Solar Sail Spacecraft to Hitch a Free Ride on a Light Breeze in 2016
Just as sailboats use wind pressure to propel through water, solar sails use the pressure from light radiated by the sun to move through space. Once the province of science fiction authors such as Arthur C. Clarke, solar sailing is gradually moving into the realm of reality. A privately funded $4.5-million mission to test solar sailing technology called LightSail now has a launch date in April 2016 and a ride to space onboard SpaceX’s Falcon Heavy rocket. Once in orbit, LightSail 1 will make maneuvers using sunlight, rather than rocket fuel. “Solar sailing has been under development at a slow pace for a lot of years,” says LightSail Project Manager Doug Stetson of the nonprofit Planetary Society, which is organizing and funding the mission. “The reason it’s hung on all these years is because of the potential for basically free propulsion throughout the solar system.”
LightSail 1 is a small spacecraft made of a stock of three 10-centimeter-wide squares called cubesats. After being carried to medium Earth orbit—more than 2,000 kilometers above the planet, high enough to escape most of its atmospheric drag—LightSail 1 will deploy four ultrathin Mylar sails that will stretch to 32 square meters (potentially large enough for naked-eye observers to spot from the ground). These sails will be bombarded with sunlight and each light particle, or photon, that impacts them will impart a tiny bit of momentum. Added up, those tiny bits should be enough to move the spacecraft without the need for heavy and expensive chemical propellant. If LightSail’s orbital speed increases once it deploys its sail, engineers will know it works.
In theory, solar sailing should be powerful enough to propel a spacecraft out of Earth orbit and into the solar system. “The disadvantage to that is it takes a long time [to move], just like it takes a lot longer to sail to the Bahamas than drive a speedboat,” Stetson says. Still, in space beyond Earth’s atmosphere without friction to stop it, once a solar sail gets going, it keeps accelerating as long as sunlight keeps hitting it. That makes solar sails an appealing option to explore the whole of the solar system and beyond. Many experts say they’re the likeliest candidate to propel the first interstellar mission to another star, with extra thrust supplied by a laser, perhaps stationed in orbit around the sun, aimed at the sail in addition to sunlight. One downside, however, is that solar sails don’t come with brakes or any means of changing trajectory or slowing down once they’re zooming. One possible solution is using a planet or star’s gravity to decelerate the craft or slingshot it along a desired path.
Those consideration are beyond the scope of LightSail 1, which simply aims to prove that the basic technology is sound—especially for maneuvering lightweight, low-cost spacecraft like cubesats, which despite their small size can still pack enough instruments for basic science, navigation and communication. “We really hope that this concept of using cubesats and solar sails together really takes off,” Stetson says. “There could be a whole new domain of solar system exploration missions that could be very inexpensive.”
http://www.scientificamerican.com/article/lightsail-solar-sailing-launch-date/
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