The idea of capturing sunlight with sails to travel among planets is not modern. It was first thought of by Kepler in 1608. But the developments achieved in the last decade suggest that solar sail technology is almost ready for frequent use.
Among the handful of projects that have been tested and deployed, there’s the Planetary Society’s citizen-funded LightSail-2, which will be launched on June 22 aboard a SpaceX Falcon Heavy rocket. The mission will see a 5-kilogram (11-pound) CubeSat deploy a boxing ring-sized sail that will be employed to propel the diminutive satellite to a higher orbit, roughly 720 kilometers (450 miles) above the ground.
The sail measures 32 square meters (344 square feet) but is only 4.5 microns thick, slightly thinner than a typical spider web strand. It is made of Mylar, a special type of stretched polyester film, and has seams every few inches so that a rip won't spread if the sail is hit by space debris or micrometeorites.
"Forty years ago, my professor Carl Sagan shared his dream of using solar sail spacecraft to explore the cosmos. The Planetary Society is realizing the dream," Planetary Society CEO Bill Nye said in a statement. "Thousands of people from all over the world came together and supported this mission. We couldn't have done it without them. Carl Sagan, and his colleagues Bruce Murray and Louis Friedman, created our organization to empower people everywhere to advance space science and exploration. We are go for launch!"
The raising orbit mission is expected to last one month, during which time the semi-major axis of the orbit will increase by several hundred meters every day. The system is not designed to maintain a circular orbit, so as one side of the orbit increases, the other will decrease. Atmospheric drag will eventually be enough to slow the craft down and make it fall back to Earth, where it will burn up in the atmosphere.
LightSail-2 is the follow-up mission of LightSail-1, which worked as a technology proof-of-concept for the upcoming mission. The Japanese Space Agency successfully used a solar sail in its IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) mission, which reached Venus in 2010, demonstrating the technology is viable for travel between planets.
More missions are currently in the works to demonstrate that this technology can be used around Earth and even in the outer Solar System.