Solar Sail???????

dmm · #1 January 8th, 2001, 05:09 PM

quote:
Originally posted by apache:
In fact, a sailboat makes the best speed when the wind is blowing perpendicular to the direction of travel.

Perhaps my memory is faulty, but IIRC my sailboat always went fastest when I was sailing with the wind, i.e., with the wind directly astern. I suppose I might have had a poorly-designed sailboat. Worse, some landlubber said that the water resistance is irrelevant to tacking. LOL! What do you think the keel/centerboard is for?

But getting back to the original topic, I think solar sails should be just a picturesque name for a technology that really has little or nothing to do with sailing or 21st century human ideas about solar sails. So the description should be changed.

General Hawkwing · #2 January 8th, 2001, 07:27 PM

IMHO solar sails should be viewed as a device that uses stellar forces to give a ship extra movement. The exact form or way of working is not necessary. Should they work in a nebulae? yes, a black hole? yes. Why? because both contain solar/stellar energy in some motion/form, therefore it would be collectable by the device.
Why do we balk at some fictional ideas but not others? Human

nature I guess.

Nyx · #3 January 8th, 2001, 08:04 PM

For those who are interested [link]http://www.ugcs.caltech.edu/~diedrich/solarsails/[/link]. This is Caltech's Solar Sail website. It has TONS of great data. If you're patient, you can find some really interesting scraps hidden inside the news of NASA's JPL site.

My own take is that NASA won't use them for interstellar missions because they are the slowest known form of space propulsion, lagging far behind even ion drives. Even with massive ground-based lasers to augment the effectiveness, they can't hold up to any other form of propulsion and are not going to be used for anything except perhaps a few satelites as a means of giving them theoretically infinited maneuvering abilities so they can keep themselves in orbit much longer than ones with only chemical burners for maneuvers.

------------------
Compete in the Space Empires IV World Championship at www.twingalaxies.com.

pagh · #4 January 8th, 2001, 09:36 PM

quote:
Originally posted by apache:
Actually, sailboats do not sail with the wind pushing the sail. They operate by the wind passing over the sail, like air passing over a wing. In otherwords, sails are nothing more than airfoils.

Aye, you're correct - when the ship is reaching or tacking. But straight downwind most sails (except the spinnaker - the big baloon-looking sail) are basically something for the wind to push against.

quote:
Originally posted by apache:
Water resistance really has nothing to do with it.

Water resistance is what keeps the ship moving in the direction it's pointed. Ships are shaped the way they are so that they move easily straight forward, but don't move laterally without a lot of effort. A flat raft with a sail will basically go straight downwind, no matter its heading. A rudder can help a bit, but you really need a keel or at least a centerboard to have any control.

The reason a sailboat leans over to the side is that the force from the wind over the sails is usually not in the direction the ship is heading - it's at an angle. Break the vector up into parallel and perpendicular components - the parallel component is what drives the ship forward, and the perpendicular component is what makes it tip to the side.

quote:
Originally posted by apache:
In fact, a sailboat makes the best speed when the wind is blowing perpendicular to the direction of travel. The only direction a sailboat can't travel is directly into the wind.

More or less. Some sailboats (like Hobie catamarans) actually do better on a close reach (sailing at an angle *into* the wind), while a spinnaker will give any ship a big boost downwind.

Psitticine · #5 January 11th, 2001, 02:52 AM

I haven't actually changed the descriptions or anything but in my own game (in my own mind, at least

), the "solar sails" are actually catching otherwise wasted emissions from the engine output. If, say, a certain number of particles collide after being fired out the back, some of them are going to go rebounding back forward. Not many, granted, but a few. Those particles are what I picture being caught by the sails.

I also picture the sails as containing an electromagnetic field of some sort so that much of the "push" is actually EM repulsion from approaching particles with opposing charges.

A rationalization? Yep, you bet. Would it work? Eh . . . well . . . beats me. Ask somebody with more of a background in particle physics.

Puke · #6 January 11th, 2001, 03:05 AM

quote:
Originally posted by Psitticine:
I haven't actually changed the descriptions or anything but in my own game (in my own mind, at least ), the "solar sails" are actually catching otherwise wasted emissions from the engine output. If, say, a certain number of particles collide after being fired out the back, some of them are going to go rebounding back forward. Not many, granted, but a few. Those particles are what I picture being caught by the sails.

hopefully not. the sail (if working in traditional sail fasion) would be deployed in front of the ship to actually pull it. if it was deployed behind, it would need to be attached to rigid struts instead of long cables (or whatever) so that it would not wrap arround the ship when it 'inflates'

geoschmo · #7 January 11th, 2001, 03:28 AM

This is a facinating thread. Very deep for a game forum. Basically everybody has had a little piece of the truth.

A ship with a square sail and no keel or rudder (a raft) will go in the direction of the prevailing wind. If you turn the sail to try and move at an angle with the wind, the wind will simply rotate your ship so that the square sail is once again perperdicular to it.

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.

A solar sail can go with the "solar wind" or at angles to it by newtons principles of equal and opposite reaction. If you turn your sail at an anlge to the solar wind it will push your ship at an angle to the wind. It will also try to rotate your sail back to perpendicular, but by use of chemical rockets or some other thrust generating device you can keep the sail at the anlge you want. Similar to the keel or rudder on a water craft.

No principle I can think of would allow a solar sail to go into the solar wind. An interstellar solar sailing ship would use the force of a star to get enough velocity. Once up to velocity, it would use the destination star's wind to brake. If you wanted to travel through a system without stopping you would have to retract the sail while approaching the star. Once past it you could extend the sail again to use that star to continue you on your journey or change course.

[This message has been edited by geoschmo (edited 11 January 2001).]