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Collimated gas

Naturevolume 417page705 (2002) | Download Citation


A hot gas, says Daedalus, is isotropic. You get the same temperature no matter how you hold the thermometer. If you want the gas to give some anisotropic push, you need a mechanical element — the rocket nozzle and the turbine blade are probably the best known. DREADCO chemists now want to generate anisotropic heat directly. Any fluid becomes isotropic with time, so fast reactions, explosions or rocket-reactions, seem most hopeful. Furthermore, all the energy is stored in the initial molecules. No entering oxygen complicates their anisotropic decomposition.

In this connection Daedalus recalls gunpowder, one of the cleverest of chemical inventions. At present it is made by simple mixing. The DREADCO team are devising a 'linear gunpowder' in which carbon fibres are laid alongside or interwoven with sulphur fibres (made by pouring molten sulphur into water), and these are interwoven with potassium nitrate whisker crystals. The resulting linear product, carefully aligned, should burn in the fibre-direction much faster than in the perpendicular one. Its gas will be hotter and moving faster in that direction, and colder at right-angles. The average temperature will, however, be as for normal gunpowder.

Even a small effect will be well worth having. In burning, linear gunpowder will eject an already-oriented gas. In a rocket, it will give added thrust. The rocket nozzle will have less to do, and will be burnt away more slowly by the cool sideways gas it feels. The DREADCO team also recalls how cordite is extruded as a gel in acetone — perhaps this too could be molecularly aligned anisotropically, thus gaining efficiency. The military would certainly value even a slight increase in the thrust of its rockets.

Of course, the biggest solid-fuel rockets are those of cold-war weapons and the Space Shuttle. Aligned and anisotropic fuels for these monsters could make them even more effective. On a smaller scale,the brass cartridge-case is now filled in bulk with isotropic propellant. Any ordinary gun would benefit from an oriented cartridge whose anisotropic propellant delivered its high-velocity molecules preferentially to the bullet and the breech, with less wasteful heating directed sideways at the barrel. And, of course, the delicate art of making fast- and slow-burning fuses for mining and quarrying would be greatly expanded.


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