Japanese Deploy Solar Sail

Chuck1318 writes "The Japanese ISAS (Institute of Space and Astronautical Science) announced the launch and deployment of the first ever large-scale solar sail. In the news release they state "Because it carries no fuel and keeps accelerating over almost unlimited distances, it is the only technology now in existence that can one day take us to the stars.""

Comments

Solar sail

[Uplore]

What I dont understand is how they intend to protect these massive sails from being shot full of holes by meteorites and space dust as it propels its way through space.

Also, seing as how it is powered by solar wind, what happens when the craft is between 2 or more stars which are all exerting equal force on the sails. With no fuel it is doomed to slow down and be 'blown' around in space.

Re:Solar sail

[whopis]

Ever seen a radiometer? or hear about the radiation pressure equation?

This is a common misconception... one that even Maxwell mistakenly believed. Apparently along with the folks at Encyclopedia Britannica as well.

Pay attention to which way a radiometer turns. If it were turning due to radiation pressure, it should act as if a force were pushing on the white side of the plates. Since the white plates reflect the light, there should be twice as much pressure on them as there is on the black plates which absorb the light. (It takes a greater transfer of momentum for something to bounce off of you than for you to catch it... think of the conservation laws).

The problem with the radiometer is that it turns the wrong directions... it acts as if something is pushing on the black side of the plates. And there is... air pressure. The black side will reach a higher temperature than the white side, and then due to the thermal transpiration, the gas near the edges moves from the hot side to the cool side, and in doing so it pushes the blades along.

Radiometers are in a near vacuum, but there is enough air pressure inside to allow this effect to happen.

What Solar Sails Are

[SlashChick]

In case you, like me, didn't know that much about solar sails, there's a great article at How Stuff Works about them: How Solar Sails Will Work. Looks like a pretty interesting technology!

calculations from NASA

[gentoo4ever]

These solar sails are pretty useless. Here http://solarsails.jpl.nasa.gov/introduction/design -construction.html are calculations from NASA guys. It looks like this Japanese sail has acceleration of few mm/s^2 and is not able to get out of sun gravitational field (and, of course, the Earth's one). It would take solar sail 100 years to get to alpha centauri if it had acceleration 10 m/s^2 (table 3 in the above link, there is "-" in the table for 5 m/s^2 and less , that is it will never get away from sun ). There was a good idea though to build a huge mirror to focus sunlight on such sail. This would effectivly increase surface area of a sail and pressure would not drop as square of the distanse from the sun.

solar wind

[N3wsByt3]

Solar sails do not use (or not primarely, exept maybe when close to the star, in the beginning) solar wind to propel itself. It uses the reflection of the sunlight; thus, photons, rather then ions.

It's also not correct that solarsails can't be used to reach other suns, because the sun there gives an oposite force. It's quite trivial, when using adaptive (rotating) solarsails, which have only one higly reflective side, to slow down or accelerate when nearing a solarsystem. And even withing a solarsystem; for an interesting project in that regard, see the planetary society where they plan to launch the first non-gov solarsail-powered probe.