The Planetary Society recently demonstrated the successful use of a solar sail, proving that space travel should be possible without the use of earth-based propellants, at least outside of our atmosphere. In theory, the technology should be usable more widely and could enable much smaller launches from the ground.
“We’re thrilled to announce mission success for LightSail 2,” said LightSail program manager and Planetary Society chief scientist Bruce Betts. “Our criteria was to demonstrate controlled solar sailing in a CubeSat by changing the spacecraft’s orbit using only the light pressure of the Sun, something that’s never been done before. I’m enormously proud of this team. It’s been a long road and we did it.”
A solar sail works not unlike a sail on an earthbound ocean ship’s sail. While there’s no atmosphere in space, and thus no wind, there are photons moving around. Photons are the small particles (or waves, per quantum physics) that light is made of. While the little “packets” of light have zero mass, they do have energy and momentum. It’s only a tiny amount of force, but when light hits something, it does push on it. By unfurling a very large sail (relative to the size of a spacecraft), enough of this energy can be gathered to move through space without fuel.
“For The Planetary Society, this moment has been decades in the making,” said Planetary Society CEO Bill Nye. “Carl Sagan talked about solar sailing when I was in his class in 1977. But the idea goes back at least to 1607, when Johannes Kepler noticed that comet tails must be created by energy from the Sun. The LightSail 2 mission is a game-changer for spaceflight and advancing space exploration.”
One of the biggest advantages to not needing fuel is that you don’t need to take the fuel to space. This lowers launch payload weights, which lowers the emissions on earth. Not packing fuel also gives the advantage of enabling longer journeys for probes and eventually human spaceflight around our solar system. However, all of these benefits are still a long ways off, as this is just a test mission with a small “CubeSat.”
The Planetary Society plans to continue using the solar sail to continue raising the craft’s orbit for about a month, and then work on deorbiting it. This will allow it to fine tune its approach to using solar pressure and learn more about what works and what doesn’t with solar sailing. When finished, they don’t want to add to the already growing problem of space junk, so they will put the craft on an unstable orbit that will eventually lead to the craft burning up in the earth’s atmosphere.
All data and lessons learned from the mission will be shared with other organizations to use. The Society presented initial LightSail 2 results this week at the 5th International Symposium on Solar Sailing in Aachen, Germany. Results are also being shared with NASA’s NEA Scout mission, which is launching a solar sail-powered CubeSat to visit a near-Earth asteroid as early as next year.
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