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"Technology : You can run, but you can't hide...
"Technology : You can run, but you can't hide...
New Scientist vol 154 issue 2077 - 12 April 97, page 20
SMART bullets that follow the twists and turns of their victims after
they have left the barrel of a gun are being developed in a US Air
Force project. According to recently declassified research by the
Department of Defense, the new bullets will allow snipers to hit
targets several kilometres away. "This technology could change the
nature of war," says Ron Barrett, an aerospace engineer at Auburn
University in Alabama who is testing prototypes of these Barrel
Launched Adaptive Munitions.
BLAMs steer by twitching their noses. Each bullet has a nose that can
swivel, changing the angle it makes with the airflow. "At supersonic
speed, very small angles generate huge amounts of lift," explains
Barrett. Angling the nose towards the target causes the bullet to veer
in that direction.
The mechanism is simple. The nose is connected to the body by a
ball-and-socket joint, and held in place by a number of piezoceramic
rods, or tendons, which change length when a voltage is applied to
them. Increasing the length of a rod on one side of the bullet while
shortening its opposite number changes the angle of the nose (see
Diagram). The nose can move by up to 0.1° in any direction.
A new type of bullet that steers itself
These simple actuators are ideal for bullets because they can
withstand the huge forces generated during firing, says Barrett. He
has already demonstrated that the prototype can survive accelerations
of more than 17 000 times gravity.
They are also able to lengthen and contract hundreds of times a
second. This is important because spinning bullets travel at several
times the speed of sound, so any control mechanism must be able to
react quickly to compensate. In wind tunnel tests, Barrett has proved
that the piezoceramic rods can produce good control of a round
travelling at more than Mach 3.
So far the work has focused on the large-calibre bullets with
diameters of 20 millimetres or more that are used in aircraft cannon.
These bullets are notoriously inaccurate because they are blown off
course by the wind and follow parabolic trajectories, dropping
significantly over distances of a kilometre or so. "The way pilots
guarantee a hit is by filling the sky with lead," says Barrett.
Because BLAMs generate lift, they can overcome the effects of wind and
gravity, giving them at least twice the range of conventional bullets.
"And with BLAM, pilots would need only one bullet to get a hit," says
Barrett.
In addition to the steering mechanism, each bullet would also need a
guidance system that tracks the target and controls the actuators.
Barrett says this is the easy part of the problem. "Accurate guidance
systems have been around for 30 years," he explains.
The idea is to "paint" the target with a laser beam and equip the
bullets with a sensor that homes in on this signal, just like smart
bombs. Each bullet would have a sensor behind a quartz window that
picks up the signal and controls the bullet. Barrett says that
suitable sensors already exist that can withstand the stresses of
being fired from a gun and can be made more or less the size of a
microchip.
But the bullets will not be cheap. Aircraft bullets cost more than $30
each. Barrett says the piezoceramic materials would add $10 to this
while the microelectronics would cost another $100. But he argues that
the increased strike rate would lead to cost savings. "You'd only fire
one when otherwise you'd fire hundreds."
Another advantage of piezoceramic actuators is that they can easily be
made smaller. "You don't have to fiddle around with tiny mechanisms as
you would for conventional actuators," he says. This raises the
prospect of smart bullets for small arms.
Laser reflection is already a common method of sighting for hand-held
weapons. But a sharpshooter must still compensate for gravity and
wind, and this limits the range of even the most accurate guns to a
kilometre or so. With smart bullets, snipers could hit targets from
several kilometres away. The gun and the laser sight need not even be
in the same place.
But a lot of research and development is needed before the first
weapon fires a smart bullet. "The technology is not yet fully proven,"
says Fred Davis, who heads the flight vehicles branch at the US Air
Force's Wright Laboratory in Florida, which funded Barrett's work. But
Davis believes that smart bullets are a practical possibility,
although he predicts they are 15 years away. He says that his
laboratory has already developed scaled down, cheaper versions of the
smart bombs that were so successful during the Gulf War."
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