
Why Space Elevators Could Be the Future of Space Travel - daredave
http://futurism.com/why-space-elevators-are-the-future-of-space-travel/
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jacquesm
As long as a major component of space elevators is unobtanium any kind of
discussion about them in a terrestrial context should focus on materials
science and how to advance it to the point that it becomes feasible. Anything
else is not productive, akin to deciding on how to spend your first billion
when you have $50 in the bank.

~~~
ant6n
Firstly, the tether of a space elevator could be tethered (EDIT: tapered),
which reduces the required tensile strength a bit.

Secondly, there are some intermediate space elevator-like constructs that have
similar ideas but are much more feasible. For example the skyhook
([https://en.wikipedia.org/wiki/Skyhook_(structure)](https://en.wikipedia.org/wiki/Skyhook_\(structure\))).
Rather than tethering to the ground it would 'hook' into the air at high
altitude, and rotate the earth at high but airplane achievable speeds. There
are a lot of engineering challenges, but its theoretically possible with
existing materials.

~~~
Terr_
> Firstly, the tether of a space elevator could be tethered

Uh... Aren't connectors already supposed to be connected?

~~~
ant6n
Oops, typo. I meant tapered. As in varying in width. You could imagine a
tether that has a 5mm diameter at the surface (in a sort of ribbon shape), but
has a diameter of 500mm at the geostationary orbit.

According to this ([http://sustainable-nano.com/2014/04/01/space-elevator-a-
last...](http://sustainable-nano.com/2014/04/01/space-elevator-a-lasting-
dream-for-a-sky-reaching-tree/)) a carbon nanotube has a factor between ground
and orbit of 1.6 or so, and for steel it's something crazy like 1.6e33.

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jbb555
A whole article about why space elevators would be better than rockets with
only the slight problem that we don't know of any way to build one with any
materials we have.

If we are allowed to do that, I think we should use star trek transporters.
They would be even cheaper and even better. We don't know how to build those
either...

~~~
yiyus
Starting construction without having the needed materials is the approach
followed at ITER. This way of working is based in a very reasonable idea:
available materials have been improving since ever, there is no reason to
think this progress will stop now.

~~~
mcv
But it's hard to even imagine what something stronger than carbon nanutubes
would look like. How much stronger than diamond-like molecular bonds can you
get?

~~~
yiyus
According to simulations, 58% [1]. Experimental confirmation is still needed.
Although we are still far from it, it is something that we could see in our
life times.

[1] [https://www.newscientist.com/article/dn16610-diamond-no-
long...](https://www.newscientist.com/article/dn16610-diamond-no-longer-
natures-hardest-material/)

~~~
wcoenen
Hardness is not the same as tensile strength.

~~~
yiyus
I know. From the linked article: "The simulation showed that wurtzide boron
nitride would withstand 18 per cent more stress than diamond, and lonsdaleite
58 per cent more." The title of the article is misleading.

~~~
wcoenen
The title of that article is accurate, where it says "stress" they are really
referring to hardness and not tensile strength. The quoted 58% comes from this
paper, it talks about "hardness" and "indentation strength" in the abstract:

[http://sci-hub.cc/10.1103/physrevlett.102.055503](http://sci-
hub.cc/10.1103/physrevlett.102.055503)

~~~
yiyus
You are right, I stand corrected. They actually talk about tensile strength in
the PRL article:

"It is noted that lonsdaleite exhibits almost identical ideal tensile strength
and only slightly larger pure ideal shear strength compared to diamond. The
significant enhancement in its indentation strength occurs under biaxial
stress loading conditions. The situation in w-BN versus c-BN is similar. All
past calculations have shown that diamond exhibits the highest strength under
various loading conditions compared to other materials, which was consistent
with all available measurements. Here we show for the first time that w-BN and
lonsdaleite exhibit higher strength than diamond under indentation."

So, indeed, diamond is still the winner here.

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spqr0a1
While a space elevator is constructable on the moon or mars, making one for
earth would needs exotic high tensile strength materials that we don't know
how to build.

A launch loop, on the other hand, has many of the benefits of a space
elevator; but the nicest feature is that it can be constructed from
conventional materials.
[https://en.wikipedia.org/wiki/Launch_loop](https://en.wikipedia.org/wiki/Launch_loop)

~~~
SticksAndBreaks
How about a active structure, like a space fountain?

~~~
jlebrech
rockets connected to each other ascending and descending constantly?

~~~
berntb
Iirc, Robert L Forward's variant was an electromagnetic cannon launching metal
pellets, which were slowed down at the top and fired back down.

The pellets would go up and down like a juggler's balls was thrown.

Since you'd regain much of the energy when you slowed them down, it wouldn't
be so energy expensive as it seems. And yes, you need vacuum pipes. And a stop
in electricity would have side effects ("Timber!"). :-)

~~~
jlebrech
some kind of ubend, and the "pellets" are magnetised?

say we drop a rocket into this ubend and it redirects the energy back up into
space?

and in orbit there are rockets that lift them the rest of the way, remove the
passengers and then drop them again.

~~~
berntb
I was clumsily trying to explain Space fountains. :-) This do discuss the
Forward thing and so on:

[https://en.wikipedia.org/wiki/Space_fountain#History](https://en.wikipedia.org/wiki/Space_fountain#History)

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adrianN
What is the heaviest planet where we could build a space elevator with current
technology? Would it work on Mars? The Moon?

~~~
jacquesm
The moon, yes:

[https://en.wikipedia.org/wiki/Lunar_space_elevator](https://en.wikipedia.org/wiki/Lunar_space_elevator)

Mars, edge case?:

[http://physics.stackexchange.com/questions/33547/space-
eleva...](http://physics.stackexchange.com/questions/33547/space-elevator-on-
mars-with-todays-technology-possible)

Good post on the subject:

[http://tsanad.blogspot.nl/2011/03/space-elevators-where-
to-p...](http://tsanad.blogspot.nl/2011/03/space-elevators-where-to-put-
them.html)

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DanielBMarkham
With the U.S. Navy having working railguns, we already have the tech to launch
unmanned cargo into orbit quite cheaply. All we need is a standardized shell
casing that can hold the cargo and provide the horizontal thrust once the
package reaches apogee.

Space elevators are cool, but why chase something with so much missing tech
when we have a solution in front of us?

~~~
FiatLuxDave
I agree with you, although I should note that the current Navy railguns are
not capable of putting shots in orbit. However, the logic behind choosing guns
over elevators is simple:

I. Actively supported towers are easier/more likely to be built than a space
elevator made of unobtainium. II. The technology to build a space fountain or
actively supported tower is more difficult than a gun, because you first have
to have a gun which can shoot objects faster than orbital speed, and then add
the recirculation plus the momentum transfer to the tower. So, an orbital gun
is a subset of the technology needed for an active tower.

One other thing which is often overlooked when discussing shooting stuff into
orbit, is that the size and cost of the gun is proportional to the size of the
projectile. If shooting from very high in the atmosphere, very small
projectiles could work without significant atmospheric losses. A railgun or
light gas gun on an airplane could easily shoot literal tons of small
projectiles, machine gun style, then land and reload (and with current tech,
replace barrels).

If a target in orbit was shot at, you wouldn't even need to have a rocket in
each projectile to provide thrust at apogee. Instead, you hit the target and
embed into it. By hitting the target at different parts of its orbit, you
avoid substantially changing the shape of its orbit, balancing out the
momentum change to keep the orbit how you want it.

This wouldn't work for anything besides bulk materials which can be broken
down into small pieces and shot like tiny bullets out of a hypersonic machine
gun. But the cost per kg for bulk materials could be very low.

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ende
It seems that getting information out of a gravity well is much easier than
mass. There's a bit of a bootstrapping problem to to develop the initial
infrastructure, but once in place it would be much simpler to just build in
space.

The problem with that of course is that terrestrial refineries and factories
are highly soecialized to their products, which means multiplies the amount of
base inf needed to construct even simple materials. If orbital manufacturing
emerges, I think it would need to adopt a new paradigm of custom fabrication
such as with 3d printing and similar technologies.

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bmcusick
Not even carbon nanotubes are strong enough to make a space elevator on Earth.
Individual CNTs (the molecules) are just barely strong enough, but you cannot
make a macroscale fabric out of them that's just as strong as the individual
molecules. And even if you did, there's no safety margin.

It's never going to happen on Earth.

However we could make an elevator today on the Moon or Mars with already
existing fabrics like Kevlar.

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thechao
This article mentions a study saying CNTs are too weak. Here's a New Scientist
summary of the flaws in CNTs:
[https://www.newscientist.com/article/2093356-carbon-
nanotube...](https://www.newscientist.com/article/2093356-carbon-nanotubes-
too-weak-to-get-a-space-elevator-off-the-ground/)

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pvaldes
hum... silly thought of the day. Why we still launch rockets from sea level
and not from some high mountain? Wouldn't be less expensive and more safe that
building 3-5km extra of space elevator?

If the mountain is higher enough, zero probability of birds crashing against
your structure, Neither clouds nor hurricanes, high visibility, free solar
energy all year around...

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mido22
funny that they mentioned 2009's “Gundam 00”, but haven's said a word about
Authur C Clarke's 1979 novel "Fountains of Paradise", the whole novel is about
this.

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jlebrech
Could a space elevator be warp based?

the early versions of warp would have to be huge anyways, so why not take
advantage of that by creating a space elevator using warp?

With warp you could technically send things through the earth's core as a form
of teleportation too.

