The project, which saw US and Australian military scientists combine resources, is on track to launch in 2018 after its latest engine trial hit the target speed of Mach 7.5 - more than seven times the speed of sound. 

It could revolutionise global air travel and prove cost-effective access to space, Alex Zelinsky, the chief Australian scientist working on the project said. 

For a jet or rocket to be classified as hypersonic, it must travel at five times the speed of sound, or Mach 5. The latest trial at the world's largest land testing site in Australia saw a rocket hit the target speed of Mach 7.5 (5760 miles per hour), reaching an altitude of 279 kilometres.

"We want to be able to fly with a hypersonic engine at Mach 7," Michael Smart, a hypersonic expert from the University of Queensland who is working on the test, told the AFP. "You could fly long distances over the Earth very, very quickly.