6:29am

Mon October 8, 2012
Krulwich Wonders...

Eat Your Heart Out, Columbus: A Sailing Ship That Travels On Sunshine

Originally published on Wed October 10, 2012 9:29 am

Columbus, they say, crossed the Atlantic at a speed of roughly four knots. That's four-plus miles an hour. When the wind gusted, he could hit 9.2 mph. In 1492, that was speedy.

Sailing has improved since then. There is now a sailing ship built by the Japanese being pushed along by sunshine through deep space. It has only one sail (The Santa Maria had many) and that sail is just 7.5 micrometers thin, about one-tenth the thickness of a human hair. And yet this little voyager is rushing along at about 328 feet per second. "It's the space equivalent of a yacht sailing the sea," says Yuichi Tsuda, deputy project manager. The Japanese have named it IKAROS, after the Greek boy Icarus who tried to fly to the sun. IKAROS has already sailed past Venus.

This is an ancient dream. In 1610, the great astronomer/mathematician Johannes Kepler wrote to his friend Galileo about how one day, it might be possible to "Provide ships or sails adapted to the heavenly breezes, and there will be some who will brave even that void."

Then, in the 19th century, James Clerk Maxwell predicted that when a wave of light hits an object, the wave might be absorbed, or reflected, pushing electrons on the surface, and thus, the whole object forward. He was right. It turns out there are indeed heavenly breezes. And they can push sailing ships, but very gently. Photons are very small, and they don't land with a punch. They wouldn't move a sailboat on Earth, because the drag from water and air would cancel them out. But in space, where it's very empty, it turns out sunshine is an unlimited, never-ending, accumulating source of power. Over time, IKAROS has gained speed — on heavenly fuel. The tricky part was getting the sail up.

In this gorgeous video, you'll see how the Japanese did it.

They released a compact rotating cylinder, which over a few weeks (this video compresses time) grew masts, radiating in four directions. Then the masts, like spring time buds, swell, open and release a square sail. It's 46 feet across. Then the masts, like sails on Earth, can be turned to change direction. Elegant, no?

IKAROS is an acronym, created by Japan's Aerospace Exploration Agency. It stands for Interplanetary Kite-craft Accelerated by Radiation of the Sun. I like the word "kite-craft." It suggests that we on Earth are like boys and girls running along a beach, catching a breeze and dreaming of far away places — which is, sometimes, not too far from the truth.

We've always been a little that way. Happy 520th, Columbus!


This form of celestrial navigation is called "Solar Sailing." What's literally happening is photons create pressure when they land on extra-reflective embedded panels in the sail. The force here, as I said, is very small, about 0.0002 pounds on a nearly 700 IKAROS instrument. This particular voyage is not a pure sailing experiment. Some of the sunshine is being turned into electric power by (I think this is right) spinning the mast and turning it into a generator, but it is now clear that true solar sailing is indeed possible. Another thing: I wondered how a ship can move against the radiation pouring off the sun. Wouldn't the sunshine push the craft away? No. In the same way that sailors can "tack" against a current, so can IKAROS. Amazing. Thanks to Chris Impey, astronomy professor at the University of Arizona, for explaining some of this to me.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

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