Thursday, July 17, 2014

Solar Sail Spacecraft Test in 2016

LightSail is designed to be the first mission
to demonstrate controlled solar sailing for
small, affordable spacecraft called cubesats.
Josh Spradling / The Planetary Society
LightSail 1 will launch onboard SpaceX’s Falcon Heavy rocket to demonstrate propellant-free propulsion.

By Clara Moskowitz

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.

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Source: Scientific American Magazine.

2014: 75th Year of Pittsburgh's Buhl Planetarium Historic Zeiss II Planetarium Projector at Pittsburgh's original Buhl Planetarium and Institute of Popular Science.

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