NEXT month, the US Army will launch a missile fuelled by a toothpaste-like
gel, instead of the usual solid fuel. The gel will improve control over
missiles, allowing them to reach targets at great distances and perhaps even
attack several objects along their flight path.
The faster a rocket goes, the more fuel it burns. So an ideal fuel-efficient
missile would go relatively slowly for most of its journey, only increasing its
speed when close to the target. But this can鈥檛 be achieved with current
missiles, because it is extremely difficult to change the rate at which solid
fuels burn. 鈥淲ith a solid, the only thing you could do is light it and go,鈥� says
Jerrold Arszman, propulsion technology manager for the Army鈥檚 Future Missile
Technology Integration project. 鈥淵ou turn the thing on, it does what it鈥檚 going
to do and then that鈥檚 it.鈥�
On the other hand, it鈥檚 easy to change the rate at which a missile burns a
liquid fuel鈥攋ust pump less fuel into the engine and it slows down. But
liquid fuels are dangerous. If a shell fragment punctured a liquid-fuel tank,
for instance, the resulting leak and puddle of fuel present a huge risk of
explosion.
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The gel fuel will prove safer than liquid fuels, but could still be pumped
into the engine at different rates. The space shuttle uses solid rocket boosters
to aid its liftoff鈥攕o the new gel fuel could make its way into space
applications, too.