Future Tense

The Coolest Thing SpaceX Just Launched Into Space Is a Sunlight-Powered Sail

An artist's concept of the LightSail 2 orbiting Earth.
An artist’s concept of the LightSail 2. Josh Spradling/The Planetary Society

At around 2:30 a.m. EST Tuesday morning, a SpaceX rocket carried a bunch of cool things into space: 24 satellites, an atomic clock, the ashes of 152 people, and itself. Because the rocket’s launch vehicles attempt to land after being fired, they can possibly be reused, potentially reducing the cost of space travel. This was the Falcon Heavy’s third time in space.

But the coolest thing on the Falcon Heavy was an unearthly sailcraft with a body about the size of a loaf of bread. If it works, it will be the first vehicle to be propelled in space by sunlight alone.

In one week, as the craft moves deeper into the far reaches of space, it is slated to exit its carrier, a satellite named PROX-1. A door will open, and a large spring will push the vehicle, called LightSail 2, into space. About a week after that, after some testing and health checks, a small coil will heat up and sever the string that’s currently keeping its solar panels tucked in. Once released, the panels will swing outward, making way for the deployment of razor-thin mylar sails that will stretch to about the size of a boxing ring.

Those sails are supposed to be able to use the pressure from light particles that hit them to give the spacecraft momentum. As this happens, a small wheel will adjust the sails as the spacecraft tacks like a sailboat jibing into and away from the sun’s photons. The photons don’t have much of a push, though. The nonprofit Planetary Society, which made the space sail, says “the photon-pressure push is only about as strong as the weight of a paperclip in the palm of your hand.” Still, simulations show that this should be enough to propel the spacecraft.

Though the Planetary Society has been working on some version of a solar sail since the late 1990s, the idea was initially envisioned by Carl Sagan, who discussed the concept on The Tonight Show with Johnny Carson in 1976. Four years later, Sagan founded the Planetary Society. Science guy Bill Nye, the group’s current president, thanked the public on Monday night for helping to crowdfund for the launch. “We are advancing space science and exploration. We are democratizing space. We are innovating. We are working to answer the two deep questions: Where did we come from? And are we alone?” said Nye. “All because of you.” The idea is that if the mission proves successful, innovations in space sailing could make travel deeper into the solar system much cheaper, replacing the need for fuel with the limitless photons provided by the sun.

The launch, which SpaceX CEO and founder Elon Musk called the company’s “most difficult” to date thanks to the large payload, was certainly impressive too. Two of the Falcon’s three fiery boosters landed upright at Cape Canaveral in Florida after the launch. The third booster was slated to return to an unmanned ship in the Atlantic Ocean, named Of Course I Still Love You, but it didn’t stick the landing.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.