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As every ancient mariner knew, traveling by sail is a simple way to go. Though the winds could be fickle and the boats pokey, the energy source that moved the ship was free, plentiful and renewable. Now the same technology that conquered the oceans of Earth may conquer the ocean of space.
This week a Russian and American consortium will announce plans for an April launch of the first so-called solar-sail vehicle, a multicasted spacecraft that will use sunlight to push itself along. To a public raised on smoke-and-fire rocketry, the idea of drawing energy straight from space seems fanciful. To the people behind the new ship, however, the technology is not only sensible but inevitable, the easiest way to reinvent the business of cosmic travel. "This allows us to use very little fuel to fly very great distances," says Bud Schurmeier, a former NASA engineer and an adviser to the project. "It’s an intriguing concept."
The idea behind solar sailing is simple. Although light is made of massless particles called photons, such ephemeral things exert real pressure, especially when they flow so close a source as the sun. Attach a sail of lightweight Mylar or other material to a spacecraft, set it up in the path of that outrushing energy, and you ought to be able to move in almost any direction.
NASA has a keen interest in solar sailing and had budgeted $ 5 million to investigate 17 possible missions. It may select one as early as next month. But while the space agency has been mulling plans, the people behind the new ship, dubbed Cosmos I, have been getting set to fly. The project is the brainchild of Russia’s Babakin Space Center, near Moscow, and the Planetary Society in Pasadena, Calif., a think tank founded in 1979 by astronomer Carl Sagan and others. The two groups had long been developing plans for a solar-sail mission but got the cash to make it happen only last year when Ann Druyan, Sagan’s widow and head of the Media Company Cosmos Studios, and Joe Firmage, the founder of US Web, threw their names and about $ 4 million behind the effort. "I had talked to people about solar sailing before," says Lou Friedman , former engineer at the Jet Propulsion Laboratory in Pasadena and director of the Planetary Society," but between the Russians’ capabilities and Ann’s vision, I knew this one would click."
The spacecraft is a 3-ft. metal with eight 35-ft. metallic wings. Mylar petals sprout from it -- though the prototype used in the April launch will have just two petals. Mounted atop a reconfigured Russian ICBM and launched from a sub in the Barents Sea, the Cosmos I will fly to an altitude of 260 miles, where it will deploy the wings and float for a minute of so. If all goes well, the wings will then be jettisoned and the sphere aerobraked back to Earth, its bounce-down on Russian soil cushioned by air bags.
By some measures, this cosmic lob shot is not that impressive, but for solar-sail scientists, the engineering is everything. Few doubt that when sunlight strikes the wings, the spacecraft will accelerate; the key is building wings that can open and pivot, allowing the ship to tack into the solar stream. If this mission works, a more ambitious orbital flight, using the eight-paneled craft, is set for the end of the year. The space-craft could circle Earth for months, surfing the sun until de signers shut it down. "There will be a grandeur to it, "says Druyan, "a 70-ft. sail that will be visible to the whole planet."
Grandeur aside, critics wonder if solar sails have a future. The technique is problematic in Earth orbit, since the changing position of sun relative to the space-craft makes constant tacking necessary. Sailing is best used for as the crow-flies shots to neighboring planets. Even in these cases, progress can be slow, since sunlight exerts, at most, 2 lbs. of pressure per square haft-mile, requiring a year or more to rev a spacecraft to interplanetary speeds. Worse, beyond Jupiter, sunlight flickers out almost entirely; to go any farther would require energy beamen from Earth orbit, perhaps by giant laser howitzers. "None of these things has been tested, "says Mel Monte-merlo, one of NASA’s solar-sailing chiefs. "We have a long way to go."
Whether that will continue to seem such a long way may depend on the spring-time flight of Cosmos I. A successful mission has a way of making impossible technologies seem possible -- a big burden for a small rocket that will, for one day at least, carry the hopes of the world’s space community.
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