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Setting Sail for the Stars

One of the many challenges of space exploration is propulsion. What method should you rely upon to get your spacecraft to its destination? Our early efforts in space all depended upon chemical rocket fuel. This fuel is dense in energy, but it also takes up space and is heavy and expensive. Worst of all, once your spacecraft runs out of fuel you're pretty much stuck.

We've been exploring alternatives to chemical rockets for several years, and one of the more promising options is the solar sail. Here on Earth, we use sails to capture the wind and transfer momentum to ships. In space, solar sails would capture photons, the basic particles of light.

Photons can deliver a very soft push. That makes it sound like they'd be terrible for spacefaring. But when billions of photons continue to deliver these gentle pushes against the reflective material of the solar sail, that starts to add up. 

What's more, photons are obviously traveling at the speed of light. That means even when the spacecraft has accelerated to incredible speeds, it still is receiving energy from colliding photons. At least, it will until it is out of range of the closest star.

In the video, we mentioned a Kickstarter project to fund a solar sail experiment that would for the first time use solar sails for propulsion (an earlier experiment successfully tested the deployment mechanism for solar sails). That project had a $200,000 goal and was promoted by Bill Nye, the CEO of The Planetary Society. Not only did the project meet its goal, supporters contributed a total of $1,241,615 to the effort. That means we should see the LightSail project unfurl its solar sail in 2016.

Meanwhile, other teams also are testing solar sails. In October 2015, NASA announced that it would use solar sail technology in an asteroid flyby mission in 2018, with the added goal of making the technology commercially available. This would allow other organizations in the space industry to take advantage of solar sail propulsion.

Will solar sails ever be used to transport humans? It's possible, though other methods such as ion propulsion are also likely. Ultimately, solar sail technology may become the effective, relatively inexpensive way we transport cargo in space.

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