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Solar-sailing satellite proves it can use light to propel through space

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Come solar sail away with me

LightSail 2’s solar sail, as seen from the spacecraft’s onboard camera
Image: The Planetary Society

The Planetary Society’s experimental LightSail 2 spacecraft — designed to fly on light coming from the Sun — has lived up to its namesake. The nonprofit today announced that the satellite has successfully raised its orbit around Earth thanks to sunlight pushing on the vehicle’s large, reflective solar sail. It marks the first time a spacecraft in Earth’s orbit has used solar sailing to change its path around our planet.

LightSail 2 has been in a low orbit above Earth since its launch on top of a SpaceX Falcon Heavy rocket on June 25th. Last week, the spacecraft successfully deployed its sail — a thin, square piece of mylar about the size of a boxing ring. Since then, the Planetary Society has been twisting and turning the sail’s position in orbit, to optimize the spacecraft’s ability to harness the power of the light coming from the Sun. And so far, this orbital dance has worked. The Planetary Society says that LightSail 2 has raised part of its orbit about 1.7 kilometers, and that this change “can only be attributed to solar sailing.”

“We’re thrilled to declare mission success for LightSail 2,” Bruce Betts, the LightSail program manager and chief scientist for the Planetary Society, said in a statement.

This demonstration is exactly what the LightSail mission set out to prove. The Planetary Society, which advocates for space travel and funding for space projects, crowdfunded the LightSail mission to show that small satellites could rely on light alone to propel through space. Particles of light do not have mass, but they carry momentum. And this light can actually push on objects in space. With a large, thin, and reflective sail, a spacecraft can capture enough of this momentum from the Sun’s light and change its position.

“This idea that you could fly spacecraft — that you could get propulsion in space — on nothing but photons is really surprising,” Bill Nye, CEO of the Planetary Society, said during a press conference. “And for me it’s very romantic that you’d be sailing on sunbeams.”

Solar sailing in space isn’t exactly new. A Japanese spacecraft called IKAROS used a light sail to propel through space on its way to Venus in 2010. However, the Planetary Society wanted to show that the same technique could be used for smaller satellites, specifically CubeSats — a type of standardized spacecraft that’s usually not much bigger than a cereal box. CubeSats have become a great tool for companies, researchers, and more who want to gather data from space using a relatively inexpensive spacecraft that is easy to build.

Maneuvering small satellites like this through space is difficult. Most satellites must rely on thrusters to be mobile — tiny engines that combust chemical propellants to push a vehicle through space. That can be a costly addition to a spacecraft, and the propellant needed for these thrusters add weight, which is precious when launching things off of Earth. Most of the time, small satellites like CubeSats cannot accommodate thrusters and can’t be maneuvered once they reach space.

Now, the Planetary Society has shown that this deployable solar sail could be added to CubeSats in the future, providing an option for these mini-probes to move through space without using traditional chemical propellants. “We have a very small spacecraft that’s doing very high performance, very capable solar sailing,” says Nye. And Nye says it cost $7 million to pull off — about one-twentieth the cost it would have been had the organization done this with an average-sized spacecraft, he claims. The organization says it will share the data it receives from this mission so that other groups can potentially use this technology in the future.

In the meantime, the Planetary Society will continue to ride on sunbeams with LightSail 2 for the next month. “We expect to continue raising the orbit really through the end of August,” David Spencer, LightSail 2 project manager and associate professor at Purdue University, said during a press conference. Eventually, LightSail 2 will get pulled back down to Earth. The spacecraft is in an elliptical orbit around our planet, and every time it raises its orbit on one side, it dips closer to Earth on the other. Soon, the thin atmosphere will drag LightSail 2 down and the vehicle — with its sail — will burn up on reentry. But at least it will have gotten some sailing in before then.