Talk:Lunar space elevator

Pearson's design

 * "Jerome Pearson has proposed a design using M5 fibre {typo?} that would weigh only 6,800 kilograms and be capable of lifting 200 kilograms at the Lunar surface; such an elevator could be sent to the Moon with just one launch of the largest existing launchers."

As I read this, 6,800 kg is the mass of the cable only; the total mass of the elevator would be much greater. The article doesn't seem to say how long a cable Pearson envisions, so it's hard to say what the other components of the system--especially the counterweight--would mass. &mdash;wwoods 05:47, 21 Nov 2004 (UTC)


 * The only reference I had was, which didn't specify. But it does sound like it's talking about the bare minimum cable, whereas an elevator would have at least a few extra bits added. (The fibre/fiber thing is just one of the usual British/American spelling differences, not a typo. Since I'm a Canadian I randomly oscillate between the two. :) Bryan 06:25, 21 Nov 2004 (UTC)

I wrote the article... yeah, I'm Canadian, so it's "fibre" here. The 6,800 mass is just the cable, but you could add a climber for a few hundred kg more. So, still within the capablities of current launchers. Pearson figures you could continue to strengthen the cable from material gathered on the Moon. - Fraser Cain, Publisher, Universe Today


 * Thanks, I've updated the article to make that clear. Bryan 00:47, 17 Dec 2004 (UTC)


 * Trouble is (unless I grossly miscalculated) the mass of the counterweight has to be orders of magnitude greater than the mass of the cable. Any old mass will do, including the rockets used to carry the elevator components, but still... An "extremely minimalist" system, for highish values of minimalist, eh?
 * &mdash;wwoods 03:03, 17 Dec 2004 (UTC)

--195.178.232.139 12:44, 21 August 2006 (UTC)There sems to have bean some misunderstanding, i wrote thew folowing question to Jerome Pearson:

> Hi I am a PhD student at Lund University (Sweden) in electrical

> engineering; this has nothing to do with my research.

> When I read the articles

>

> http://en.wikipedia.org/wiki/Lunar_space_elevator

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

>

> and then your report to NASA at

>

> http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf

>

> I fond some numbers in the articles above that seems to be

> misunderstandings and want

> to sort this out so I can correct the wikipedia article.

>

> The articles say that you proposed a cable with a mass of 6800 kg

> capable of

> lifting 200 kg at the lunar surface. And that this could be launched in

> a single shot with a conventional rocket.

>

> As I read the report you proposed a cable with a mass of 6100 ton

>(6 100 000 kg)

> with a strength (with safety factors) of 2000 N with cross section of

> 0.69 mm^2 at the lunar surface per ribbon and in total tree ribbons.

>

> In both cases the used fibre is M5.

>

> I think the numbers in the articles sounds unrealistic as the mean

> cross section of the ribbon could not be more than 0.025 mm^2. 200 kg

> sounds as someone has "converted" 2000 N to 200 kg using the untrue

> assumption g appreciative = 10.

>

> Have you proposed booth designs or are the articles wrong?

>

> Regards

> Lars Lindgren

I got this answer:

>Dear Mr. Lindgren:

>

>Thank you for your inquiry. I produced the numbers in the report to NIAC,

>but not the numbers in the Wikipedia article. No one consulted with me on

>the Wikipedia article, and I have no idea who wrote it. (This is

>surprising, since I invented the lunar space elevator.) I stand behind my

>NIAC report numbers.

>

>You might also want to consult the discussion and papers referenced on the

>Space Elevator page of the STAR, Inc. website, at www.star-tech-inc.com.

>

>Jerome Pearson, President

>Star Technology and Research, Inc.

>

Based on this i will change the numbers and remove the proposal with a single launch.

Fibre Material
There may be cost advantages in building the lunar space elevator from fibreglass rather than M5. Fibreglass is made from silicon which is the second most common element in Lunar soil. M5 is made from carbon which is very rare on the Moon and has to be brought from the Earth. The skeleton of the cable can still be made from M5. Andrew Swallow 05:49, 11 September 2007 (UTC)

Silicon nanotubes have now been made. They may be sufficiently strong that a ribbon can be constructed from them using materials mined on the Moon. This would significantly increase the lifting mass of the cable. Andrew Swallow (talk) 10:42, 11 December 2009 (UTC)

Basalt fiber is easier to make than glass fiber, and has many superior physical properties. Basalt is abundant on the Moon, so is a strong candidate to evaluate.Charles (talk)

Height of L1 and L2
The height of L1 and L2 given in this article and Pearson's report are different. The ones in the report also have an error band. The correct values need determining. Andrew Swallow 19:24, 15 April 2007 (UTC)

Mystery solved. The report used figures from the centre of the moon rather than its surface.

Near side L1 = 58,021 +/- 3183 km from the centre of the moon Far side L2 = 64,517 +/- 3539 km from the centre of the moon

"Center of gravity" vs "center of mass"
"A lunar space elevator ... is similar in concept to the better known Earth space elevator idea (a cable suspended above Earth, with its center of gravity in geostationary orbit)." -- "Center of mass" would be better in in this context than "center of gravity", yes? (center of gravity also redirects to center of mass) -- 201.51.239.119 17:59, 9 June 2007 (UTC)


 * No, I don't think so. The center of gravity would be at geostationary orbit, but the center of mass would be much further out, close to the counterweight. But I welcome a third opinion. 81.235.136.245 00:25, 2 September 2007 (UTC)


 * Center of gravity is a term used implying gravitional force acting on an object is equivalent to the total force acting through the center of mass. In this case the lunar elevator is stabilized by a counterweight such that the design tension load is kept on the cable/tether stucture attached to the lunar surface.  The center of mass created by the counterweight and tether together would be only slightly above the lunar surface synchronous orbit.  Otherwise the tension in the tether/structure would be too great.   So there are three forces acting on the structure:  gravity through the center of mass of the system, centrifugal force out from unbalanced mass above the synchronous orbit, tension in the tether/structure to the surface.  Lazyquasar 02:56, 25 September 2007 (UTC)


 * Careful here, gravity doesn't act at the centre of mass in any significantly non linear gravity field.WolfKeeper 03:30, 25 September 2007 (UTC)

Key connection enabling Satellite Solar Power ?
There has recently been renewed interest in Satellite solar power as a partial solution of terrestrial energy problems, so far stymied by high launch costs from Earth. The combination of the Pearson lunar cable with the Moon's abundant solar energy, silicon and oxygen (present in common oxides) offers the possibility of making solar cells on the Moon, raising them to L1 with the Pearson cable, assembling them there into SSPSs, and then moving them (with ion-electric drives) for use in Earth geosynchronous orbits.

The question of the availability of carbon on the Moon, as the material of choice for such cables, deserves careful study. Carbon minerals on Earth (coal, carbonate rocks like limestone, etc) are apparently mostly derived from organic precursors, yet carbonates and other carbon minerals are common enough in meteorites to suggest that they may not actually be very rare on the Moon. Wwheaton (talk) 19:41, 16 April 2010 (UTC)

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"flung outward into the solar system"
The diagram's caption reads:
 * An L2 elevator would mirror this arrangement on the Lunar far side, and cargo dropped from its end would be flung outward into the solar system.

Surly this is not correct. Cargo dropped off L2 would still be in orbit around the Earth, just in an orbit that is higher than the moon. 209.255.238.212 (talk) 19:07, 12 July 2017 (UTC)


 * Elevators don't stop at l1 or L2, they go past them, and are terminated with a counterweight. Otherwise you would be correct.GliderMaven (talk) 19:43, 12 July 2017 (UTC)


 * Regardless, it would need to be extremely far from L2 to be "flung outward into the solar system" (which is a pretty meaningless phrase anyway, since we're in the solar system, but I assume it means escape Earth's orbit). Do we need to calculate how for out beyond L2 it would need be to escape orbit? I'd rather not, since that would be Original Research. How about we find a citation for the statement, or get rid of it? We could replace it with "would be dropped off beyond the moon's orbit," which is self-evidently accurate. 73.61.20.24 (talk) 14:30, 13 July 2017 (UTC)
 * If you were going to drop something off with near zero relative velocity, it would need to be dropped off at the edge of Earth's Hill Sphere in order to be "flung" away from Earth into a solar orbit. That's 1.5 million kilometers away from Earth. That is, in fact, exactly where the L2 point is. So if the tether extends beyond L2, then releasing anything from the end of the tether (even at zero relative velocity) would implicitly put it into a solar orbit, because it's beyond the outer edge of the Hill Sphere. More realistically, you could release a payload with a little bit of velocity (from climbing the tether), and then let it go. The payload would then activate its own internal propulsion system to meander off in the direction it wanted to go.
 * Dropping something off the edge of Earth's gravity well (in practice, at least, if not technically true) via tether would allow you to get a payload into interplanetary space with no fuel expended. "Free", more or less. &mdash; Gopher65talk 17:49, 26 November 2018 (UTC)

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Lunar Elevator Cannot Approach the Poles
The article says, "A space elevator could be anchored near a lunar pole, though not directly at it," but this contradicts Pearson's "Lunar Space Elevators for Cislunar Space Development" (2005), which is the major source of information in the article.

What Pearson says is Using a ribbon of M5 fiber, the LSE bottom end could be towed to a latitude of about 36 degrees and retain about half its strength for lifting payloads. The maximum latitude attainable by M5 is 52.5 degrees, but that takes all its strength, leaving no margin for lifting payloads. Even carbon nanotubes could reach a latitude of only 76 degrees, which still leaves a distance of 426 km overland to the pole. This means that a tramway will be required to reach the poles, no matter what the material.

However, taking half the stress limit to reach 36 degrees saves only about 1000 km of tramway, but it halves the throughput of the entire system. Much higher productivity can be obtained by just using a vertical configuration, and taking the tramway the entire 2700-km distance from the equator to the pole.

So a more accurate statement would be that a space elevator does not have to be anchored precisely at the equator, but very much deviation adds stress to the cable and reduces the throughput of the system so much that any practical implementation will be anchored near the equator and use a tramway to reach higher latitudes.

Greg (talk) 18:35, 4 October 2021 (UTC)

What keeps it up at L1
"At these points, the effect of the Moon's gravity and the effect of the centrifugal force resulting from the elevator system's synchronous, rigid body rotation cancel each other out. " That doesn't seem to fit what I think I understand about what happens at the Lagrange points or with this elevator. Midgley (talk) 00:18, 7 January 2022 (UTC)