Posted May 15, 2015

Planetary Society sets sail to space

Don't miss this on May 20th. On that day a satellite will be launched carrying a solar sail: a large reflective sheet that can accelerate a spacecraft by the pressure of sunshine. It's a pet project of one of the coolest science communicators around: Bill Nye, the science guy. And it's privately funded, and you can help.

Ever felt the pressure of sunshine while sunbathing? Probably not. But it's there, caused by photons, light particles that hit stuff and bounce off it. Light pressure pushes on everything by a force that can be calculated. It's different for different sources of light but in the case of sunlight at the Earth's distance from the Sun it's about 9 micronewtons per square meter for a perfectly reflecting surface.

What does that mean? Skipping the paperwork and assuming some realistic figures, suppose you have a 900 kg spacecraft and a 1000 m2 sail (about 30 x 33 m). Ideally, the solar sail would give this thing 1 m/s of extra speed in almost three hours (10.000 seconds).

What? That's nothing. In space you need kilometers per second, not meters.

Sure, but keep in mind two things. First, once you're in space you have lots of time. After one year you will have gained three kms/s. Second, you can have a bigger sail. A size of 1 km2 (that's huge) will increase your speed a thousand times faster.

Of course, if you have a heavier spaceship, maybe containing humans, supplies and whatnot, you bring the figure down again.

But that's far into the future. Right now the Planetary Society is planning this test flight in low Earth orbit, when they will deploy a sail of 32 m2. The orbit will be so low that atmospheric drag on the sail will slow it down more than sunlight will speed it up. Deployment itself is the main thing that will be tested. As you can see in the video below, such a sail is very thin indeed, and folding it out is no easy matter. Also, in the weightlessness of space it will be different. Hopefully easier, but different nonetheless.

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There have been some tries at solar sailing and most have not been very successful. The Planetary Society is now having a go without government money. The society has members who supply money and they have sponsors as well. Members include Mr. Nye and Neil DeGrasse Tyson, well known and popular science communicators. Both are in the video below.

And now they're launching a Kickstarter too. This solar sailing project still needs some money. How much and what for, you can read all about it on their Kickstarter page but why not watch their Kickstarter video first:

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And all of this, remember, is still just testing a prototype. Next year it will be for real: a privately funded solar sailing craft will then be launched into an orbit 720 kms high, where the sail can really do its job. We'll keep you posted. :-)


About Herbert Blankesteijn

Herbert Blankesteijn is a technology journalist from the Netherlands who has written for many prominent Dutch newspapers. He presented and directed television and radio programmes and has 10 books to his name. Herbert is interested in nascent fields such as 3D printing, drones, robotics and the private space business.