Lunar Space Elevator ?

[rogerinnh]

An "elevator" to space from the surface of the Earth has to be in geosynchronous orbit in order to have its Earth end stationary over a point on Earth. Is it possible to have an elevator to space from the surface of the Moon? Or does the moon have such a long rotational period (about 28 days, I think) that the elevator would have to be enormously much longer than one from Earth in order to be geostationary (or would that be lunarstationary?) ? How long would a Lunar space elevator have to be?

 

[heyscottie]

A "lunastationary" orbit occurs at the distance of the Earth from the moon. Therefore, a lunar space elevator would need its center of mass to be located as far away from it as earth, or > 200000 miles.<br /><br />And I'm thinking that the fact that Earth is in the neighborhood would mess it up.

 

[jjkeighe]

<blockquote><font class="small">In reply to:</font><hr /><p>As it's estimated to take about 60-100 GPa's of hardness for the earth elevator cable (such a substance does not currently exist, or might never. Who knows?)<p><hr /></p></p></blockquote><br />Actually there is such a material in existance. They are called BuckyBalls. Now mind you that they are experimental not to mention at the moment difficult to make. A Buckyball, or Buckminsterfullerene, is really a carbon-60 molecule. The 60 atoms are arranged like the vertices of a truncated icosahedron. An icosahedron is a regular polyhedron with 20 faces. It has 12 vertices, so to truncate it we need a regular polyhedron with 12 faces, like a dodecahedron. Check here: http://micro.magnet.fsu.edu/micro/gallery/bucky/bucky.html for more on BuckyBalls. Also SuperBuckyBalls with Fullerines.<br /><br />If we were able to manufacture these in large amounts in say Freefall such a project as the Terra Elevator could be undertaken as well as a short one from the moon. with this strength the cable could easily just be 10000km long and still provide stability with a counter balance at one end. i.e. a NEO (near earth object). <br /><br /><br /><br />If somebody with multiple personalities tried to commit suicide, is it considered a hostage situation?

 

[alokmohan]

After discovery or invention of nanocarbon space elevator to moon is no problem.

 

[alokmohan]

Nanocarbon is supposed to be tough.

 

[nacnud]

Yup, but so far not tough enough.

 

[bobw]

Why wouldn't libration be a problem with the L1 point? The Moon's axis is tilted 6.5^o so the lunar attatch point will wander around within a circle with a radius of 122 miles centered on the Earth-Moon line and will vary about 7 miles along the line (altitude) during each lunar sol.<br /><br />Are the current designs for earth strong enough to sustain this kind of additional load? The fuel needed to compensate sounds expensive, too. <div class="Discussion_UserSignature"> </div>

 

[rogerinnh]

THanks to everyone for their responses to my initial posting on this topic. What led me to start thinking about this was a book that I'm reading by Kim Stanley Robinson, called "Red Mars". It provides a pretty thorough description of how a space elevator could be built on Mars, using a captured asteroid as the "counterweight" and source of materials for building it.

 

[bobw]

I guess you could call it metastable but I was thinking it would be more like a trout on the end of a fly line lol. Those trout tire out pretty fast. I've been thinking about how to tune the structure to a 28 day harmonic frequency. Maybe we could put the counterweight at a node. <br /><br />EDIT: I'm sorry, I meant resonant frequency. <div class="Discussion_UserSignature"> </div>

 

[nomentatus]

There's a confusion here between the strength need to create a space elevator from earth, and the strength needed for a moon elevator. The moon has one-sixth the gravity, and although a longer cable would be needed to pass the L1 or L2 point, the strength required would be many orders of power less when you do the physics. Well within current material technology, I believe. For a lunar elevator, there's no technical barrier as far as materials are concerned. Money and imagination maybe. <br /><br />So it shouldn't be surprising that "Lunar Space Elevators for Cislunar Space Development" (PI: Jerome Pearson of Star Technology and Research, Inc., Mount Pleasant, S.C.) is one the proposals under study by the NASA Institute for Advanced Concepts (NIAC)<br />http://www.gsfc.nasa.gov/topstory/2004/0930niac_phase1.html

 

[nomentatus]

Well... no. This in incorrect for a few reasons. The lower escape velocity on the moon isn't anything near zero, the same energy benefit applies to materials transported by elevator as by rail gun, and it's a whole lot easier to shoot materials through L1 or L2 at great relative speed than to stably place them there. (This doesn't nec apply to L3 and L4 since they are in the track of the Moon's orbit.)<br /><br />You can't just shoot something into orbit for similar reasons - objects accelerated by a single vector (one time boost) will form an elliptical "orbit" that returns to the original point (minus precession, etc). In other words, their path will intersect with the planet or moon's surface again with a helluva thump, rather than neatly and magically entering a circular orbit. Instead, you'll need as much energy again to adjust the orbit to a circular one, by moving the second focus point of the ellipsis.<br /><br />L1 or L2 are in a sense "orbiting" earth, as the moon is, but at very different speeds and angles than the surface of the moon is. I believe you'll find that a single vector, from lunar surface can't get you to L1 or L2 at zero velocity (at the lagrange point). Sorry. So, energetically, the lunar elevator makes a lot more sense, unless you want to go to L3 or L4 - but these are a bit costlier to get to energetically.<br /><br />Of course, it depends how much material you're moving. If you just want to move one ton, ever, there's no economic case for a lunar elevator. But if you want to create large projects, then it pays.

 

[nexium]

If 58,000 km from moon to L1 is about correct, a lunar elevator may be practical, when and if space rated CNT = carbon nanotube tether is available in lengths to 380,000 km. Much shorter is possible, but about 380,000 km will be best for Earth to moon and moon to Earth transport. 380,000 km allows most of the trip to be made on the tether, except the 100 miles to Earth at the moon's closest approach. The Earth end will be easier than reaching Earth orbit as it circles the Earth at about 1100 miles per hour, slower briefly due to trancients that travel on the tether. Cargos for destinations other than Earth can be released from the tether at the point best for a sling shot = gravity assist manuver around Earth. If optimistic projections for the CNT tether become reality, a reel of CNT ribbon one micrometer by one millimeter = one billionth square meter cross setional area, delivered to approximately L1 may surfice to start the project. 380,000 km will have a mass of 0.38 metric tons (assuming average tether density is one= same as water) plus the reel and two robotic climbers that will add strengthening strands, and do other chores, delivered to approximately L1. Strain will be greatest on the portion betweem L1 and Earth, so the quality of the CNT, thickness and/or the width will likely need to be increased for this portion, bringing the launch mass to a few tones. The moon end will the need to be attached to a winch that is well anchored as the tether will sometimes pull with about the force of the maximum Earthbound pay load, when no pay load is attached. The winch can fine tune the tether or pull up to the safe strength of the tether in an emergency. We will want to use the winch sparringly as it's energy use can be high. The climbers can keep strengthening the tether to increase it's payload and margin of safety by adding one thread at a time. The tether may be damaged by micro meteorites daily, so the climbers will be kept busy making repairs. The tether can

 

[bobvanx]

I like this idea alot. For one thing, it puts a space station at L1, quite naturally riding the top of the Lunar cable. That means craft from Earth only need enough deltaV to get to L1, and cable cars can then deliver mass down to Luna.<br /><br />Lessee, why are we bringin' anything from Earth to our moon... Nope. Can't figure it. Assuming there's water in the shadowy poles, I don't see what Luna needs from Earth.