Blowing up rockets in midflight is easy - as long as you've got a fast enough computer.
That's the thinking at Artis, the Virginia firm trying to outfit the Army's armored vehicles with so-called "active protection" technology - defenses that can stop incoming projectiles before they ever have a chance to hit. If the approach works, it could not only protect U.S. forces from rockets and missiles. It could shield troops from the most lethal roadside bombs, as well.
Rocket-propelled grenades and anti-tank missiles are some of the most potent weapons in the guerrilla arsenal, because they can punch through even the thickest armor. The Israelis, for instance, saw 40 of their tanks get hit by the projectiles in their 2006 war in Lebanon. So U.S. and Israeli defense contractors have tried all sorts of ways to blast these munitions while they're still hurtling toward their target - to hit one speeding bullet with another, essentially.
But pulling off that trick shot requires a whole bunch of split-second calculations: from detecting the incoming rocket to figuring out its flight pattern to deciding when to fire the countermeasure. To do it all, you need a whole heap of processing power.
"Active protection is a testament to how fast computers are these days - especially when you're not burdening them, by running an operating system," says Artis CEO Keith Brendley.
Artis' approach is a little more algorithm-intensive than others. Rather than blast the projectile early in its flight, Artis' Iron Curtain system waits to fire its countermeasure until the very, very last moment, when the munition is just a few inches away from ramming into its target. Iron Curtain doesn't shoot out at the projectile. Mounted on the vehicle's roof, it shoots straight down.
The idea is to minimize the harm to any civilians nearby - and to get as good a look at the incoming munition as possible before firing. But waiting does have a drawback; it means those life-or-death, bullet-on-bullet calculations have to be made even quicker that they would ordinarily.
"The further away from the vehicle, the harder the problem becomes," Brendley, a former computer modeler at the Rand Corporation, tells Wired.com. "Which would you bet on: the physics becoming easier or the computers getting faster?"
Iron Curtain has pulled off the feat dozens of times in military trials, and is now undergoing safety reviews and component-level testing by the Army's program manager for blast-resistant vehicles. Once that $5 million testing period is done - likely by the end of the year - it's on to limited user tests, where the Iron Curtain will be mounted on the armored, off-road vehicles currently used in Afghanistan. The system won't be heading to the war zone immediately, despite what you may have read in previous reports. But by this time next year, limited production of Iron Curtain could be underway.
Brendley, meanwhile, is looking for even tougher targets to knock down. Rocket-propelled grenades fly at 295 meters per second - pretty damn fast. But Iron Curtain's smacked away these weapons so consistently, Brendley started looking at even quicker threats: namely, the explosively formed projectiles that were, for a time, the deadliest weapon of the Iraq insurgency. These "superbombs" fire out armor-piercing jets of molten metal at a blinding two to four kilometers per second - 10 times as fast as the grenades.
Darpa - which originally backed Iron Curtain - provided a bit of cash for Artis to build a "brassboard" pre-prototype for this superbomb-smashing system. In tests held over the Christmas week, the Artis system held its own.
"Even I was surprised," Brendely says. "Let's face it: it's kind of hard to believe you can intercept something that fast."