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Okay, so some space miners fly into space to get Helium-3, and then fly it back to earth to sell to non-space people. Flying into and off the earth is rather expensive, so they want to simply take an elevator into space, but they can't find anything big enough to build it off. Flying into and off the moon is less expensive, but still pricey. As it turns out, building elevators from the moon to space isn't too much of a problem, since it has less gravity!

What would a moon-to-space elevator be made of. How much material would be needed for one? How expensive would it be?

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    $\begingroup$ @RichardGrant OP is referring to an elevator from the moon to lunar orbit. Not from the Earth to the Moon. $\endgroup$ Oct 6, 2015 at 1:49
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    $\begingroup$ escape velocity of Earth and Moon are 11200m/s and 2400m/s respectively so much easier to reach orbit from Moon, also speed of rotation at the equator for Earth and Moon are 464.9m/s and 4.6m/s respectively meaning your cable must extend much longer to hold the space elevator. $\endgroup$
    – user6760
    Oct 6, 2015 at 3:24
  • $\begingroup$ If price is the motivation, the miners wouldn't use a space elevator at all but instead a mass driver. Think a train track along the moon that accelerates the payload. Once the payload reaches escape velocity (660 km/h) you let it go and it will fly off into space. A few tens of km of rail is a lot cheaper than a space elevator, even if you use maglev rail. Just make sure the spacecraft can be locked to the rail roller coaster style so it doesn't fly away too early. $\endgroup$
    – JanKanis
    May 1, 2021 at 22:52

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Whereas Carbon Nanotechnology will be needed to create a tether on an Earth-bound elevator, a Lunar elevator is possible with current technology using high-strength commercially available materials such as Kevlar, Spectra or M5 Fibre according to https://en.wikipedia.org/wiki/Lunar_space_elevator

There are two points in space where an elevator's docking port could maintain a stable, lunar-synchronous position: the Earth-Moon Lagrange points L1 and L2. L1 is 56,000 km away from the Earth-facing side of the Moon, (at the lunar equator) and L2 is 67,000 km from the center of the Moon's far side, in the exact opposite direction. 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. The gravitational stability of these Lagrange points are not permanent, (L1 and L2 are in unstable equilibrium along a straight line between Earth and Moon,) but so long as small inertial adjustments are made to account for minor gravitational perturbations, any object positioned there can remain stationary.

Both of these positions are substantially farther up than the 36,000 km from Earth to geostationary orbit. Furthermore, the weight of the limb of the cable system extending down to the Moon would have to be balanced by the cable extending further up, and the Moon's slow rotation means the upper limb would have to be much longer than for an Earth-based system, or be topped by a much more massive counterweight. To suspend a kilogram of cable or payload just above the surface of the Moon would require 1,000 kg of counterweight, 26,000 km beyond L1. (A smaller counterweight on a longer cable, e.g., 100 kg at a distance of 230,000 km — more than halfway to Earth — would have the same balancing effect.) Without the Earth's gravity to attract it, an L2 cable's lowest kilogram would require 1,000 kg of counterweight at a distance of 120,000 km from the Moon. The average Earth-Moon distance is 384,400 km.

As a comparison, an elevator's journey from Earth will be around 96,000 kilometers, or about 59,651 miles, well beyond geostationary orbit (which is roughly 35,800 km altitude).

An estimated price tag for an Earth elevator is \$6 billion to \$20 billion USD using nanotechnology that still needs improvements due to length manufacturing limitations. https://en.wikipedia.org/wiki/Space_elevator_economics

If you figure a low ball of \$6 billion for about 96,000 kilometers of materials give us around \$62,500 * 120,000 to a figure of around 7.5 billion using a high tech solution estimate that is not needed.

A closer estimate would be approximately \$1.8 billion according to:

http://forum.kerbalspaceprogram.com/threads/122175-How-expensive-would-a-Lunar-Elevator-be-%28approx-1-8-billion%29

And the publication they got their numbers from,

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

Other interesting links:

http://www.techtimes.com/articles/16363/20140925/space-elevator-will-be-reality-in-2050-promises-japanese-construction-firm-obayashi.htm

http://www.technologyreview.com/news/534796/nano-manufacturing-makes-steel-10-times-stronger/

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  • $\begingroup$ You may want to note that ending the elevator at the L1 and L2 points is only possible because the Moon is tidally locked and doesn't rotate with respect to the Earth-Moon configuration (for the most part). $\endgroup$ Oct 6, 2015 at 14:49

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