A sail is something you’d expect to see on a boat in ocean, not in space. But that’s just what a Japanese spacecraft called Ikaros is using to fly through the solar system.
The name means Interplanetary Kite-craft Accelerated by Radiation Of the Sun, but it is similar to a character in an ancient Greek story named Icarus. [In the story, Icarus fly through the sky using wings made of feathers and wax. Unfortunately he got too close to the Sun, melting the wax that held his wings together and fell from the sky. The same isn't expected to happen to Ikaros.]
The Ikaros spacecraft was launched in May this year. A few days later after launch it unfolded its 20-metre sails. The sails, which are thinner than a human hair, are made of a special plastic sprayed onto aluminium foil.
Instead of wind, the sails on Ikaros use the tiny energy from each particle of sunlight to push it forward.
To steer, the spacecraft has tiny rockets. But it can also use a series of liquid crystal squares along the outer edge of the sail. When the liquid crystals are black, light from the Sun is absorbed by the crystals and doesn’t push on the sail as much as when the crystals are clear.
So by making the crystals along one edge of the sail black, the spacecraft will slowly turn in that direction.
The spacecraft’s sails also have solar cells to collect energy from the Sun, which are used to power experiments.
In December, Ikaros will fly past Venus, and then spend its time orbiting the Sun.
Japanese scientists plan to build a 50-metre version of Ikaros to fly to the planet Jupiter and study nearby asteroids.