Solar Sail???????

[Strangeone]

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Originally posted by geoschmo:
A ship with a square sail and a keel or rudder can follow the wind or go at angles to the wind (but still with it) because the friction of the water against the keel or rudder will keep the ship from rotating.

A ship with a triangular sail can go into the wind at angles by aerodynamic principles similer to how a wing on an aircraft generates lift.

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Actualy ships with square sales can sail up wind like ships with wing shaped sails. the difference is that they just can't get quite as high up (i.e. closer to the wind). This is called pointing. Most modern keel boats can get to within 30 degrees of the wind when beating up wind (zig zaging up wind). The older square sailed boat usualy managed 45 degrees or 60 degrees (including the drift). The thing to remember is that even with a square sail, you could turn it around the mast and have one part of the sail near the bow and the other part near the stern. This allowed you to point the boat at less than 90 degrees to the wind and still catch the wind. The shape of the sail is inefficient for this but not ineffective.

Strangeone. (who was a sailing instructor at one point in his mis-spent youth).

[Emperor Zodd]

We have a lot of sail boaters here. Not me, I'd rather skim across the surface at high speed in my bass boat!

[DirectorTsaarx]

Here's an idea: maybe the "solar sail" is capturing the solar wind (and other emanations, like background radiation in nebulae) and feeding that energy into the engines as a kind of "overdrive". That avoids the problem of it acting as a "sail". It would really be more of a ramscoop... hmmm... now I have more ideas... I'll have to go off and think now...

[Nyx]

*Sigh*

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For those who are interested http://www.ugcs.caltech.edu/~diedrich/solarsails . This is Caltech's Solar Sail website. It has TONS of great data.

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The site has some detailed explanations of what solar sails are, how they work, and how they can be used to let a vehicle approach the star.

#1 Solar sails do not harness the solar wind:

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Many people assume that because here on Earth they feel wind but not sunlight, that solar sails must be pushed by the solar wind. However, there is a very big difference between space and Earth. Earth is wrapped in a thick layer of gas that is felt as wind whenever it moves. In space, there is no air to move around and cause strong winds like we feel on Earth. The solar wind is an extremely tenuous flow of particles ejected by the sun which exerts very little force on anything it hits. The reason people worry about the solar wind is because many of the particles have an electric charge that can hurt people and electronics, or can push a magnetic sail.

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#2 They approach a star not by tacking, but by narrowing an orbit (a very slow process).

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Solar sails are more complex. The force produced by sunlight on a solar sail is the addition of the forces from the incoming sunlight and the reflected sunlight. This force always points away from the sun, and is at an angle that is close to a right angle to the surface of the sail. If this force is angled back along the solar sail's path, the spacecraft's orbit will start to shrink, bringing it closer to the sun. If the force is angled foreward along the spacecraft's path, the orbit will grow and the solar sail will head farther from the sun.

This is the general idea behind "tacking into the sun" for solar sails. In real practice, the behavior of a solar sail is more complicated because sunlight pushes not only along the spacecraft's orbit, but also straight out from the sun. These effects are beyond the scope of this document, however.

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You can find all kinds of neat ideas, including several different designs of potential solar sails, and some fun facilities to make use of them. For example, NASA was considering using a massive ground-based laser (5-million megawatt) on continual fire to propel a solar-sailed raft to Alpha Centauri, until the ion and plasma pulse rockets turned out to be both cheaper and faster.

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