Sandia National Labs | Self-guided bullet can alter trajectory in flight, navigating to laser-painted target

February 2, 2012

Sandia Labs | Sandia researchers have invented a dart-like, self-guided bullet for small-caliber, smooth-bore firearms that could hit laser-designated targets at distances of more than a mile (about 2,000 meters). The four-inch-long bullet has actuators that steer tiny fins that guide it to its target. (Images here.)

Sandia’s self-guided bullet prototype can hit target a mile away. The 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 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. 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.

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. 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 advantagous.

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,” Sandia researcher Red JonesJones stated.

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.

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