Moon Elevator Could Be Sooner Than You Think

The big expense in getting people to orbit or the moon or any other space destination is the cost of escaping the Earth’s gravity. One often-proposed solution involves building a giant space elevator from some point on the Earth to orbit. That sounds great, but the reality is the materials needed to make a giant stalk reaching from the ground to orbit don’t exist today. Cables or other structures for such an elevator would have to be so impossibly thick as to break under their own weight. However, a recent paper from a researcher at Cambridge and another at Columbia suggest that while you can’t build an elevator from the Earth’s surface to orbit, we may have the technology to build a tunnel that anchors on the moon and lets out in Earth’s orbit.

Before you dismiss the idea out of hand, have a look at the paper. A classic space elevator proposal has one point on Earth and the far end balanced with a counterweight keeping the cables under tension. The proposed lunar elevator would minimize these problems by having most of the bulk in space and on the moon.

Honestly we aren’t good enough with physics to tell how serious this might be, though it does capture the imagination. However it may work though, it isn’t a panacea. With current building materials, such a construction could in theory go from the moon to a geostationary orbit. It would be possible to come closer, at the expense of paying a higher price for the weight and force on the thing. There really isn’t any free lunch.

Then again, a lot of the cost of getting into space is getting out of the Earth’s gravity well, so this isn’t as attractive as some proposed elevators that go from the surface to orbit. However, going to the moon or anywhere along the elevator would be easy and inexpensive. In particular, the paper identifies a Lagrange point base camp which would essentially be part of the way along the elevator.

This isn’t the first time we’ve looked at elevators to the sky. If we could get a handle on carbon nanotubes, we could be in business. Maybe a future Hackaday prize will be a ride on a space elevator.

56 thoughts on “Moon Elevator Could Be Sooner Than You Think

  1. I’m wondering at the fundamentals – the earth is rotating, moon is revolving around earth ! The tall elevator would change direction, gradually phasing in and out of alignment, unless the elevator itself moves as an inertial frame w.r.t. rotation.

    1. The elevator is attached to the Moon on one end, and the other end is above the surface of the Earth. The whole thing moves around the Earth at the same rate as the moon. The Earth end would always appear to be approximately the same angle east of the Moon (allowing for some variation due to the Moon’s elliptical orbit).

      So yes, the end would move around the Earth. However, you could know where the end would be at any time, and launch a low-powered rocket (relatively speaking) to the near end of the elevator.

      1. I’d not think in rockets. The gain that can be made is to use an airplane that utilizes the Earth’s atmosphere to overcome the gravity well. The problem then becomes how to synchronize the airplane’s movement with the moving end of the tube.

        I’d even think that it’s not necessary at all to have an actualy tube. Just a huge cable to which you can fly with your winged airplane, attach to, and then use a cable-climber mechanism to pull yourself up the cable all the way to the moon.

        In general, it takes just as much ‘work’ (in physics sense) as shooting yourself to the moon on a rocket. But it might use a lot less energy because the used mechanisms are more efficient. Pulling yourself up a cable, without slippage, is a lot more efficient than pushing yourself up on a cloud of expanding gasses.

        1. Forget anything in the atmosphere. Gravity 20 km up is still like 99% of gravity on the surface, so one is faced with pretty much the same material problem for the cable as if it’d reach down to this surface.

          Advantage of a moon elevator is the much lower gravity there. Having just 16% gravity means one is suddenly just 3 times above what a Dynema rope of constant thickness could withstand, a rope of raising thickness towards the center point becomes manageable. It could weight just 7 tons total ( = 1 rocket launch for transport).

        2. Avoiding the need to accelerate to orbital velocity saves an enormous amount of energy. Without some “anchored” mass, there is no easy way to get back the energy spent to get to orbit. So you pay through the nose to get to orbit, then pay through the nose to decelerate again when you return to Earth .. and there are some lesser nasal payments in between in order to make the transition between earth and lunar orbit.

          All that said, a kg of mass in low earth orbit (say, at 400km) has about 30MJ of kinetic energy, and about 4MJ of potential energy. A liter of gasoline has about 46MJ. So lifting something lifted to 400km has about 1/8 the energy of something orbiting at 400km, but if we didn’t need overcome air resistance and lug fuel along, it would still be pretty cheap to launch stuff into orbit. And you could theoretically recover a lot of that energy for any mass that is subsequently deorbited.

          There are a number of rocketless launch ideas out there. The back of the envelope figures are actually attractive (a liter of gasoline per kg .. that’s pretty damn cheap). Of course, the practical problems are significant .. else going into orbit would be already be an utterly ordinary occurrence.

          But, I suspect that it’s inevitable that rocketless launch will overtake rockets at some point. Once the annual expenditures on rocket launch hit a level where capital investment in rocketless infrastructure makes sense, it should draw the needed investment.

    2. This is the first thing I thought of. https://what-if.xkcd.com/
      In short, the end on Earth would be moving around at a pretty high speed so there’s that. Also the distance between the Earth and the moon is not constant, it’s +- 50,000Km so I guess we’ll just have a winching mechanism or something on the moon powered by uh nuclear that we elevaterd up there or something. Then we get the beautiful problem of oh dear god this cable will cost a fortune who the hell will pay for it. Oh also when the cable breaks I guess we have to send a rocket up to do some EVA repairs, that sure seems long term sustainable with all the space debris.

      The idea is bunk and the authors just wrote something to get news headlines.

  2. I was wondering the cost of this thing. TGV rail costs around $15m per km. Its 384400km to the moon (all according to google). That’s around $5.7tn to build. If you could imagine the costs might be similar.

    If you use the Boston tunnel to approximate it’d be $3847.5tn. So maybe that’s not a good one!

    1. The paper actually talks about this on page 8.

      “We can see that for present-day materials a spaceline could be constructed which reaches geostationary orbit… 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.”

      From the table of materials they have on page 4, they’re probably assuming a cable made of Zylon (https://en.wikipedia.org/wiki/Zylon). I couldn’t find a price for just Zylon, but I did find a place that sells a mixed Zylon/Carbon Fiber fabric (https://compositeenvisions.com/carbon-fiber-bronze-zylon-hm-fabric-plain-weave-3k-50-127cm-5-5oz-186-48-gsm/) for $0.32 per gram. At that price, 40,000 kg would cost $13,000,000 (thirteen million dollars) — a surprisingly reasonable amount.

      40,000 kg is roughly twice the mass that a Falcon Heavy can deliver to the Moon. If you’re buying a Falcon Heavy and using enough of its capacity that it can’t self-recover, it seems to cost about $150 million per launch, so $300 million is about how much it would cost to get all of the material to the Moon.

      If the project was properly managed (and if this paper’s math is correct), this “spaceline” might plausibly be planned, fabricated, launched and assembled for ten billion dollars — less than the planned cost to renovate JFK International Airport, or many other successful megaprojects (https://en.wikipedia.org/wiki/List_of_megaprojects).

    2. furthermore, the escape velocity from the Moon is 2.38km/s, well within railgun teritory…if you’re basing the thing on the Moon, an elevator probably does not make sense if you can build an electromagnetic accelerator.

      1. A railgun/mass driver is probably the better choice for moving bulk cargo off the moon, as it should be able to run 24/7 shooting several 20 kg packages per minute, but those packages will have to be inanimate as even tardigrades have trouble withstanding 5,000 G accelerations. Space elevators are better for delicate cargos like people.

          1. Yeah, I wondered why that wasn’t mentioned in the paper – they say that transport from the Earth end of the cable to the Moon end would be “free” because it could be solar-powered, but there could also be energy stored in “falling” units that is then used to lift them on the next trip up.

  3. As with all human creations one really has to ponder what will happen when the proverbial excrement hits the fan and someone screws up. Lets face it Humans have a great track record of screwing up.

    1. Hindenburg, lets face it was a disaster just waiting to happen.
    2. Titanic, the unsinkable ship.
    3. Russian Rockets have failed more than a few times in spectacular fashion.
    4. China wiped out a village while testing one of their rockets.
    5. How many power plants both Nuclear and other have demolished surrounding areas?
    6. Space Shuttle incidents.
    7. I recall a Satellite that suffered from an Imperial/Metric argument.
    8. Deep Sea drilling has had its fair share of mistakes and caused some serious environmental issues.

    So let me see, we send a cable up that connects Earth to the Moon, its anchored in place by whatever means and an elevator zips up and down taking stuff up and down. now if that cable breaks or fails what is going up is going to come down at a great rate of knots and where is it going to land?
    Sure the cable weight per meter may not be much and you could say its going to be as lite as a feather however that’s still some 8 ton that is going to be falling toward the earth at a speed of 240km/h.

      1. I was thinking that as well until I saw that the end point would be above geostationary orbit, there are very few objects above geostationary.

        UV-C on the other hand would rapidly decompose Kevlar without the addition of an external UV protective coating (extra weight). And even though Dyneema is better in regard to UV-C it would still decompose (~20% weaker after ~500 hours of exposure ***) without an external UV protective coating (extra weight).

        *** Take the numbers with a grain of salt because they are taken from the ISO 4892-2 accelerated weathering testing which would include water vapour in addition to the 10nm UV from the high pressure Xenon lamp to help speedup the breakdown (ref: search for “CIS-YA102-Ultraviolet exposure of UHMWPE fiber from DSM Dyneema”).

          1. The cable is anchored to the surface of the moon and ends just before it reaches GEO. There are no populated altitudes between GEO and the moon’s surface, with the possible exception of L4/L5, which are some distance from the path of the cable.

    1. This isn’t about connecting the earth to the moon via a cable, thats just not possible at all.

      Its about a space elevator on the moon where the smaller gravity well allows a system to be built using technology and materials we already possess.

      1. Still, the point is valid though:

        Any kind of “space elevator” implies the risk of having considerable mass come tumbling down (whatever direction “down” may reference), and it’s going to be over a _way_ larger area than a toppling windmill or stray rocket. It might be a “gift wrap cord” of nano carbon curling up neatly within a football field, or it may be an “oil pipeline” tumbling down in more-or-less of a line across tens or hundreds of kilometers. An interesting day that would be.

      2. It is at least theoretically possible, with a free end arbitrarily close to the Earth’s surface. It would take something like 25% of the worlds annual production of UHMWPE to lift one kg from the Earth end.

        From a practical standpoint, I agree .. not gonna happen .. it’s the wrong design, and practical issues probably make it genuinely impossible.

        However, low earth elevators are entirely possible, and staged tethers may well be how stuff goes into space in the future. Basically drag stuff into low earth orbit, then accelerate to orbital plus a needed delta V to reach geosynchronous orbit some other waypoint (thank you, vacuum), then recover the kinetic component of the transition orbital energy for reuse (how?), then drag the load to the moon on a cable.

    2. The Hindenburg wasn’t a disaster, it was a miracle! It was a catastrophic mid-air explosion and fire, in which 62 of the 97 people on board survived!

      But it wasn’t just luck, it was a trait, all the airship where that safe. The only reason so many people died in the Arkon accident was because they drowned after the crash while waiting to be rescued. When the Macon crashed of the coast of California the crew had life jackets, 81 people lived, there where 2 fatalities.

      1. A hurry it up timeline for press coverage against a known looming t-storm front was the demise of the Hindenburg. Sound familiar? A Shuttle had it’s demise the same way. The first craft to fly around the world with paying passengers no less was the Graf Zeppelin, two of which earned the first “mile high” club rating. It was scrapped and turned in to fighters and bombers after the Hindenburg disaster, a flawless career.

    3. This is a very legitimate issue .. if it breaks at the moon end, it will be a fairly heavy cord that will be snaking around the earth roughly 10 times, over the course of approximately 10 days. .

      For the first few days, the free end would be whipping around at 1000 miles an hour .. and the the tip would flailing around like a hypersonic bullwhip due to oscillations in the cable.

      If the free end managed to catch on something in the early phases, inertial forces would snap the cable, and the resulting fragments would be angry, lethal, supersonic strings that slice through anything in their path until the impacts managed to slow them to a halt.

      Once the earth end gained enough purchase, the moon end would coming in at supersonic velocities, so there would be a continuous sonic boom around it. As wild as a continuous sonic boom might sound, this would be a welcome phase .. at least it’s not spraying ropey shards of death.

      You would probably need to evacuate a zone for several hundred miles either side of the equator, and I suspect a lot of folks would not make out if the danger zone intact. It would almost certainly be one of the most memorable technological disaster stories in human history.

      1. I think you might be neglecting it burning up on reentry as soon as it hits the upper atmosphere. It could potentially damage some satellites but I doubt anything would reach the surface

        1. if it snaps, it will immediately start falling to the earth .. the free end has considerable force pulling on it. But, it wont accelerate as if it’s under a uniform 1 G load. There is considerable mass trailing behind the Earth end, and that mass has a declining gravitational load on it. At the earh Moon L1 point, the tether is in free-fall. Beyond that, part of the tether is getting pulled toward the moon. The point being, when it hits the earth, it will not be going at anywhere near the speed of an object dropped from the tether’s earth-terminal height .. it will be going much slower.

          The structure may well burn up, but I’m not sure it will burn completely .. and even if tit does, a continuous “ring of fire” wrapping around the earth for 10 days straight might not be all that benign.

          In any case, depending on earth end elevation, there is no guarantee that the free end will hit the atmosphere at a speed that generates significant aerodynamic heating. and when the structure does hit supersonic speed, it’s not a blunt shock wave .. it’s essentially going to be an infinite, needle like body, so depending on the details of its motion as it enters the atmosphere (how much speed is longitudinal, how much is transverse), it might actually be fairly aerodynamic. Working out an estimate for reentry forces seems like a genuinely interesting problem.

          In any case, if it snaps, it falls to earth. If it snaps at the moon end, drag (atmospheric, or mechanical) will spool it around the equator nearly 10 times,. If it burns in the atmosphere while doing this, which it might well do, that seems like the best possible outcome. I’m not so sure that would be a benign event. If it doesn’t burn up, it would probably wreak a lot of havoc.

          UHMWPE seems like the most promising material. It’s not the strongest readily available fiber, but it’s up there, and it has an exceptional strength to weight ratio .. and weight is a factor in this application. The reduced weight reduces the potential energy of the structure a bit. As a bonus, it has poor heat resistance (melts at 147 C), so it’s much more likely to decompose on reentry than, say, Zylon.

          And hopefully I’m not coming off negative .. rocketless launch is the future. Various momentum transfer systems, lifts and whatnot will take over from rockets at some point. A cislunar tether system from the moon surface to, say, geosynchronous orbit definitely seems like a promising candidate as part of the infrastructure.

  4. you still need to pay the gravity tax to launch a rocket so a spacecraft can rendezvous with the geosynchronous station. it would be significantly cheaper to just use a cycler ship for personnel. ion tug for freight (next generation ion drives, solar, and/or space nuclear reactor required). end goal of having a lunar surface shipyard, foundry and fuel depot.

    1. It’s possible to make a low earth elevator .. but you need a lot of low earth orbital mass to do it.

      And there are various other rocketless launch technologies .. rockets will probably become a minor component in near earth space tech not too far in the future.

      Once you have enough mass in space, you can recover launch energies. If there is a zero sum mass balance (as much stuff.going up as.is.coming down), it may take very little net energy for a.l round trip.

      At some point, there is likely to be a surplus of mass coming to earth vs leaving earth, and at that point, orbital infrastructure will likely become a major source of clean energy.

      1. Uh.. No it’s not? You can’t have a LEO station as a space elevator anchor. The orbital velocity there is about seven to eight kilometers per second relative to the surface. It wouldn’t be able to be attached to the ground, and if it was dangling in the atmosphere at all then drag would either pull the station down or more likely destroy the elevator cable. It has to be in GEO or no dice. And at that point it has too much mas for any matter to achieve the necessary tensile strength.

        Some active structures which cycle mass around magnetic tracks inside at a very high speed to maintain structural integrity could work, but they likely wouldn’t have stations at the top since that would vastly increase the amount of mass they’d have to cycle to stay up. So a launch loop or something to that effect would be possible and get you above the atmosphere at least, but you’d still need to achieve orbital velocity somehow. Which is most of the rocket.

        We probably aren’t going to be free of rockets in space any time soon.

        1. It’s possible, for example, if you have a continuous ring, and if the speed of rotating mass is a bit above orbital velocity.

          And you don’t even need a complete ring. If you have an evacuated tube near the ground, say, 2000 miles long and accelerate a mass inside of it above orbital velocity, the mass will lift the structure. Of course, you need to figure what to do at the other end of the tube to grab am object moving over 17000 mph, but space is exciting that way.

          https://en.m.wikipedia.org/wiki/Orbital_ring
          https://en.m.wikipedia.org/wiki/Launch_loop

  5. Besides all this, aren’t elevators only any use if we want to leave the earth completely? XKCD pointed out “Reaching orbital speed takes much more fuel than reaching orbital height.” but the vast majority of are space missions are to orbit, not beyond.

    1. The higher you go, the lower orbital speed is. So if you built one up to geostationary orbit you could get some serious infrastructure up without a lot of rocket power. You’d inherit enough rotational momentum from Earth to just about reach orbital velocity. Of course it’s mostly academic because not even carbon nanotubes have nearly enough tensile strength to make a space elevator on Earth, despite what lots of people and the original article imagine. It’s a lot closer than steel, but still way, way off.

      And I don’t see the purpose of a lunar-to-geostationary elevator at all. Getting into orbit from the moon is practically free. The whole dang thing is made of alumina oxides, i.e. solid rocket fuel. This would be massively expensive, probably won’t work due to complications we’d doubtlessly discover down the line, and if it ever broke off and fell to earth it would be an extinction-level event. And it’s not like we’d maintain it forever. Same goes for Earth-based elevators; any failure would release the equivalent of a full-scale thermonuclear war as it fell and wrapped itself around the equator.

      All space elevators are basically unobtanium science fiction dreams. May as well say we’ll build a Ringworld or any other BDO from a Larry Niven book. Without Niven’s scrith, we won’t be building any of these ever.

    2. This. The thing I wasn’t getting a first was, since there isn’t a huge delta-vee between geostationary orbit and lunar, and I was wondering how that could save enough money to make it worthwhile. The trick is that payloads launched to the Earth end of the cable don’t need to be anywhere near orbital velocity. They essentially launch mostly up, and only need to reach the velocity that the cable end is at. Of course, they have to avoid everything along the way, all of which IS moving at orbital speeds.

  6. We need Jules Verne.

    If we do this, we will have cables to LEO long before any cables to the moon, so I’ll deal with just LEO.

    Primary motivation for the space elevator idea is to move cargo to and from LEO for easier access to space than a huge and risky energy intensive rocket. We’re looking for a result that becomes as mundane as the street in front of your house.

    Seems a cable encircling the planet in LEO at the equator, with cable spokes/elevators to the surface of the planet, is likely what we would end up with.

    So assume we have some manner of cable to space working. How much mass could we move up to LEO before it has a significant slowing effect on the planet’s rotation? Seems likely to be non-consequential, but someone has to do the math and check.

    1. The slowing effect would be less significant than that caused by ocean tides, until the amount of mass being moved got REALLY big. Also, remember that the tides are transferring momentum from the Moon to Earth, while this momentum transfer would be the other way. I think.

  7. First, build a big moon space elevator. Big enough to slowly alter the moon’s orbit. Slowly, pull the moon down to geostationary orbit. Then the problem is solved, and we can have a space elevator between the two, and perhaps a second one on the far side of the moon.

  8. Geostationary is a great deal closer to the Earth than the moon currently is. The moon controls the tides. Closer moon, MUCH higher/lower tides and now locked into position by geostationary moon. So which two continents do we flood, and which oceans do we dry up to farm?

    Gosh, we really DO need Jules Verne.

  9. In addition to all the other issues mentioned above, there is also the 400KV potential difference between the top of the atmosphere and the ground – a space elevator would literally be the world’s biggest lightning conductor, in addition to causing large atmospheric disturbances in the area around it.

  10. A CME and resulting aurora would be a problem. Our power lines on the planet’s surface suffer from these. A Carrington event does need to be brought into consideration. I think it will shoot down ALL the surface to space cable ideas.

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