Transcript: Solar Sails

Description: Solar sails could provide a way to move satellites or spaceships without using a lot of rocket fuel. TechRepublic VP Bob Artner explains how a sail works in space where there is no wind -- or is there?

For TechRepublic, I'm Bob Artner and my topic today is Solar Sails. What are they? How do they work, and why are they important?

Let's take the last one first. Solar sails could be important because they could provide a way for us to put satellites or spaceships in different places without a lot of rocket fuel, without any proportion at all, and you can imagine how important that could be. How do they work? Well the question might be, how can you have a sail in space where there's no wind. Well, that's where it gets kind of fun because in fact there is wind in space. If you have the sun here, any star actually, it emits not only ray, but it emits particles called photons in every direction that there is sunlight. So in the same way if you have a boat on earth and you have to forgive my drawing here, and here's a sail. If you say wind on earth is pushing in this direction, you can see it's pretty straightforward to send a boat that way.

In the same way, you could create a very thin membrane, which we call a solar sail and if enough photons push against this, it could go in this direction, but what if you want to send your ship in a different direction. Is that possible? It is, and we do that by tacking the sail craft. That's another sail term.

Let's assume here that we have the sun you know. Let's assume here's the earth and I'm not drawing it to scale obviously and here's the earth's orbit and let's say we launch a ship into orbit next to earth and we have a solar sail and we deploy it. But instead of having it be at parallel to where the light is going, lets turn the direction of the sail this way and in that example, light hits, the photons hit at an angle and then actually changes the effective force pushing against the craft out in that direction and that tends to make the craft to go out farther and expand its orbit. And if you do exactly the opposite, here's the sun again and here's the earth and its orbit. What's changed the direction of that sail? Let's put it this way: in that case the photons pushing against it are exerting a force in this direction that causes the craft to actually move in at a narrower orbit.

So by changing the degree and the angle of the sail we can actually cause the spacecraft that's attached to it to move in different directions. That's why solar sails are important. No proportion, easy to use. It's a technology that's been used on earth for thousands of years and in the coming months, you're going to see several experiments by different space agencies to see if we can get them to work in space.

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