Post Av8eHONKQkWjplb7kO by BLatro@vis.social
(DIR) More posts by BLatro@vis.social
(DIR) Post #Av1qPO4lGaYCZ6lxIm by BLatro@vis.social
2025-04-30T01:57:49Z
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I got looking into companies that are thinking about making space elevators, and ended up looking into luna elevators instead. (LiftPort seems a contender here.) This is a good overview of the luna elevator concept (from 5 years ago).https://www.youtube.com/watch?v=L1ytpj3y21EUnlike Earth-based space elevators, a luna elevator could reach from the surface of the Moon to close to Earth.What's more, we could make one now, if we wanted to. No exotic new materials needing to be invented.#MoonElevator #SpaceElevator
(DIR) Post #Av1qPPBt7ZqU1V7A36 by publius@mastodon.sdf.org
2025-06-11T18:14:24Z
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@BLatro The difficulty with an Earth-based space elevator is that the space-lift capability required to build it is so large that the elevator itself would be irrelevant for decades or generations to come.Now, the lunar elevator is interesting, and I've known some people involved with the proposals. The problem I see can be summed up in the word "nutation" : the latitude and longitude of the subterrestrial point wanders, as does the altitude of the L1 point over the surface, by thousands km.
(DIR) Post #Av2IAmhaDqKHJZkx60 by BLatro@vis.social
2025-06-11T23:25:24Z
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@publius Hmm. But would it matter? We land craft on the Moon and it's a moving target. I see a lunar elevator as being useful for getting people from Earth orbit to the Moon and back, and for getting what's mined on the Moon to Earth orbit. It'd save having to lift heavy stuff from Earth to orbit, if that stuff's available on the Moon. Also you wouldn't need rocket fuel to get people from Earth orbit to the Moon. Sunlight would power the elevator. Or are you worrying about the elevator breaking?
(DIR) Post #Av2zCcM3xYSjpdoKf2 by publius@mastodon.sdf.org
2025-06-12T07:27:43Z
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@BLatro "Breaking" isn't a concern, because you wouldn't be able to anchor the tether to the surface. There's just too much relative motion.What this means is that you need some kind of rocket vehicle with a complete, fully-featured guidance-&-navigation system (fortunately these have gotten cheap) for the "last step", between the bottom of the elevator and the surface, either way. Now, it's obviously not near as much propellant as you need to get to orbit, but it does add complexity.
(DIR) Post #Av4dlTguLzzeQChM8G by BLatro@vis.social
2025-06-13T02:36:43Z
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@publius Which surface are you talking about? It sounds like you mean the Earth - which the Moon elevator doesn't connects to.
(DIR) Post #Av5WaYd19TgU1mgU1w by publius@mastodon.sdf.org
2025-06-13T12:51:08Z
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@BLatro Let me put it this way. You cannot anchor a "lunar elevator" to the surface of the Moon. The reason is, there is no orbit you can put the thing in which is stationary with respect to the surface of the Moon.If you envision the L1 libration point as lying on the line connecting the centers of the two bodies, the motion of the body of the Moon around its center means that the projection of that line on the surface wanders, sometimes quite quickly.(cont'd)
(DIR) Post #Av5WsopZeMLJUXGUlM by publius@mastodon.sdf.org
2025-06-13T12:54:26Z
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@BLatro Then, the position of the L1 point along the line is proportional to the length of the line, and the masses of the two bodies. Because the center-to-center distance between Earth and Moon varies by about 10% over the course of a month, so would the length of a "lunar elevator".As a result, the orbital dynamics require its "downward" end to be freely moving and not in contact with the surface.
(DIR) Post #Av6icdJM6aNpjrCgBU by BLatro@vis.social
2025-06-14T02:40:38Z
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@publius OK. The surface you mean is the Moon's surface.Looking at LiftPort's approach, they envisage starting the elevator's construction at L1 and building in both directions until one end reaches the Moon, at which point they anchor it and continue building the Earth-end.https://www.youtube.com/watch?v=j9XVHhkWxpIAre you saying the Moon end would not be in sync with the Moon's surface? Or not be able to be put in sync with the Moon's surface? Presumably by the use of rocket's on the Moon end of the elevator.
(DIR) Post #Av73KoF0pM7rSiVwno by publius@mastodon.sdf.org
2025-06-14T06:32:45Z
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@BLatro You cannot anchor the tether at the Moon end. The motion of the lunar surface, in three dimensions, is such that it would either break your tether or disturb its orbital dynamics to the point that the phrase "whip it out of orbit" would apply.It would be necessary for the Moon end of the tether to hang free, and be reached (in a fairly short hop) by rocket vehicles.
(DIR) Post #Av75Kg4bOZ7W2Qi4pM by BLatro@vis.social
2025-06-14T06:55:11Z
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@publius So assuming you're right, there's still a way to make it work.But what about moving stuff along the elevator? That'd affect it's orbit too, right? Which means it might become uneconomic unless the elevator's made very heavy. And making a heavy elevator could prove uneconomic too, so a chicken and egg problem.
(DIR) Post #Av7Et16saRIIiRDxaK by publius@mastodon.sdf.org
2025-06-14T08:42:05Z
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@BLatro It's far from a simple problem. Now, if the object being moved is sufficiently small with respect to the mass of the overall elevator system, and its movement is sufficiently slow, then the orbital motions will be perturbed only slightly, and the gentle thrust of ion or Hall-effect thrusters can keep the elevator in place. And you need that kind of station-keeping anway.The question is less, "can the technical problems be solved?" than "what is the objective to be served?"
(DIR) Post #Av8eHONKQkWjplb7kO by BLatro@vis.social
2025-06-15T01:01:26Z
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@publius The objective to be served is to move people and stuff from Earth orbit to the Moon and back at a cheaper rate than using rockets to do it. If you're building stuff in Earth orbit, (space stations and such), would it be cheaper to make the parts on the Moon and elevate them to Earth orbit than making them on Earth and using rockets to get them to orbit?
(DIR) Post #Av9RMltNJmrZyKmXnU by publius@mastodon.sdf.org
2025-06-15T10:11:24Z
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@BLatro It depends what the stuff is. This is a topic which I have studied for a long time, and my preliminary judgement is, the first thing required is something like the Grumman "Beam Builder" which can take aluminium strip and construct it into framework trusses for space platforms.Once that is demonstrated in orbit using metal brought from Earth, there's a strong case for supplying metal and oxygen from a lunar-surface installation. Those things are simple to make and rugged to ship.