Solar-sailing era begins in space
Like many a sailing voyage, Louis Friedman's "cruise" began in a saltwater harbor. But his tiny craft's destination is unlike anything a wind-whipped sailor has ever experienced.Skip to next paragraph
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Tuesday, Cosmos-1 is slated for launch from a Russian ballistic-missile submarine beneath the Barents Sea. If all goes well, the craft will unfurl its reflective sails 528 miles above earth to become the first spacecraft to harness the gentle nudge of sunlight for propulsion.
The $4 million mission, spearheaded by the nonprofit Planetary Society in Pasadena, Calif., and privately funded, is designed to demonstrate that solar sails can play a key role for space travel within the solar system.
But first, the baby steps.
"Getting into orbit and opening the sail will be big milestones," says Dr. Friedman, executive director of the Planetary Society. Beyond that "we'd be happy with any small change in acceleration we can measure" as the sails turn sunward and ease the craft into ever higher orbits.
Since the 1920s, when two Russian scientists laid the conceptual foundation for solar sails, the notion has captured the imagination of rocket scientists and science-fiction writers. Like their oceangoing counterparts, solar sails are driven by pressure. But instead of wind, the pressure comes from light hitting the sails' reflective surface. Craft can be steered by changing the solar sails' orientation toward the sun.
"Cosmos 1 is really a bold first step," says Neil Murphy, who heads the space physics group at NASA's Jet Propulsion Laboratory in Pasadena, Calif. NASA hopes to fly a solar-sail craft around 2010 as part of a program for testing new technologies.
A solar sail can't overtake a chemical rocket on a cosmic drag strip. Its initial acceleration is far too slow. But because the acceleration is constant, over long distances solar sails - in principle - can draw even with and perhaps overtake their chemical counterparts. With the right design, a Pluto-bound solar-sail craft could make the trip in less than five years. A mission currently planned for Pluto, launched by a chemical rocket and getting a kick from Jupiter's gravity, is slated to take nine years. And since they don't need fuel or motors, solar sails leave more of a craft's mass available for scientific instruments or cargo.
Space visionaries have rubbed their hands over the space travel possibilities solar-sail craft might open. Among the options: cheap mail runs to Mars, or even unmanned visits to the sun's nearest stellar neighbors.
Robert Zubrin, president of the nonprofit Mars Society, goes a step farther and looks to the day when solar sails are hoisted around "arks" filled with colonists and the ecological support they would need to sustain themselves as they travel to distant solar systems. Dr. Zubrin, who has conducted light-sail studies for NASA's Institute for Advanced Concepts in Atlanta, says that with the right kind of sail design, craft theoretically could achieve speed as high as 2 percent of the speed of light, which begins to make interstellar travel thinkable. The ark would get its push from powerful lasers instead of sunlight.
Indeed, if the Cosmos 1 mission meets its major objectives, mission managers may try to give the craft a slight push with microwaves beamed from earth-based satellite dishes.
Solar sails represent a fuel-free way to hold satellites in orbits that would otherwise be unstable, notes David Chichka, an assistant professor of mechanical and aerospace engineering at George Washington University in Washington. They open possibilities for reliable satellite communications over the poles. And they would allow "space weather" satellites to operate much closer to the sun than they do now, leading to earlier warnings of solar storms that can endanger astronauts, shut down communications satellites, and trigger blackouts.
The 220-pound Cosmos 1 was built in Russia. The funding comes from Cosmos Studios, a multimedia company set up by Ann Druyan, wife of the late Carl Sagan, who cofounded the Planetary Society, as well as from other contributions.
The craft's sail consists of eight triangular segments which combine to form a maneuverable mirror covering nearly 6,500 square feet. Each segment "is about as thick as the sandwich wrap in your kitchen drawer," says Dr. Friedman, the project's director. The plastic is coated with mylar to give it the reflective qualities it needs.
The first three to four weeks of orbit represent a shake-down period to ensure all systems are functioning well. Then Friedman and his colleagues will see if they can use the sails to speed the craft enough to boost its orbit.