
The Quest to Build an Elevator into Space - Thevet
http://gizmodo.com/the-quest-to-build-an-elevator-to-space-1638192427
======
geuis
When I talk about this and people ask why, and when people comment "why", this
is my response.

The space elevator is the Panama Canal of our time.

People dreamed of building it for close to a hundred years before it was
finally achieved. Multiple companies and countries tried and failed. Once it
was achieved, it changed the world.

This is so much more important. Instead of just linking two hemispheres, the
space elevator opens up all of space to us. It's like the Bering land bridge
20k years ago or first cheap ships that could reliably cross the Atlantic.
It's all of those things a thousand fold.

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weavejester
An alternative to a full space elevator is the rotovator or rotating sky hook.
Instead of building a single tethered cable that reaches up to geostationary
orbit, you instead build shorter, untethered cables that rotate end over end
in their orbit.

These structures can then be used to assist conventional rockets. Place a
rotovator in low orbit, then send up a suborbital rocket to hook onto the end
of the cable when at its lowest point. Detach half a rotation later, and the
rocket is flung into a higher orbit.

There's a more detailed discussion here:

[https://www.reddit.com/r/technology/comments/2h07ku/japanese...](https://www.reddit.com/r/technology/comments/2h07ku/japanese_company_obayashi_announces_plans_to_have/ckoc2j6)

~~~
3rd3
[https://en.wikipedia.org/wiki/Momentum_exchange_tether](https://en.wikipedia.org/wiki/Momentum_exchange_tether)

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DennisP
People got enthused about this after Brad Edwards, mentioned in the article,
led a NASA study on space elevators about a decade ago, which found it to be
surprisingly feasible. Here's their final report (pdf):
[http://www.niac.usra.edu/files/studies/final_report/521Edwar...](http://www.niac.usra.edu/files/studies/final_report/521Edwards.pdf)

The material would be carbon nanotubes a couple centimeters long, bound
together by a reasonably strong epoxy. They estimate a cost in the low tens of
billions of dollars, by using seven shuttle flights to deploy a minimal
elevator, and using that to pull up additional elevator material. They examine
a lot of practical issues and find solutions for them.

~~~
noir_lord
We live in a world where an individual has the resources to make a credible
stab at a space elevator....that is amazing.

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trhway
i wonder why before various unobtanium requiring structures we wouldn't try
some rail/coil gun in a [close to] vacuum tube going several kilometers up a
mountain. After all, 2000 years ago it was possible to build that
[http://en.wikipedia.org/wiki/Roman_aqueduct](http://en.wikipedia.org/wiki/Roman_aqueduct)
, so building something like it up the Kilimanjaro (or any other mountain near
equator like this
[http://en.wikipedia.org/wiki/Nevado_Sajama](http://en.wikipedia.org/wiki/Nevado_Sajama))
should be pretty doable today.

Or how about just this
[http://en.wikipedia.org/wiki/Project_Babylon](http://en.wikipedia.org/wiki/Project_Babylon)
for starters - was worked on by a guy who knew what he was doing:

"The barrel was to be 156 metres (512 feet) long, with a bore of 1 metre (3.3
feet).[3] Originally intended to be suspended by cables from a steel
framework, it would have been over 100 metres (300 feet) high at the tip. The
complete device weighed about 2,100 tonnes (the barrel alone weighed 1,655
tons). It was a space gun intended to shoot projectiles into orbit, a theme of
Bull's work since Project HARP."

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3rd3
[https://en.m.wikipedia.org/wiki/Spacegun#Technical_issues](https://en.m.wikipedia.org/wiki/Spacegun#Technical_issues)

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hyp0
Wait... most of the energy of going into orbit is in accelerating to orbital
speed (lateral), not getting away from earth (vertical).

An elevator's top, in a geosynchronous orbit) rotates much faster than the
bottom (describing a larger circle, covered in the same time).

Therefore, a payload moving up the elevator would either need to be
accelerated laterally somehow, or it would bend the elevator over. There's no
getting away from needing the energy for lateral acceleration - it must be
supplied somehow.

Piping fuel up (instead of blasting it up in a rocket) may be more efficient,
but consider that its mass too will need lateral acceleration.

    
    
      \edit
    

Fuel in the form of electricity plus reaction mass, to be sent at extremely
high velocity, would probably have the least mass, and so minimize this effect
(I think, high voltage electricity, to reduce the current, because the
electron mass itself may have an effect at these scales!).

Another alternative, for the reaction mass, is earth-encompassing rings at
different altitudes. You can accelerate it without throwing it away.

Of course, at lower altitudes, you can just use air... maybe there's even
enough (for this purpose) at quite high altitudes...

Finally, I think the basic solution has been a counter-weight: as one goes up
(needs to speed up to orbital velocity), one comes down (needs to slow down
from orbital velocity). If it was just one elevator each, the accelerations
would be imparted at different points, twisting the evelator. But I guess a
series of elevators - or even a continous elevator (like a conveyer-belt... or
escalator...) would smoothen out this effect as much as you like, and only
needs electricity to power it... and, any acceleration of the electron mass
would also balance out, because they also go up and down in a circuit (or down
and up for space solar panels). Sorry, nothing to see here. _EDIT_ I see now a
reply mentions this solution, upvoted.

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mrfusion
I thought centrifugal force held it straight up and you're taking a tiny
amount of energy from the earths rotation when sending up payloads. Please
correct me if I'm wrong.

~~~
idlewords
This is the correct answer. Angular momentum in the system is conserved; as
you move mass up the space elevator, the earth spins (imperceptibly) slower.

Note that the tether only moves at orbital velocity at one point. Below that
point, if you want to get into orbit, you must accelerate laterally after
releasing the tether.

~~~
hyp0
So the cable pulls the payload across, to (lateral) orbital speed: this was my
point about the payload bending the cable over.

1\. The cable has to be strong enough to do this (which may be reasonable,
given how strong it needs to be anyway - plus it's in tension)

2\. The cable will still be bent over, by a force imparted at the payload. If
the bottom is attached and the top is "fixed" in geostationary orbit, the
force will move the payload laterally (lagging the orbit - west), looking like
a kind of arrow, or "V" on its side. The force on the cable itself might be
OK, as the force is in tension; and the curve of the bend might be gradual
enough. (Or maybe it would end up straight, but tilted westward?)

It will also pull on both earth and satellite, slowing both.

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lotsofmangos
I been trying to think about this from a different angle and have been trying
to work out how long you could make a self-supporting fuel and oxygen line by
putting a lightweight triangular gantry with three small adjustable rocket
engines and a fuel pump every hundred meters or so. This wouldn't need stupid
materials as it would not be under the same tensile loads, but it will have a
maximum length that depends on overall fuel consumption of the structure vs
the flow rate of pipe you can haul.

Also, it would be constantly burning fuel, so it has pretty high running
costs.

edit - you could also make an electric version of the same thing that pumps a
reaction mass like water, but then you need to be able to fire it very fast
out of the nozzles otherwise the water line becomes unwieldy very quickly, so
I figured using chemical fuel might make things simpler.

~~~
civilian
Yeahhhhhh that is not an effective strategy at all. Rockets upon rockets. It
sounds like an idea hatched in Kerbal Space Program.

The best "ground powered" structure would be the space fountain:
[http://en.wikipedia.org/wiki/Space_fountain](http://en.wikipedia.org/wiki/Space_fountain)

~~~
lotsofmangos
Back of an envelope calculations seem to indicate that a 200km one is possibly
feasible using normal petrol, tho I wouldn't like to bet on geostationary. The
space fountain has it's own issues, such as engineering the deflector and
making the giant electromagnetic tube. What I am suggesting is far simpler.

edit - and the I had the idea before Kerbal came out, so if it is total
madness, I promise you they are not to blame.

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gpsx
So what happens if the cable snaps? I assume this would happen at the height
of a geostationary orbit where tension is the highest. And this is an ungodly
tension so I assume it would be pretty violent. On top of that the cable will
not fall straight down because the top of the cable is traveling much faster
than the bottom (you could view this as the coriolis effect). It seems you
would have 22,236 miles of cable wrapping itself around the earth.

~~~
badsock
It's more of a ribbon than a cable - it would float gently down.

~~~
gpsx
The tip would be going over 5000 mph relative to earth, not including the
speed because of the snap. I don't know if it would float gently, but it
probably would burn up once it hit the atmosphere.

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nathanathan
I would like to know if electromagnetic flux pinning is strong enough to use
instead of a cable. I'm imagining a scenario where pairs of rotating
superconductor panels in orbit lift a giant solenoid into space by flux
pinning its magnetic field as they rotate upwards.

~~~
adaml_623
You're probably going to have to draw a diagram to get your basic concept
across a wee bit better.

~~~
nathanathan
I've asked about the concept here as well:
[http://forums.xkcd.com/viewtopic.php?f=18&t=109979](http://forums.xkcd.com/viewtopic.php?f=18&t=109979)
I suggested a two designs and the one I mentioned on hn has an ascii drawing
about halfway down the page.

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Sebpereira
I believe lifting cargo outside orbit is not the greatest strength of an
orbital elevator, instead it most useful feature would be on gathering sun
rays which have not been diminished by the atmosphere. But there are many
challenges to achieve that: [http://io9.com/5984371/why-well-probably-never-
build-a-space...](http://io9.com/5984371/why-well-probably-never-build-a-
space-elevator)

~~~
jessriedel
The atmosphere only attenuates sunlight by a factor of order unity. Won't it
always be much, much cheaper to build slightly larger solar panels?

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virtue3
I think the counter argument to the space elevator magic material was always
that if you could make something that light and that strong...

use it to make cheaper/lighter rockets.

~~~
shalmanese
The Space Shuttle is already 96% propellant to 4% structure
([http://www.nasa.gov/mission_pages/station/expeditions/expedi...](http://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html)).
You're going to get much appreciable gains from lighter rockets.

~~~
virtue3
I was being kind of sparse in details, sorry.

Having a material that can self support itself into orbit can potentially
unlock practical variations of:

[http://en.wikipedia.org/wiki/Steam_rocket](http://en.wikipedia.org/wiki/Steam_rocket)

whose main problem is: The simplest design has a pressurised water tank where
the water is heated before launch, however, this gives a very low exhaust
velocity since the high latent heat of vapourisation means that very little
actual steam is produced and the exhaust consists mostly of water, or if high
temperatures and pressures are used, then the tank is very heavy.

Although, that would also require the material to be very heat resistant as
well. Which might be problematic. Compressed air might also work at that sort
of level of material as well. At least for initial launch stages until you
need to switch over to another type of propellant (or a more controllable
engine).

~~~
derekp7
I thought the Space Shuttle was already primarily a steam rocket. It held
liquid oxygen and hydrogen, which was combined, ignited, and the result is
high temperature water (steam).

Another way I wondered about, is to have a cold water tank with a nuclear
reactor in it. As long as you ignore the safety part of the equation, do the
physics work out? That is, would you get more thrust than from recombining
hydrogen/oxygen?

