Since the time humans have ventured into space, they have been limited by many obstacles. The most challenging one was running out of power, usually hydrazine fuel, that steers the spacecraft.
For centuries, travelling through space propelled by the sun’s photons was only a science fantasy and the idea was first put forward in the 1600s by Johannes Kepler. Carl Sagan, a cosmologist, believed it could be more than that, and in the 1970s he began promoting the building of solar sails for space exploration.
After 10 years of planning and over 40,000 private donations worth $7 million, on June 25, 2019, Planetary Society launched the first ever steerable solar sail into orbits around Earth. The spacecraft is named as LightSail 2. It was launched by a SpaceX Falcon Heavy rocket and on July 23, LightSail 2 successfully deployed its solar sail. Its solar sail is about the size of a boxing ring, and made from a thin Mylar material.
Photons from the sun is a source of propulsion for the solar sail. Although photons have no mass, they can impart momentum when they bounce off a highly reflective surface – this is a light sail. In the vacuum of space, there’s no air resistance to slow down the sail. With enough photons, and enough time, a light sail can accelerate to incredibly high speeds.
With the Planetary Society’s LightSail 2 sending data home, teaching mission controllers to sail in space, these will be valuable lessons for future missions that might use this technology as an actual method of propulsion.