BACKGROUND: Three undergraduate students at Johns Hopkins University have built a model airship that will aid professional engineers who are designing a military craft to conduct surveillance at the outer edge of the Earth's atmosphere.
HOW IT WORKS: The 17-foot-long helium-filled blimp has four propellers and is outfitted with sophisticated electronics that enable it to fly by itself. It follows computer commands to move itself to a predetermined location, but the craft can also be steered manually using a wireless remote controller. An on-board video camera transmits real-time images from about 50 feet above the ground.
WHY IT'S USEFUL: The student model was designed to test and refine the guidance, navigation and control of such a craft for a larger version being developed by the university's Applied Physics Laboratory. Dubbed the High Altitude Reconnaissance Vehicle (HARVe), the airship would be stuffed inside a missile, which would carry it to near-space altitude. Once released from its carrier, a mammoth balloon would self-inflate and carry a gondola equipped with sensors and propellers. The full-sized system would be an inexpensive disposable airship that would hover high over a military location for several weeks, sending images of ground activity and relaying communications. Then the airship would either disintegrate or be destroyed.
LIGHTER THAN AIR: Blimps, or airships, operate on similar principles to hot-air balloons. In 1780, two French paper makers, the Mongolfier brothers, noticed that smoke from a fire built under a paper bag would cause it to rise into the air. The hot air inside expanded, and thus weighed less, in terms of volume, than the surrounding air. This creates "lift," enabling an object to float. The Mongolfiers put the concept to practical use in 1782 when they built the first hot-air balloons. In 1852, another Frenchman, Henri Giffard, built the very first airship, or dirigible. Its enormous envelope was shaped like a cigar and filled with hydrogen, a gas that is lighter than air at normal temperatures -- such as is helium. Giffard's machine was also outfitted with a steam engine, which turned a propeller to create thrust, and rudders to help with steering.