Take two Sandia engineers who also are hunters, get them talking about the sport, and it shouldn’t be surprising when the conversation leads to a patented design for a self-guided bullet they think could help war fighters.
Sandia researchers Red Jones and Brian Kast (both 6531) and other colleagues have invented a 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).
“We have a very promising technology to guide small projectiles that could be fully developed inexpensively and rapidly compared to other proposals,” Red says.
Sandia hopes to partner with a private company to complete testing of the prototype and bring a guided bullet to the marketplace.
Researchers have had initial success testing the design in computer simulations and conducting field tests of prototypes, which can be built relatively inexpensively using commercially available parts, Red says. The project was started with funding from the Laboratory Directed Research & Development program.
While engineering issues remain, “we’re confident in our science base and we’re confident the engineering-technology base is there to solve the problems,” he says.
Sandia’s design for the 4-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.
Like a well-thrown pass in football
Most bullets shot from rifles have grooves, called rifling, that cause them to spin in order to fly straight, like a football thrown in a long NFL pass. To enable a bullet to turn in flight toward a target and to simplify the design, the spin had to go, Red says.
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 says.
Computer aerodynamic modeling showed that the concept would result in “dramatic improvements” in the bullet’s accuracy, Red says. 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 much closer, to 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 a lot 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,” Red says.
Actuator performance promising
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 is 30 hertz, so that means we can make corrections about 30 times per second. That means we can overcorrect, so we don’t have to be as precise each time,” Red says.
Testing has shown the actuator performance is promising 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.
A nighttime field test using a tiny light-emitting diode, or LED, attached to the bullet showed the battery and electronics can survive flight, Red says.
Researchers also filmed high-speed video of the bullet radically pitching as it exited the barrel. The bullet pitches less as it flies down range, a phenomenon known to long-range firearms experts as “going to sleep.” Because the bullet’s motions settle the longer it is in flight, the rate of inaccuracy is less at longer ranges, Red says.
“Nobody had ever seen that, but we’ve got high-speed video photography that shows that it’s true,” he says.
The bullet could have uses for the military, law enforcement, and recreational shooters.
Sandia researchers who helped Red and Brian develop the technology are: engineer Brandon R. Rohrer (6533), aerodynamics expert Marc Kniskern (5422), mechanical designer Scott Rose (6531), firearms expert James Woods (6531) and Ronald Greene (5416), a guidance, control and simulation engineer.
“It was one of the coolest things I’ve ever worked on,” Red says. “I worked with a great bunch of people who are incredibly bright, incredibly motivated, and who solved a great array of problems. It was awesome.”