Two Hours to Tokyo?

For any engineering geeks here in the DANGER ROOM, let's get your thoughts on this story about a Maryland-based firm that says it's solved one of the key barriers to developing a hypersonic aircraft (there are quite a few more barriers, however):

* “Hypersonic space planes could revolutionize the transportation industry, much like jet planes did for subsonic commercial aviation 50 years ago,” said Astrox President Ajay Kothari. “Seemingly remote parts of the world would be nearly as accessible as a two-hour drive.”*

*Mechanical engines don’t work at hypersonic speeds. Moving parts simply cannot work at 3,500-7,500 miles-per-hour, or 5-10 times faster than the speed of sound, according to Kothari. *

*Instead, hypersonic jet engines typically employ rectangular, duct-like engines with no moving parts, also called scramjets. Air enters the engine inlet at hypersonic speeds and is compressed to supersonic speeds, after which it is mixed with fuel and ignited. The air leaves the engine traveling faster and at a higher pressure than when it came in-creating thrust. *

*But the large surface areas created by rectangular designs generate tremendous heat transfer into a vehicle, requiring extra fuel loads just to cool areas around the engine chamber. “Not only are the large surface areas inefficient, but the extra fuel also adds significant volume and weight to the aircraft,” said Kothari, who holds a patent on an inward-turning vehicle design. “Single-stage-to-orbit travel utilizing a rectangular-shaped engine design would be difficult.” *

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*Kothari’s engine is shaped like a funnel, where air comes in through a circular opening, increases in pressure as it passes through, then leaves with more thrust and less heating than through a rectangular design. The challenge is injecting fuel into the fast-moving air efficiently as it travels through the engine. *

“Roughly speaking, you’re looking at the air flow traveling 1,000 meters-per-second inside the combustor,” said Yu. “The combustor is a meter long, so you have one millisecond for everything to happen-not just the fuel and air mixing-but the burning as well. “The combustion is fast, so that’s not the problem,” explained Yu, “but before combustion can occur, you have to mix your fuel with the air quickly. This is more difficult when the air’s traveling at such high speeds.”