The world's first solar sail is being prepared for launch Tuesday from a Russian atomic submarine in the Barents Sea. The private U.S.-Russian consortium sponsoring the takeoff calls the spacecraft Cosmos 1. Its designers say the large, lightweight reflective sheet will revolutionize space propulsion by using the gentle shove of sunlight rather than costly fuel.
A solar sail might do for space missions what fabric sails once did for sea travel. It would use free, natural energy to move a craft across distances in the heavens not now possible, partly because of limits to the amount of heavy fuel that can be carried.
"It's the only known technology that can lead us to interstellar flight, to the stars," says Louis Friedman, the president of a private U.S. space advocacy group called the Planetary Society. The group is working to fly Cosmos 1 with the Lavochkin Association, one of Russia's largest aerospace companies, and the Space Research Institute in Russia.
"It gets all of its propulsive energy from the sun. The sunlight photons, the energy of sunlight or light beams, is what propels the spacecraft. So it's something that you can travel both through our own planetary system, maybe to other planetary systems, without any fuel," says Mr. Friedman.
Photons are light particles that would hit the sail and push it with a minuscule force, causing it to accelerate slowly.
Cosmos 1 is actually made up of eight sails shaped as triangles. They are to be deployed from the Russian submarine on a converted nuclear missile. After reaching Earth orbit, inflatable tubes are to open the sails, which are configured like giant windmill blades. The blades can be turned to reflect sunlight in different directions, allowing the complex to change direction.
A U.S. space agency scientist developing solar sail technology, Keith Belvin, says advances in lightweight materials have made such a spacecraft possible only in the past decade, although they have been envisioned since the 19th century.
"To make a solar sail work, it has to be extremely lightweight, about 10 grams per square meter or less," he explains. "So we've been developing very thin space durable films over the past few years. These lightweight membranes enable us to reflect the sun's light and to capture that momentum coming from the sun's light."
Planetary Society president Louis Friedman says the Cosmos 1 mission could last several weeks or even months.
But will a solar sail really work? One prominent scientist has scoffed at the idea, saying it contradicts the laws of thermal physics. The late Thomas Gold of Cornell University said solar sails are designed to be perfect mirrors, reflecting all the light that hits them. However, this would mean no heat would be transferred to the sails. Before his death last year, Professor Gold told VOA that all work involves some heat exchange, and without it, no work can occur.
"It's as if you had an automobile without a radiator. It wouldn't work. There would be no way of losing heat, you see," he explains. "The mirror has no way of losing heat. So it directly conflicts with the laws that control the obtaining of mechanical energy from heat. The sun is just a heat source, of course, so therefore the solar sail cannot work."
But both Louis Friedman and U.S. space agency scientist Keith Belvin reject Thomas Gold's assertion, saying it is based only on the 19th century theories of the thermodynamics of heat engines. They say solar propulsion has worked in small communication reflectors put into the upper atmosphere in the 1960s and for the positioning of U.S. spacecraft since then.
"We've actually used it on a few spacecraft where we trim the space craft," Mr. Belvin noted. "Sometimes the attitude control is not proper and we'll rotate a solar array to get the right propulsive force from the sun's light to actually trim the spacecraft. So it's already been demonstrated in space. It's not of concern for us."
Space agencies around the world will be watching the Cosmos 1 test flight to see what they can learn from it.
Louis Friedman compares it to the first flight of an aircraft by the Wright brothers in 1903.
"If we can prove the concept and advance the technology that way, it will be a great boost. We hope to succeed," he adds.