Glossary / Space
Solar sail
A way of travelling by catching, on a large thin sail, the slight push that sunlight exerts. It uses no fuel.
Light pushes on whatever it strikes. The force is tiny, but with no air resistance in space, a craft that keeps receiving it accelerates little by little. In 2010 JAXA's IKAROS unfurled a sail 20 metres across and 7.5 micrometres thick and demonstrated acceleration by light pressure in interplanetary space for the first time[1].
Needing no fuel, it is free of the constraint of the rocket equation. Tilting the sail changes the direction of travel. The force is small, however, and weakens with distance from the Sun. Unfolding a very large sail without tangling it, and keeping it in shape, are the practical challenges.
Related terms
- Rocket equationThe equation stating that a rocket's gain in speed depends on its exhaust velocity and on the ratio of its starting mass to its burnt-out mass.
- Ion engineA thruster that ionises a gas such as xenon and accelerates it electrically to high speed. Its thrust is tiny, but it uses propellant extremely efficiently.