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Last Updated: Monday, 15 November, 2004, 23:00 GMT
Jet speed record attempt delayed
Infographic

The US space agency (Nasa) postponed an attempt to fly an experimental jet to 10 times the speed of sound on Monday.

All of the necessary pre-flight checks could not be completed in time.

The agency's X-43A scramjet is trying to break the world speed record for an "air-breathing" vehicle - a mark it set in March when it went to Mach 7.

While capable of reaching rocket-like speeds, it does not carry an oxidiser on board to ignite its hydrogen fuel; it gets its oxygen from the air.

Scramjet (supersonic combustion ramjet) technology could one day usher in a new generation of space propulsion systems.

"Nasa's goal has been to get to space more routinely and in a safer fashion," Joel Sitz, project manager for the X-43A, told the BBC News website.

'High-risk, high-payoff'

Monday's effort was aborted after avionics checks took the mission beyond its two-hour launch window. Another attempt to fly the X-43A will be made on Tuesday.

"The troubleshooting we had to go through today with our avionics took us so much time," said Griff Corpening, a chief engineer connected with the scramjet programme. "All indications now are that we should be go for [Tuesday]; the weather looks to be about the same and all the systems onboard are go at this point."

Scramjets could be used to carry a spacecraft high into the atmosphere, after which a rocket would take over to propel the payload into space.

"We can't replace rockets, but we could use air from the atmosphere for two-thirds of the trip. That might give us the ability to carry bigger payloads for the same amount of money," Sitz added.

The X-43A is one of three planes built as part of Nasa's $230m (124m) Hyper-X programme, described by the agency as "high-risk, high-payoff".

The first flight in June 2001 ended prematurely when the booster rocket veered off course and had to be destroyed. But the second, in March 2004, was a resounding success - setting a new aircraft speed record of Mach 6.83 (8,150km/h or 5,060mph).

This comfortably beat the previous record set by the Blackbird SR-71 spy plane which achieved Mach 3.2.

Final flight

Despite this, the future of US hypersonics research looks bleak. Plans to develop a larger hypersonic vehicle - the X-43C - were scrapped following President Bush's announcement in January that America would revive manned missions to the Moon by 2015 and attempt an expedition to Mars.

X-43A test flight, 27 March 2004   Image: Nasa
The March flight was recognised by Guinness World Records
As a result, funding has been channelled into the development of a conventional rocket-powered vehicle, at the expense of longer-term programmes such as Hyper-X.

On 15 November, the third and final flight will take place over the Naval Air Warfare Center Weapons Division Sea Range.

At about 2100 GMT, a B52B aircraft will take off from Edwards Air Base in California, carrying the scramjet and its attached Pegasus booster rocket.

At an altitude of 12km (40,000ft) and a speed of Mach 0.8, the B52B will release the paired X-43A and booster.

The booster rocket will launch the X-43A to 33.5km (110,000ft) where the test plane separates from its booster. The aircraft then coasts for about five seconds in order to stabilise before igniting its engine and continuing under its own power.

We can't replace rockets, but we could use air from the atmosphere for two-thirds of the trip
Joel Sitz, Nasa
The engine works by burning hydrogen fuel in a stream of supersonic air which is drawn in through a front inlet and compressed by the forward speed of the aircraft. Unlike a conventional jet engine, there are no rotating blades to compress the air.

The rapid expansion of hot air from the exhaust nozzle provides the engine with its thrust.

Getting fuel to ignite in a supersonic air stream has been likened to "striking a match in a hurricane"; so, successful combustion relies on controlling temperature and pressure within the engine.

The plane will be exposed to greater temperatures for the Mach 10 flight. So engineers have added a composite carbon thermal protection system to the plane's wing leading edge, its nose and vertical tail.

"On the nose, we expect to see temperatures of around 3,600F (1,980C). On the Mach 7 flight, they were closer to 2,000F (1,090C). Temperatures will be nearly twice as hot," said Joel Sitz.

Ocean dump

In addition to Nasa's programme, a group at the University of Queensland in Australia plans to conduct two Mach 8 flights and a Mach 10 flight in September 2005.

The Queensland team will test three separate scramjet configurations designed by the UK's QinetiQ company, the US Defense Advanced Research Projects Agency (Darpa) and the Japanese Aerospace Exploration Agency (Jaxa).

The US Air Force has a programme called HyTech, which is aimed at developing a hypersonic cruise missile.

The X-43A should travel about 1,370km (850 miles) before plunging into the Pacific. As with previous X-43A vehicles, it will not be recovered.

The attempt is the culmination of four decades' worth of work by different generations of scientists.

"The last X-43A flight did show evidence of thrust - something that people have sought since the 1960s," commented Professor Douglas Fletcher, of the department of aeronautics and aerospace at the Von Karman Institute in Belgium.

"It's nice for those people who have now retired to finally see the results of what they worked for."




SEE ALSO:
Guinness recognises jet record
31 Aug 04 |  Science/Nature
Nasa jet smashes speed record
28 Mar 04 |  Science/Nature
Nasa's Mach 7 technology
28 Mar 04 |  Science/Nature
Nasa hypersonic jet fails
04 Jun 01 |  Science/Nature


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