LightSail 2 Opens Its Sails in an Early Test of Tech That May Make Interstellar Travel Possible

A photo released today showing the recently unfurled solar sails.
Image: Planetary Society

A tiny spacecraft in Earth orbit has successfully deployed its solar sails. Called LightSail 2, the craft will now use the power of the Sun to lift its orbital height even further, in what’s considered an important test of this promising means of propulsion.

LightSail 2 is a crowdfunded project run by the Planetary Society, a nonprofit space organization. The goal of this proof-of-concept mission is to test the viability of using solar sailing as a means of propelling CubeSats and other objects in space. Eventually, a massively scaled-up version of this technology could take us to the outer realms of the Solar System—and even through interstellar space—at relativistic speeds.

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Artist’s conception of LightSail 2.
Image: Planetary Society

In 2015, the Planetary Society conducted a preliminary test with LightSail 1, but the version currently in space will attempt to use its solar sails to raise its orbit by a measurable amount.

On Tuesday, July 23, around four weeks after it was delivered to Earth orbit by a SpaceX Falcon Heavy rocket, LightSail 2 passed its first critical test: the deployment of its solar sails. The Cubesat itself is about the size of a toaster, but with its four triangular, razor-thin sails unfurled, the structure measures 32 square meters (340 square feet) in size.

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The Planetary Society confirmed the successful deployment on its website, saying all of its “major systems are reporting nominally.” Mission controllers for the project are monitoring the spacecraft from their facility in San Luis Obispo, California.

At 2:00pm Pacific time on July 23, LightSail 2 had entered into solar sailing mode. Its momentum wheel, which works to orient the spacecraft’s position, was operating as expected, while “attitude control system data showed the solar sail was angled to within 30 degrees of its expected orientation—a promising early sign the spacecraft is tracking the Sun properly,” noted the Planetary Society.

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The first images of the unfurled sail, taken by the spacecraft itself, were released earlier today in a Planetary Society tweet.

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Mission controllers are still evaluating the integrity of the deployment, including a review of the spacecraft’s telemetry data. Assuming everything’s okay, LightSail 2 will start to raise its orbit by harnessing the power of the Sun.

Here’s how it works, according to the Planetary Society:

Light is made of packets of energy called photons. While photons have no mass, they have momentum. Solar sails capture this momentum with sheets of large, reflective material such as Mylar. As photons bounce off the sail, most of their momentum is transferred, pushing the sail forward.

The resulting acceleration is small, but continuous. Unlike chemical rockets that provide short bursts of thrust, solar sails thrust continuously and can reach higher speeds over time. Sunlight is free and unlimited, whereas rocket propellant must be carried into orbit and be stored onboard a spacecraft. Solar sailing is considered one possible means of interstellar space travel.

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The Planetary Society is hoping to see LightSail 2 raise its orbit by a measurable amount, which shouldn’t be a problem. The spacecraft is expected to move at a rate of several hundred meters per day. The craft is currently 720 kilometers (450 miles) above the surface of Earth.

In addition to moving small satellites in orbit, large solar sails could conceivably be used to propel heavier spacecraft through the Solar System.

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The Breakthrough Starshot project, for example, is envisioning a laser-powered solar sail that could be used for interstellar journeys. Incredibly, these light-propelled “nanocrafts” could travel at speeds approaching 20 percent the speed of light. At that rate, such a craft could reach our nearest stellar neighbor, Alpha Centauri, in just 20 years.

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Artist’s conception of IKAROS.
Image: JAXA

The Planetary Society is not the first group to experiment with solar sail technology. In 2010, the Japan Aerospace Exploration Agency (JAXA) successfully tested IKAROS, a 196-square-meter (2,110-square-foot) solar sail. Unlike LightSail 2, however, IKAROS is an interplanetary traveler, currently making its way through the inner Solar System.

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Looking ahead, JAXA is planning to send a 2,500-square-meter (26,900 square foot) solar sail to Jupiter’s orbit, where it will study the gas giant’s Trojan asteroids, and then return to Earth. This project is scheduled for launch in the early 2020s.

The era of the solar sail, it would appear, is upon us.

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About the author

George Dvorsky

George is a senior staff reporter at Gizmodo.