LightSail-2 Mission Shows Solar Sailing’s Potential for Spaceflight

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Sail on, pushed by the wind of sunlight.

Over the past week, engineers have demonstrated how they can steer LightSail-2, a small privately financed spacecraft with a billowing silver sail. The technology could be used to propel future space probes through the solar system.

Most space missions today are propelled by engines that provide bursts of acceleration with limited amounts of fuel. The rest of the time, the spacecraft are coasting.

By contrast, with LightSail-2, particles of light from the sun bounce against the spacecraft’s 344 square feet of sails — roughly the area of a boxing ring — generate a modicum of force, the equivalent of the weight of a paper clip pushing down on your hand. But because the sun always shines, the sail offers a continuous nudge that adds up over time to faster speeds — all without needing any fuel at all.

Officials at the Planetary Society, the nonprofit organization that is running the mission, announced the achievement during a telephone news conference on Wednesday.

“We’re thrilled to announce mission success for LightSail-2,” Bruce Betts, the program manager and the society’s chief scientist, said in a statement.

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The Planetary Society has been pursuing the LightSail program for a decade, financed by 40,000 donations totaling $7 million. LightSail 2 launched on June 25, one of the payloads lofted by a SpaceX Falcon Heavy rocket. The spacecraft, about the size of a loaf of bread, successfully deployed four triangular sails of shiny Mylar a week ago.

As it circles around Earth, 450 miles above the surface, the spacecraft has been swinging its sails to catch the sunlight, much like a sailboat tacking in the wind. In the past four days, it has raised one side of its orbit by more than a mile. At the same time, the orbit is becoming more elliptical, and the other side of the orbit is swinging closer to Earth. That makes the spacecraft catch more of the atmosphere, and the drag will eventually pull LightSail-2 to its demise in about a year.

This demonstration of raising the orbit altitude is to continue through the end of August. LightSail-2 will then remain in orbit performing other solar sailing experiments.

The Planetary Society launched an almost identical LightSail-1 four years ago, but the orbit of that spacecraft was too low to overcome atmospheric drag and demonstrate actual solar sailing. However, that mission allowed engineers to solve problems and make improvements on LightSail-2, which has largely performed without problem.

The same technology could be used for a variety missions, perhaps to keep a satellite sitting above Earth’s poles, ferrying cargo to Mars or a long-duration mission to distant comets.

“For me, it’s very romantic that you’ll be sailing on sunbeams,” said Bill Nye, the chief executive of the Planetary Society.

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