
Japan starts space elevator experiments - Futurebot
https://www.electronicsweekly.com/news/business/japan-starts-space-elevator-experiments-2018-08/
======
snowmaker
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](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.

~~~
rapnie
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:

[https://www.businessinsider.com/400-billion-manmade-
mountain...](https://www.businessinsider.com/400-billion-manmade-mountain-
netherlands-2011-8?international=true&r=US&IR=T)

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..

~~~
de_watcher
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.

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

------
cstross
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](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 ...

------
ridgeguy
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.

~~~
jimmcslim
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?

~~~
leereeves
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.

~~~
schiffern
>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](https://en.wikipedia.org/wiki/Retrograde_and_prograde_motion)

~~~
leereeves
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.

------
timonoko
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.

~~~
roryisok
Seveneves is a great read!

------
ghaff
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.

~~~
djsumdog
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.

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

(SPOILER!!!)

... 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 :-)

~~~
hutzlibu
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)

------
blahedo
> _"...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.

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

~~~
bencompanion
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.

~~~
jessaustin
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.

~~~
peeters
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.

------
mortenjorck
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.

~~~
TheSpiceIsLife
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.

~~~
cptaj
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.

~~~
tomatotomato37
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

------
zmix
> _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...

~~~
dmurray
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.

------
stcredzero
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.

~~~
TeMPOraL
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.)

------
sandworm101
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.

~~~
Torkel
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 :)

~~~
eponeponepon
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.

~~~
sandworm101
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.

------
breatheoften
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.

~~~
on_and_off
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.

------
DEADBEEFC0FFEE
Google was reported to be looking into this a few years ago. And determined
that there was no material strong enough at the time.

[https://www.extremetech.com/extreme/180682-google-x-
admits-i...](https://www.extremetech.com/extreme/180682-google-x-admits-its-
working-on-a-space-elevator-teleportation-hoverboards)

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

~~~
ObsoleteNerd
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).

~~~
DEADBEEFC0FFEE
Fair enough. We have to start somewhere. Perhaps a tether climbing rig will be
be useful in future megacity skyscrapers.

~~~
djsumdog
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.

------
pier25
I know nothing about physics... but wouldn't the space station need to counter
the cable tension?

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

~~~
twic
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.

~~~
jandrese
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.

~~~
theothermkn
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.

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

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

~~~
theothermkn
> 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...](https://www.esa.int/spaceinimages/Images/2009/02/Hypervelocity_impact_sample))
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.

~~~
Aeolun
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).

------
yohann305
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

~~~
cuddlybacon
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.

~~~
mrep
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.

~~~
TeMPOraL
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.

------
mtgx
Isaac Arthur thinks an orbital ring is a better idea:

[https://www.youtube.com/watch?v=LMbI6sk-62E&index=9&list=PLI...](https://www.youtube.com/watch?v=LMbI6sk-62E&index=9&list=PLIIOUpOge0LsGJI_vni4xvfBQTuryTwlU)

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).

------
avmich
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](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...

------
zepearl
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).

~~~
comboy
Centrifugal force would keep straightening it up.

~~~
zepearl
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.

~~~
jaggederest
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.

~~~
joering2
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..

------
yohann305
Someone patented space elevators in 2015.

[http://patft.uspto.gov/netacgi/nph-
Parser?patentnumber=90858...](http://patft.uspto.gov/netacgi/nph-
Parser?patentnumber=9085897)

No comments...

~~~
zepearl
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).

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

~~~
skissane
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).

~~~
zepearl
Again, "teleportation" would be a "speculative" patent (you have thought about
the concept but didn't present anything that works). If you would/could take
ownership of only its "concept" then I would reply "screw you - I would take
ownership of [humanity]" and you would become nothing. Yo :)

------
chriswarbo
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).

------
rietta
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?

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

[http://gassend.net/spaceelevator/breaks/](http://gassend.net/spaceelevator/breaks/)

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.

~~~
cantagi
_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.

~~~
Hextinium
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.

------
stretchwithme
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?

~~~
Filligree
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.

~~~
darkmighty
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](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).

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

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

------
sigmaprimus
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?

~~~
mojomark
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.

~~~
chriswarbo
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)

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

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

------
somegraypoupon
There was an interesting talk about space elevators at the 33rd chaos
communication congress
[https://youtu.be/EtMJgEggVWQ](https://youtu.be/EtMJgEggVWQ)

------
m3kw9
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

------
mothsonasloth
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

[https://www.youtube.com/watch?v=wfU524OBKhc](https://www.youtube.com/watch?v=wfU524OBKhc)

[http://halo.wikia.com/wiki/Space_elevator](http://halo.wikia.com/wiki/Space_elevator)

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

------
BenJahman
I wouldn't like being stuck in that elevator!

------
cryptozeus
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

~~~
black6
FTA:

> 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.

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

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

~~~
yters
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?

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

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

------
ourmandave
_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.

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

~~~
p1mrx
For a space elevator, the "space station" is near geosynchronous orbit. 36000
km / 200 km/h is roughly 8 days.

------
scalablenotions
This is one day where you REALLY don't want the elevator to jam on the way to
the office.

------
coygui
Anyone has watched GUNDAM OO?

