Researchers say that the new Supersonic Combustion Ram Jet (scramjet) could revolutionize military warfare, air travel, and space flight.
Recent atmospheric tests in Australia by the international consortium Hyshot have helped answer some questions about the technology, but American researchers achieved a more significant breakthrough in the scramjet's development during a test flight in the United States last summer.
Scientists took the scramjet engine off the drawing board after 30 years of research and got a glimpse of the scramjet's capabilities in a short test flight. The test was funded by the Pentagon's technology incubator, the Defense Advanced Research Projects Agency (DARPA).
"They've always flown them in wind tunnels and things of that nature," DARPA program manager Preston Carter said. "And the test that we've done recently was able to fly a vehicle powered by a scramjet in free flight -- that is, no wires attached, flying through the air -- for the first time."
Scramjets have no moving parts. Instead, they use aerodynamic compression inlets to mix oxygen from the air to ignite hydrogen or other fuels. That will let rockets travel with a lot less liquid oxygen on board, reducing costs.
Theoretically, scramjets could allow aircraft and missiles to travel at up to Mach 10, or 10 times the speed of sound. That's more than three times faster than existing jet engine technology. It would make missiles harder to shoot down and could allow commercial jets to fly cross-country in less than an hour.
"There's a lot more room to store extra fuel or extra payload, and so a scramjet-powered vehicle can fly at speeds that are normally reserved for rockets with much greater efficiency," said Jason Tyll, an engineer at Gasl Labs, which is participating in the testing.
But scramjets work only while in the Earth's atmosphere and only at speeds above Mach 4. So scramjets still need help reaching high speeds from additional rockets and jets.
In space travel, for example, scramjets would operate in the middle of a journey -- after a traditional rocket pushes the aircraft to Mach 4, and before it runs out of atmosphere to burn at the edge of space. After that, rockets will take over again to complete a trip.
To propel a scramjet to its threshold speed of Mach 4 in last summer's test, researchers at Gasl Labs used a 130-foot-long light-gas cannon at Arnold Air Force Base in Tennessee. The gun blast fired the scramjet past Mach 4 when its internal systems kicked in. Then, for the first time ever, a scramjet moved forward on its own thrust in free flight.
"We can draw the analogy to the Wright brothers and where we are," Carter said. "The Wright brothers, the first time they flew, they flew 120 feet for about eight seconds. We flew 240 feet, about twice the distance, but for only 35 milliseconds. That's only the beginning."
With more testing ahead, researchers say it will be another decade before scramjets are used by the military, and at least 20 years before they're used in commercial air travel and in space.
