Flight By Light
By Jon Sung
An alien species checking in on us every now and then throughout the course of human history might reasonably come to the conclusion that we are a race of sailors. We've been sailing for centuries, far longer than we've been driving cars or flying airplanes; a solid, sail-powered craft was the first efficient means we had to traverse great distances and explore what lay beyond our own shores. "A tall ship and a star to steer her by," in the words of poet John Masefield, has been an enduring symbol of exploration, freedom and courage.
It's no surprise then that we'd eventually turn to the sail as a model for exploring beyond the confines of Earth. The Planetary Society is getting ready to launch a privately funded, solar sail-powered vehicle in 2016 named LightSail-1.
Now, you may be saying to yourself, "That’s crazy! How would a sail work in outer space? There's no wind up there!” First of all, you should know better than to talk that way to Bill Nye, the Planetary Society's CEO (yes, that Bill Nye). Solar sails don't use wind for propulsion—they use light. Just as a stiff breeze pushes on a square of canvas, so too can a rain of photons on a sheet of super-thin Mylar. In 2010, the Japanese launched a solar sail-propelled probe named IKAROS that successfully demonstrated the technology works. It took IKAROS a little over six moths to reach Venus, and the probe continues the orbit the Sun.
Sending things into space is always a chore because you're trying to lift something out of the reach of Earth's gravity, not to mention move it around once you're up there. Since conventional rockets need a lot of fuel to make that happen, you have to strap big tanks to the sides of your ship, which makes it heavy; every additional ounce of weight—like passengers and scientific equipment—has to be carefully considered before being loaded into your spacecraft. Do you want that infrared telescope? Or do you want to be able to get to the Moon and back? Solar sails don't require fuel; once you get up there, the light streaming from the sun provides your motive power. So forget those gas tanks and pack all the telescopes you want!
Solar sails do have a couple of drawbacks, though. They need to be pretty big in order to catch the amount of photons they need to work, but they also have to be light enough that the photons will actually move the sail. This means the sail itself is huge, but extremely thin, which makes it vulnerable to space debris and micrometeoroids.
It's also unclear what the maximum range of a solar sail vehicle would actually be: if it gets too far from the sun, LightSail might cease accelerating or lose the ability to maneuver.
There's also been some loose talk of, well, a curse at work: the Planetary Society tried to launch a solar sail mission in 2005 that never got off the ground, and a test of LightSail's radio system was recently bedeviled by problems, albeit fixable ones. But a curse would be a ridiculous notion, especially for a society led by Bill Nye. What self-respecting person (or guy) of science would believe in such things for more than an attosecond?
So we're rooting for you, LightSail! We'll be watching in 2016. Let's give those notional alien observers something to talk about!
Jon Sung is a contributing writer for XPRIZE and copywriting gun-for-hire to startups and ventures all over the San Francisco Bay area. When not wrangling words for business or pleasure, he serves as the captain of the USS Loma Prieta, the hardest-partying Star Trek fan club in San Francisco.