Scramjets could power advanced hypersonic aircraft
The first ever free flight of a scramjet - a revolutionary new type of propulsion system - has been carried out by the US Defense Advanced Research Projects Agency (Darpa).
The scramjet grabs most of its fuel from the air it rushes through. Mechanically simple - it has no moving parts - it has proved very tricky to develop, chiefly because it only starts to work at speeds above Mach 5.
The test was of a 10-centimetre- (four-inch) diameter, 20% model of a conceptual missile fired from a gun. The projectile experienced a peak acceleration of approximately 10,000 Gs, and emerged from the gun at Mach 7.
After the titanium projectile was launched, it used its scramjet to cover a distance of 80 metres (260 feet) in slightly over 30 milliseconds. Eventually, the scramjet could power hypersonic aircraft and spacecraft into orbit.
Elation and disappointment
Scramjet engines provide propulsion at speeds above Mach 5 by capturing atmospheric air to mix with on-board fuel. These air-breathing engines are therefore more efficient than conventional rocket motors because they do not need to carry an oxidant with them.
This means future hypersonic vehicles will have room to carry more payload.
The major problem in their development is that the method only works at high velocities. The approach taken to reach scramjet take-over speeds has been to attach them to a rocket booster and then operate the scramjet once the rocket has reached high speed. This is what the Darpa scientists have done.
In June, Nasa scientists were disappointed when their attempt at being the first to fly a scramjet had to be aborted. Australian scientists will be disappointed as well.
Researchers at the University of Queensland's Centre for Hypersonics hoped to be the first to fly a scramjet on 13 August, but had to postpone their test until October because of technical difficulties.
Researchers expect scramjets will first be commercially applied to satellite launches. Eventually, scramjets may revolutionise air travel, allowing passenger aircraft to fly to London from Sydney in just two hours, making in-flight movies obsolete.