Sandia’s design for the four-inch-long bullet includes an optical sensor in the nose to detect a laser beam on a target. The sensor sends information to guidance and control electronics that use an algorithm in an eight-bit central processing unit to command electromagnetic actuators. These actuators steer tiny fins that guide the bullet to the target.
Most bullets shot from rifles, which have grooves, or rifling, that cause them to spin so they fly straight, like a long football pass. To enable a bullet to turn in flight toward a target and to simplify the design, the spin had to go, Jones said.
The bullet flies straight due to its aerodynamically stable design, which consists of a center of gravity that sits forward in the projectile and tiny fins that enable it to fly without spin, just as a dart does, he said.
Computer aerodynamic modeling shows the design would result in dramatic improvements in accuracy, Jones said. Computer simulations showed an unguided bullet under real-world conditions could miss a target more than a half mile away (1,000 meters away) by 9.8 yards (9 meters), but a guided bullet would get within 8 inches (0.2 meters), according to the patent.
The four-inch-long bullet has actuators that steer tiny fins that guide it to its target. (Photo by Randy Montoya). All rights reserved by Sandia Labs
Plastic sabots provide a gas seal in the cartridge and protect the delicate fins until they drop off after the bullet emerges from the firearm’s barrel.
The prototype does not require a device found in guided missiles called an inertial measuring unit, which would have added substantially to its cost. Instead, the researchers found that the bullet’s relatively small size when compared to guided missiles “is helping us all around. It’s kind of a fortuitous thing that none of us saw when we started,” Jones said.
As the bullet flies through the air, it pitches and yaws at a set rate based on its mass and size. In larger guided missiles, the rate of flight-path corrections is relatively slow, so each correction needs to be very precise because fewer corrections are possible during flight. But “the natural body frequency of this bullet is about 30 hertz, so we can make corrections 30 times per second. That means we can overcorrect, so we don’t have to be as precise each time,” Jones said.
Testing has shown the electromagnetic actuator performs well and the bullet can reach speeds of 2,400 feet per second, or Mach 2.1, using commercially available gunpowder. The researchers are confident it could reach standard military speeds using customized gunpowder.
And a nighttime field test, in which a tiny light-emitting diode, or LED, was attached to the bullet showed the battery and electronics can survive flight, Jones said.
The current record for sniper accuracy is a british Corporal Craig Harrison killed two Taliban with consecutive shots at a distance of 2.47 kilometres (8120 ft) in Helmand Province, Afghanistan last November (2009). He then fired a third shot and hit the Taliban’s PKM machinegun in perhaps the most prodigious feat of marksmanship in military history.