T. Marshall Eubanks

Spinning a sling, we whirl a stone. Its speed builds, and if released at the lowest point, it flies farthest. In space, the gravity of the Sun acts as the strap: the probe dives as close to the star as possible, and at the moment of maximum speed, a brief engine thrust, like a yank of the hand, gives it a huge boost.

A handful of coins accelerates to one-fifth the speed of light. That's what Coracle interstellar probes will be like — tiny spacecraft weighing just a few grams, each with an ultrathin sail film. A powerful laser beam pushes them forward: light presses on the sail like wind fills a yacht's sails, except instead of air, it's a stream of photons.