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Japan starts space elevator experiments (electronicsweekly.com)
447 points by Futurebot 6 months ago | hide | past | web | favorite | 286 comments

It's unclear to me if this is real or the continuation of a publicity stunt from Obayashi (who has been getting press about their plans to build a space elevator for years).

I'm as excited about the theoretical concept of a space elevator as anyone. But the problem remains that no one can produce a cable even close to strong enough. This article has a good description of the material science problem: http://www.spaceward.org/elevator-when. Basically, we would need to find a material that is at least 10x, probably 25x as strong as any cable today.

Carbon Nanotubes are theoretically strong enough, but no one knows how to manufacture them. The longest carbon nanotube tether that has ever been manufactured is only a few inches long, a millimeter in width, and not particularly strong due to imperfections in the manufacturing process.

Obayashi is planning a 10m cable. Even building a 10m cable made of carbon nanotubes would require a Nobel Prize worthy breakthrough.

The fact that we are talking about a japanese company called Obayashi making a carbon nanotube elevator to space is very cyberpunk to me.

Reminds me of Ono Sendai making wetwire jacks to the internet.

Makes me think of Gunmm/battle angel alita

I agree on the publicity stunt feeling. Space elevators are thought-provoking stuff of science fiction. It would be fantastic if we could build them.

Most I've read on the subject (this article included) are very thin on details, or point out the great scientific hurdles and breakthroughs that still need to be overcome / made.

This article made me think of the publicity stunt some years ago to build a mountain of 3,560 feet high in The Netherlands for $432 billion. The stunt was taken seriously and became world news:


If this is indeed a PR stunt I wonder if it would reflect positively or negatively on Obayashi? Would be like proposing an unrealistic, probably under-priced project. Of course they don't say when it can be realized..

There is a very good youtube channel by Isaac Arthur where they look at different options.

There is better stuff like the orbital ring which looks very expensive but actually feasible with current technology.

I watched that entire video on space elevators - very fascinating.

We're only 1 to 1.5 orders of magnitude away from having a material strong enough? Maybe I've been working with computers for too long, but that sounds excitingly achievable.

Yeah, just wait 6-7 years and Moore's law should take care of it.

Okay, that's a joke people. There's no moore's law for carbon nanotube extension (that I know of). There is an analog of electric battery price reduction over time, about 15-30% per year. Here's a graph of it - https://electrek.co/2017/01/30/electric-vehicle-battery-cost....

Of course whenever we see a little bit of a pattern, we use a little bit of our ability with this language called math, and declare a law. Calling it a short-term pattern that may or may not continue into the future wouldn't help us feel smarter than the other people in the room.

Yet it somehow helped you.

Material science is tough. Check out engine/turbine material science developments. It can take >decade to get new materials into planes.

Yeah but isn’t that because aviation is an extremely highly regulated industry?

Those regulations are there for a reason. Safety is important. You don't want your space elevator climbers to fall down. A ripped cable would also be a pretty expensive accident.

Imagine untangling it.

<spoiler> Stanley Kim Robinson has very colorful description of space elevator falling on Mars. Basically it should loop around the planet accelerating during the fall, likely supersonic in the end and flatten everything in its path.

As a rule, the aviation industry auto-regulates first, and government regulators come later. That's the patter on most of the changes.

So, not really. It's a highly regulated industry, but this is not the bottleneck.

A space elevator seems like a much better concept for the Moon. If we could make a permanent Moon base with a space elevator, then it would be possible to use materials from the Moon to assemble things in orbit. Such a base would make it possible to start exploring the rest of the Solar system in earnest.

Launching from the Moon is cheap - magnetic rail and solar power can do the job and cut the need for propellant significantly and there is water enough to make e lot of propellant for delta-v's you'll need. With all that slack, we can relax a bit with mass and use simpler techniques to build ships. A lot of 3D printing and automated manufacturing.

On the not-so-bright side, we'll have to develop new metallurgy and other industrial processes based on local chemistry.

Where would the counterweight have to be for one end to be in high Earth atmosphere, balancing atmospheric drag with lift and gravity? My math tells me the end would be traveling at a relatively tame 260 kph.

Putting an elevator (or more likely a sky hook) at a lunar Langrange point makes some sense, because the tether doesn't have to reach the entire distance if we allow for 0.2km/sec injection/drop-off speeds. That's important, because lunar elevator/hooks are much longer than earth based equivalents, even though their strength and taper ratios are much more achievable (e.g. polyethylene 4:1). You'd want to keep launched weight for the tether as low as possible.

A huge advantage is that a hook at the far lunar Lagrange 2 would be very close to escape velocity (e.g. asteroids or GEO).



Article says they are going to use a steel cable.

Where did you see that? I see this in the article: "Carbon nanotube is the most likely material to be used for the cables."

A steel cable would have far too low a strength to weight ratio to work in a space elevator.

The first paragraph in the article says “…aim to launch two small (10 sq cm) satellites connected by a 10m steel cable from the International Space Station.”

The part you quoted refers to the material that might be used for a 96,000 kilometer cable.

This isn't the first such experiment (with tethers in space) but previous ones (such as the Shuttle tether experiments from 1996 onwards: https://www-istp.gsfc.nasa.gov/Education/wtether.html ) discovered some unanticipated and terminal problems ... and as they flew aboard a time-limited Shuttle mission there wasn't really any scope for attempting repairs/fixes on orbit. Also, it's arguably obvious with 20/20 hindsight that trying for a 20km long tether on the first experiment was maybe slightly over-ambitious ...

I'm curious about space elevator phenomena related to lateral ∆V.

At Earth's equator (zero altitude - i.e., on the ground), an object moves spinward at about 0.46 km/sec. In geosynchronous orbit, an object has to move at about 3.07 km/sec.

A space elevator car ascending from stationary on the equator to a terminal at geo altitude would require a tangential (lateral) ∆V of 2.61 km/sec. This is in addition to the energy needed for ∆ altitude-related potential energy change. Am I thinking about this right?

The faster the ascent, the greater the lateral reaction force on the elevator because ∆V/time increases. Has anybody done that model? I didn't find anything in a brief search.

The lateral ∆V also suggests it could get windy on ascent because the atmosphere rotates with the earth on a macroscopic basis. Maybe later tonight, I'll calculate lateral wind velocity as F(altitude) and see if I can fold in pressure drop to get wind pressures as F(altitude).

I would love to see even a prototype attempt in my lifetime.

(In case you were unaware, this is the Coriolis force)

But this is the vertical component of the Coriolis force, which is usually negligible. Yes?

I’m not sure but I think since angular momentum is conserved, and angular velocity remains constant at all distances to Earth’s center here, then there will not be any lateral forces due to Earth’s rotation about its own axis.

While total angular momentum is certainly conserved in any rotationally invariant system (read: Earth + space elevator + objects traveling upwards + atmosphere), the situation only for an object traveling to space in the elevator is different:

Angular momentum is given by

L = I * ω

where I is the moment of inertia and ω is the angular velocity. Let's assume that we put the internet (https://m.youtube.com/watch?v=iDbyYGrswtg) into the elevator and ship it off to space. Let's also say that the internet has a mass m and is of negligible diameter compared to Earth's radius. Clearly, its angular velocity ω will stay constant, assuming that the space elevator was built perfectly straight and perpendicular to Earth. However, the internet's moment of inertia I = m r^2 will not stay the same but increase quadratically with its radial position r and its angular moment will thus have to increase, as well. If you take the initial radius to be Earth's radius (~6,300km) and the final radius to be the geostationary orbit (~36,000km), the quadratic dependence will give you an enormous difference in angular momentum which will have to be accounted for by some torque that we apply to the internet.

It doesn't matter where this torque comes from--for instance we could imagine the internet to have some kind of jet propulsion engine, where the emitted gas's angular momentum would exactly match the internet's change in angular momentum, so that total angular momentum is conserved.

Moreover, it could actually be a small torque, provided that we move the internet at a small velocity in the perpendicular direction. (Recall that the change in angular momentum is given by the integral of the torque over time, so the smaller we want the torque to be, the slower we have to move the internet and the longer it will take the internet to reach its final position.)

Now what happens if we don't provide said torque? Recall that I assumed earlier that the angular velocity ω of Earth and the elevator (and thus the internet) be constant. If we don't provide the mentioned torque, moving the internet upward will increase the moment of inertia of the system Earth + space elevator + internet due to more mass being located farther away from the axis of rotation. By conservation of angular momentum L = I ω, the entire system's angular velocity then has to decrease, similar to a figure skater stretching out her arms while rotating in order to slow down. All this assumes, however, that the space elevator's cable is completely rigid in the lateral direction and doesn't move under the effective torque it will feel as the internet moves upward. In practice, however, this will not be the case unless further measures are taken which counter the effective torque on the cable and keep the cable perfectly perpendicular to Earth. (Only then Earth's rotation will actually slow down under the backreaction.) This seems somewhat difficult to achieve, though, and I think the better way would indeed be to equip the internet with a jet propulsion engine which provides the necessary angular momentum.

[EDIT] Made the part about backreaction on Earth and stability of the space elevator a bit clearer.

> Let's also say that the internet has a mass m

silly, the Internet doesn't weigh anything! ;-)


That's from 2011. It probably weighs at least one watermelon by now, given Netflix etc.

Seriously, the whole description became needlessly opaque by using the internet, of all things, as the example.

Wouldn’t payloads travelling up the space elevator and departing for the rest of the solar system and beyond ultimately deprive the earth of angular momentum and send it hurtling towards the Sun?

Not hurtling toward the sun, but payloads traveling up the space elevator would slow the Earth's rotation (the 24 hour daily rotation about the Earth's axis) in the same way an ice skater spins slower when they spread their arms.

When the payload detaches from the elevator, the angular momentum of the Earth about the sun does decrease (some of the AM goes with the payload) but the mass of the Earth also decreases, and the angular velocity of the Earth about the Sun doesn't change.

>the angular velocity of the Earth about the Sun doesn't change.

It does if your spaceship escapes from Earth in a prograde[1] direction (equivalent to Earth throwing a ball forward, causing a retrograde reaction upon the Earth). This type of escape trajectory is necessary to reach any destination farther from the Sun (Mars, asteroids, etc). It's a tiny change obviously, but it's non-zero.

Note that returning from Mars/asteroids and aerobraking should add angular momentum, speeding up the Earth and at least partly counteracting this effect.

[1] https://en.wikipedia.org/wiki/Retrograde_and_prograde_motion

You're right, the portion of a rocket's exhaust that is recaptured by the Earth would raise or lower the angular velocity a bit, depending on direction, and gravity between the Earth and the spacecraft would have a tiny effect in the opposite direction.

Those are separate from the disconnect I was talking about; I meant a gentle disconnect after which the spacecraft remains in orbit.

It does remove some momentum from the elevator, and sends it down towards Earth.

The system is not connected to Earth, so it doesn't change the planet's orbit.

What about at the poles?

Seems like that would negate the lateral problems, but maybe I'm just introducing a twisting one instead...?

Then you have an enormously large tower held up by nothing but its own strength instead of being naturally pulled into space. Also takes additional delta-v to get satteliges into common orbits post release.

This is arguably more doable than cables. I've been told that it's completely possible to build steel structures several miles tall (and the main reason we don't is b/c elevators become a problem).

We can build massive steel towers (e.g. https://en.wikipedia.org/wiki/X-Seed_4000 would be 4km tall), but they would still be nowhere near space (one common definition of reaching space is https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line which is at 100km).

A space elevator would reach at least 36,000km to hit geostationary orbit ( https://en.wikipedia.org/wiki/Geostationary_orbit ). Most designs are even longer, to provide a counterweight.

No known material could support a tower that tall (towers need compressive strength; elevators need tensile strength). It would need to rely on 'active support' or 'dynamic structures', like a space fountain ( http://www.orbitalvector.com/Orbital%20Travel/Space%20Founta... )

A friend of mine who studies engineering told me that masonry has infinite compressive strength meaning, in theory, it's possible to build monumental structures out of stone.

The base needs to be large enough to support the weight, so you get less of a tower and more of a mound (like the great pyramids).

We can get to about 9km using stone by climbing Mount Everest.

I think it would be the same ∆V requirement (for geosynchronous orbital altitude). But it's not possible to have a geo orbital plane (so the subsatellite point is stationary on the Earth) that is out of the equatorial plane.

What if the cable isn't radial?

Edit: And bowed, basically in equilibrium with lateral forces.

The Giant Space Wheel (of Seveneves) is so much more attractive than space elevator. That is a large mass on geostationary orbit having smaller pods rotating at the end of ropes. Those pods can be lowered to atmosphere and synchronized with earth rotation. Elevator pod comes down and can stay down maybe couple of hours and then jerked back to heavens. All energy comes from the sun - collected at the center station. Safe because pods can be quickly reeled back to space and stay out of atmosphere until conditions are optimal.

Another inteersting idea is an orbital ring - basically a rotating cable around Earth in LEO, which is accelerated by a maglev-train-like platform. The platform travels "along" the ring at high speed, but it can be made to stay "at one place" from Earth surface perspective (i.e. geostationary). The cable ring is rotated at orbiting velocity (or higher), so the centrifugal force counteracts gravity, keeping it in place.

Does it need similar cable strength as the space elevator (as mentioned elsewhere in this discussion), or are its requirements easier to hit?

The mass of the pod is much less than the end-station of the space elevator. So the cable can be very thin at the far end. If the cable is tapering smoothly it weights 1/4, but it need not to do that, I think it tapers in some kind of exponential curve. So 1/16 might be quite reasonable assumption, but one needs recent college education to calculate that. On the other hand there are strong centrifugal forces, as the pod speeds up from standstill, which is also vividly described in Seveneves book.

There is an exponential relation between the length of the cable and how strong a material you need for it.

It comes from the cable needing to support itself, not unlike the rocket equation that comes from the rocket having to propel its own fuel.

Seveneves is a great read!

For those looking for a popular culture examination of space elevators--albeit from a number of decades back--check out Arthur C. Clarke's The Fountains of Paradise. It also deals with some of the engineering issues, though again it's quite old.

Also the Mars Trilogy (Red Mars, Green Mars, Blue Mars) by Kim Stanley Robinson.

Honestly that's my favorite Sci-Fi novel series of all time. Just give Red Mars a try and I prosome you won't be able to put it down.

Given a major plot arc in the trilogy was...


... the destruction of the space elevator by a terrorist organisation and the consequent destruction on the surface of Mars as the cable, released from its counterweight, wrapped itself around the planet... I’m not sure it’s a great example :-)

To be fair, the "terrorists organisation" was not called like this in the book and was just shown as one party in the war of independency from earth. And the elevator was controlled by earth and brought down earth troops who hunted down the resistance. So you can argue it was a valid military target ... terrorist(in my definition) target civilians. They just acted very rughless.

But I liked in the book, how it did not actually took sides, but just showed the implications of what violent struggle/war for independency on mars means for different sides. And mainly from the perspective of Nadia, the engineer who build things. And she sees everything just gets destroyed and smashed. (I got moved a bit by the memory)

On extraordinarily rare occasions, mankind has been known to learn from cautionary tales.

Gave it to my father after reading it. He thought it was too slow and didn't have enough of a narrative arc, and he opted not to finish reading.

I loved the trilogy, though.

It is really slow in places. Robinson loves to flesh out the environment of Mars. Beautiful trilogy, really enjoyed it, but it is an occasional slog.

my Dad totally got into it, we read pretty much everything KSR wrote... :)

I enjoyed Red Mars. At some point I stopped with the rest of the series. Should pick it up again from the beginning.

The Three Body Problem Trilogy (officially named the Remembrance of Earth's Past trilogy) by Cixin Liu goes into space elevators a good bit. The Three Body Problem sets up the technology involved, while the other books develop the subject further.

> "...six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, ... eight days ...."

Whooooa. Let's think about this for a second. Eight days means people need to sleep (and not just sitting up in a chair, no matter how comfy). At 1m x 2m per bed that would be a 15m x 4m space even without aisles to walk between the beds or down the middle or any sort of privacy separators. Also, a bathroom and actual washing facilities of some sort are mandatory, and a kitchen with at least minimal food-prep capabilities (even if it's mostly pre-made); modern airplane galleys only need to deal with trips in the tens of hours.

18m x 17.2m is really really not a lot of space for all that.

Seems doable, to pick a random example: https://en.wikipedia.org/wiki/HMS_Endeavour 30m long, 8.9m beam, complement of 94.

six oval shaped cars with those measurements each is about 780 square meters in total. The average Tokyo condo is about 65 square meters (for a family of three). Somewhat unpleasant for 30 people but not really that small. Like 3 people in one Tokyo apartment density wise.

”Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, connected by a cable”

I can’t see how one would read that other than as each car holding 30 people.

You would need an extra comma to make it six cars holding 30 people in total:

”Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m, holding 30 people, connected by a cable”

I read it as the entire elevator carrying 30 people, and this article seems to confirm it (https://www.zmescience.com/research/japanese-space-elevator-...)

Having 30 people in one car including gear, provisions and sharing sanitation seems absurdly small if not logistically impossible

But the original sentence is ungrammatical either way. Under your interpretation there’s still a missing “and”: “each measuring 18m x 7.2m and holding 30 people”.

The missing "and" is a tiny grammatical error, whereas the missing "," Someone mentioned is a large grammatical error. Tiny grammatical errors are OK -- language grammars change over time because many people start making the same tiny grammatical error until it becomes part of the accepted grammar of the language.

to be safe I would suspect any one of the three cars must be able to support all persons on the trip. they are pretty much of out reach of help shortly after leaving.

it might be interesting to see what type of personality tests them use before allowing anyone to actually board one of these should they ever come into existence.

It's an elevator to _space_. There are going to be some comfort compromises, especially on these early iterations.

Comparing to a typical submarine, it's three times as much space per person. Submarines typically have 30 square feet pp, 18m x 17.2m for 30 people is 93 square feet.

7.2, not 17.2, so about 46 sqft per person. Point taken, but if a submarine is the point of comparison... yeah, that's really really not a lot of room.

8 days of uncomfortably close quarters on ascent may be a good way to psychologically prepare folks for a perhaps slightly-less cramped orbital experience.

You forget this is Japan, where tons of people sleep on trains almost every day - often on their feet.

Not to mention the existence of 'capsule apartments'...

There's one practically derelict building of capsule apartments, it was a failed experiment. Capsule hotels are a thing, but not apartments.

Don't actually need much for 8 days. Provide video games, pizza, and a relief tube. People do it all the time.

Hey, Stephenson had people living long-term in spaces that size, in Seveneves. That didn't turn out so well, but eight days isn't that long.

Tube beds could be close packed, and people could sleep in shifts. Also, one can survive just fine with just a washcloth and towel, and a source of warm water.

Beds can stack.

Astronauts wear diapers, painfully lose their fingernails when working in spacewalks. Having to bunk in submarine style accommodation for little over week is nothing.

okay i had never heard of the fingernail thing. that sounds awful. I wonder if later designs helped? My immediate thought is: fill those finger spaces with clay like material -- to spread the load across the whole surface of the finger, not just the nail.. but yowtch. glad I never chose that career.

How much space would they get on the ISS either ways? It'd be a good practice.

The end of this cable would be 36000km up, compared to the ISS's 400km. The first space elevator would primarily be used to shift stuff, rather than people at first - there's no point having convenient transit for people if they've got nowhere to go at the other end.

That's where the end of the cable is, but there's no rule that that's where anyone has to get off the elevator.

Interesting thought. Note that getting off 300 km up would not put you in orbit; you would lack the orbital velocity required for that. So if you get off there you'd have to burn around 8 km/s of delta-v, which is quite a bit of fuel to haul up.

For efficiency you'd want to go higher. There'd be a point much higher than 300 km where detethering would put you into a highly elliptical orbit where the periapsis is 300 km. Then you'd just have to burn retrograde to circularize. Off hand I'm not sure what the math for that would be but it should be pretty simple algebra.

Actually the cable will extend well beoynd that point. 36Mm is the altitide where the elevator would be travelig at orbital speed. Jump out any lower and you will drop back to earth. Unless you jump very hard (using rockets or something).

They’re not going to ISS, they’re going somewhere in geosynchronous orbit.

But it's still an apt comparison. People live for long periods on the ISS, and the amount of space isn't likely to get any bigger during their mission.

There is - and I don't mean to pun - plenty of space in space. Space stations could be quite roomy.

They'll be roomy just as soon as it isn't exorbitantly expensive to transport material to space. So, possibly sometime after this elevator is operational...

The slightly counter intuitive point is that you only have to transport wall material.

An inflatable "house" is conceptually completely possible.

Airplanes have to be small because of air resistance. Space stations have no such constraints.

Inflatable, sure, but not a balloon. Micrometeors/space junk are a threat, and more so for bigger inflated objects.

Yeah, the walls need to be strong enough. Whatever that means long term.

The mathematical argument of 2D vs 3D still holds.

Shouldn't we just knock the people out for the 8 day trip?

And how exactly do you plan to 'knock out' people safely for eight days, or even just a few? Heck, even for just a few hours without medical equipment and personnel?

I think the safety/ease of sleep makes people think anesthesia is about as easy to manage. In reality, it requires a highly trained professional to be monitoring 24/7, and even that involves very significant risks.

The medical technology for human stasis doesn't seem particularly unattainable, when compared against building a carbon nanotube tether into orbit. Some mammals are able to hibernate for months.

General anesthesia kills 1 in 100,000 patients, and that's with medical personnel standing by in actual hospitals, much less a skeleton crew of people strapped to a spacebound elevator.

We don't understand ourselves or our bodies anywhere near as well as we can understand or advance materials science. My money is on new cables before reliable stasis.

So far, for humans, that lives within same realm that warp drives occupy in science fiction.

No, we don't even know if warp drives are allowed by the laws of physics. We have a pretty good idea how to do hibernation: Saturate the tissue with some cryoprotectant and freeze it very quickly. The problem is that we don't have a cryoprotectant that is sufficiently non-toxic and we can't freeze anything as big as a human quickly enough.

Of course we know. Bend space and don't travel faster than light. We JUST need exotic matter of sufficient energy density to carry around.

Yeah and since nobody knows whether the exotic matter needed actually exists, we don't know whether bending spacetime in the required way is physically possible.

On the other hand, we can successfully freeze and thaw bunny kidneys.

And some way of resolving the resulting time travel paradoxes.

If bears were capable of warp drive, then I would agree with you.

If bears will be the ones to take space elevator trips, then we're set.

It’s cool that any kind of space elevator experiment is happening at all, but temper your expectations with the numbers: this is a 10m cable. It is literally a 1:9,600,000 scale model of a real space elevator.

This isn't a scale model of a real space elevator at all.

From the article: Shizuoka University and contractor Obayashi aim to launch two small (10 sq cm) satellites connected by a 10m steel cable from the International Space Station.

I don't see any ways in which this is a space elevator related experiment.

They're testing the cart pulley system in space. Sure, the cable itself is the core technology needed for this, but you still have to work on the rest of it. These nanosats are a good, cheap way to move the TRL forward a bit.

I actually wonder if that is the true purpose and not what the media glued together out of "thing moving on cable." It could just as well be a test for a space tether or cable centrifuge, with any space elevator research being a secondary thing

> using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people

Hmmm...is that 30 people/car or 30 people/6 cars? You will be enclosed with them on 18m x 7.2m, that's 120m², for 8 days!

The former case would sound like torture, in the latter case it could be done comfortably, though, but it would still require some good nerves by the travellers...

120 m² is a substantial 3- or 4-bedroom house. People endure a lot worse for much lower payoffs than going to space.

In spacecraft, Soyuz is about 6 m³ for three astronauts for two days. Apollo was 6 m³ for three astronauts for two weeks. The Japanese proposal is spacious in comparison.

30 per car

Given enough investment, Stirling engines could beat internal combustion for many applications due to a theoretical efficiency advantage. However, economies of scale and many decades of R&D give internal combustion such a huge advantage, that this probably will never happen.

At what point does the 20 year amortized cost of a system involving a space fountain or launch loop acting as the 1st stage of a vastly simplified and downscaled rocket break-even with some small multiple of the 20 year amortized cost of a space elevator? I suspect that this multiple might be small enough that economies of scale and optimizations of other systems could keep space elevators out of the picture forever.

ICEs gave us another boost in civilization, expanded the scale of our economies, which eventually led to enough R&D in electric engines that the latter are slowly but surely replacing ICEs now.

Maybe the same thing will happen here? The system you've described could open the Solar System for us, and time + advancements in in-space manufacturing could eventually lead to people building space elevators as an alternative.

(Also, Earth is not a good place to get the experience in building space elevators. The Moon is much better, and probably Mars would be a good candidate later on.)

Carbon nanotubes are cool, but i will believe space elevators possible once someone shows me a carbon nanotube rope i can climb with. I'd settle for a bike or motorcycle chain. A nanotube-based shoelace would be worth a noble prize or two.

Given strength and size and other properties that carbon nanotube ropes would need have... Wouldn't a carbon nanotube shoelace be like the worst idea ever? ...strong as a steel cable, but so thin as to be hard to see and handle. And brittle and not so good at bending. => First it slices up your hands when you tighten it and then it breaks when you tie it :)

I believe the expectation regarding carbon nanotubes in the sphere of space elevators is that they would be woven and layered into a sheet of human scale; these sheets would be used to construct a curved ribbon for the gondola to climb.

You could apply the same principle and weave a bootlace from them, but the limits of current technology would render that an exceedingly expensive bootlace.

Given the amount needed for a space elevator, it better be cheap as shoelaces. At 10s of thousands of miles they should have more than enough on hand to disrupt the shoelace market.

Its going to be very interesting when carbon nanotubes are combined with cloth.

Ripstop cloth is a mix of plastics and line giving a fexible cloth that is very very strong. Its also airtight so you can inflate it (for a time - its not 100% without a bladder)

Inflatables wings. Hulls.


On a practical note, if you drop something on your foot you need to be able to take your shoe off quickly - cutting the laces is often the best approach. Shoe laces as strong as steel would likely lead to you losing your foot.

Same goes for titanium wedding rings...

If you can biuld large enough nanotubes that you can weave them into rope, you can engineer in any properties you want. Anything from graphite dust to diamond is an option.

Fyi, the military has a specific way to lace boots so the laces can most easily be cut to remove the boot.

I don’t think rope is a good analogy for nanotubes. I think you want to see it used as a cable, like in suspension bridges or trawling. It should be something that is permanently under tension.

A nanotube suspension bridge would be pretty amazing to see.

It could be that shoelaces and space elevators turn out to be on the same side of some tipping-point technological breakthrough.

I’m guessing you mean to say carbon nanotube shoelaces.

But it’s amusing to think of it the other way: any society technologically advanced enough to have invented the shoelace will inevitably invent the space elevator.

We can already make CNT based fibers at scale fairly cheaply. Would happily sell you a shoelace for much less than the $1M that a Nobel prize comes with...


(Though note that this is not one long nanotube, but a macroscale fiber made by extruding micron-scale CNTs in a special way so that they align.)

I saw a bunch of people throwing out good sci-fi space elevator examples and had to drop a reference to the space elevator in Neal Stephenson’s Seveneves. The descriptions are epic and do a good job of giving a real sense of placiness to the result of truly enormous engineering.

Then let me drop a reference to Sundiver by David Brin, which is the start of the uplift cycle.

The elevator is by far the least interesting idea of these novels which center about a future where we have uplifted (given sapience) monkeys and dolphins. We are also trying to survive in an unkind universe where Earth is a third world political power that is making religious fanatics angry.

Google was reported to be looking into this a few years ago. And determined that there was no material strong enough at the time.


That aside, how might adversaries disrupt such an expensive and precarious venture? Seems a very hard to defend machine.

99% of the comments about this story online think that they're talking about making one NOW. They don't think they can do it now. They're starting initial research into a few isolated systems required to do it one day in the future when materials science and all the other aspects catch up.

It will take decades of R&D, but someone might as well start on the bits we can do now, like a system for climbing the tether (which this is, and it's being done purely in space).

Fair enough. We have to start somewhere. Perhaps a tether climbing rig will be be useful in future megacity skyscrapers.

The base tether point would need to be far away from anything! In the book Red Mars by Kim Stanley Robinson, one is placed in Trinidad and Tobago.

The most dangerous part would be slowly dropping the cable; lower it to the point where it could be pulled into a magnetic clamp -- without destroying everything in its path.

I know nothing about physics... but wouldn't the space station need to counter the cable tension?

Most theoretical designs that have been proposed would require a very large counterweight, e.g. a captured asteroid.

Or you just build the cable out beyond geosynchronous orbit. The further out your counterweight mass is, the more force it exerts, so, AIUI, the most mass-efficient way to do it is an extension of the cable.

The problem is how you keep the tether from dragging behind the orbit when you do that. Space elevators require a fairly delicate balancing act to keep the mass directly over the base of the elevator, otherwise they turn into giant slings.

The center of mass of the cable-counterweight system orbits at geosynchronous height. Also, the gradient of gravity will Stabilize the attitude in the desired orientation.

None of this should be construed as an endorsement of space elevators, though. They will never happen on Earth as it exists now. Over and above the material science, you have to clean out LEO of all satellites before you even start construction. It’s just a really dumb idea all around.

Could i interest you in a sling-on-a-ring architecture?


You build an orbital ring above the altitude of the LEO satellites, use non-synchronous skyhooks to pick up payloads from inside the atmosphere at an altitude that can be efficiently served by aeroplanes, and then fling them the rest of the way to geosynchronous or interplanetary transfer orbits by accelerating them along the ring.

I thought the base station would be a ship that can be moved to avoid collisions with satellites.

The satellite issue is why I don't think a space elevator as currently conceived will ever make it.

If you have a cable capable of holding a space station and counterweight, no satellite is going to stop it.

> If you have a cable capable of holding a space station and counterweight, no satellite is going to stop it.

A satellite impacting the tether will definitely "stop" it, in that it will, at the very least, melt an impact crater into it if the cable is wide enough to not be cut. It is unlikely that the cable will be that wide. I feel like a broken record, lately, but the dominant concerns of impact modeling at orbital velocities are (a) mass and (b) energy. Everything traveling at 8 km/s effectively splashes into whatever solid object it hits, both because the room temperature shear resistance of the materials involved is orders of magnitude less than the shears involved, and also because the kinetic energy is dumped into thermal energy, melting or vaporizing the materials involved. One tends to get results like: (https://www.esa.int/spaceinimages/Images/2009/02/Hyperveloci...) That link notes that pressures of 365 GPa are reached, and typical yield stresses of theoretical nanotube cables are around 100 GPa.

A carbon nanotube cable is unlikely to be more than an inch or two across at LEO. You need that kind of strength to beat the space-elevator-equivalent of the rocket equation, which governs the taper needed to get the cable to even support its own mass in Earth's gravitational field.

Fair point. I stand corrected (or at least, until I spend more time thinking about this myself, I’m much inclined to believe you have a much better idea than me).

further -> farther

i remember reading here on HN someone explaining why space elevators are not possible. I can't recall why, but he/she had very convincing arguments.

Anyone here remember that thread and can link it back here? Thanks

Kelly and Zach Weinersmith discuss space elevators in their book Soonish. The summary of the downsides is:

* If would need to be the most precisely engineered thing we've every produced just to stand a chance of being good enough.

* Because of that, it will be particularly sensitive to wear and tear. How the maintenance would work is an open question.

* It will probably attract terrorists like crazy.

* It needs to never get struck by lightning. It is a particularly attractive lightning rod.

* It generally should avoid bad weather. Whatever it is attached to on Earth needs to be able to move. When moving it you have to avoid not only the bad weather but everything in space, too.

* If the cable breaks, bad things could happen. Bad things can range from burning up in the atmosphere to it whipping around in space damaging satellites, or anything else.

I love the idea of space elevators, but I agree that it probably won't be practical on earth for a long time if ever.

> It needs to never get struck by lightning. It is a particularly attractive lightning rod.

Haven't buildings solved this problem with lightning rods?

On another note, I am personally fascinated by space elevators which is why I am somewhat interested in going back to the moon where we can build a space elevator with today's tech, avoid all of these problems, and have a large body of resources to build/fuel spaceships with.

Yeah, I've never seen a reasonable explanation for that either. If the car is a Faraday cage, and the cable is conductive and grounded, what's the problem?

The only thing I can think of is that all that energy unloaded into cable at once might ablate some of it, causing it to no longer be able to handle the tension.

The tether near the counterweight (in orbit) experiences the greatest stress. This means it needs to be thicker, which means more weight...which means more stress. The ratio at which stress/weight climbs is determined by density and tensile strength. Basically only one material we know of meets these requirements, and manufacturing at scale is far away.

Once you figure out how to make them en masse, now you have to figure out how to secure the strands into a bundle.

Less of a challenge than warp drive, but still...quite hard.


I'm not sure a space elevator is 'impossible' in the way that faster-than-light communication is. I suspect they argued that the engineering challenges will never be solved - which is a fair argument.

I think the argument was that we don't have materials that are stong enough and light enough and cheap enough at the same time.

IIRC Specifically there are no materials we can currently produce (at that scale) which would be capable of supporting the weight of the cable alone. Let alone cars that ride along it.

At least we now know the cabin dimensions with a precision of two significant figures.

The only other open question is whether it shall be painted in the same colour as the bike-shed.

"That [rocketry pioneer] Professor Goddard, with his 'chair' in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react -- to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools."

That's a colorful quote from a NYT editorial in the 1920s arguing that getting rockets into space would not only be impossible, but obviously so. When Musk announced his intentions to autonomously land and rapidly reuse rockets it was mostly dismissed. Certainly companies, full of world class engineers, that had been launching rockets since before he was born probably knew a bit more about what is or not possible than some programmer with an undergrad in physics and negligible real life aerospace experience, right? Then it became, 'We've looked into it already, of course. It's perhaps theoretically possible, but it's a complete waste of money and in way economical.' Then it became, 'Shit we're a decade behind technologically!'

There are a practically infinite number of ways for why any given nontrivial thing might not be possible, and quite a bit fewer ways that it can be possible. So it's generally quite easy to formulate compelling and intelligent arguments against the viability of something (not that my little paraphrasings above were intended to be intelligent). But these arguments are not necessarily as meaningful, or productive, as they might seem. Think of how much of our technology today would have seemed impossible, or extreme long-term future tech, not that long ago -- even to those most qualified to make such judgement. This of course does not mean anything is possible, but it does mean we'd likely be a much more backwards civilization if not for the headstrong visionaries among us doing what conventional knowledge told us ought not be able to be done.

i remember lots of engineering issues around the cable due to waves and twists..

Isaac Arthur thinks an orbital ring is a better idea:


He has other videos on ways we could get into space more cheaply, including by space elevators (which he basically doesn't think are feasible).

Let me quote Pyotr Makovetskii, the book "See the root cause" ("Zri v koren'" in Russian), from chapter 28: (http://n-t.ru/ri/mk/sk028.htm)

"And overall, such a tower is a diabolical invention. Rotating in equatorial plane it will knock off everything it encounters. And since any satellite orbit intersect the equatorial plane, sooner or later all satellites with orbit lower than the tower height will be knocked down. At the base of the tower will lay remnants of almost the whole cosmonautics."

I'd assume this closes naive discussions about space elevator, at least until the proponents will explain what they are going to do with the problem of hitting satellites. Yet I see this problem again and again with hardly any progress in this area...

Thinking about a "counterweight" orbiting a planet to which it is connected by a cable:

as the cable offers resistance to the planet's atmosphere, and as the planet's atmosphere is active/changing, the "thing orbiting" would still have to have an excellent aerodynamic shape to survive the planet's atmospheric effects, right? (as e.g. the lower part of its cable would probably soon or later be "pushed" by winds therefore initially speeding up the counterweight but lowering its altitude - and/or later after some iterations of push/pull generating maybe a slingshot-effect, sending it into a potentially full crash-course towards the atmosphere/planet's ground).

Geostationary orbit is really high. To say that it's well above the atmosphere is a huge understatement. If your counterweight gets anywhere near the atmosphere, it's already dead, everyone aboard is dead, the elevator is dead, a fair chunk of the earth's surface is dead, etc.

Centrifugal force would keep straightening it up.

Yes, but probably only in general (meaning only from a theoretical point of view without considering external forces)?

E.g. as soon as the cable has headwind (in the opposite way of the planet's rotation) the cable would slack off, the thing in orbit would slow down & lower its altitude (how much? Would it anyway have to always skim the upper atmosphere?) => then as soon as the cable gets tailwind the opposite would happen, with relative slingshot-effect.

For practical purposes the atmosphere ends at 500km altitude. The cable is going to have to be 36,000 kilometers long. Atmospheric effects are pretty much rounding error at that point - imagine trying to swing a 10 foot long pole by blowing on the first inch.

Just fantisizing here, but helium baloons go over 50km up; can this elevator cable be vertically supported by solar-powered helium-filled heat packs alongs its way, with horizontal stabilization of large fans blowing in oposite direction (lower atmosphere) and tiny rocket boosts in above-atmosphere region similar to how sattelites correct their orbits?

Just fantasizing here..

Ok, you're right from that perspective :)

Someone patented space elevators in 2015.


No comments...

Thanks for the link. I'm personally very conflicted about patents. In this specific case I classify it as a "speculative" patent => I'm totally against this it.

Patents should be allowed only for something that exists / can be demonstrated (which would ensure that patents are something somebody invested in, and therefore at least believed in).

I believe the patent for warp drive has been rejected due to lack of a prototype.

Yeah, I wonder if anyone has patented human teleportation...

Don't patents only have a 20 year lifespan? If you patent human teleportation, and nobody actually develops it in the 20 year life of your patent (a prediction which is highly likely to be true), then you've simply wasted your filing fees, made a charitable donation to the patent office (and your patent attorney).

Again, "teleportation" would be a "speculative" patent (you have thought about the concept but didn't present anything that works). Have thought and (re-)written again and again about it, but it's too complicated for me to express => I'm temporarily defeated, sorry folks :) - still love all your posts :) . Pls. don't give up :) .

I think in this case there's so much "prior art" that the patent would be invalidated at the first challenge.

An organisation capable of building a space elevatoren surely would have the resources to fight a patent troll... Or just pay up some royalties that likely will be insignificant in the overall budget.

I really like the space fountain concept: it's utterly ridiculous, but completely feasible. It also doesn't need to be as big as a space elevator to be useful (a partial space elevator wouldn't work); space fountains can be as big or small as desired, and applications like radio towers have been mentioned.

It would be nice to see even a metre long demo, which I imagine might be possible as something like a student project (4 coil guns exchanging ball bearings).

The experiment sounds great. But should this work and a real cable to orbit is built, what happens when the cable snaps!? Can such a structure be made failsafe?

Kim Stanley Robinson [0] explores some of the failure modes when bad actors are involved. Bad actors with serious weapons. People on the satellite end get flung off into space, the cable wraps itself around the equator, and people on the elevator had better hope that there are nearby spacecraft to pick them up.

[0] https://en.wikipedia.org/wiki/Mars_trilogy

There are various simulations of what may happen. Here is one that demonstrates what may happen if the cable breaks at various points.


In summary, if the cable breaks at the base, the elevator will fly harmlessly into space. If it breaks at the counterweight, a large portion of the cable (several thousand miles long) will collide with the Earth’s equator.

The piece that falls to Earth ends up wrapping faster and faster, this causes centrifugal force on the tip, increasing the tension in the ribbon. Often the ribbon breaks on its way down and some fragments go flying out of Earth's gravity well. I didn't expect this at all.

The space elevator would become a space whip. I wonder whether this has a use case, like getting hardened unmanned space probes to speeds required for interstellar missions, or just much faster missions to other planets in the solar system.

Space elevators can be used this way because once the tether goes beyond geostationary orbit the tether is going above orbital velocity. Go far enough and its above escape velocity. So you just drag a probe out far enough and let go and it will escape the gravity well.

Harmless, except for the passengers.

Some proposals include spacing charges along the cable to break it into small sections and enable it to come down more safely. Of course, this means lining your vulnerable cable with explosives, which seems like a bit of a design smell.

Physics would tend towards "No."

Assuming a catastrophic break near the upper end of the cable (before the counterweight), there's not much you can do to keep it from coming down.

Perhaps unless you decide to detach the cable at the earth end? You might be able to react to a break faster than the cable can fall.

Even if you could react and cut the cable in 1 ms, if the counterweight is disconnected, the rest of the cable is coming down to Earth.

Depending on what it's made of, a break in the cable wouldn't be instantaneous, but happen in stages. Perhaps cut the earth end at the red alert stage up top.

That's what safeties are for! We already have a lot of engineering around making elevators safe. TLDR the elevator will clamp on to the rails to slow the free fall. Neat info below on snapping elevator cables and some of the things that would help you. https://science.howstuffworks.com/science-vs-myth/everyday-m...

What rails? They're not going to run more than one of these difficult-to-build structures up for each elevator. There will be a single cable, and the car will climb it. What happens if the cable snaps will depend on how far up the car is. Low enough, and it will descend to the surface on a builtin parachute. High enough, and it will perform some portion of an orbit, before descending on its parachute.

Once you have a space elevator, it’s relatively easy to send up some rockets and demolition explosives that just sit on the cables at appropriate locations and stay there waiting for a disaster; should the cable be broken by malice, accident, or natural causes, the explosives can cut the falling cable into pieces small enough that the rockets can safely guide to the ocean (or orbit, whichever has the lowest delta-v).

The travel pods, likewise, can always have rockets on them whose sole purpose is to get the passengers to safely. Yes, it means you’re taking up more mass than you strictly need to, but the great thing about a space elevator is that the mass is no longer a hyper-critical parameter.

But yes, no rails here.

Presumably you could have redundant cables. But two almost adjacent cables would still be exposed to many single points of failure, especially any caused by a deliberate attack on the system.

And just a cable falling could be a significant disaster by itself.

The rails? The car will travel over a stationary structure, not be pulled up by a pulley like a conventional elevator is. So it is failure of that stationary structure that we are talking about.

I don't understand how a space elevator would be advantageous in terms of the energy required to get something to space. The load still has to reach orbital velocity.

Will the station at the end of the tether still need a rocket to deal with the additional mass? Is the fact that this rocket only has to go up once the core advantage?

Wouldn't the load going up the elevator pull the tether to one side?

Since rockets lack infinite thrust, they take a finite amount of time to reach space. While they're doing so, they need to fight gravity -- ~all the thrust that's directed downwards, as opposed to horizontally, is wasted energy.

There are more reasons to build a space elevator, but that's a big one. It really would be far more energetically efficient.

The big problem with rockets is actually that you have to carry your propellant with you, and progressively waste energy accelerating your own propellant. Finite time or limited thrust don't actually affect this (increasing the exhaust velocity does though -- at the cost of energy efficiency). It's the infamous tiranny of the Rocket equation (https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation)

To get near 100% efficiency, it follows from the kinetic energy formula and conservation of momentum the body you're pushing against must have a much larger mass than you[1].

So discounted exotic phenomena, the only way to travel efficiently through space is to push off a very large mass, departing at full velocity, or in the case of near-Earth travel, simply push Earth.

The space elevator is essentially an elaborate staircase. It is in a stable equilibrium, and climbing it doesn't steal energy from the counterweight (which in fact doesn't move in fact because it is in constant tension); you're just pushing Earth away.

In the grand scheme of things the very low efficiency of maybe 10% (in my guesstimation) to LEO isn't so bad (not even the maybe ~5% interplanetary efficiency); especially considering the costs of space systems in general in comparisson to fuel cost. This small fuel cost makes reusable rockets quite an attractive option near term (as noted by SpaceX).

But long term, that's quite a steep inefficiency. If we were to endeavor large scale colonization or exploration of exoplanetary resources it seems to me either a kinetic launch system or at least a space elevator variant would be a necessity.

[1] Derivation: M1 v1=M2 v2 => v1^2 = (M2/M1)^2 v2^2; M1 v1^2 + M2 v2^2 = E => M2^2/M1 v2^2 + M2 v2^2 = E; M2 v2^2 (1+M2/M1) = E => K2 = E/(1+M2/M1).

As M1->infinity, all the kinetic energy goes to K2 and none to K1 (which is why you don't give Earth any meaningful energy by walking).

The advantage of going up by pulling oneself up on a space elevator over pushing oneself up with a rocket, is that one doesn't have to push oneself up with a rocket.

The tyranny of the rocket equation! The energy use of a rocket isn't just "how much energy is needed to have that kinetic energy and that potential energy", but also includes the energy needed to lift and accelerate the fuel used to provide that energy, as well as the fuel needed to provide that energy, as well as the ... and so on.

Isn't the rocket equation just a momentum equation? Does it escape that? If we brought something up, would we not pull the satellite it's attached to down, requiring more momentum from somewhere?

No, the elevator has counterweights at both ends which each pull on the tether more than the object being moved due to gravity and centripetal force. The object on earth pulls more though which keeps it tethered. The elevator that is moving than exerts extra force to propel itself up but not more than what would drag the top counterweight down, thus, the rope still stays fully extended.

Think of it like holding a rope tight between your arms and putting a robot that moves on it but ends up not exerting enough force to cause it to slack. Your arms (earth/space teather and the in space counterweight) and the object being moved would keep the same overall motion between all 3 objects (your body would just turn).

The space elevator is similar except earth is way more massive than the object being moved so nothing really changes. Also, due to gravity, you have to expend extra energy to move from the bigger object (earth) to a smaller object (space elevator counterweight), aka, the minimum energy cost of moving things out of gravity wells.

If by "Does it escape that?" You mean "would a space elevator not be subject to the rocket equation?", then yes, it would not be subject to the rocket equation.

The rocket equation is about reaction mass that is carried by the thing expelling it. It does not apply to climbing a rope, nor does it apply to the flight of a helicopter.

Regarding pulling the satellite down,

Pulling down on the weight at the end is something we have to do anyway to keep it from flying out away from earth.

The station at the end is in orbit, so it's the difference between trying to climb a ladder to the Moon, and trying to jump to the Moon.

At the risk of being too pedantic, a rocket is much more like farting yourself to the moon than like jumping. The benefits of ladders remain.

A rocket is heavy because it has to carry all its own fuel. A space elevator does not.

I think the advantage would be that you only have to deal with dynamic forces the static force of gravity would not be a problem. The diffrance between a bridge and a helicopter.

Maybe the required energy would be sucked out of the earth's rotation, but that seams insane.

There are two types of energy at play here: the gravitational potential energy and the kinetic energy of the orbiting object (necessary to maintain an orbit).

As you climb the cable, the force of gravity pulling you back to earth decreases, and the centrifugal force pulling you away from earth increases. The difference between these two is the force you need to provide to climb the cable.

I believe you are correct for tethers much shorter than geosynchronous orbit. Below geosynchronous orbit, the force of gravity is higher than the centrifugal force. Therefore, an object climbing a space elevator will have to provide energy equal to the integral of the difference between the centrifugal force and the gravitational force across the distance traveled. The remaining energy (the remaining gravitational potential and the kinetic energy of the orbit) will be leeched from the orbiting counterweight (requiring the counterweight to have a rocket to maintain orbit, as you suggested)

For tethers that extend beyond geosynchronous orbit, it is possible to for no energy to be removed from the counterweight (instead, all the non-climbing energy will be taken from the rotation of the earth). Imagine that we place a counterweight on a tether beyond geosynchronous orbit. This counterweight and the earth it form an orbiting two body system. The tether will be under tension (the force necessary to keep the counterweight in synchronous orbit) -- let's call that force T. A climber that scales the tether will exert some force T_1 on the counterweight, pulling it towards the earth. However, as long as T_1 is less than T, the counterweight will remain where it is. The force of the table on the earth will become T_2 = T - T_1. In other words, a portion of the force necessary to keep the counterweight in orbit will now be applied by the climber instead of by earth. The energy that the climber must apply is the same as before, but the counterweight is not affected. The remaining energy, by process of elimination, must come from the rotation of the earth.

Geosynchronous orbit is 42 km from the center of the earth while the ISS orbits 7k km from the center of the earth. I expect the experiments are being done at the ISS for convenience rather than from a plan to build a space elevator to the ISS. The article also cites speed and distance numbers that imply reaching a geosynchronous orbit.

To answer your questions more directly: 1) below geosynchronous orbit, yes. 2) No, the ability to extract energy from the earth's rotation is the main advantage. 3) Yes, but for a counterweight beyond geosynchronous orbit, the tension on the tether will pull it vertical.

Geosynchronous orbit is 42 km from the center of the earth while the ISS orbits 7k km from the center of the earth.

...although I'm not sure that's right either. The point is that anything 42 km from the center is still very much inside the earth.

Sorry, dropped a k on that 42. Should be 42k km. Though there are clearly no calculations here, using the distance from the center of the earth is standard for gravitational calculation. It makes more sense to say that the ISS is 7000km/42000km=1/6th of the distance to a geosynchronous orbit than to say it's 400km/35000km=1/90th.

How does the load have to reach orbital velocity? I think there is some disconnect here..

If they could do it would be so cool, and another one of Arthur Clarkes ideas turned to reality after Geo Stationary satellite.

I will file this next to graphene, where these pursuits do everything in our wildest dreams except exit the lab.

I'm a bit confused the ISS is only 408km from the earth's surface so why would it take 8 days at 200kph? Unless they are including the speed of orbit in which case the earth is already rotating at 1600 kph. What am I missing here?

My bad, missed the explanation below, go synchronization requires a much further distance than the iss. So I guess they will also have to make a new station or shuttle system to get to the iss.

Getting from GEO back down to LEO would require pretty serious energy to reduce your altitude. You could possibly get off the elevator early, but you would need to then get up to orbital speed for whatever altitude you're at, which would be non-trivial for LEO.

The ISS will almost certainly be decommissioned by 2030 anyway, and we're not going to have a space elevator by then. There'll still be other stuff in LEO that we want to get to though.

They said the tetger would be 36,000 km. 36,000/200kph = 180 hrs... 180hrs/24hrs/day = 7.5 days.

Why the tether needs to be 36,000km long wasn't mentioned.

In terms of angular speed (e.g. revolutions per minute), lower orbits are faster, higher orbits are slower (think of a Mercury year versus a Neptune year).

The ISS circles the Earth every 92 minutes. If we dropped a cable from the ISS (or another satellite at the same height), the anchoring point (e.g. something like a floating oil platform) would also have to circle the Earth roughly every 92 minutes. That's not feasible.

Satellites at 36,000km circle the Earth every 24 hours, which is the same speed that the Earth rotates. If the satellite is orbiting around the equator, going the same direction as the Earth's rotation, then we would not have to move the anchor (the Earth's rotation would do it for us)

it's the height above earth's surface for a geostationary orbit.

All this talk about nanotubes, when the real question is:

What kind of music are they going to play on the way up???

There was an interesting talk about space elevators at the 33rd chaos communication congress https://youtu.be/EtMJgEggVWQ

I like the start the small and ramp up method they are using. This should get plenty of investors mouth watering if they can prove it works and can scale

My favourite Space Elevator concept was from the Halo franchise.

There would be multiple elevators on the continents of the planets that were tethered to orbital platforms.

They didn't seem to survive the covenant well



How can the forces exerted by weather patterns still make this viable?

I wouldn't like being stuck in that elevator!

If they build this from japan, how would they deal with earthquakes ? Last thing you want is to be flying off to space in 18 x 7 m car


> Obayashi envisages a space elevator using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, connected by a cable from a platform on the sea to a satellite at 36,000 kilometers above Earth.

36000 km is GEO, so it would be near the equator, away from land and safe from quakes.

Pretty much all approaches I've read about involve building 'top-down' from orbit, often with the earth end meeting an ocean going platform which would allow for a bit of movement in the cable.

So many dumb major tech projects. Don't take your ideas from sci fi authors.

Maybe so, but can you please not post unsubstantive comments to HN?

It's substantive, pointing out there are many major tech projects these days based on pipe dreams born of sci fi books. The fact there are so many means either our tech leaders are not very smart, are scamming the government funds, and/or are out of good ideas. Which leads to the bigger question, what has happened to our vision for the future?

I believe you that you had those words in mind, but they're not what you posted.

Well, I appreciate you civilly correcting me, which you seem to have a good history of doing, so I apologize for my tone.

The cars would travel at up to 200kph and arrive at the space station eight days after departure from Earth.

These early cable experiments are important, but someone should also be working on the composing an 8 day Elevator Muzak score that won't drive you insane.

I think copyright won't apply after the first half hour.

Enforcement might get interesting since jurisdiction will be a question. The RIAA and MPAA will probably be the first two organizations to have extra-planetary legal claims.

I'd pick Max Richter. His Sleep¹, which is nearly 8.5 hours, would be a good start.

1: https://en.wikipedia.org/wiki/Sleep_(album)

I'm sure James Last's heirs will be happy to supply the required stock.

The entire R Kelly "Trapped in the Closet" on repeat could be a strong contender.

Stairway to Heaven is about 8 minutes long, so they better work hard on speeding the elevator up to match that.

At more than 13g I'm not sure that, "a new day will dawn for those who stand long, and the forests will echo with laughter"... after experiencing that.

3.4x10^7/(500)^2 = a m/sec2

For an 8min20sec flip time. 20+g if you really want the 8min.

Only if they want this to be a fancy burial service where we slingshot your corpse into space for kicks.

Another version of the Euthanasia Coaster? https://en.wikipedia.org/wiki/Euthanasia_Coaster

I don't doubt there's a market for that service.

An expensive way to die still...

Yes, but it's a completely different market from folks desiring a space elevator.

Also, it makes the need for muzak nonexistant because all your passengers are dead and can't hear it anyway. Seems to me that defeats the purpose of trying to time the trip to coincide with the length of a particular song.

Also completely pointless - playing David Bowie to a space suit in a convertible that's fired into interplanetary space.

It seems to me that you missed the joke…


It just wasn't really that good.

Shepard Tone -- the whole trip

You'd need to accelerate at 68 G's[0] (foreward for the first four minutes, backward for the last four). Not neccesarily unsurvivable, but your passengers (and most cargo) are likely to be unpleasantly pastelike.

We should probably treat it more like commercial air travel than compressive-structure elevator rides.

0: 200kph*8day/8min/2min => 67.981081 gravity

TIL forwards acceleration is called "eyeballs in" and backwards is called "eyeballs out".

It looks like 6 Gs is about as much as is feasible for an extended period of time.

Brief search didn't get me anything about longest ride on a centrifuge, which I guess would be the only way to test G-tolerance over extended periods. Where 'extended periods' means > an hour.

Any pointers to 6 Gs as being tolerable, for how long? Tnx.

Don't know, I was quoting a figure for 10 minutes. 6 gs for 10 minutes will get you to 35 km/s, which I believe exceeds any rocket launches so far.

I don't think 68 Gs is survivable at all. At least not for more than a fraction of a second. 46 Gs for a few seconds is the most a human has survived that we know of.

10 Gs for 1 minute is lethal.

> unpleasantly pastelike.

I don't think you'd get actual paste, but yes, 8-minute space elevator rides aren't looking very physically possible.

There’s only so much bossa nova one can endure.

What is kph? I can't be 200 km per hour and have it take 8 days.

For a space elevator, the "space station" is near geosynchronous orbit. 36000 km / 200 km/h is roughly 8 days.

In SI, that would be kilo pico hour. But yeah I'm pretty sure it's kilometers per hour in American.

I assume the author meant km/h or 200 km per hour as you have guessed, and if the satellite it 36000km high / 200km it would take 180 hours or 7.5 days.

8 * 24 * 200 = 38,400 km.

Geostationary orbit is 35,786km above the equator, so 8 days feels a fair approximation.

Music? The first four days will be safety announcements. The last four will be debates as to who is responsable for cleaning up all the vomit. A week of near-zero-g in a room with 30 people will not be fun.


Why would it be "zero-g" you're not in orbit?

You are moving from ground (1g) to geostationary orbit at zero. It will be a slow progression from one to the other (with a very slight lateral acceleration) but imho once below .5g anyone who is going to get air/sea/space sick wont see much difference.

Ah good point - I was just thinking about lower down.

Is humor against HN rules? I regularly see such posts being downvoted and it doesn't make sense to me.

Most humor can be categorized as "insubstantive comments" and those are discouraged.

It is possible to crack a joke here and get it upvoted, but it's hard to pull it off. I even once had a joke upvoted by quite a lot,* like 50 points or something, but most jokes are downvoted not because humor is forbidden, but because insubstantive comments are discouraged.

Some humor is downvoted for being uncivil because a lot of humor is basically poking fun at people or mocking them. A lot of humor is not nice at all. HN tries to meet a very high bar for civility.

* Under my old handle and it hit 59 points:


I posted a joke a couple of days ago about "the Xzibit pattern" which ended up at 10 points, but it fluctuated a lot so it probably got something like 40 up 30 down. Would be interesting to see the breakdown of votes on HN.

I'm just glad you can't see the # of votes here for other comments. Helps prevent bandwagonning, though that still happens for downvotes once the css kicks in.

Well said. That's about as succinct a sum-up as I've heard. This might actually belong in the FAQ as it might save some folks a bit of confusing cultural acclimation upon arriving at HN from parts distant such as reddit or slashdot (is that still a thing?).

At any rate, way better than "harumph! HN hates fun!"

But if you note my "joke" actually illustrated a point of physics about which at least one person was confused: the expected g-forces. So it wasnt insubstantive, certainly not as insubstantive as the parent comment about elevator music.

Can I ask why you retired your previous handle?

The short version is that I made the leaderboard and it looks like a feminist handle. There's more factors involved, but that's the crux of it.

No, it’s not against the rules, but downvotes aren’t there to enforce the rules.

It’s just a culture thing. HN tends to be more news and factually focused than reddit/Twitter/etc. People here just prefer to stay on topic, especially since humor is very different between people and can be very hit or miss.

yup, coming here and the top comment actually being something insightful or some point worthy of discussion instead of some sarcastic comment or joke like elsewhere is what makes this place.

The use if my joke is evident in the immediate reply, the confusion over g forces. There is no reason an informative comment cannot also be funny.

Weird to me that they aren't accelerating till the midpoint and then breaking till the destination at a constant 1g. Gets around the space sickness by providing artificial gravity and should take ~hours rather than ~days.

That trip would only take an hour, but I don't think you could build a cable and drive system capable of operating at 18 km/s.

Just for a bit of fun perspective, that’s 7 km/s faster than reentry velocity! Even if you felt like dealing with the heat, it would cost an ungodly amount of energy which kind of defeats the point of an elevator. On the other hand, you could ignore radiation shielding if the trip is short enough? Not worth the trade off I think.

Wouldn’t you hit that velocity far above the troposphere, where there’s much less air resistance?

Not sure if this would work, but how about using a wire with evenly-spaced metal beads, then using a magnet (a large one like used in MRI machines) to pull up the cart? You'll probably have to turn the magnet on/off at a specific frequency, depending on the momentum of the cart, which could be a challenge.

power = force * distance / time

If you want constant acceleration, you need to maintain constant force. A higher-velocity vehicle applies that force across a greater distance per unit time, and therefore requires more power.

Accelerating 1 metric ton at 1g requires 9800 N. So at peak velocity (18 km/s), that's 180 megawatts per ton, which is more than 700 times the power to mass ratio of a Tesla P100D.

Surely friction is an issue at much faster speeds? I guess the fastest trains go 400+ KPH, with the fastest being maglev. I assume, though can't tell from the article, that the space elevator has physical contact with the cable, and I can't think of how one could reproduce maglev tech when going vertically.

So, there's surely a safe speed limit built into the materials being used? It's probably faster than the speed they're starting out with, but I kinda assume it can't be fast enough to shorten the trip to hours from days.

As an aside, moving people is probably not the most profitable use of the thing for the foreseeable future, as cool as that sounds. Getting a satellite into orbit for a tenth the cost is revolutionary (though they mention the cost compared to the shuttle, which is much more expensive than rocket transport...so they may be cherry-picking numbers to make this seem more revolutionary than it is).

Anyway, I can't think of how they could accelerate much beyond the fastest non-maglev train speeds without tearing apart the cable and car, but I may be underestimating the strength of carbon nanotubes, and whatever other component materials they're using. Perhaps there's a materials nerd here who knows.

Because it would require you to reach an improbably high velocity (especially for pulling yourself up a cable)--and you'd do so relatively quickly using an improbably large amount of energy in the process.

you're already experiencing a constant 1g right now :-)

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