November 18, 2004


This seems to be a fruitful year for aerospace matters: Space Ship One succesfully completed the three sub-orbital flights required to win the Ansari X-prize (btw, the Ansari brothers are Iranian businessmen). Now, Nasa's experimental hypersonic plane X-43 topped itself flying at Mach 10 on November 16.

This is an impressive achievement not for the speed in itself (rockets and space vehicles at re-entry are even faster), but because the X-43 was propelled by an exotic engine, a scramjet. This particular engine has no moving parts, and incoming air is compressed only by being forced at high speed into the properly shaped engine inlet. Indeed, the plane hd to reach its operative speed and altitude with the help of a booster rocket.
This compressed air is mixed with hydrogen and the mixture ignited, releasing energy that pushes the combustion gases even faster out of the engine nozzle, thus producing thrust.
I talked to people in the field (not the X-43 project, tho) and they told me that fluid dynamics in hypersonic conditions is a real bitch - the fluids behave quite differently than in normal conditions. And keeping a smooth combustion is extremely difficult. But the engineers and scientists at NASA did it.

Hypersonic air-breathing planes are interesting for various reasons: they're very fast, and much more convenient than a rocket. Rockets, in fact, need to carry around both combustible and oxidizer (and believe me, some oxidizers for rocket applications are very very nasty, and the fuels not much nicer) and are basically single-use. A scramjet, instead, takes oxygen from air, and can be used and reused like any other jet engine.

US military is very interested in very fast bombers and cruise missile, for quite obvious reasons. But the possibility of flying from say, London to Hong Kong in half than the current time is attractive also for civil applications - it would be hypercool indeed.


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