Solar Sail???????

Baron Munchausen · #1 January 8th, 2001, 07:01 AM

quote:
Originally posted by Puke:
but working on magnetic pricipals as you say, or working on other field / wave related principals it could function without a star. granted, it might have a hard time in deep space, but if nebulae are cool enough to disable shields or sensors then they certainly have enough background radiation puttering about to power a sail. we have definitly observed black holes cranking out all kinds of radio / microwave / high frequency wave output, so they should not have any problem powering a sail either.

as someone else pointed out, the simple answer is to look at it a little more abstractly, and maybe change the description from 'bounces photons at 90 degrees to generate force' to something more like 'manipulates naturally occuring fields and background radiation to indirectly propell a ship.'

I suppose you could call it "Electromagnetic Sail" then, and make a graphic image of some big magnetic coils to replace the sail thing. But then it doesn't belong in the stellar harnessing tech field.

apache · #2 January 8th, 2001, 07:09 AM

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. Water resistance really has nothing to do with it. 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.
Anyways, I may be wrong about the actual arc of motion allowed by a passive sail, but the way it would move in other directions is by orienting the sail in an angle to the path of the solar wind. The wind particles hit, and bounce off of the sail, and so by Newton's 3rd law, generate an equal and opposite force. The way the sail is oriented determines the direction the desired reaction force will be in. And so you can move the ship in directions not along the path of the solar wind.

Trachmyr · #3 January 8th, 2001, 08:41 AM

And don't forget about tacking! Zig-Zaging at angles allowing a sail to gain thrust, making the overall direction to be towards the sun...

BTW, I made solar sails a normal engine type.. with low speed (but some bonous movement, which means a lot since I use the "Engines Needed per Move" field in vehiclesize.txt), no supply usage, and made them appear at Stellar Manip 2... reducing Stellar Manip to 4 levels, and reducing cost from 10K to 5K... Gives a nice alternative for utility vessels.

[This message has been edited by Trachmyr (edited 08 January 2001).]

dmm · #4 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 · #5 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 · #6 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 · #7 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.