A crowdfunded spacecraft has successfully sailed on sunlight while in orbit around the Earth.
LightSail 2 was launched in June by the space advocacy group the Planetary Society as a secondary payload on a SpaceX Falcon Heavy rocket.
On 24 July, the tiny craft – which measures just 10 x 10 x 30 cm – deployed a 32-square-metre reflective sail. The society reported that the extra thrust received by the sail changed the shape of its orbit by about 2km at its furthest point from Earth.
Although photons of light do not have any mass, they do carry energy and this means they have momentum. A reflective solar sail captures that momentum and transfers it to the spacecraft, just like a sailing ship captures the momentum from the wind. Solar sails are attractive prospects because they could be used to manoeuvre in orbit without the need for fuel or engines. Larger versions could also travel between planets.
LightSail 2 is only the second time a solar sail has been used to propel a spacecraft. In 2010, the Japan Aerospace Exploration Agency used a much larger solar sail (196 square metres) to fly the Ikaros spacecraft past Venus.
