The LightSail mission: From concept to reality

This year, The Planetary Society celebrates its 45th anniversary. Since 1980, the Society has been empowering members to advance space science and exploration through public education, political advocacy, innovative science and technology projects, and international collaborations. One particular effort has been ongoing for much of the organization’s history: solar sailing. In 2019, LightSail 2 succeeded at using sunlight alone to change its orbit around Earth, achieving a goal that The Planetary Society had been working toward since its very beginnings. 

The concept of sailing on sunlight stretches back much farther than our organization. After observing Halley’s Comet in 1607, Johannes Kepler mused that people might one day surf on the same force that causes a comet’s tail to spread: “Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void.” 

It would take centuries for Kepler’s romantic idea to get serious consideration. In the 1970s, engineer Jerome Wright discovered that a spacecraft propelled by the gentle push of sunlight might be able to rendezvous with Halley’s Comet in 1986, marking a full-circle moment for the concept. 

NASA was interested and funded a Halley solar sail spacecraft study. One of the engineers on the project was Louis Friedman, who would later become a co-founder of The Planetary Society. The spacecraft’s eventual design resembled two spinning ceiling fans stacked on top of one another, each with six blades measuring more than 6 kilometers (4 miles) long. Ultimately, the design was deemed too ambitious, and the U.S. did not send a mission to Halley’s Comet. 

In 1980, Friedman, Carl Sagan, and Bruce Murray founded The Planetary Society. All three were solar sail enthusiasts, with Murray having supported the Halley sail study when he was the director of NASA’s Jet Propulsion Laboratory and Sagan having written a popular article about the concept for Parade magazine.

As an independent, nongovernmental group, The Planetary Society was able to forge connections with Soviet scientists during the Cold War. After the fall of the Soviet Union, Russia converted some of its submarine-launched missiles into satellite launchers under the name Volna (Russian for “wave”). In 1999, the Society’s Russian colleagues came to them with a proposal: Work with us to build a solar sail and we’ll fly it on the Volna. Thus was born Cosmos 1, the world’s first solar sail spacecraft.

Cosmos 1 was equipped with eight triangular solar sails held rigid by inflatable booms approximately 15 meters (50 feet) long. Each sail could be individually tilted, allowing the spacecraft to maneuver and track the Sun. The Society’s contribution to the mission was funded by members as well as Cosmos Studios, a venture by Carl Sagan’s widow, Ann Druyan. 

A 2001 test flight using a scaled-down version of Cosmos 1 ended with a Volna mishap. The full-scale Cosmos 1 launched in 2005, but its Volna rocket failed 82 seconds after launch, sending the solar sail plummeting into the sea. 

NASA reentered the solar sailing game in 2008 with NanoSail-D, a technology demonstration aimed at deploying a solar sail from a CubeSat — a small, modular spacecraft the size of a loaf of bread. Like Cosmos 1, the flight of NanoSail-D ended prematurely due to a rocket mishap when its SpaceX Falcon 1 failed to reach orbit. 

For a time, NASA considered giving a NanoSail-D flight spare to The Planetary Society. That effort stalled, so the Society decided to develop its own similar mission called LightSail. 

Like NanoSail-D, the spacecraft would be based on a three-unit CubeSat. Unlike NanoSail-D, LightSail would be equipped with attitude control, cameras, and two-way communication. And unlike Cosmos 1, LightSail would be a mission undertaken entirely by The Planetary Society, not just as a partner. 

Starting in 2009, the LightSail program was funded by members, donors, and 23,500 Kickstarter backers. The initial spacecraft development was completed in 2012, and in 2015, LightSail 1 hitched a free ride to orbit aboard an Atlas V rocket. It successfully tested the deployment of its sails and beamed an image of those sparkling sails home to Earth.

LightSail 2 lifted off in 2019 aboard a SpaceX Falcon Heavy, flying to a high enough orbit where the gentle push from sunlight could combat atmospheric drag. During its three-year mission, it became the first small spacecraft to successfully demonstrate controlled solar sailing and was the first to do so in Earth orbit, even raising its orbit some of the time. 

From Kepler’s celestial musings to LightSail 2’s triumphant flight, The Planetary Society’s solar sail story has been one of ambition, setbacks, and perseverance. What began as a mission to the world’s most famous comet evolved into a crowdfunded spacecraft that soared gracefully around the world, carrying humanity a little closer to harnessing the push of sunlight for space exploration.