An experimental spacecraft began its mission today. A solar sail, called LightSail 2, was launched from the US Space Station Cape Canaveral. It should not be driven by fuel, but by particles of the sun.

At the launch, the sail was still folded to the size of a loaf of bread. A missile took it to 720 kilometers altitude. In more than a week, if all systems work properly, the SAIL must open. It will be 5.6 by 5.6 meters tall, similar to a boxing ring.

It will orbit the Earth at an altitude of 720 kilometers for a year to test the technique. It can be seen from the ground, but it is no more northerly than Portugal, Spain, Italy, and Corsica.

The sun is constantly swinging light particles into the universe. Photons, they’re called. They hit the sail of the LightSail 2. That’s a tiny force, but it’s incessant and there’s little friction, so it should be enough to move forward.

To steer, it can change its mind. If a probe barely has to bring fuel, a mission becomes a bargain. In the long run, a sail might be able to sail to other stars.