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.
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.