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Last Updated: Wednesday, 17 November, 2004, 15:23 GMT
Q&A: Nasa's jet speed record
The US space agency's X-43A "air-breathing" test plane has flown almost to Mach 10, setting a new world speed record for aircraft.

X-43A, Nasa
The X-43A was carried to speeds of Mach 9 by a booster rocket
But how does this revolutionary technology work and what uses could it have?

How fast is Mach 10? Put it in perspective for me.

At the altitude the X-43A was flying, Mach 10 is in the region 11,000km/h or 6,800mph. That's 10 times the speed of sound. At that speed, you could cross the Atlantic in well under half an hour.

Concorde, the fastest commercial passenger aircraft, could travel at Mach 2.

The X-43A broke its own speed record set in March of Mach 6.83.

Before this, the record for jet-powered flight was held by SR-71 "Blackbird" spy plane, flying at Mach 3.2.

Rockets and rocket-powered planes are capable of flying at greater speeds, however. The experimental X-15 rocket-engined plane flew at Mach 6.7 on October 3, 1967.

So what's the difference between a rocket-powered vehicle and a scramjet?

Infographic
Subsonic engines have rotating parts to compress air
Scramjets burn hydrogen fuel in a supersonic air stream
Air is compressed by fast forward movement of vehicle
Rapid expansion of hot air out of exhaust produces thrust
Scramjets are able to burn their fuel - in this case hydrogen - without the need to carry heavy tanks of oxidiser, as rockets must.

Instead, they draw their oxygen from the air, which is naturally compressed by the forward speed of the vehicle and the shape of its inlet.

Conventional jet engines have rotating blades to compress the air. But scramjets have no such moving parts.

The fuel is ignited in a supersonic air stream, a technical challenge that has been likened to "striking a match in a hurricane". Successful combustion relies on critical control of temperature and pressure within the engine.

What possible applications could this technology have?

One of the dreams, for many proponents of "hypersonic" technology, is the prospect of passenger airliners using scramjet engines.

X-43A, Nasa
Nasa's hypersonic programme is on ice, despite the success
Theoretically, such a vehicle might be able to travel from London to Sydney in two hours or less.

Another is the prospect of reusable single- or two-stage-to-orbit space launchers. The US Air Force is also looking at scramjet technology with a view to developing hypersonic missiles.

However, some researchers are sceptical that hypersonic technology can be harnessed for these types of real-world applications.

Some have wondered if scramjet engines can truly produce more net thrust than the high overall drag on the vehicle at these speeds.

Will Nasa continue with the research?

The future of this technology inside the agency seems very uncertain.

A Nasa programme to build a larger scramjet vehicle, the X-43C, has been cancelled amid the drive to produce a vehicle capable of returning to the Moon and journeying to Mars in order to fulfil President Bush's vision for space exploration.

This said, officials at Nasa have indicated that they will talk to industry partners about taking the gains from the X-43A forward.

How fast can scramjets go?

Dr Alan Paull, leader of a scramjet group at the University of Queensland in Australia hopes to extend his present programme to contemplate scramjet engine tests between Mach 8 and Mach 12.

Theoretically, the "envelope" within which scramjet travel is efficient is between Mach 5 and Mach 15.

Eventually, it is possible that various engine technologies could be incorporated into one vehicle; the engine would switch between modes as the craft flew faster and faster.

Scramjet mission (BBC)




BBC NEWS: VIDEO AND AUDIO
Watch the launch of the X-43A Scramjet




SEE ALSO:
Superfast Nasa jet pushes Mach 10
16 Nov 04 |  Science/Nature
Guinness recognises jet record
31 Aug 04 |  Science/Nature
Nasa jet smashes speed record
28 Mar 04 |  Science/Nature


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