Moon SE

[AztecBill]

L2 for the Earth/Moon is 321,571.4 KM from the moon. We could create a SE from there to the moon using the same method as the proposed SE from Earth. We would eliminate atmosphere, weather, and atomic O2 problems. No Space Debris problem means we could have a fixed base. This wouldn't do much for the Earth gravity well problem but would give us a simple free return from the moon. This would most likely have to wait until an Earth SE is built.

A moon mining base would sure love to have a cheap Earth return method.

If a payload was released on the Earth-side of L2 you wouldn't need much to change the vector to miss Earth and use Earth to sling shot elsewhere.

I don't think there could be any ESE to MSE movement without a large delta V added due to major differences in their orbit rate - 24 hrs versus 28 days.

Has this been talked about?

[publiusr]

The rotation of the moon may be too slow for the SE to work there in the usual sense.There is no Geosynch point for moon-orbit which does not pass well within Earth's influence.

But your suggestion is that a tether may be started at an L-point and moved towards the Earth on one side and the moon's surface on the other. This ribbon would be quite taut with two very massive bodies pulling at it on either end. No part of the ribbon would ever touch the lower atmosphere of Earth--being an orbiting docking target.  This should also generate tremendous electrical power if lower down.

In the same way that some have suggested Single-Stage-To-Tether spacecraft capture missions from Earth, the same might be done here, out of the atmosphere. But you would have to talk to the orbital dynamics boys on that one.

http://www.dogpile.com/info.dogpl/search/web/single-stage-to-tether
http://www.spacetethers.com/sstt.html

I think it would be best to focus on the construction of lunar cycler craft of great size.

[AztecBill]

I used the earth to moon distance by mistake. The moon-earth L1 point is  51,700 km from the moon.

EM L1 is the point where the Earth's Gravitational force is equal to the Moon's Gravitational force and the centripetal force from circling the Earth. You would stay in an orbit of the Earth directly between the earth and moon. Your "orbit" would be below where your speed would normally place you because the moon is pulling you. As you move toward the Moon from there the net forces pull you toward the moon. As you move toward the Earth from there the net forces pull you toward the Earth.

The Moon SE would be deployed from that spot (51.7 K km) the same as the Earth SE would be deployed from GEO.

[AztecBill]

The rotation of the moon may be too slow for the SE to work there in the usual sense.There is no Geosynch point for moon-orbit which does not pass well within Earth's influence.

The Earth is in GMO  

[mspeten]

The Moon SE would be deployed from that spot (51.7 K km) the same as the Earth SE would be deployed from GEO.

Deployed from L2 and extending a considerable distance above L2 to acquire the centripetal force needed to offset the gravitational attraction below L2. To be useful, that elevator would need to be quite long ~631,700km above the lunar surface to yield the same angular velocity as the 100,000km earth elevator. Also, a lunar elevator going through L2 would be basically useless for getting to or from earth; the L2 elevator will always face perpendicular to earth, throwing any object away (useful if you want to go away). It requires less than 1/20 of the deltaV to get off of the moon and into orbit (also very little to land, but not as cheap as using a heat shield and coming in with a parachute - as on earth). Vehicles arriving at or leaving the moon will need rockets for orbital captures, etc. anyway, we may as well land/takeoff with them, too.

The other location on the moon that one might build an SE is extending through L1 (toward earth) with a large (>thousands of tons) mass on its end. This mass would be more strongly attracted to earth than the moon, and thus hold the elevator vertical with respect to the moon. The ribbon could be longer and the mass smaller, but I'm not sure that an L1 elevator would be stable if it was. Another thing to think about is that an L1 elevator only gets you above lunar gravity (trivialized above). You'll still need rockets to get to any meanigful orbit around earth.

[Greg Broomfield]

The ribbon could be longer and the mass smaller, but I'm not sure that an L1 elevator would be stable if it was.

The longer the more stable.

Another thing to think about is that an L1 elevator only gets you above lunar gravity (trivialized above). You'll still need rockets to get to any meanigful orbit around earth.

Or simply detach from the L1 SE counterweight for a fuel free ballistic Earth re-entry (maybe a bit of directional thrust should be used to avoid burning up).

[mspeten]

The longer the more stable.

Does longer = more stable in this situation? I would (without knowing what I am talking about) expect an L1 elevator to swing wildly at the end due to long periods of solar pressure, gravitational influence from the sun, etc. Didn't this get discussed somewhere? I couldn't find it.

Or simply detach from the L1 SE counterweight for a fuel free ballistic Earth re-entry (maybe a bit of directional thrust should be used to avoid burning up).

Just releasing would send you into a very high/low elliptical orbit. You would still need a de-orbit deltaV.

[AztecBill]

Deployed from L2 and extending a considerable distance above L2 to acquire the centripetal force needed to offset the gravitational attraction below L2. To be useful, that elevator would need to be quite long ~631,700km above the lunar surface to yield the same angular velocity as the 100,000km earth elevator. Also, a lunar elevator going through L2 would be basically useless for getting to or from earth; the L2 elevator will always face perpendicular to earth, throwing any object away (useful if you want to go away). It requires less than 1/20 of the deltaV to get off of the moon and into orbit (also very little to land, but not as cheap as using a heat shield and coming in with a parachute - as on earth). Vehicles arriving at or leaving the moon will need rockets for orbital captures, etc. anyway, we may as well land/takeoff with them, too.

The other location on the moon that one might build an SE is extending through L1 (toward earth) with a large (>thousands of tons) mass on its end. This mass would be more strongly attracted to earth than the moon, and thus hold the elevator vertical with respect to the moon. The ribbon could be longer and the mass smaller, but I'm not sure that an L1 elevator would be stable if it was. Another thing to think about is that an L1 elevator only gets you above lunar gravity (trivialized above). You'll still need rockets to get to any meanigful orbit around earth.

The 51.7K km I refereneced was the distance for L1 not L2. I mistakenly said L2 in the first post.

[Greg Broomfield]

Does longer = more stable in this situation? I would (without knowing what I am talking about) expect an L1 elevator to swing wildly at the end due to long periods of solar pressure, gravitational influence from the sun, etc.

A problem with the L1 point is that it moves around a lot due to the Sun's (and other passing bodies) influence.  The ribbon must be at least as long as the L1 point's position when it is furthest from the moon.  A bit of extra length allows the Earth's gravity to ensure that the c/w always remains on the Earth side of L1.  Yes the c/w would move a lot due to the influences you mention, but a least it won't fall down.

Just releasing would send you into a very high/low elliptical orbit. You would still need a de-orbit deltaV.

Yes, you would be right there.  A bit of a brain fade on my part.  

[AztecBill]

A problem with the L1 point is that it moves around a lot due to the Sun's (and other passing bodies) influence.  The ribbon must be at least as long as the L1 point's position when it is furthest from the moon.  A bit of extra length allows the Earth's gravity to ensure that the c/w always remains on the Earth side of L1.  Yes the c/w would move a lot due to the influences you mention, but a least it won't fall down...

Of course the c/w would be earthward from L1. Movement won't hurt anything - remember it is a monthly cycle so the movement would be slow. When the moon's SE leans the most would be a good time to release payloads that could enter the Earth's atmosphere at an angle to use it as brakes. With the right calulations maybe a free return.

[publiusr]

That sounds good to me.

The other location on the moon that one might build an SE is extending through L1 (toward earth) with a large (>thousands of tons) mass on its end. This mass would be more strongly attracted to earth than the moon, and thus hold the elevator vertical with respect to the moon.

This would solve the bulk of the atomic oxygen problem. The mass at the end of the tether would have to weigh more than the cargo being delivered. Some retrorockets at the base of the car would be needed for a LEM-like landing in case of failure--but it would save on propellants and only need to be used once.  As rocket stages ascend they dock with and enlarge the weight--adding to its mass--allowing still heavier cargoes to be deposited. Eventually, factories on the moon send mass up--and you will have a bit of infrastucture.

[publiusr]

Here is an interesting website:

http://www.space.com/businesstechnology/technology/technovel_tether_041109.html

Perhaps this first, then a lunar SE--lowered down perhaps?

[publiusr]

A nice article on the subject...

http://www.universetoday.com/am/publish/lunar_space_elevator.html

http://www.m5fiber.com/magellan/m5_fiber.htm

Congrats to the folk at Liftport proper:
http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=h_mit_elevator-test_02.jpg

That is very impressive.