Special Reports

The first scramjet powered by the jet fuel JP-10 has made its first free flight. The craft is being developed for use in missile warfare.

It launched aboard a booster rocket from the Wallops Flight Facility in Virginia, US, on 10 December. The scramjet (supersonic combustion ramjet) separated from the booster after rising above 18,300 metres (60,000 feet). During its 15 seconds of free flight, the craft sped to 5.5 times the speed of sound before splashing down in the Atlantic Ocean, as planned.

“It could be air-launched off the wing of an aircraft, eventually,” says Bryce Hallowell, spokesman for Alliant Techsystems (ATK), which developed the scramjet.

ATK is trying to create an engine that could cruise 965 kilometres in one trip. That would allow a military aircraft to drop the missile far from the target, while the missile would still reach its destination in minutes.

No moving parts

Scramjets are a type of engine that can take in oxygen from the air at hypersonic speeds and use it to burn fuel. This means vehicles do not have to carry an oxidiser, as rockets do, meaning a lighter airframe.

In a traditional jet engine, fan blades compress the air for combustion, but a scramjet engine simply uses its immense speed to push the air and requires no moving parts. In the test, the booster rocket pushed the scramjet to hypersonic speeds at which point the engine begins to pull in its own air and uses it to combust fuel.

Some previous scramjets have used hydrogen fuel and achieved even higher speeds than mach 5.5. But at these extreme speeds, the vehicle would need to be constructed from exotic materials to protect it from the high temperatures caused by air friction.

The test was part of ATK’s Freeflight Atmospheric Scramjet Test Technique (FASTT), which is sponsored by the US Defense Advanced Research Projects Agency (DARPA) and the US Office of Naval Research.

In 2004, NASA and ATK broke the world record for aircraft speed with the X-43A, which flew at nearly 10 times the speed of sound. The X-43A was attached to a Pegasus rocket which was dropped from the belly of a B-52B aircraft before igniting. That scramjet burned hydrogen fuel for 10 seconds and reached a peak speed of Mach 9.6.