Pretty please, with sugar on top, don’t call it seeing through walls. That shorthand — with its connotations of the First Earth Battalion trying to phase through brick — gets Army engineers gritting their teeth. Instead, this cream-colored handheld senses through the wall, seeing if any live human being is behind it before a squad kicks down the door to see for itself.
At least that’s how Douglas Graham explains the AN/PPS-26 STTW (“Sense Through The Wall,” get it?) device, which looks a like a cross between a gas-meter reader and an ’80s video game console. Graham, a spokesman for Program Executive Office Soldier — the Army office that develops everything soldiers wear or carry — hoists the maybe-five-pound plastic device in his right hand and clicks a button with his index finger to turn it on. He places it up to one of the hundreds of plastic barriers that separate the display stands for exhibitors at the annual Association of the U.S. Army conference in Washington.
A tiny screen above Graham’s hand lights up with a spider’s-web display, calculating positioning by degrees above the STTW and distance from it, measured in five-meter intervals. With his thumb, Graham clicks the other button on the device, firing off a radar that detects motion on the opposite side of the barrier. Suddenly, the display shows yellow dots flitting from place to place. Those are people, evidently getting bored by whatever weapons display the kiosk hosts.
PEO Soldier recently awarded Raytheon and L3 two multi-million dollar contracts to build 30 STTW units so testing on them can begin. “Imagine the physical wear and tear if you’re knocking down doors and you don’t know if someone is behind them,” Graham says.
Probably a relief. But it doesn’t exactly make the wall functionally transparent, a long-standing goal of the Pentagon’s Darpa researchers. there’s a lot that the STTW doesn’t do.
For one thing, it can’t sense through metal. If a potential adversary is hiding in any kind of metal structure, the STTW won’t know it. And even when placed against “wood-framed houses, mud or adobe,” the buildings STTW can sense through, a wall thickness of more than eight inches will throw the device off.
For another, the motion detected is slight: someone standing still needs to breathe, and the STTW pick up on the resulting chest movements. But if a chair falls or a painting drops, that gets detected as well, even if the yellow dot representing it disappears pretty quickly. All of which sounds like a unit operating the STTW will have to deal with uncertainty in what it picks up.
Then there’s the biggest unknown. The yellow dots can’t tell if someone’s an adversary or a civilian. “It can’t tell you if a person is a child or an adult, carrying a gun or not,” Graham says. “It could be a cow or a chimpanzee or a human being.” In other words, don’t use it as a targeting device.
That said, it’s better than not knowing if there’s any sign of life inside a room you’re about to enter, hostile, friendly or chimpanzee. “If you know something’s alive behind that wall, it just allows you to adjust,” Graham says. Figuring out what exactly is on the other side of a wall may require some adjustments of its own.
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