World's first solar sail to be launched late this month (July 2008) / La NASA y SpaceX en un histórico intento de desplegar una vela solar

The late Cosmos 1

Or the beginning of August. If it seems that you've heard about this before, you're right: a solar sail called Cosmos 1 was supposed to be launched in 2005 as well but that never made it to orbit. Three years later and another attempt is read to be made. This one is called NanoSail-D.

The launch will be made with SpaceX's Falcon 1, which has so far failed to have any 100% successes in two tries, but the second very nearly made it to orbit (some sloshing about about 5 minutes in is what triggered a system that shut off the engine, if I remember correctly) and they've been spending a lot of effort since then to make sure that this flight is successful, so let's hope that it is.

Here's an article at space.com about the subject. This time it's NASA that has contracted out the rocket. Here's what the article says:

If successful, this will be the first deployment of a solar sail. An earlier effort mounted by the Planetary Society, Cosmos I, failed three years ago. Science fiction fans have been looking forward to this for generations. As Arthur C. Clarke's wrote in his 1964 short story Sunjammer.

"Hold your hands out to the sun. What do you feel? Heat, of course. But there's pressure as well — though you've never noticed it, because it's so tiny. Over the area of your hands, it only comes to about a millionth of an ounce. But out in space, even a pressure as small as that can be important — for it's acting all the time, hour after hour, day after day. Unlike rocket fuel, it's free and unlimited. If we want to, we can use it; we can build sails to catch the radiation blowing from the sun."

The most exciting aspect about a solar sail is that it is the only technology we have that is self-sustaining; it doesn't require any extra fuel like chemical rockets, ion drives and so on. I haven't read as much about the subject as I should but since solar energy depends on the amount of sunlight available that makes it most promising for going about the inner solar system, or starting from the inner solar system on a New Horizons-type high speed flyby mission.

Wikipedia also has a bit on the sail (I've removed the non-metric numbers because it's time to give up old habits):

A team from the NASA Marshall Space Flight Center, along with a team from the NASA Ames Research Center, have developed a solar sail mission called NanoSail-D which is scheduled for launch aboard a Falcon 1 rocket in 2008.^[13] The structure is made of aluminum and plastic, with the spacecraft weighing less than 4.5 kg. The sail has about 9.3 m² of light-catching surface. A NanoSail-D mission dashboard was recently released.^[14]

4.5 kg - that's light. I know a cat here in Korea that weighs about that much.