If you wanted to cross the ocean by ship, you’d probably choose an engine-driven vessel over a sail-driven vessel. The engine will get you where you’re going faster; it enables the ship to be much larger than it could be if it were driven by a sail; and it requires much less manual intervention to keep it going. Besides, you won’t be at the mercy of unpredictable winds. In oceangoing vessels, the technological progression from sails to internal-combustion engines solved a great many problems while creating only a few new ones, such as the need to obtain and store significant quantities of fuel and the pollution that results from burning that fuel. Of course, since the planet is conveniently spherical, you’re always a finite distance from the nearest port where you can fill up. If, on the other hand, you wanted to circumnavigate the globe without stopping for fuel, sails would be the way to go. The trip would take longer and the ship would be smaller, but you’d never have to worry about running out of gas.
This is the very thinking behind an ostensibly retro design for future spacecraft: by ditching the fuel and engines you can enable much longer journeys, albeit with some trade-offs. Outfit your ship with a giant sheet of lightweight and highly reflective material, and you’ve got a solar sail, a propulsion system that can take you to the distant reaches of the galaxy without any fuel—pushing you along with the gentle power of light from the sun. [Article Continues…]