A Carl Sagan Inspired Solar Sail Is Set to Launch Next Week

In the 1970s, Carl Sagan talked about a sail that could propel a spacecraft using sunlight. His legacy might come to life next week.
Chris Young
The Planetary Society's LightSail 2Josh Spradling/The Planetary Society

“Forty years ago, my professor Carl Sagan shared his dream of using solar sail spacecraft to explore the cosmos,” said Planetary Society CEO Bill Nye in a statement this week.

“The Planetary Society is realizing the dream.”

In the 1970s, famous science popularizer Carl Sagan highlighted the potential of solar sailing in his television talk show and books.

Now, thanks to Space X and the Planetary Society, we might be about to see the fruits of his vision.


Launching the solar sail

If all goes to plan, next week will see the launch of a SpaceX Falcon Heavy rocket that will deposit 24 satellites into space. The mission, called Space Test Program-2, will release its payload into three different orbits.

Amongst these satellites is the Planetary Society's LightSail 2 spacecraft. If successful, the spacecraft will be dropped off at a circular orbit 720km above the Earth's surface and will be able to propel itself with sunrays.

Light Sail 2 is the result of ten years of research by the Planetary Society aimed at bringing Carl Sagan's vision to life. It's surprisingly small — roughly the size of a shoebox — as it is only being used to test solar propulsion and doesn't need to carry a payload.

A space theory come to life

There are, of course, no air molecules in the vacuum of space to propel a traditional sail. Instead, Light Sail 2 will rely on photons from sunlight.

Theoretically, the continual acceleration of photons can propel spacecraft. The process would be more gradual than chemical propulsion, though it wouldn't need the vast amounts of fuel.

Using a boxing ring-sized sail that can pick up radiation pressure, the spacecraft should be able to 'sail' through space.

If all goes according to plan, Light Sail 2 will be the first spacecraft to sail around the Earth using sunlight. In the not too distant future, it could help propel small satellites and spacecraft. 

Further down the line, maybe it could even help achieve Carl Sagan's dream of catching up to Halley's Comet.

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