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Earth provides many obstacles to building large structures. Earthquakes and strong winds are just two of them.

As far as I know there are no quakes on the Moon nor are there any winds.

Question

Ignoring meteor strikes, what is the tallest man made structure that could be built on the moon? Could it be taller than any of the mountains? Could it reach out far enough to form a landing pad for orbiting space-craft?


Assumptions

(a) The structure is not a simple pyramid made of moon rock. It must be much taller than its base is wide - similar to tall buildings on Earth.

(b) There are sufficient building materials and these can be anything that is found on the Earth or the Moon.

(c) The building can perch on top of an existing mountain if that helps.

(d) Firm enough rock foundations can be found to prevent toppling. However there is no Unobtanium to ensure the strength or rigidity of the structure itself.

(e) Ideally the structure is so tall that its top is effectively orbiting the Moon in the direction of the Moon's spin. In this way it can act as a landing pad for spacecraft.

(f) Possibly it is even taller than in (e). This way the top of the building is being flung away from the Moon and so exerting tension on the building to allow its top to extend beyond orbital height. The landing pad would be lower. A lift would allow relaunch without power from the craft.

(g) There is some unspecified but effective way of protecting against meteor strikes.

(h) Just to be clear. This is a building with foundations on bedrock (as stated above). Thus I want the structure to be built from the ground up and therefore stable at every intermediate stage of its construction. There should be no rocketry or dangling sky-hooks during the building process.

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    $\begingroup$ So basically a space elevator on the moon? $\endgroup$ – Trioxidane Jul 23 '20 at 12:39
  • $\begingroup$ @Trioxidane - Yes, but only If it can feasibly be that tall. Otherwise simply the tallest plausible skyscraper. I have added the requirement that no Unobtanium is available so real building materials must be used. $\endgroup$ – chasly - supports Monica Jul 23 '20 at 12:44
  • $\begingroup$ you can build a space elevator on the moon using existing materials, Kevlar or Spectra fibers are strong enough. en.wikipedia.org/wiki/Lunar_space_elevator $\endgroup$ – John Jul 23 '20 at 13:58
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For (e) any rigid tower would I guess by definition be orbiting the moon above a set point. But not because it is in a geostationary orbit. It doesn't look like the moon really has geostationary orbits due to the influence of the Earth's gravity.

https://www.quora.com/Does-the-Moon-have-a-geostationary-orbit-If-so-what-is-its-altitude

For (f) you are basically talking about a space elevator. Based on information from Wikipedia: The elevator's "top" would have to be at one of the Earth Moon Lagrange points with a counter weight further out. The "highest" (furthest from the surface) is L2 iwhich is 62,851 km +/- 3,539 km from the center of the Moon's far side, then add on your cable for the counterweight.

https://en.m.wikipedia.org/wiki/Lunar_space_elevator

I hope this is high enough for you.

Edit: To address concerns about feasibility and need (or not) of unobtainium, wiki suggests this is possible with current materials and technology "since the Moon's surface gravity is much lower than the Earth's, the engineering requirements for constructing a lunar elevator system can be met using materials and technology already available. "

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  • $\begingroup$ Thanks. I am and always have been very skeptical about the "long cable space elevator". I just can't credit that the cable could be strong enough or that maintenance would be feasible. That's why I want to build upward by conventional means. This ensures a stable configuration throughout the building process. If I can't get high enough to provide a landing pad then so be it. I just want to know how high is reasonable. $\endgroup$ – chasly - supports Monica Jul 23 '20 at 12:55

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