To enable SWARM vehicles to communicate in such complex ways, much secure data must be transmitted. Castelli's team plans to equip the planes with transceivers that can send data at high bit rates via the Iridium satellite network. Another option: a line-of-sight communications link being developed by the Office of Naval Research, in which a radio transceiver sends encrypted data over a 10- to 20-mile range.
A SWARM plane is designed to be launched from a catapult or, possibly, a helicopter and to operate at 60 knots, meaning it can be employed in most weather. The vehicles don't need to return home-from the military's perspective, $2,000 equals disposable-so their wingspan is short. "If I had to land it, the wingspan would be three times longer," says Dave Lacey, an aeronautical engineer on Castelli's team. The major inflight challenge is stability, since small planes with simple avionics are susceptible to rough weather. To compensate, the plane's dihedral wings tilt up at the tips to keep the aircraft from rolling.
The plane's engine will be made of ceramic and plastic, lightweight materials that are preferable to metal because they are cheaper, they can't be easily detected by radar, and they can withstand higher temperatures, enabling the engine to burn fuel more efficiently. That's important because the miniature planes have a target range of 1,500 miles but gas tanks that hold just 1.5 gallons of diesel. But the SWARM engine design has some drawbacks as well. For one, diesel engines are loud, so the SWARM prototypes are anything but covert (Castelli hopes to fix this flaw with noise reducers). More important, the two-stroke engine stalls in the thin atmosphere of higher altitudes, so the SWARM devices will only be able to fly at heights of between 500 and 8,000 feet.
Castelli is convinced that for SWARM devices to be widely used in military missions, large and small, the machines must be disposable so that losing a few will not be a concern. He chose the target price of $2,000 to match the cost of sonar buoys that the Navy uses and frequently discards. He's earmarked $400 for avionics, $200 for the engine, and $900 for communications, with the remaining amount allocated to the generator, airframe, and the command module. So far, though, at prototype stage, it's been impossible to get production costs lower than $16,000.
Starting in 2004, 10,000 SWARM planes will be produced annually, Castelli says. The first tests of the SWARM system are under way in the Pacific, where the Navy is using prototype planes to search for whales and other marine mammals before testing munitions, high-powered low-frequency sonar, or missile defense interceptors-systems that can disrupt the animals' ability to communicate, feed, and navigate.
Next up for the SWARM team, after formation flying is perfected, is to bring the cost of the vehicles closer to the $2,000 target by redesigning the avionics so that the entire system can be shrunk and integrated into a chip. After that, Castelli says he wants to focus on creating a network of sensors for the planes that would combine digital audio and video files from the entire SWARM fleet and send them back to base. Such a system would provide more detailed remote information than anything the military has today. All in all, not a bad legacy for a flock of pelicans.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.