Scramjets in Action: Hypersonic, Here We Come
Wednesday, June 20th, 2012
by AJ Plunkett
It’s a tough job when it’s the seconds that you celebrate.
A few weeks ago, NASA, the U.S. Air Force, as well as Australian scientists and engineers, took another step toward hypersonic travel by taking a scramjet engine from Mach 6 to Mach 8 — for 12 seconds. Big deal, say you? Didn’t NASA power its unmanned X-43A scramjet to a record-setting Mach 9.6 back in 2004? Yes, but only for 10 seconds. Didn’t the Air Force announce a couple of years ago that the X-51A scramjet had flown for about 200 seconds? Yes, but only at Mach 5.
So what’s the celebration for now? The HIFIRE team’s engine achieved combustion and higher speeds with a lighter weight and simpler to use fuel. That opens up possibilities for longer flights or heavier payloads. And maybe a more affordable way into space.
Going hypersonic is not easy.
By definition, hypersonic flight begins at Mach 5, or five times the speed of sound (more than 5,900 kilometers per hour, or more than 3,700 miles per hour). For decades, researchers have pursued the goal of hypersonic flight to — well, in part, just to see if we can do it.
Also, the ability to regularly fly at hypersonic speeds would mean being able to get from, say, New York to Tokyo, or New York to Sydney, in just two hours. It could also open up more cost-effective access to space. And, it would mean the ability to deliver a missile to another continent on very short notice.
The problem is that when an aircraft goes hypersonic it creates a friction and a heat that ordinary air-breathing ramjet engines just can’t handle. Rocket aircraft, such as the U.S. Space Shuttle, can hit up to Mach 25, but they have to use massive amounts of liquid oxygen as part of the fuel-burning process. For instance, the Shuttle weighed only 165,000 pounds empty, but had to carry 226,000 pounds of liquid hydrogen and 1.4 million pounds of liquid oxygen to achieve orbit, according to Popular Science magazine.
But what if you could fly at hypersonic speed without the need to carry all that liquid oxygen? What if you could simply use oxygen already in the atmosphere and force it — or ram it — through the engine at supersonic speeds? Then your supersonic combustion ramjet engine — scramjet — could be “smaller, lighter and faster.”
The recent research flight by the Hypersonic International Flight Research Experimentation program (HIFIRE) was, in part, to test using a hydrocarbon fuel in place of a hydrogen-based fuel. While hydrogen is more reactive, according to NASA, the hydrocarbon fuel offers benefits like “operational simplicity and higher fuel density,” meaning the aircraft could carry more fuel and fly farther, or take on more payload.
The HIFIRE team, which launched its experimental scramjet from the Pacific Missile Range Facility on the island of Kauai in Hawaii, included scientists from NASA’s Langley Research Center in Virginia, the U.S. Air Force Research Laboratory, and Australia’s Defense Science and Technology Organisation.
They are not alone in their efforts to go faster and higher. A few years back, China announced it was pursuing hypersonic flight. And just days after NASA announced its most recent success, Russia’s acting Deputy Prime Minister Dmitry Rogozin called for his country to resume hypersonic research to catch up to advances in the field.
The world’s not hypersonic yet. Though we’re getting closer. By the second.
AJ Plunkett is a freelance writer in Virginia with experience in covering defense and aerospace industries as well as the military. AJ blogs via Contently.com.