Space Matter: LightSail 2 and The Science of Solar Sailing

Space Matter is a weekly column that delves into space science and the mechanics of spaceflight. From the latest discoveries in the universe around us to the fits and starts of rocket test flights, you’ll find analysis, discussion and an eternal optimism about space and launching ourselves into the cosmos.

A solar sail: It sounds romantic and fantastical, but what is it exactly? The image of a spacecraft sailing among the stars, much like a sailing vessel on our ocean, is powerful. But the analogy isn’t exactly correct; to put it succinctly, solar sail spacecraft are craft that rely on pressure from solar radiation (not solar wind) for propulsion.

The sun gives off an immense amount of radiation, and it affects our life here on Earth. Think: auroras, geomagnetic storms, and more. We’re thankfully protected by our planet’s large magnetic field; outside of our planet’s atmosphere, though, spacecraft are vulnerable to solar radiation. This radiation, in the form of photons, has no mass but it has both energy and momentum. Solar sail spacecraft are equipped with sails covered in a mirrored material. When photons bounce off these reflective sails, it propels the craft, working as a sort of engine. The acceleration is slow, but steady, and over time, solar sail craft can reach high speeds.

Solar sails have a long and colorful history. The ability to sail through the stars was first posited four centuries ago by Johannes Kepler after he observed comets with their long tails through a telescope. Over the years, we’ve refined our understanding of how solar sails could work (and most importantly, that they’re dependent on solar radiation, rather than solar wind, to function). Since the 1970s, we’ve been using solar sails in a limited manner on spacecraft and satellites, but they haven’t seen wide or regular use in space. That might be about to change, thanks to The Planetary Society.

The Planetary Society is a nonprofit space travel advocacy organization founded by Carl Sagan, Bruce Murray, and Louis Friedman in 1980. Its current CEO is Bill Nye. Neil deGrasse Tyson is on its Board of Directors. It’s got some serious science chops, and now it’s getting into the spacefaring business with its solar sailing craft, LightSail 2.

The LightSail project relies on CubeSat technology. CubeSats are at the core of the current small satellite revolution. They are miniaturized satellites that come in standard size increments—roughly 10 × 10 x 10 cm. Satellites can be composed of multiple CubeSats; the idea is to work in multiples of the given dimensions. This makes the costs of deployment into space predictable and reduces the risk inherent in launching. Their small, standardized size also makes them easier to launch because they can piggyback on larger payloads.