There's Now A Satellite Sailing In Earth's Orbit On The Rays Of The Sun

The LightSail 2 with its mylar sail deployed. (Courtesy of The Planetary Society)

For the first time in human history, a spacecraft is orbiting Earth propelled by solar sails. The craft is harnessing the light of the sun, reminiscent of how ye olde tall ships captured the wind. And remarkably, it wasn't the government spearheading the project. Or private industry. We can thank our very own Pasadena-based nonprofit, The Planetary Society, for this scientific leap.

The LightSail mission -- more than a decade in the making -- was officially declared a success on Wednesday. LightSail 2, a small satellite with a large rectangle of shiny mylar attached, has shown it can raise its own orbit powered only by the sun. (LightSail 1 successfully tested the sail deployment system and helped work out some of the kinks back in 2015.)

"For me, it's very romantic that you'll be sailing on sun beams," said Bill Nye (yes, that Bill Nye -- in addition to his career as the "Science Guy", he's been CEO of The Planetary Society since 2010).

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And the mission is sort of romantic in another way: it was a team effort combining help from universities, private companies, NASA's Jet Propulsion Lab and donations from everyday people. The total mission cost was $7 million, and $1.24 million of that came from a Kickstarter campaign.

"[The donors] are truly the heroes of this story. This mission success moment belongs to them," said Jennifer Vaughn, COO of The Planetary Society.

LightSail 2 is the second successful solar sailor, following Japan's IKAROS. But for those keeping score, the team says it also achieved a number of firsts: the first spacecraft to use solar sailing for propulsion in Earth orbit, first crowdfunded spacecraft to demonstrate this propulsion technology, and the first CubeSat to demonstrate solar sailing.

CubeSats are small satellites that have become popular as an affordable alternative to the much larger commercial satellites we're accustomed to hearing about, but their small size means they often can't accommodate the fuel and thrusters needed to move through space. That makes solar sailing an exciting possibility, because the sun is an unlimited, free fuel source that doesn't have to be carried onboard a spacecraft.

"[LightSail 2 is] demonstrating to folks that we can use light as a fuel to push our spacecraft along," says John Bellardo, a computer science professor at Cal Poly San Luis Obispo who worked with the LightSail mission.

HOW DOES SOLAR SAILING WORK?

Nye gives an explanation of solar sailing here:

The concept relies on the special properties of light, which is actually made up of tiny bits of energy called photons. You can think of those photons as little ping pong balls of light hitting the sail, says Michael Fernandez, a physics student helping with mission control operations at Cal Poly San Louis Obispo.

"And if you can imagine hitting something with a ping pong ball, that object would start moving further and further away," he said. "Now that push is extremely small, so the sail has to be very large in order to get any sort of push at all."

The sail is 32 square meters, so it would fill up a large living room, he says, and that big sail had to fit inside a spacecraft the size of a breadbox and then open once in space.

Diagram of the LightSail 2 with its sail deployed. (Courtesy of The Planetary Society)

HOW WE GOT HERE

For The Planetary Society, the quest for successful solar sailing goes back years. In 2005 , the group launched a similar spacecraft dubbed Cosmos 1, but it was lost due to a rocket failure. The lessons learned there lead to the LightSail mission.

LightSail 2's big moment required a lot of preparation. The spacecraft launched on June 25 from the Kennedy Space Center in Florida, hitching a ride on SpaceX's Falcon Heavy rocket.

After it separated from the rocket, the mission control team sent up software patches for the attitude control system, which controls the direction of the spacecraft, to make sure it would be ready to start sailing.

"For solar sailing, we need to point the spacecraft in a very specific direction relative to the sun and be able to make these 90 degree tacks twice in orbit," said David Spencer, LightSail 2's project manager.

The deployment of the sail last week was a key milestone for the mission, which is why the team was so excited to see the photographic proof of the sail opened up and working.

"We had the cameras take a photo, and we could physically see the sail had deployed, so that was really encouraging, and it was just really exciting for us," Fernandez said.

Once the sail was opened, the spacecraft had to raise the height of its orbit around the Earth. In the past four days, its orbital high point has increased by 2 kilometers, according to The Planetary Society. It will continue to increase its orbit for the next month or so.

Scientists want to push this technology further. The International Symposium on Solar Sailing, an annual conference devoted to the topic, is now in its fifth year.

And there are other upcoming missions set to incorporate the technology, including Near Earth Asteroid Scout, or NEA Scout.

LightSail 2 will continue to orbit until about 2020, when it's expected to re-enter Earth's atmosphere. The Planetary Society will map its movements until then. They've said that with the sails deployed it could also be possible to see the spacecraft with the naked eye when it's over your area.

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