By

Ada Zielinska

JOHANNES KEPLER is remembered for writing down the laws of planetary motion. But the 17th-century astronomer also liked to and, one day, he noticed that their tails always pointed away from the sun, no matter which direction they were travelling in. To Kepler, it could mean only one thing: the comet tails were by a wind from the sun.

The idea must have seemed exotic in Kepler’s day, but he floated it in a 1610 letter to his friend . “Provide sails adapted to the heavenly breezes, and there will be some who will brave even that void,” he wrote. You would be forgiven for smiling at the thought. But Kepler was right. The sun produces a wind in space and, in principle, it can be harnessed.

There is no shortage of reasons to try. , but their limitations are serious. Their finite supply of propellant puts a cap on the manoeuvres they can make. Build a solar sailing ship for space, though, and you can tap into the effectively limitless source of power that Kepler noticed all those years ago.

There is a craft demonstrating this in Earth orbit right now. With no need for fuel, this technology could also enable long-term observation posts in space. Meanwhile, NASA has advanced plans to sail to asteroids in regions of usually inaccessible space – and who knows what we might find when we begin to explore such places. We may be on the cusp of an exciting new age of sail.

When the wind …