SIX REASONS WE’RE NOT GETTING A MOON ELEVATOR

A while ago, several news outlets of varying degrees of reputability reported on the intentions of a company called Liftport to build a space elevator, but not on the Earth where it’d be accessible by human beings.  They want to build one on the moon.  But first they have to figure out if it’s possible.  And before that, they have to do some stuff with balloons.  It’s complicated.  I’ll explain.

First, the reason you’d want to build a space elevator is to get into space.  That’s pretty clear.  A space elevator, were it to function in an ideal way, would get you and your belongings to space for much less money than doing it with rockets.  Here’s why.

A rocket works by filling a giant tube with fuel, pointing it upward, and then lighting the fuel on fire.  The fuel then explodes, hopefully without exploding the whole rocket along with it, and the force of the explosion pushes the rocket upward.  The problem is that in order to propel the weight of whatever you’re trying to get into space upward, you need a lot of fuel, and that fuel weighs a lot in and of itself, so you need more fuel to lift it, but then that fuel weighs a lot, and you need a container to hold it, and then the container needs more fuel to lift it, and what it boils down to is that in order to get a lunar lander to the moon that weighed about the same as two large SUVs, we needed a rocket that weighed about the same as 361 Tyrannosaurus Rexes.

I realize that is not a useful visualization for you.

I realize that is not a useful visualization for you.

In human numbers, the lunar lander required a vehicle 650 times its own weight just to get to the Moon.  At the moment of launch, the Saturn V was getting seven inches to the gallon.  For further perspective on how much fuel is spent just lifting other fuel, I offer the fact that 96% of the weight of the Saturn V is fuel, and 4% is the container to carry it.  By comparison, only 94% of the weight of a soda can is soda.  Which means that a soda can, a device specifically designed to hold and carry liquid, is actually worse at it than a device that’s trying to carry as little liquid as possible.

Or, to sum up, rockets suck.  Unfortunately, they’re the best we have at making stuff go really really fast, and in order to escape Earth’s gravity you have to go really really fast.

But what if you didn’t have to go really really fast?  Right now, we’re wasting a gigantic amount of energy making machines that can jump all the way to the top of the building, but what if we could make one that could take the stairs?  That’s the idea behind a space elevator.

A space elevator would put a cable up in the sky, with one end anchored to the Earth and the other end anchored to a satellite in a geosynchronous orbit.  The centripetal force of the satellite being spun around the earth would keep the cable tight in the same way that swinging a rope around your head keeps the rope straight, except the rope is over 25,000 miles long.  Vehicles on earth would climb the cable to the end, at which point they could release from it and get whipped off in whatever direction we want, to the moon or Mars or to send probes to Jupiter or the moons of Saturn or wherever.  It will not be useful for anything beyond our own solar system, for reasons I’ll explain in a moment.

Now you know all the background information on how this is supposed to work.  Time to go into the problems.

In case you're new here, I have a tendency to break up long blocks of text with pictures of animals.

In case you’re new here, I have a tendency to break up long blocks of text with pictures of animals.

1. WE CAN’T BUILD A SPACE ELEVATOR

Never mind the cost.  Currently, satellites in geostationary orbit sit at about 26,000 miles from the Earth.  Orbit time and distance are inexorably tied together, and a geostationary satellite has to orbit once every 24 hours (23:56, technically) to stay directly over the same place on Earth, which is handy if you’re physically attached to that point as well.  Unfortunately, that satellite is technically in freefall, because that’s how orbit works, so you can’t pull on it (like with a huge freaking cable) or it’ll fall out of the sky.  If we push it farther away but force it to orbit at the same speed, it’ll start to experience centrifugal force pushing it outward, which is the whole point because that’s what keeps the cable tight.

Do not EVEN START with me on how I really mean centripetal force.

Do not EVEN START with me on how I really mean centripetal force.

So how far away do we put it?  Let’s say 30,000 miles, and let’s also say that the cable (which we’ll get to) weighs 16.8 lbs/ft, because I did some research and that’s what 75mm steel cable weighs and that’s the biggest thing I could find and it’s a moot point anyway (again, we’ll get to that).  Let’s be wildly optimistic and assume that we only need one strand, and that it has to stretch the full length of the elevator.  If it were 30,000 miles long, it’d weigh 2.661 billion pounds.  Now we need to know what amount of weight has to be at the end of that cable such that, when it’s spun around the Earth in 23 hours and 56 minutes, it’ll pull the cable tight with a force of 2.6 billion pounds.

Wolfram 1

According to Wolfram Alpha, the counterweight at the other end will need to weigh slightly shy of a hundred billion pounds, which I can confidently say, without doing any math, is more than the combined weight of everything we’ve ever put into space.  And keep in mind that this counterweight will have to be put up there conventionally, with rockets, before we attach the cables to it.  That amount of weight is so prohibitively impossible that the word “prohibitive” is laughably insufficient to describe it.  We’d have to launch one Saturn V — the most powerful rocket in human history — per day for the next 2700 years just to get the counterweight put together.  It literally cannot be done.

But surely there’s a balance here somewhere.  We need the counterweight to be heavy enough, and far away enough, to hold the cable tight, but the farther away it gets, the heavier the cable gets.  Using Wolfram|Alpha’s formula tool, I did some math.

Wolfram 2

Math.

I used 100,000 pounds because that’s the largest mass we can put into orbit with a single rocket launch, I used 15 degrees per hour because that’s how fast a geostationary orbit goes, and I used 250,000 miles for reasons I’ll explain in a minute.  Would you like to see how much tension that counterweight can put on the cable?

Wolfram 3

A little bit more than 20,000 pounds, and that’s not even close to enough.  Even if we were somehow able to attach it to a shoelace, a quarter-million-mile shoelace would still weigh over 4,000 tons.  In fact, even if we were able to use some sort of magical Elvish rope that weighed literally nothing, 20,000 pounds of tension isn’t even enough to lift anything meaningful.  The lunar module that went to the moon weighed twice that.  And that’s at a distance of 250,000 miles, more than ten times geostationary orbit.  Why did I use that number?  Because that’s how far away the moon is.  In order to build an elevator this big, which we’ve already established is not big enough to be useful, you’d have to go to the moon anyway.

To boil all that down into one concise point, there simply is no way to build a space elevator that will be useful.

2. IT’S NOT FAST ENOUGH

Let’s just go ahead and throw the last 1200 words of detailed explanation out the window, because fuck it, my time’s not that valuable, and assume that you could attach a lunar module to an elevator, ride it 26,200 miles up in the sky, and then detach at the moment of your choosing to get flung off like a Foxtail toward the Moon or Mars or whatever.

I'm pretty sure these had an objective other than "whip it at your friends and loved ones as hard as possible," but I don't know what it was.

I’m pretty sure these had an objective other than “whip it at your friends and loved ones as hard as possible,” but I don’t know what it was.

Are you going fast enough?

Luckily, this uses the same centripetal force calculation as all the math from the last point, so I used that and it turns out you’re going about 6800 miles an hour.  Fast, yes.  That’ll get you to the moon in only 36 hours, which is twice as fast as the manned missions.  It’s also fast enough to get you to Mars at the same speed as the MRO, the satellite that orbits it and beams data from our various rovers back to Earth.  But that took seven months, and that’s pushing the boundaries of how long humans can survive in space.  Getting to Jupiter without additional gravity assists would take almost ten years.  NASA has a spacecraft going to Jupiter right now called JUNO, which started off faster and has gravity assists that will ultimately boost it to 98,000 mph, and it’s still going to be a three- to four-year trip because using gravity assists means you have to go the long way.  A space elevator simply can’t give you useful interplanetary speed without rocket assistance, and that kind of defeats the point of using an elevator in the first place.

3. IT DOESN’T SAVE ANY ENERGY

One of the big reasons that people like the idea of a space elevator is that it would make it cheaper to get stuff into space than the current methods.  Given that in today’s dollars, each Saturn V launch would cost over a billion dollars, they have a point.  But the reason it’s expensive to get stuff into space is that it’s hard.  Each launch used 203,000 gallons of kerosene and 360,000 gallons of liquid hydrogen to propel it upwards, along with 418,000 gallons of liquid oxygen to help it all burn faster and hotter.

All told, and assuming perfect efficiency, that’s 42.02 gigajoules of chemical energy released to put a 100,000-pound payload in TLI (trans-lunar injection), which means it has enough energy to get out of low earth orbit and to the moon.

Now let’s assume that we want to just climb up all that distance to the elevator.  We’ll be going against the force of gravity, and that takes energy, described as gravitational potential energy (U).  U is defined as energy an object possesses because of its position in a gravitational field.  If you’re using it to calculate the U of a bowling ball held six feet off the floor, it’s pretty simple math because the strength of the Earth’s gravity is practically identical between the ball and the floor.  At 26,000 miles, though, it’s about 2% of what it is here on the surface, so the equation changes.  Incorporating Newton’s Law of Universal Gravitation, which accounts for the fact that gravity gets weaker as distance gets larger, the formula for gravitational potential energy between two masses in space becomes:

U=(-G*M*m)/r

where U is the energy value, G is the universal gravitational constant, M is one of the masses (Earth), m is the other one (the payload), and r is the distance between their two centers of mass.

Assemble all that together, and the gravitational potential energy of a 100,000-pound payload, 26,000 miles above the surface of the Earth, is 372.5 gigajoules.  That’s nearly nine times as much energy as it takes to use rockets, and that energy has to come from somewhere.  Presumably it’d be electric motors, but those are only 85% efficient at best, so then we’re talking about 438.2 gigajoules, over ten times the energy of rockets.

That’s why rockets don’t go straight up.  They go up for a while, then start to lean sideways, at which point they’re not gaining height so much as sideways speed.  An object in orbit is basically in free-fall, but it’s moving sideways so fast that it misses the thing it’s orbiting, and that’s how the Apollo missions got to the moon.  First they got into orbit, then used that lateral speed of orbit to help fling the lunar module toward the moon.  A space elevator can’t do that, because it’s attached to a cable.  It just has to slog straight up.

That was a lot of text and math and stuff.  Have an adorable animal.

That was a lot of text and math and stuff. Have an adorable animal.

So that about wraps up the problems with a space elevator on Earth.  It’s literally impossible, and even if it were possible it’d be wildly inefficient, and even if it weren’t wildly inefficient it’d be too slow to be useful.  But as you recall from the title, this is about a space elevator on the moon.  See, everyone knows you can’t make a space elevator on Earth; that’s why LiftPort wants to make one on the moon in the first place.  Granted, a lot of those problems are solved on the moon.  We do have cables strong enough to hold the counterweight, because the payload will be lighter and the gravity isn’t as strong.  Rockets are still more efficient, because again, the gravity isn’t as strong, so maybe it’s possible.  Maybe.  And that’s where LiftPort comes in.

4. LIFTPORT’S PLAN WON’T WORK

LiftPort is a website.  I’d call it a company, but it doesn’t have any products or any money, otherwise it wouldn’t be begging people on Kickstarter for a paltry $8,000 to do something with balloons.  I’m not even entirely convinced that it employs more than one person.  Nonetheless, that website has has many drawings of a lunar space elevator, which on closer inspection is intended to get people to the moon.  The “ribbon,” as founder Michael Laine calls the cable, will extend 156,000 miles from the moon toward Earth.  The idea is that there will be a point along the cable, 34,000 miles from the surface of the moon, where rockets from Earth will be able to rendezvous with a station and then take the elevator down to the surface of the moon.  34,000 miles is the lunar equivalent of a geostationary orbit, so the gravity at that point should be basically nil, meaning everything farther away than that is pulling away from the moon and everything closer in is pulling down toward the moon.  The spaceship would be able to float at that point on the cable while the elevator went down.

So let’s crunch some numbers again.  I’ll use his number for the radius of the ribbon and, since he didn’t give one, I’ll assume a 100,000 pound counterweight because it’s the biggest thing we can put into space at once.  Here’s the centripetal force:

Wolfram 4

Are you seeing that?  Fifteen pounds.  If you set that cable in motion, a fucking toddler could pull it out of orbit.  You may be baffled at such a low number, and rightly so, but it’s because the Moon basically doesn’t rotate.  It does a full rotation every 29.5 days.  It’s “tidally locked” to the Earth, which means that it’s always facing the Earth with the same side.  We don’t see it spin at all.  Think back to the metaphor of swinging a bucket around on a string.  If you don’t spin, the bucket can’t hold the rope tight and it falls down.  Same problem here.  Even if the moon spun as fast as the Earth, it would only generate about 15,000 pounds of tension, which isn’t enough to hold up the cable itself.  And even imagining a weightless cable, 15,000 pounds is barely enough to support a standard elevator car like you’d find in any building in the world, let alone a special one that can carry astronauts and their gear and be reinforced to survive space.  It simply can’t be done.

The only caveat I can think of is that since the moon is always pointed, as it were, toward the Earth, the counterweight will be well within the pull of Earth’s gravity as well, and that’ll provide some additional pull.  Maybe that’ll help?

No such luck.  A quick visit to Wolfram|Alpha tells us that the gravitational force experienced by a 100,000-pound weight suspended 84,000 miles from the Earth is a little over 200 pounds.  Not helpful at all.  And even if it were, the moon isn’t quite static with regards to the Earth.  It wiggles.  And it gets closer and farther by about 30,000 miles every month.  Here’s what that looks like in time-lapse form.

Moon

So the Earth can’t help, and that leaves us back where we started, with a moon rotating too slowly to hold a cable tight.  Again, even ignoring the massive, glaring problem that there does not exist a material light enough or strong enough to make a cable from that’ll support its own weight on these scales, this is simply not possible.  Which leads me to my next conclusion:

5. LIFTPORT DOESN’T KNOW WHAT THE FUCK THEY’RE DOING

The actual Kickstarter campaign was for $8,000 dollars to “climb to the sky.”  The project was to make a platform, suspended from balloons, that would hold a ribbon up to a platform.  The other part of the project is to build a prototype robot that will climb that ribbon to the platform, thus demonstrating that it can be done.  Here’s the thing: I believe you.  Climbing to a balloon on a tight ribbon is not hard.  A helium balloon can generate a LOT of tension on a cable that a robot could climb.  That’s because balloons work on buoyancy.  Centripetal force is completely irrelevant in this instance.

What does not exist, anywhere in this project, or the articles written about the project, or the website itself, is a simple explanation of the difference between this supposed proof of concept and the real thing.  There are no numbers on the material that he’s planning to build the ribbon out of, or the tensions this will have to endure, or the size of the counterweight, or what it’ll be made out of, or how it’ll be anchored to the ground, or the elevator cab itself.  There are no specs on how the cab will be powered.  There’s no science at all.

There IS this lovely sci-fi picture, which might as well be a dragon with a jetpack for all the scientific viability it portrays.

There IS this lovely sci-fi picture, which might as well be a dragon with a jetpack for all the scientific viability it portrays.

The only thing that has numbers is the distance, and they’re all suspiciously round numbers.  Nothing is specified to measurements more precise than the nearest 5,000 kilometers, which makes me think that he hasn’t actually done any of the math for space-scale implementation.  Reading through the page for the lunar elevator isn’t encouraging either.  Listen to some of these quotes:

For 40 years, we have not had a rocket capable of “soft-landing” on the Moon. Because of this, the Moon has remained “out of reach” for two generations. However, we have seen significant breakthroughs in the technologies of rocketry, robotics, materials science/nanotechnology, computing, communications, and energy (what we at LiftPort call “Civilization Shifting Technologies” or CST’s). But despite these breakthroughs, the status quo remains that we still cannot land “…a man on the Moon and return him safely to the Earth.”

Well, you might want to update that, given that China just did a soft landing of an unmanned craft about a month ago, using a rocket less than a fifth the size of the Saturn V.  And the technology isn’t hard, we just don’t have the money to build more Saturn Vs right now.  We haven’t been back to the moon because we can’t be bothered, not because we can’t.

Once the Lunar Elevator is fully functioning, astronauts and equipment will be able to soft-land cargo on the Lunar surface. Compared to flying the Space Shuttle, humankind will be able to travel 1000 times farther for 1/10th the price. Using our models, we believe we can build a LSEI that can transport three dozen people to the Moon per year “…before this decade is out.”

YOU DON’T HAVE MODELS.  You have drawings that would have taken about an hour to create, with numbers that have absolutely no explanation behind them.  You have also offered no evidence whatsoever for that “1/10 the price” business.  And the Space Shuttle is a shitty example because it was designed to shuttle people to and from low earth orbit, which it did successfully over 200 times.  This is like saying that you’ve designed a boat that will cross rivers BETTER THAN A LAMBORGHINI.

But this kind of lofty-yet-empty rhetoric is all over the website. Their mission statement includes this:

“LiftPort Group has sometimes been referred to as an “Idea Factory”.  Because of the kinds of projects we work on, I’ve sometimes modified this to be a “Dangerous Ideas Factory” – because our projects shake the status quo.”

Yeah, everyone’s so goddamned scared of you, especially since you don’t have any money and have resorted to fucking Kickstarter to fund a viability study for your viability study.  There’s also this.

Quote

That’s Michael Laine quoting himself.  In an inspirational fashion.  I should stress again that LiftPort has not actually built anything or proven that anything they’ve designed can be built.  The overwhelming impression is that Michael Laine is a guy with harebrained ideas and delusions of grandeur.

6. NO ONE IS PAYING ATTENTION

Everything I’ve written here is easy math.  I took physics for three years in college, but my career is by no means scientific.  I used Wolfram|Alpha for basically all of it, something anyone with the time could have done.  Do you think I know off the top of my head how much energy is released by burning liquid hydrogen?  No.  I looked that shit up.  And I found that the numbers aren’t even close to feasible.  Not even close.  If they were close, I’d chalk it up to some confounding variables and materials engineering and say “maybe not right now, but one day we could do this.”  But they’re not.  This is so preposterously impossible that it’s on par with cold fusion.  It cannot be done not because we don’t know how, but because of the fundamental laws of orbital mechanics and kinetics, all of which are centuries old.  It simply cannot be done.

But that didn’t stop people from reporting on this like it was only five years away, a number that they presumably got from Laine himself.  Time covered the story.  So did Forbes.  So did The Economist.  And all of them did so objectively, which means that none of them bothered to ask the simple question: “is this crazy?”

I’m not trying to be a naysayer here.  I’m not some grumpy cynic who wants to shut down the dreams of a generation and say that none of us will ever set foot on another celestial body.  I’m a realist who knows that to do so will be unfathomably difficult, and it will take a long time, and it will take a lot of effort and money and technology.  I fully believe that we will put a man on the surface of Mars, but I would be not at all surprised if it didn’t happen in my lifetime.  I think we might even get to some of the moons of the outer solar system, like Triton and Titan and Ganymede and Europa.  I don’t think humanity will ever reach another solar system though.  Ever.  Barring some sort of breakthrough like warp drive or mass relays, the distances are just too great.  We have a collective delusion that we can do anything if we just try hard enough and believe and stuff, and that’s not the case.  There will be limits.

The problem with dreaming too big is that it leads to disappointment.  We’re apathetic about the space program now because as soon as we landed on the moon in the 60s, we got it in our head that we were headed to infinity and beyond, and that hasn’t happened.  We have a fucking space station over our heads right now, orbiting the earth at 17,000 miles per hour, with human beings living in it who are not only able to live there, but able to grow plants and conduct research and float around in their jammies and vote in presidential elections and post to YouTube.  In terms of technological detachment, they may as well be in the next town over, but they’re in fucking space.  And no one cares.  We put an SUV on Mars, using a landing sequence so convoluted that it would have seemed unrealistic in a J. J. Abrams movie, and no one cares.  And every time someone promises that Mars will be as big as the moon in the sky, or that the planets will align and you’ll be able to jump and float in the air for a second, or that you’ll be able to take a vacation to the moon in your lifetime, there will be people who don’t understand why that’s impossible who are let down and start to care a little less about space.

That’s the problem here.  It’s not that you have a dream of easy transport to the Moon; that’s great.  It’s that you have no idea how to do it, but you’re convinced that you do, and you’ve convinced at least 3400 people on Kickstarter to donate their hard-earned money to support you, all of which will be pissed away on balloons.  And the next time NASA needs money to build a rocket that will work, those people will be the first to think “oh, it’ll go to Mars?  Yeah, right.  I’ve heard that before.”

So stop it.  Or at least tone it down.  You’re ruining the future for the rest of us.

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10 thoughts on “SIX REASONS WE’RE NOT GETTING A MOON ELEVATOR

  1. artor1 says:

    I agree that putting a beanstalk on the moon is fucking stoopid, and there is no need to warrant the attempt. But having one from the Earth would open the rest of the Solar system to us, and it’s not as impossible as you make it out to be. Sure, we need to figure out how to make the cable, which is the trickiest part of the problem. But that cable will probably be some kind of carbon nanotube, and the scenario described in Kim Stanley Robinson’s Mars series has the engineers capturing a carbonaceous asteroid. (something that is already being planned for) The mass of the asteroid could be consumed and re-worked to manufacture the cable, which is gently lowered to the ground from orbit.
    Let’s just hope nothing happens to snap the cable. Robinson writes that into the story, and it’s NOT something I’d ever want to see happen on Earth!

    • DangerOnion says:

      The cable is not the prohibitive issue. The issue of rotation is still there, and unsolvable. There’s no way to speed up the rotation of the Earth, and the centripetal force provided by the Earth’s rate of spin is not enough to be useful.

      • Willy the winks says:

        I’m not going to dispute your calculations but unfortunately you’ve misapplied the math. A space elevator doesn’t require any centripetal force to hold its position. It maintains its position because it’s center of gravity is in geosynchronous orbit. Think of it as a very very long thin satellite. To build one, you start with a satellite in geosynchronous orbit. Then, for every kg of elevator spooled out below an equal amount of counterbalance must be spooled out above. Always keeping the center of gravity at the geosynchronous altitude. Eventually, the lower edge of your elevator would just kiss the surface of the earth. Actually, if desired you could stop just a few meters short of the surface but then you would need a step ladder. Sure, there would be huge engineering obstacles to overcome but the billions of tons of materials and forces required suggested in the original article are orders of magnitude too much.

      • DangerOnion says:

        You’re sort of right, if we’re only talking about a stable orbit. A stable geosynchronous orbit is technically an equilibrium between centripetal force and gravity. But we’re talking about moving cargo. The typical cargo payload of the Shuttle was roughly 50,000 pounds. That means that there has to be enough extra weight spooled out away from the earth/moon to hold that up, and the force exerted by that weight is proportional to the speed of rotation. And the moon just doesn’t spin fast enough.

  2. beachcomb says:

    I quite like looking through a post that can make men and
    women think. Also, many thanks for permitting me to comment!

  3. Willy the winks says:

    I agree that the company/website/kickstarter page you mention originally is a pipe-dream and possibly fraudulent. However, on a theoretical level, it’s theory appears to be sound (in fact they are just regurgitating orbital strategies from the 50’s 60’s and 70’s). What they are proposing is a Lagrange elevator. The Lagrange points proposed are stable orbital points in their own right and an elevator would work in pretty much the same way as a geosynchronous elevator. One would park a satellite in the L1 or L2 position and spool out ribbon towards earth and the moon simultaneously. Again, as long as the center of gravity is kept on the Lagrange point the elevator is going to be stable. Lunar spin (or lack of) doesn’t impact the elevator in any way, no spin required. The suggestion that the counter weight be placed at the 190000km mark is a matter of orbital convenience as it coincides with an important orbital transfer point.

    • DangerOnion says:

      That won’t work either. There’s no way to anchor a satellite at the L1 position to both the Earth and Moon, as the Earth is still spinning relative to the moon. Anything anchored to the Earth would have to be geostationary, and the Lagrange points are not. It is impossible to tether any point on the surface of the Earth to something at any Lagrange point. L2 is even worse, as the Moon would then be directly between the Earth and the satellite. It would obviously be impossible to connect the L2 point to the Earth, and the moon’s wobble would preclude any attachment to its surface either.

      • Willy the winks says:

        Hey DangerOnion.

        Just want to start out that I do enjoy discussions of this nature and that is all I intend here. Sometimes these anonymous online conversations escalate unnecessarily. I have no desire to piss anyone off. This is your sandbox…if you want to end the discussion just let me know and I’ll scuttle off.

        It is true that there is no way to directly tether the earth to the moon because they are not both tidally locked. The earth spins some thirty times too fast. No serious lunar elevator ever proposes this. The lunar elevator proposed (by me, many scientists and our goofy friends at lift-port) does have the lunar end anchored but the earthside end just dangles, hanging deep into the earth’s gravity well. Ideally, the near earth end is positioned at a convenient orbital transfer point.

        The whole earth to moon system would consist of two elevators and a small fleet of transfer vehicles. A transit from the earth to the moon would begin with a ride up the earth elevator to geosynchronous orbit, it would continue further up the elevator to the counter-balance end station. The counter balance end station would be able to provide the payload an extra boost of delta-V. Using the extra velocity from the end of the elevator the payload, in a transfer vehicle, it would be able to transit the distance to the near end of the lunar elevator. Finally, the payload could descend the lunar elevator, past the Lagrange point, all the way to the lunar surface (in one model, directly to one of the lunar poles).

        The whole system is pretty elegant…a minimum of mass, a minimum of energy expended. As I suggested above, there is a whole host of engineering obstacles to overcome but none seem impossible. The lunar elevator seems especially promising because the lower gravity of the moon allows for current levels of technology…we’re not waiting for new technologies to be invented.

        The idea of an L2 lunar elevator is usually reserved for flinging payloads deeper into the solar system. Launching from an L2 counterbalance end point should provide a nice delta-V kick for payloads destined for mars or the outer gas giants.

        I had read an interesting paper a few years ago on an earth based elevator. I couldn’t find it again tonight, unfortunately. However, I did find this link at the NASA institute of advanced research http://www.niac.usra.edu/studies/472Edwards.html It’s about a 100 pages long and I just gave it a read. Around page 45 there’s an interesting image of using multiple elevators for an earth to mars payload transfer. Similar in nature to the earth moon dual elevator configuration I describe above.

        I’m an avid consumer of science fiction and after reading about space elevators years ago, it became a pet research project of mine. I’m currently re-reading the works of Kim Stanley Robinson and my interest in space elevator technology was re-ignited.

  4. Samuel Williams says:

    What about putting a space cannon on top of it? Maybe another facing the other direction so the cable isn’t toppled. There’s your lateral acceleration.

    Less energy efficient than going the same distance with rockets, but when you get to that altitude the atmosphere doesn’t prevent technologies that rely on a large initial velocity with air resistance. And maybe some balloons attached to counteract the weight, inflated at altitude so your material doesn’t burst and your balloon density can get periodically lower.

    I haven’t done any math on this next idea, but I’ve heard the idea floated that it may be possible to use energy from earths magnetic field to generate electricity, considering you have a giant conducting wire thousands of km long.

    • DangerOnion says:

      The cannon idea might work, but you still have to generate kinetic energy from chemical, which is what rockets do, so I doubt it’d be more efficient to fuel a cannon than to fuel a rocket. The balloon idea won’t work, unfortunately. Balloons pull “upward” because they’re buoyant. It’s a matter of density; they’re lighter than air, so they pull away from Earth’s gravity. There’s no atmosphere at 26,000 miles, though, so there can’t be any buoyancy.

      I’d never heard of the magnetic field idea, but the fundamentals are sound. There’s energy there, I just have no idea how much or how hard it would be to get to it.

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