Solar Sails: How Sunlight Can Push a Spacecraft

A beginner-friendly look at solar sails and how tiny pushes from sunlight can move spacecraft without conventional fuel.

Light can push

Photons have no rest mass, but they carry momentum. When sunlight strikes a reflective sail, it transfers a tiny amount of that momentum to the spacecraft. The push is very small, but in space it can build up over time.

What a solar sail looks like

A solar sail is usually a very large, lightweight reflective sheet connected to a compact spacecraft. The larger the sail and the lower the mass, the more effective the sunlight pressure can be.

Why use one?

Solar sails do not need to burn fuel for continuous thrust. That can make them useful for missions where slow but steady acceleration is acceptable.

How steering works

By changing the angle of the sail relative to sunlight, a spacecraft can adjust the direction of the force. This allows mission planners to raise or lower orbits and change trajectories gradually.

Future possibilities

Solar sailing may be useful for long-duration scientific missions, small spacecraft and concepts that need efficient propulsion over very long periods.