If the test is successful, it will beat the record set in March by another X-43A, which powered up its scramjet engine and performed flawlessly for 11 seconds, attaining speeds of seven times the speed of sound, or Mach 7.

  

Scramjet stands for supersonic combustion ramjet, a new type of engine that burns fuel in a stream of air compressed by the forward speed of the aircraft.

  

Conventional jet engines use rotating blades to draw in and compress air, and cannot obtain supersonic speeds.

 

Safer, affordable

 

Nasa says that ultimately scramjets will provide safer and more affordable high-speed flight in vehicles more like airplanes than rockets. Unlike rockets, scramjets can be throttled back and flown like an airplane.

 

A modified B-52 bomber carries
the experimental X-43A aircraft

Nasa calls it a "high-risk, high-payoff research programme".

  

The US space agency on Friday confirmed that the test flight will be launched from southern California on Monday, weather permitting.

  

A B-52B heavy launch aircraft will take off from Nasa's Dryden Flight Research Centre in California at 1pm (2100 GMT) carrying the X-43A and a Pegasus booster rocket under its right wing to an altitude of 12,000m.

 

Separate

  

The X-43A and its booster will then separate from the B-52B and launch to an altitude of 29,000m, where the scramjet engine will ignite, propelling the X-43A at Mach 10, or 7000 miles per hour, for about 10 seconds.

  

"A high-risk, high-payoff research programme"

Nasa

The plane will perform a series of pre-programmed manoeuvres for about 10 minutes before splashing down in the Pacific Ocean in a repeat of the scenario of last March. It will not be recovered after its plunge.

  

The X-43 is a small machine, just 3.65m long, with a wingspan of 1.5m.

  

The $230 million project spans 20 years of research. Other countries, including France and Japan, are also exploring scramjet technology.

  

Nasa has built three X-43s. The first had to be destroyed in flight in June 2001. The second broke the world speed record on 27 March 2004.