Space Elevator From the Moon to Geostationary Earth Orbit

The new lunar space elevator study differs from previous proposal would be anchored on the moon and stretch 200,000 miles toward Earth until hitting the geostationary orbit height (about 22,236 miles above sea level). We do not have materials for a space elevator from the Earth to Geostationary orbit. The moon spaceline would be longer but would only have to overcome the moon’s gravity.

The biggest hurdle to mankind’s expansion throughout the Solar System is the prohibitive cost of escaping Earth’s gravitational pull. In its many forms the space elevator provides a way to circumvent this cost, allowing payloads to traverse along a cable extending from Earth to orbit. However, modern materials are not strong enough to build a cable capable of supporting its own weight.

The Spaceline is a new analysis of lunar space elevators. By extending a line, anchored on the moon, to deep within Earth’s gravity well, we can construct a stable, traversable cable allowing free movement from the vicinity of Earth to the Moon’s surface. With current materials, it is feasible to build a cable extending to close to the height of geostationary orbit, allowing easy traversal and construction between the Earth and the Moon.

The most efficient solution is one in which we start at the Earth-end of the Spaceline with a constant area cable, as thin as is practical, which extends until the point at which it reaches its breaking stress, then tapers outwards from that point to avoid breaking. Past the Lagrange point, close to the Moon, where the tension (and therefore the allowable area) reduces again, there may be another section of uniform cable reaching down to the anchor point on the Moon’s surface, though whether this second uniform-area section is possible depends on the value of h.

For sufficiently high α, or large h, the cable may never reach its breaking stress, and the most efficient solution is just that of a uniform-area cable. This hybrid cable, by construction, cannot break but can collapse. In fact the same constraints (and solutions) apply here as did for the uniform-area cable. As long as h is less than ∼ 0.24, the cable will not collapse; for larger h, other solutions such as an anchor weight can similarly be implemented.

A line was made of a cable with a0 = 10^−7m2 : its total mass would then be around 40,000 kg. This is about twice the mass of the original lunar lander, and would make transporting and constructing such a cable completely plausible. The raw cost of the materials and transport could be numbered in the hundreds of millions of dollars.

40,000 kg could be transported to the moon with about four launches of a SpaceX Falcon Heavy. However, a lunar lander would need to be developed. A single mission with a SpaceX Super Heavy Starship could also transport the spaceline. There would need to be work done on the deployment.

Many technological and sociological challenges stand between the idea and it’s execution. However, this is a doable project. It would provide benefits for industrializing the Earth-Moon system.

Building a base-camp at the Lagrange3 point is one of the most immediately useful and exciting utilities of the spaceline. A small habitat there could house many scientists and engineers, much like the Antarctic base camp. This would allow experimentation and construction in a near-pristine, gravity-free environment.

There are two huge advantages of fabricating and assembling structures at the Lagrange point rather than any other stable orbit:

• No debris – The region of space between Earth and geostationary orbit is filled with the remnants of past missions and abandoned satellites. Also, stable (and thus long-lived) fast moving orbits can exist here, raising the fear of bombardment with naturally occurring meteoroids. The Lagrange point has been mostly untouched by previous missions, and orbits passing through here are chaotic, greatly reducing the amount of meteoroids.

• Non-dispersive – If you drop a tool from the ISS it will seem to rapidly accelerate away from you. This is because of the slight difference in the gravitational force felt at different distances from the Earth, leading to orbits that quickly diverge. This makes it a difficult and dangerous place for construction. The Lagrange point has an almost negligible gradient in gravitational force, the dropped tool will stay close at hand for a much longer period. With small corrective thrusters or a minimal system of tethers, many objects (habitats, science equipment or spacecraft) can be held in a stable configuration indefinitely. Space now has a ”next-door”.

Manned large-scale construction projects would become much easier to build and maintain. These could include a new generation of significantly larger space telescopes, a network of isolated gravitational wave detectors and particle accelerators on scales much surpassing what can feasibly be built upon Earth’s surface.

Similarly, the base camp itself can be extended, with prefabricated panels added to allow increased space for habitation and experimentation. Scientific and industrial testing in vacuum or zero-gravity environments can be undertaken over longer periods and bigger scales than previously imaginable.

There is one caveat though, the nature of the Lagrange point between the Earth is unstable. The effective potential (in the corotating frame) is a saddle point. If an object undergoes small displacements in the tangential direction (constant radius) the will feel a restoring force back to the Lagrange point. However, if the object wanders in the radial direction (towards the Moon or Earth) it will be pulled more and more strongly in that direction. Thus to keep an object at the Lagrange point indefinitely there needs to be a corrective force in the radial direction.

The spaceline naturally provides this force, and this is one of the two major reasons why constructing a spaceline makes a Lagrange point base camp significantly easier to use and maintain. The other being that it allows material transport easily to and from the base camp (via a spaceship carrying material from Earth, or directly from the surface of the moon), without the need for coordinating rocket flight through a region of space that may quickly fill with delicate habitats and scientific equipment.

In the simplest version of the safeline there can be a force of up to 100N either towards Earth or the Moon before there is any danger of the cable breaking or collapsing.

Arxiv – The Spaceline: A Practical Space Elevator Alternative Achievable With Current Technology.

SOURCES – Arxiv The Spaceline: A Practical Space Elevator Alternative Achievable With Current Technology
Written By Brian Wang,

59 thoughts on “Space Elevator From the Moon to Geostationary Earth Orbit”

  1. I (gasp!) thought The Moon is a Harsh Mistress was over rated.

    It may be a case of Shakespeare syndrome (it’s a well known classic so I’ve encountered all the good lines and ideas dozens of times already so anything good isn’t new and anything new isn’t good.)

    Among other issues, I had serious problems accepting the fundamental basis of the plot. If you can grow food on the moon by digging tunnels, using lights, and mining increasingly rare ice for water, then what’s to stop you digging farm tunnels on Earth where water is abundant and transportation costs are much less?

    Getting back to the point. It’s been argued a few times here on NBF that once we have multiple groups moving decent masses around the solar system (no matter what the tech) that anyone who can afford it is going to insist on systems capable of stopping/deflecting/destroying any such mass that is on a collision course with them.

    Given that we all hope such movement occurs, because otherwise we are probably facing a future of tech and economic stagnation, this kind of means that such defence systems are mandatory in a view of the future.

    A bonus is that they’ll also be really useful should any naturally occurring mass on a collision course turns up.

  2. Redirectors, several points to consider.
    They may be the first SSP part in Space, to support Earth rectennae and small Earth radar, for an otherwise non-Space project.
    They may not be needed at all for L5 or LSP, as the market for H seems suddenly booming. Solves everybody’s intermittency problems where used, may be hard to keep up with. New, remote use is the ideal for SSP, and they can start from scratch with H just fine, it would seem.
    They are very close to the rectennae, as seen from GEO on out, so are like an off ramp rather than another road.
    Thanx for the discussion!

  3. I have seen absolutely no estimates for how bright 20-200 Tw total GEO SPSs would be. Nor the space junk considerations. Nor the station keeping compared to L5, let alone Moon. Nothing at that scale at all.
    In fact, the big problem isn’t what kind of SPS to do, but to get SSP in the *popular* discussion for global heating. Put it on the Moon seems understandable and obviously scalable, and they all use the same beam and rectennae. There will be all sorts of in Space solar as well as all sorts of SSP to Earth, eventually. But people need to see the possibility of O’Neill type expansion that is possible. It is about global heating, not just Space.

  4. Have you run any calculations on the brightness of a SPS at geostationary orbit from Earth? My expectation is that it would be visible, but at worst as bright as a star or planet. Remember, specula reflection means most of the light would never be seen from Earth.

    So so far everybody who has run the numbers has concluded that geostationary is the right place to put an SPS. With the exception of the lunar power people who think panels on the moon itself would be enough cheaper to make up for the added complexity.

  5. The power beaming redirectors, especially at the beginning, are primarily to balance Earth transient sources, and more importantly to save the money we spend moving stuff around before we burn it, but even more importantly to allow the burning to be at the site where the stuff is extracted so the CO2 can be used right there as a filler and sequestered. Then, the proven rectennae can accept power from anywhere, with a proven beam technology thru the atmos.
    The amount saved by a large L5 in station keeping alone, over multiple GEO sats, would seem to counter costs of this redirector system too.
    LSP and L5 sat seem about the same here. Other L sats to avoid redirectors seems too expensive. I’m actually fine with any kind of SSP at this point, but the *cell* sell seems to get harder the closer to Earth the big things are going to be. Don’t underestimate the negative reaction to light pollution, in particular, but also junk.
    Gut reaction for me is that GEO is about the last place we actually want to develop. Save it for things that really need the G.
    And L5 is the first!

  6. Then they are probably going to insist on something like a couple satellites in lunar orbit armed with big messy weapons that can quickly take out said systems if such were to become . . . expedient.

    Heinlein’s The Moon is a Harsh Mistress is a great book, but the powers that be may take it more as a cautionary tale . . . not to prevent the lunies from revolting, but for having a plan and the tools to carry it out if they do.

    One thing the book made clear was that the only reason the revolt had a chance of success was that Earth was too reluctant to nuke the lunar cities (for economic reasons, not humanitarian).

  7. At no point did I say it wouldn’t work. Obviously it’s physically possible. I just don’t think they’re cost effective relative to putting the SPS in geosynchronous orbit, if you’re going to put it in orbit to begin with.

    Your link is to a proposal to generate the power on the Moon itself. *IF* building the solar power plant on the Moon were sufficiently cheaper than putting it in orbit, that might pay for the redirection system doing it necessitated.

    But if you’re generating the power on a satellite to begin with, the redirectors are at best an unnecessary expense, since you can just put the satellite in a stationary orbit over your rectenna and do without them.

  8. Yes, I know how that works; I was studying electrical engineering while in the L-5 society. You use the pilot beam as a phase reference for the elements of the phased array antenna. Producing multiple beams from the same array is possible, too, but adds complexity.

    I still think placing the SPS anywhere but geosynchronous adds unneeded complexity. But, just thinking about it, you *could* place an SPS at L3, L4, and L5, and have every place on Earth that’s reasonably close to the equator be in view of at least one at all times. Handoffs would be at predictable times, anyway.

    But, imagine that you’re trying to finance the first SPS; Surely, “It will always be in view of the one and only rectenna you need to build to get the system working!” would be a major selling point, compared to, “We need to build at least three, and find multiple customers around the world so that they don’t have extensive downtime.”

    That alone would be enough to dictate building the first in geosynchronous orbit.

  9. The space fountain is basically just a launch loop stood on end.

    There are all sorts of structures based on stored energy rather than material for their strength; For instance, you can stack opposed superconducting loops to build a tower, too, with cable in tension between them.

  10. The capital cost of large projects like this won’t be justified by the flow of goods. A mass driver and a reverse mass driver would be a lot cheaper and even those require a decent flow of goods. Overall reusable rockets are the best for now.

  11. Nice link!

    The ratios of tether: payload mass are much lower than I’d have thought. You can send stuff to Mars with a 15:1 ratio! And not send it from LEO, send it from a suborbital flight.

    If BFR can put 100 tonnes in LEO, then you could put up a 7t suborbital craft (5 times the size of the old Spaceship1 craft), catch it, and throw it to Mars. Repeat as needed.

    Or for that matter you could use the 1950s tech X-15.

    And the proposal is reassuringly complex. It has annoying details and complications. Implying it is at least partway along the Rickover spectrum from a pure paper (powerpoint) design through to something that might work.

  12. I like the space fountain myself. Smaller, with a much smaller footprint. And it seems a much simpler thing to bootstrap from the ground in the first place.

  13. If you look at the article you are replying to has a table of commercially available materials, their strengths, and a graph of how it fits the requirements.

    And by “commercially available” I don’t mean you can get it in milligram samples from Aldrich like carbon nanotubes. I mean you can go down to the local sporting goods store and purchase a 500 m long reel of 100 kg breaking strain Dyneema, intended for deep sea fishing line.

  14. yeah, there are much nicer lunar elevator counterweight to GEO transfer orbits that work out decently, and a few for dropping directly to earth reentry, without the counterweight foot being near GEO.

    I kinda get the feeling this paper might have been prompted by the thught that GEO graveyard sats could be directly harvested for counterweight mass without significant deltaV, but that ultimately doesn’t work out that nicely. That said, pushing dead sats, or their crunched up parts in bags, to L1 to feed a growing lunar elevator counterweight isn’t terrible per se in terms of deltaV.

  15. But the weapon of mass destruction argument applies to any possible system that can put chunks of the moon into orbit. Rockets, mass drivers, gas cannon, sky hooks, magic teleportation devices, floo powder… anything.

    It wouldn’t be any worse for a lunavator. Indeed as Brett points out a rotorvator needs mass to flow both ways or it loses it’s momentum and falls out of position. So that is possibly one of the least suitable for war type of launchers.

    Anyway, the major powers have been able to nuke each other for a lifetime now, so it’s nothing new.

  16. It’s just you, because the rest of us are well aware that there ARE materials that would support their own weight like this, for the Moon. Which has much less gravity than Earth.

    You can also pull it off on Mars using existing materials.

    Earth? No, not really. Too much gravity. In fact, if Earth gravity were about 50% higher, you probably couldn’t get off Earth with chemical rocketry, either.

  17. is it just me or does everyone seem to forget that there is no material that could even support its own weight like this, so forget about lifting something..

  18. If I understand, the rail gun runs current thru the projectile, causing all sorts of wear. Mass driver is more gentile, so less military in use, as it is a linear motor. But just fine for lunar launch and less wear.

  19. It seems odd that they are talking about extending the lunar elevator down to GEO rather than just down to where if you let go of a spacecraft it will go into an elliptical orbit with perigee at GEO (or LEO would be better).

  20. Yes, I like the Loftrom Launch loop, too.

    My prediction of what’s coming is that nobody is going to beat SpaceX on rocket launched payloads to orbit, but they’re going to lower the cost to orbit enough that the traffic will finally get high enough to make high infrastructure low unit cost launch techniques like the Launch Loop economically feasible.

  21. Will we ever be?

    The main motivator for tight control and desire to access these weapon technologies, is the certitude that it would be used by others to bully us if we didn’t have it.

    Even those relinquishing them align themselves to those that do, to ensure any attack is discouraged by ally retaliation (a more abstract safety net, but that’s the intent of the country mutual defense pacts) .

    This certitude comes from experience: there are plenty that will use that power to wipe out the current powers if they had the chance.

    Until everyone has the same cultural make-up and values, we will never cease stockpiling guns wishing not to use them, but just in case.

  22. We should perhaps think of the whole Earth-Moon system, cislunar, as a giant L spot, compared to being in another solar orbit. That would really be drifting off.

  23. Yes, like a violin string. But the whole lunar thing plus the Moon is the reaction mass, my nit pick.
    Also, Loftrom Loop still looks good to get the mass driver above the atmos.

  24. What I mean by that is that, once you’re traveling faster than the speed of sound in the material, the little bit you’re interacting with at any given instant has no immediate help from neighboring bits in supplying momentum to you. It instantly changes speed, and then the neighboring bits have to bring it back to a stop.

    As you pass through that speed of sound, the momentum deficit you’re creating is actually traveling with you and accumulating, rather like the sonic boom of an aircraft traveling at mach 1, except worse because it’s got no place else to dissipate to. So you really need to be traveling much slower, or much faster, than the speed of sound in the tether material, near that speed has bad consequences.

    This is part of why a rotovator needs a significant mass at the attachment point, to buffer the momentum.

    I’ve really pretty much concluded that actual skyhooks have little going for them for this reason. Rotovators and mass drivers are the way to go.

  25. Well, but a rotovator does kind of have to outweigh its payload by a substantial margin, so a near term rotovator isn’t going to launch anything sizeable at Earth. And the throughput is quite limited unless you have equal payloads going in both directions to balance the momentum, because any momentum deficit has to be made up gradually by use of high ISP propulsion.

  26. The screens and even the radar can be pretty sloppy. See LSP transmitters for example. A broad pilot beacon is sent by the customer requesting service. That same path is used to *inform* the beam. Majic! And 80s tech I don’t have a deep understanding of, but some idea. A radar that already knows where to look. And it can look to many places at once.

  27. Sure, but a lunar rotovator can put you directly into a transfer orbit to Earth, and if you want, one that intersects the Earth for direct entry.

  28. Dave, in theory, which have to be in the geostationary position is the center of mass of the whole thing. For this reason in the upper part you need a “reaction mass” that allows a close center of mass. But there are other issues that are worst than that. For example internal dynamic oscillation, torsional effects, thermal effects, solar wind pressure, and others that can generate dynamic instabilities that in my humble opinion invalidate the concept as is showed.

  29. This proposal has very little practical use to get to the Moon because of that difference of relative speeds.

    Anything going to geosynch distance to rendezvous with this will have to slow down to a near halt to do so, wasting fuel and complicating things, because for starters, they will no longer be in orbit!

    But it can have a use for getting heavy stuff from the Moon to Earth, because dropping from the elevators’ end would take any payload into a very eccentric low Earth orbit, probably requiring very little fuel to be a re-entry one.

  30. There’s that thing about not being civilized again.

    Governments on Earth might be very reluctant to let an organization on the moon have something that could throw very large masses at the Earth with relative abandon.

    Similar problem to rail guns, which also appear to be very nearly feasible as of the article (from June of this year) linked below:

    Heinlein made such a scenario the basis for “The Moon is a Harsh Mistress,” one of his very best, IMHO.

  31. Well, it is *mostly* in orbit (edit: Earth!), as a single structure attached to Moon as lightly as possible. And enuf to absorb the momentum of the payloads as it runs.

  32. “The cable stops being a cable, as such, and acts more like reaction mass.”
    Nit pick, but it *is* the reaction mass. Too fast and you will get a violin!

  33. I figured that was what you meant by “redirecting screens”. However, to achieve a decent spot size without requiring an unreasonably good “figure” on a reflecting surface miles in diameter, (Which would have to be rotating at a variable rate the whole time!) you’d need to combine a rectenna with a phased array transmitter, and suffer substantial conversion losses. Well, maybe you could use some sort of variable metamaterial to accomplish the same end, but it wouldn’t be cheap, because it would have to be miles in diameter.

    Seems like an unreasonable complication to add, especially when starting out. Better to just put the satellite in geosynchronous in the first place.

  34. “an SPS at GEO can always be in sight of the same receivers”
    That is what the otherwise useful redirecting screens are for, to be “in sight”, for power beaming. Of course, the radars can hit multiple rectennae, being phased array, directly or thru the screens. So the need to be overhead is gone!
    The plan to have *a* sat over *a* rectenna may be an unneeded cost.
    (edit: the rectennae are also phased array style, in that they can get the juice from any and all directions).
    The cable at GEO sounds really good for comsats, as they do need to be *there*.
    “An SPS would have to get VERY large to become a light pollution problem from geosynchronous orbit.”
    The plan for LSP is 20-200 Tw. Much less is not enuf!

  35. No, if you have a tether attached to the Moon, that extends all the way to geosynchronus “altitude”, it won’t be in orbit, it will be hanging in tension from the Moon.

  36. This again.

    This is impossible. A geosynchronous satellite BY DEFINITION is perfectly balanced between Earth’s gravity and it’s momentum carrying it out into space.

    Putting a tether on it using it to climb up creates an opposing force on the satellite, which will pull it into a decaying orbit.

    I’m sure there’s some “expert” who will disagree, but you’re wrong, and self-deluded.

  37. The downside of a solar power satellite at L5 is that the Earth is rotating under it. While an SPS at GEO can always be in sight of the same receivers.

    An SPS would have to get VERY large to become a light pollution problem from geosynchronous orbit. Particularly since specular reflection would result in almost all of the light reflecting from it missing the Earth for most of the orbit.

    You probably at some point want to just run a cable all the way around the Earth at geosynch, so that the satellites there don’t have to do station keeping anymore.

  38. I have a problem with long things in Space. They can get tangled up with each other. Short rotovators seem far better. Mass driver!

  39. Yet, when building many Solar Power Sats, the GEO area is good!
    How about “one” large sat at L5. The aperture of the radar is large enuf that the focus is to *normal* Earth rectennae, the size (dia, not power) used by *normal* Space Solar Power plans. The power is what results with that size at the beam density limit near the radar, whatever that turns out to be. Redirecting screens near Earth are used for hemisphere not directly below the sat, if we are not yet converted up to H economy for that amount of power. Thus the need for GEO goes away.
    And we can start with the redirecting screens for balancing Earth wind and solar, or to avoid moving molly queues before burning. This gets the system started before much is launched.
    Even tho the radar “looks” the same size a GEO radar would, the cells are much furrther away, so far less light pollution.
    As more power is needed, put one more at L4, perhaps L1, or even the Moon’s surface. Whatever it takes to DO SOMETHING about global heating, not to mention opening Space to O’Neill!

  40. Well, that’s good. I still don’t see what extending to near geosynch gets you, except for using cable instead of a more massive counterweight closer to the Moon. When the counterweight can be lunar soil, probably not worth it.

    In lunar gravity, and vacuum, you could probably electrostatically couple to the tether, without contact, rather than using electrically powered rollers. Likely you’d use the rollers to get up to speed, first. There’s an instablity problem as your payload approaches the speed of sound in the cable material, though. The cable stops being a cable, as such, and acts more like reaction mass.

    Basically, if you can do it with a fixed skyhook, you can do it with a rotovator, and faster.

  41. To be fair they are not planning on actually having it reach into the geostationary orbit.

    build a cable extending to close to the height of geostationary orbit,

    But every other issue still stands. Including the points raised by Strangelove and Citroen below.

  42. A possible solution to the throughput problem is using two cables: one for climbers going up, and another for climbers going down. Then you can have multiple climbers. But this adds a lot of extra load on the cables, and adds the complexity of moving the climbers from one cable to the other at the endpoints.

  43. A skyhook hanging from the Moon to the altitude of geosynchronous orbit would circle the earth once a month. Its ‘orbital’ velocity would be about 100 meters per second.

    A body IN geosynchronous orbit circles the Earth, by definition, once a DAY. Its orbital velocity is 3,070 meters per second.

    So every satellite in geosynch would be sweeping past this beast at a relative velocity of just under 3,000 meters per second, passing it almost every day.

    Can you say this is a “collision hazard”? Yes, I think you can. The only thing that would be worse would be deliberately putting something into a retrograde orbit at geosynch.

    If you want to get from LEO to the lunar surface, you can do it with a combination of rotovators. If you want to get from lunar surface to L1, you’d terminate the skyhook well short of the Earth for safety reasons.

    You would never build it as far as geosynch.

  44. I think that one of the main problems is the dinamic of the system. I think that probably there are dynamic movements and oscilations that have not been well analyzed.

    Also differential expansion and contraction from the sun side of the cable and the shadow side probably will add important effects on both dynamic and structural behaviour.


  45. That paper is based on failure of imagination. All the talk of an elevator is projected on the lunar case. Total delta-v for transfer from LLO to GEO is about 1km/s. LLO-GEO transport powered by nuclear-electric engine can move any reasonable mass without restrictions on time, dimension or acceleration. Luna-LLO transport powered by nuclear-thermal engine can move the same, using lunar oxygen as propellant, with no concerns about radiation effects. The cost of flight would be great many orders of magnitude smaller, also time to construct that, than any elevator. That elevator is a textbook case of failure, same as famous paper reactors described by Rickover in 1953. Mentally replace “reactor” with “elevator” in the text below.

    An academic reactor or reactor plant almost always has the following basic characteristics: (1) It is simple. (2) It is small. (3) It is cheap. (4) It is light. (5) It can be built very quickly. (6) It is very flexible in purpose (“omnibus reactor”). (7) Very little development is required. It will use mostly “off-the-shelf” components. (8) The reactor is in the study phase. It is not being built now. [..] The tools of the academic-reactor designer are a piece of paper and a pencil with an eraser. If a mistake is made, it can always be erased and changed. [..] The academic-reactor designer is a dilettante. He has not had to assume any real responsibility in connection with his projects.

  46. The L1 base would about 58000km above the moon. Assuming race-car like climbing speed of 290km/hr, that’s still a 200 hour trip. Over 8 days, which might be ok if you’re sending up low volumes of cargo – but how soon would the elevator pay for itself that way? Earth would be ~290,000km from L1, so 1000hr.

    And because the tether won’t be moving fast relative to Earth and not at all versus the moon, climbing away from Earth or the moon a modest more distance won’t gain you much in the way of escaping Earth’s gravity.

    Well, I guess because of gravity falling off with radius, and the rocket equation being exponential, climbing up one lunar radius (5500km) from the moon could give pretty good fuel savings to orbit.

  47. What’s the killer app? Moving water ice from the Lunar South Pole to GSO? Does it do that more efficiently than other methods? It’s obviously cool to figure out how to make any sort of real space elevator out of existing materials, but it’s application isn’t obvious.

  48. It’s not clear to me how such a cable actually helps in moving cargo from Earth to Moon.

    It’s apparently still an unsolved problem how to get an “elevator” to move along the 22 000 mile cable of an Earth to GEO space elevator without the trip taking so many days that it’s not possible to get enough tonnes/day to pay for the thing.

    This is 10 times longer, and hence 10 times slower. Numbers I’ve seen for a Surface to space elevator have values like 3 days. So this would be a 30 day trip.

    (I suppose the fact that it would be much lighter, and hence much cheaper to build, would help with the economic side. We’d still be looking at extremely long travel times.)

    Surely a rotovator would be the project to start with?

  49. If L3 is inhabited, it would make sense to create an artificial magnetosphere to protect people, and electronics from solar wind, and less energetic cosmic rays. You’d still want water ice, or something else with lots of hydrogen surrounding habitations, but you’d need a lot less. Some huge high temperature superconducting coils might make a good energy storage device too.

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