Sniper bullet homes in on target like a guided missile(2)

Sniper bullet homes in on target like a guided missile

DARPA declined requests for further comment about the workings of the EXACTO system, but developments done at another organisation can provide some hint to how DARPA's system may work.

In 2012 Sandia National Laboratories, a subsidiary of Lockheed Martin, announced that it had developed a prototype self-guided bullet. Sandia's 4in-long round contains a guidance and control system coupled with an 8bit CPU that controls tiny fins connected to electromagnetic actuators. The bullet has a sensor on its tip that can detect and follow a laser, guiding the bullet to its target. The company estimates its bullet could hit a laser-designated target 2,000m away. According to Sandia's patent, computer simulations have shown an unguided bullet under real-world conditions could miss a target more than 1,000m away by 9m, but a guided bullet would get within 0.2m.

Sandia's bullet has actuators that steer tiny fins that guide it to its target. (Source: Randy Montoya/Sandia National Laboratories)

Red Jones, a researcher at Sandia, said that in order to make the bullet steerable, it had to be able to travel straight and not spin like a typical bullet when fired. He likens the guided bullet more to a dart -- where the fins and the forward-sitting centre of gravity keep it from spinning. "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.

Since the bullet is small-calibre it doesn't require a costly inertial measuring unit used in guided missiles. "As the bullet flies through the air, it pitches and yaws at a set rate based on its mass and size," Jones said. "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 30Hz, 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's tests have shown its bullet can travel up to 2,400ft/s (Mach 2.1) and could possibly reach standard military speeds using customized gunpowder. By comparison a .50-calibre round travels anywhere from 2,800ft/s ton 3,000ft/s on average.

Sandia declined to comment on any further developments with its self-guided bullet but said it is looking to partner with a private company to bring the bullet to market. The plan is to target military and law enforcement as well as recreational shooters.