Rocketing through the stratosphere, gulping oxygen and turning it into jet fuel, the High-tech "scramjet" has been described as the "future aircraft" of the 21st century. But here's the thing: It's the 21st century here already.

And scramjets are just about ready for prime time.

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Introducing Lockheed Martin's planned SR-72 hypersonic, scramjet-powered strategic bomber. Source: Lockheed Martin.

What exactly is a scramjet?
Short for "supersonic combustion ramjet," a scramjet is, at its core, an engine technology aimed at cutting weight. Airplane and rocket fuel requires oxygen to combust, you see. But at very high altitudes, where atmospheric drag is minimal (permitting faster flight), oxygen is also rather scarce. Accordingly, when flying in the stratosphere, rocket engines generally need to carry their own oxygen to use as fuel.

Scramjet technology is designed to eliminate the need to carry oxygen. Instead of bringing it "along for the ride," a scramjet-equipped aircraft will scoop up oxygen as it flies, decelerate it, compress it, and combust it -- generating thrust. At high altitudes, scientists estimate that a scramjet-powered aircraft could reach theoretical speeds of anywhere from Mach 12 to Mach 24 (9,134 mph to 18,269 mph).

Already, NASA experimental flights have tested scramjets capable of flying at Mach 9.8 (7,460 mph). That's already fast enough to fly from Los Angeles to Sydney, Australia, in 1.5 hours flat. 

Who makes a scramjet?
Tellingly, a scramjet traveling at that speed could "fly" those 1.5 hours carrying commercial air travelers -- but it could just as easily be carrying bombs. So it should come as no surprise that two of the leading aerospace companies looking into scramjets are defense contractors Boeing (NYSE:BA) and Lockheed Martin (NYSE:LMT).

A couple years ago, Lockheed made headlines with its announcement of a planned hypersonic bomber (dubbed alternately the "SR-72" or "Son of Blackbird") that will travel at Mach 6 itself -- and launch missiles traveling at Mach 5. Add those two numbers together, and we could soon see a ground-launched combat aircraft capable of striking adversaries at a combined Mach 11, hitting any target in the globe within an hour of take-off.

Not to be outdone, Boeing's X-51 Waverider experimental vehicle is already test-flying speeds approaching Lockheed Martin's distant target...

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Neck and neck with Lockheed, Boeing's X-51 Waverider can already fly at altitude of 60,000 feet, and speeds in excess of Mach 5. Source: Wikimedia Commons.

At the same time, commercial airplane builders are also working hard to make scramjet a reality. Over in Europe, for instance, Airbus (NASDAQOTH:EADSY) is hard at work designing a "Zero Emission Hypersonic Transport" (ZEHST) that will carry up to 100 passengers between continents at speeds up to Mach 4.1.

Across the Channel in Britain, a little company called Reaction Engines is well under way on testing a Synergistic Air-Breathing Rocket Engine (SABRE) with scramjet characteristics. Its project has the backing of the British government, the European Space Agency, and most recently, the U.S. Air Force. Once complete and certified for flight, Reaction Engines believes SABRE engines will achieve speeds of Mach 5 or better, and hit heights of perhaps 17 miles.

What you really want to know: "When do I get to ride a scramjet?"
Unless you're a test flight, the answer is probably "not just yet." Until the manufacturers -- Boeing, Lockheed, Airbus (NASDAQOTH:EADSY), and Reaction Engines -- get all the kinks worked out of this technology, you'll want to cool your jets and wait for this technology to mature.

What's more, perfecting an entirely new engine technology won't come cheap. Nor will amortizing those development costs across a fleet of new airplanes. Reaction Engines, for example, estimates its SABRE-powered "SKYLON" spaceplanes will have to cost $1.2 billion apiece. (For context, that's three times the price of Boeing's costliest jetliner using conventional engine technology, the Boeing 777-9X). 

That said, the advent of scramjet-powered air travel could be closer than you think. Airbus expects to have its ZEHST on the market by 2050, running 20-mile-high milk runs between New York and London in one hour flat. Chris Goyne, Director of the Aerospace Research Laboratory at the University of Virginia, thinks commercial hypersonic flight could happen even sooner than that -- perhaps within the next 25 years. Most optimistic of all, Britain's Reaction Engines expects to run SKYLON's first test flight by 2019.

Fingers crossed.

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Reaction Engines first scramjet-powered aircraft could be coming to an airport (a spaceport?) near you -- and sooner than you think. Source: Reaction Engines.

Fool contributor Rich Smith does not own shares of, nor is he short, any company named above. Neither does, or is, The Motley Fool. You can find Rich on Motley Fool CAPS, publicly posting his stock picks and pans under the handle TMFDitty, where he's currently ranked No. 331 out of more than 75,000 rated members.

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