An experimental spacecraft has set sail in space. LightSail 2, developed by space advocacy group The Planetary Society, has unfurled a solar sail and begun harnessing sunlight to propel itself through space.
The craft was launched on 25 June aboard a SpaceX Falcon Heavy rocket. Now, the small boxes that held its sails have opened. The mirrored sails are each just 4.5 micrometres thick – thinner than a human hair – and together have a surface area of 32 square metres.
When photons from the sun hit the shining sails, they bounce back off and impart a small amount of energy, which propels the craft forward. The push is weak, but over time momentum will build up, allowing the spacecraft to accelerate.
The spacecraft’s predecessor, LightSail 1, unfolded its sail in 2015 but did not perform any controlled manoeuvres before falling into Earth’s atmosphere and burning up. LightSail 2 was launched into a higher orbit, so it will experience less friction from the atmosphere and fly around the planet for up to a year before it falls.
In the future, light sails like this may be a viable way to propel small satellites through the solar system and maybe even beyond, without requiring the huge amount of fuel that traditional spacecraft need. Even though the acceleration is slow, sunlight is constant and could theoretically bring the spacecraft to impressive speeds over time.
And light sails do not necessarily have to be solar powered – some have proposed sails that are propelled by powerful lasers that could build up momentum faster, maybe even fast enough for interstellar journeys.