ever free flight of a scramjet was conducted by the US Defense Advanced Research Projects Agency (Darpa) in 2001. Its engine was fired from a gun in an enclosed facility on the ground.

A year later, University of Queensland researchers flew their HyShot scramjet on a missile.

X-43A, Nasa

The BBC's Oliver Conway
"Part aircraft, part rocket"

Experimental jet 'a success'
16 Aug 02 |  Science/Nature
Q&A: Hypersonic jets
30 Jul 02 |  Science/Nature
Scientists score scramjet success
06 Sep 01 |  Science/Nature
Nasa hypersonic jet fails
04 Jun 01 |  Science/Nature

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