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capturing stuff at lagrange points using solar sails?

Posted by: TerraMrs - Wed Sep 10, 2008 11:04 pm
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capturing stuff at lagrange points using solar sails? 
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Post capturing stuff at lagrange points using solar sails?   Posted on: Wed Sep 10, 2008 11:04 pm
just thought of this a month ago or so, anchoring a solar sail to an asteroid and using it to drop the asteroid into a lagrange point thereby rendering it stationary and available for easy use. any thoughts? any ideas how large the sail would have to be to do it in a period of 10 years or so for a relatively small 'roid in an orbit without a huge delta v requirement relative to the lagrange orbit? i thought of trying to calculate this then realized it would be incredibly difficult without software, anyone ever use something that could do this with minimal programming?

i don't know about you guys but it'd be pretty sweet to have all the stuff you need to build an awesome space station sitting halfway between here and the moon.

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Post Re: capturing stuff at lagrange points using solar sails?   Posted on: Thu Sep 11, 2008 6:04 pm
TerraMrs wrote:
just thought of this a month ago or so, anchoring a solar sail to an asteroid and using it to drop the asteroid into a lagrange point thereby rendering it stationary and available for easy use. any thoughts? any ideas how large the sail would have to be to do it in a period of 10 years or so for a relatively small 'roid in an orbit without a huge delta v requirement relative to the lagrange orbit? i thought of trying to calculate this then realized it would be incredibly difficult without software, anyone ever use something that could do this with minimal programming?

i don't know about you guys but it'd be pretty sweet to have all the stuff you need to build an awesome space station sitting halfway between here and the moon.


Biggest problem here is purely the physics of orbital mechanics. You have to induce a HUGE change in velocity to stop something at a LaGrange point. Getting there isn't hard - stopping when you DO get there is the hard part. That's the problem with building (or in your suggestion parking) a station there or with landing there! We're generally going thousands of miles/hour on a trans-lunar trajectory, and we'd have to come to a dead stop to meet up with the station. It's why Apollo 13 didn't turn around then they encountered their problem, they went around the moon on a 'free-return trajectory'. The 'free' part is not having to expend any propellent to turn around...

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Post    Posted on: Thu Sep 11, 2008 10:53 pm
i guess the actual lagrange point is relatively unimportant as long as it's in a stable orbit with respect to its distance from the earth. since you're not actually stopping the object (as that would cause it to fall into the sun), if you have something already in an orbit with similar energy as compared to the desired one, you should be able to provide a small, relatively constant acceleration over a period of several years that will bump it from the old, useless orbit into the new, accessible one in a very predictable and safe manner. i was thinking lagrange since it's a gravitationally stable position and therefore it would probably be easier to insert something in there, rather than give the earth an entirely new moon. such a feat would be clearly impossible with rockets due to the absurd amount of fuel that would be needed to move anything of substantial size, whereas a solar sail could be made arbitrarily large while still representing a trivial portion of the mass, in order to provide the necessary dE over some reasonable timespan to alter the orbit.

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Post    Posted on: Fri Sep 12, 2008 6:11 pm
TerraMrs wrote:
i guess the actual lagrange point is relatively unimportant as long as it's in a stable orbit with respect to its distance from the earth. since you're not actually stopping the object (as that would cause it to fall into the sun), if you have something already in an orbit with similar energy as compared to the desired one, you should be able to provide a small, relatively constant acceleration over a period of several years that will bump it from the old, useless orbit into the new, accessible one in a very predictable and safe manner. i was thinking lagrange since it's a gravitationally stable position and therefore it would probably be easier to insert something in there, rather than give the earth an entirely new moon. such a feat would be clearly impossible with rockets due to the absurd amount of fuel that would be needed to move anything of substantial size, whereas a solar sail could be made arbitrarily large while still representing a trivial portion of the mass, in order to provide the necessary dE over some reasonable timespan to alter the orbit.

But even if it's only moving at 1cm/hour but weighs a million kilograms you have an enormous amount of power necessary to stop it where you want it. And LaGrange point orbits are not totally stable, you still need some orbital adjustments to keep objects there (see the WMAP satellite information).
But to use it as a space station or just as a source of material is very expensive in terms of stopping off there. It's why we're not building a space station at the Earth/Moon L1 point in order to land on the moon. The asteroid and solar sail idea is a good one! In fact, we'll need just that in a geosynch orbit for a space elevator (assuming somebody works out the tether technology). So learn all you can about it!


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Post    Posted on: Fri Sep 12, 2008 6:33 pm
i think it's L4 and L5 that are the stable ones (no fuel needed to keep it there). there are asteroids captured at most of the gas giant's (stable) lagrange points. if i recall L1 is where SOHO is located at. the idea isn't for it to be a stopover point, but for it to be its own installation, for manufacturing or science doesn't matter. it would be nice to have somewhere stable where you could build big ships for trips to mars or farther, where launching from earth would not be practical.

the thing with orbits is that a small change can frequently make a big difference, so if you have something that almost has the right kinetic energy, it shouldn't be too hard to get it in the right orbit. the hard part would be making sure the orbit will in fact insert said object into the L point in a reasonable amount of time, and that it won't hit anything (probably more important). i think the hardest part of this would be finding the right asteroid, since your conditions are so specific. after that, well anchoring a sail to the asteroid is no mean feat, and neither is steering it, but hey we can already fly by asteroids i'm sure these other things would be doable.

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