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Microspies

Can tiny aircraft deliver the big picture?

“We will make our thrust here,” the colonel says. “The rocket launchers will be along the ridges. We will release the gas from the warehouse by the field—here. They will never think it is coming from there because the lights will be on. They will expect the gas to come from the water tower. All units must be in position before dawn. We will take them completely by surprise. Aah, these flies!”

He slaps his hand down so hard that coffee splashes from his cup, then inspects his palm with a satisfied expression before wiping it on his thigh.

Six miles away in a subterranean bunker a video monitor goes blank. A bespectacled lieutenant in a camouflage shirt sighs and gets up from her chair. She stretches, then crosses the room to an open door. “Frank,” she says, leaning in, “can you send some more flies?”

In his cluttered office in the Los Angeles suburb of Simi, Matt Keennon tosses a diaphanous creature into the air. Tremulous but purposeful, it flaps its way across the room, where waiting hands catch it. Cradled in them, it flutters a moment longer, then subsides when its captor’s fingers—huge, clumsy things beside the ethereal flier—click off its master switch.

The little creature is called the Microbat. It was built at the California Institute of Technology’s Micromachining Laboratory by a team of graduate students overseen by Yu-Chong Tai. The effort also involved AeroVironment, which is headed by Paul MacCready, a multi-disciplinary engineer famous for, among other things, the Gossamer series of human-powered aircraft. The youthful Keennon is AeroVironment’s project manager for micro air vehicles (MAVs), a new class of aircraft being funded by the Defense Advanced Research Projects Agency (DARPA). The toys in this game are small, but the players are big.

The Microbat’s thorax and wing-flapping mechanism consist of tiny sticks of carbon fiber. Its wings are gossamer plastic webs supported by a network of stiffeners that were not built up of separate components but etched from single sheets of titanium alloy by the same photolithography techniques that are used for the mass production of computer microcircuits. The Microbat carries no payload, and it serves no purpose other than to demonstrate the feasibility of a small electric ornithopter that can operate only at low speeds and indoors, where a drop of rain or a puff of wind will not immediately destroy it. More important, it demonstrates the possibility of building parts of flight vehicle structures by chemical micro-machining. Both demonstrations are prophetic.

Slow-moving, moth-like airplanes (as well as crawling robotic cockroaches and other sci-fi stuff) are where reconnaissance seems to be headed now. So-called MEMS (micro-electromechanical systems) manufacturing techniques, derived from the tools of computer chip manufacture, will get it there.

 DARPA’s involvement with toy-size airplanes began at a workshop entitled “Future Technology-Driven Revolutions in Military Operations,” conducted at the RAND Corporation in Santa Monica, California, in 1992. Bruno Augenstein, a RAND scientist, chaired a panel discussion on power supplies for “mobile microrobots,” then a completely hypothetical class of military vehicle. Despite initial skepticism, the idea that an airplane that would fit in the palm of your hand might be a useful reconnaissance device gradually took hold.

In 1995 DARPA put out a specification for a small camera-carrying aircraft. Six inches—an arbitrary value, but one that has turned out to make practical sense—was the basic constraint: The entire aircraft had to fit within a six-inch sphere.

DARPA also specified a typical mission. The midget spyplane would fly one kilometer, just over half a mile, to a target; loiter there for half an hour in turbulent winds of up to 25 mph, perhaps maneuvering among obstacles such as buildings while repeatedly climbing to 350 feet and descending again; then return to its base. It had to be quiet and inconspicuous, its launching and control system had to be easily portable and operable by an unskilled person, and the whole system had to be both robust and cheap.

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