Space sailing

[Torque]

won't they just use thrusters for maneuvering, collaspe the sail and rear thrusters to slow down?

[Mini D]

PS...

Reducing the sail size on one side would not slow down the object. It would reduce the acceleration on that side causing a spinning of the object.

[Mini D]

Originally posted by Torque
won't they just use thrusters for maneuvering, collaspe the sail and rear thrusters to slow down?

If that's what they were saying, we wouldn't be discussing it. They say they can do it with a sail. I obviously know more than a room full of engineers when I say I don't see how that's possible.

[Chairboy]

I guess I didn't read the argument too closely before I responded.  I don't see how tacking the sail could be used to slow down, just for turning.

Lesse, methods that could be used to slow down...  I wonder how feasible it would be to energize the structure of the sail to generate a magnetic field to increase the drag profile of the spacecraft?  Eg, the kind of field a Bussard ramjet uses, except instead of being used as a funnel, it's more like a drogue chute.

If you're travelling to another star, you can just the star itself to slow you with its light, of course, but for insystem travel, it'd probably be all about clever orbits.  I doubt solar sail travel will ever be terribly speedy in-system, but it might be cheap.  Heck, Niven had banks of high powered lasers on Mercury (solar powered) that would be used to provide boost to sails.  Those lasers proved useful when the Kzin dropped in too.  You put the ship into a transfer orbit to your destination, then retract the sail and perform an aerobraking maneuver to slow down.

[Mini D]

I don't see how tacking the sail would even turn the craft... only start accelerating it in a different direction that could never actually aproach a tangent to the source. Basically, I could get it to accelerate to the left or right, but I'd never be able to stop it from accelerating forward much less reverse that acceleration.

The only thing I could think that would do it is if the sails were transparent from one direction and the photons were traveling in infinite directions. Hell... that may be it in a nutshell, but the article didn't really mention that.

[SageFIN]

I think that if the craft is orbiting the Sun, then slowing down would just mean using the sail so as to decelerate the tangential component of the velocity thus killing off the crafts angular momentum.

In the case that the craft was moving away from the Sun in a straight line, then just furling the sail would do the trick... unless the craft was moving at the escape velocity, or faster.

[GRUNHERZ]

Originally posted by Mini D
PS...

Reducing the sail size on one side would not slow down the object. It would reduce the acceleration on that side causing a spinning of the object.

Yep, that last post of mine was wrong.

But in reference to "accelerating in a different direction" that pretty much defines a turn.

Doing that lowers forward acceleration - forward mening the orginal course.

[Tumor]

Originally posted by Chairboy
It's awful funny that a fellow named 'lasersailor' would lack such basic comprehension of how laser sails are supposed to work...  basic predictive design theory established 20+ years ago suggested that the structure be designed for distributed stress management so that if a portion of it was holed, it wouldn't kill the whole structure.

Secondly, the thinness of the material lessens the amount of mass that would be converted to energy on impact, meaning that it would be more likely to punch a tiny hole through it then, say, to go off like a stick of dynamite.

NERD!

[Mini D]

You're not turning the craft grun, you're sliding it. It's like playing 1942 without using forward/back... you move from right to left but you're always going forward.

Sliding would be a more accurate term than "turning"

[lasersailor184]

Funny how a guy named Chairboy criticizes me when he forgets how much **** is just flowing around randomly in space.

Death by a million paper cuts.

[GRUNHERZ]

Its original forward moment will not stop fully, you will add a new force that will act sideways. These forces combined will alter the crafts course - effectively turning it.

Just draw a two vector diagram, one representing the stong original forward vector an a new weaker (shorther) sideways vector. Whats the new direction made by the two?

[Chairboy]

Originally posted by lasersailor184
Funny how a guy named Chairboy criticizes me when he forgets how much **** is just flowing around randomly in space.

Well, I guess you must be right.  Good thing you came along, imagine the egg on their faces when the scientists find out!

I'll call JPL immediately and tell them they're wasting their time.  I think science owes a great debt of gratitude to you, Lasersailor!  Millions, if not BILLIONS of dollars have been saved!  All the PHDs on the project couldn't see the one basic flaw that you could.  It just goes to show you that amateurs CAN still contribute.

Everyone else here, I guess the thread is over.  Decades of solar sail research, punctured like that by a 20 year old.  Wow.

[ChickenHawk]

A physicist from Cornell University says the Solar Sail won't work.

http://www.newscientist.com/article.ns?id=dn3895

Say Thomas Gold is wrong and it actually does work.  I don't see how you could turn it either.

Imagine a hovercraft that has only vertical thrust and no directinal thrust.  Put up a sail in a light breeze.  How are you going to make it change direction?  All you could do is make it spin.

Since there is no friction in space (or not enough to speak about)  you won't be able to slow it down either unless you are fighting a force of gravity.  Will the solar sail be enough to overcome the force of said gravity?

Also, you could never travel to Venus or Murcury as you would always be traveling away from the sun and never be able to turn around.

If it works cool.  But I think they better get the trigectory right from the get go becouse I think it will only travel in a straight line.

[Zippatuh]

I’ve seen a few things about this but the last I heard the actual size of the sail would need to be about the surface area of Texas in order to get enough acceleration and keep it once outside the solar system.

Most of the stories I’ve seen on it though are for manned missions, one direction.  I’m sure the size of the space craft would have a lot to do with the sail size.  However, something has to be wrong somewhere… I don’t think that 260 feet would be large enough.  I also don’t think you could go towards the sun with it, thus Venus and Mercury would be out.

As for the post above where someone mentions a pebble puncturing the sail, no maybe not one pebble, but what about a comet trail, or a million pebbles broken up from an asteroid that’s not been charted, a multitude of objects that has the ability to destroy the surface over time.  This of course has a lot to do with the sail size.  If it truly has to be as big as I’ve heard, it isn’t really feasible, although a cool idea.

[Shamus]

Somthing to think about...multiple stars of differing vectors.

shamus