For TechRepublic, I'm Bob Artner and my topic today is SolarSails. What are they? How do they work, and why are they important?
Let's take the last one first. Solar sails could beimportant because they could provide a way for us to put satellites orspaceships in different places without a lot of rocket fuel, without anyproportion at all, and you can imagine how important that could be. How do theywork? Well the question might be, how can you have a sail in space wherethere's no wind. Well, that's where it gets kind of fun because in fact thereis wind in space. If you have the sun here, any star actually, it emits notonly ray, but it emits particles called photons in every direction that thereis sunlight. So in the same way if you have a boat on earth and you have toforgive my drawing here, and here's a sail. If you say wind on earth is pushingin this direction, you can see it's pretty straightforward to send a boat thatway.
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 goin this direction, but what if you want to send your ship in a differentdirection. 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'sassume here's the earth and I'm not drawing it to scale obviously and here'sthe earth's orbit and let's say we launch a ship into orbit next to earth andwe have a solar sail and we deploy it. But instead of having it be at parallelto where the light is going, lets turn the direction of the sail this way andin that example, light hits, the photons hit at an angle and then actuallychanges the effective force pushing against the craft out in that direction andthat tends to make the craft to go out farther and expand its orbit. And if youdo exactly the opposite, here's the sun again and here's the earth and itsorbit. What's changed the direction of that sail? Let's put it this way: inthat case the photons pushing against it are exerting a force in this directionthat causes the craft to actually move in at a narrower orbit.
So by changing the degree and the angle of the sail we canactually cause the spacecraft that's attached to it to move in differentdirections. 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 thecoming months, you're going to see several experiments by different spaceagencies to see if we can get them to work in space.
