
People Are Still Trying to Build a Space Elevator - dnetesn
http://www.smithsonianmag.com/innovation/people-are-still-trying-build-space-elevator-180957877/?utm_source=twitter.com&no-ist&is_pocket=1
======
garethrees
The article says, "His conclusion: The space elevator could be built with
existing technology—minus the super-lightweight tether necessary to make the
whole thing work." In other words, it cannot be built with existing
technology.

NASA uses the idea of "Technology Readiness Level (TRL)" [1] to help assess
speculative technology, the (obvious) idea being that each stage of deployment
of a technology relies on passing tests at previous stages.

On this scale, it's not clear to me that space elevators are at TRL1 ("basic
principles observed and reported") yet. Space elevators depend critically on
having a material that's strong enough to build the cable. Feasible designs
for climbers, debris avoidance systems, power transmission and so on, can't
make up for the lack of this critical component.

[1]
[http://www.hq.nasa.gov/office/codeq/trl/trl.pdf](http://www.hq.nasa.gov/office/codeq/trl/trl.pdf)

------
eternauta3k
The article could have mentioned Skyhook [1], which can be built with existing
materials.

[1]
[https://en.wikipedia.org/wiki/Skyhook_%28structure%29](https://en.wikipedia.org/wiki/Skyhook_%28structure%29)

~~~
cl42
The way these are described in Seveneves is _awesome_. I didn't realize
there's so much theory behind it!

------
Balgair
Carbon nanotubes are seductive. They are very strong, diamond like, in that
circularized plane. But when you extend the tube to macro dimensions, you have
problems with phonons and the 'rogue waves' that add up over such long
distances (relative to atoms). These phonon effects can and do add up to break
the nanotube as there is so much energy in the phonon that it overcomes the
intermolecular bonds. You can help a bit with an onion layering of nested
nanotubes, each a little bit bigger. But that doesn't get you much further.
Doping the tubes with other atoms reduces the strength by a lot, but may
increase the length. Isotopes of carbon, like C10 or C14, do help a fair bit.
However, they tend to be too radioactive to be stable for a project like this.
You'd have to continually replace the rope as the dopant isotopes would decay
away and the nanotubes would self destruct again. In the end, we need new
ideas to help with this. Perhaps some strange electron-phonon interaction? I
don't know.

~~~
icebraining
Yes, but so what if you need to continuously replace parts of the cable? As
long as you can identify the damage and cheaply perform the repair, it doesn't
seem that bad.

~~~
Balgair
The idea is that the cable would be one long crystal, not sections. You'd have
to continuously extrude the crystal from orbit to the ground or something. You
can't bolt in new pieces. Whatever the solution will be, cheap is not one of
the answers. Just the maintenance on it would be a world-wide effort. And for
what? Cheap orbital travel? The real hard part is to find a reason to leave
Earth that the oceans and Antarctica don't already fulfill. The only one I can
think of is orbital foundries or other processes that need 0g. Living space we
have a lot of, though cold, Antarctica has air, something Mars and Venus do
not.

------
w1ntermute
> pls don't ask me about space elevators until someone at least builds a
> carbon nanotube structure longer than a footbridge

[https://twitter.com/elonmusk/status/559557786514632704](https://twitter.com/elonmusk/status/559557786514632704)

------
CountHackulus
Yes, people are still working on it. It's not going to get built if no one
tries.

~~~
meddlepal
Some things aren't worth trying because they are batshit insane.

~~~
zatkin
It might be more cost effective to build a really long, narrow elevator into
space vs. paying $450 million per launch of a rocket/large spacecraft.[1] And
keep in mind that launching a large spacecraft usually carries less than 12
individuals.

[1]
[http://www.nasa.gov/centers/kennedy/about/information/shuttl...](http://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html#10)

~~~
dogma1138
Not really this is like saying that It would be more cost effective to build
jumbo jets instead of sail boats in the 15th century. Even if an alien
descended from the sky and gave you the materials to build it we don't have a
single analogy as far as the actual engineering and construction process goes
to even begin drawing blue prints.

So yeah in the "long run" it might be more cost effective but it's irrelevant
you can say the same thing about any hypothetical technology but you can't
stop spending money in the mean time if nothing else we need to be able to be
really good at launching extremely heavy payloads and building stuff in micro-
gravity before we can even begin to start dreaming about how to build a space
elevator. We also need rockets that can go out quite far and come back with a
huge payload like a small asteroid for the anchor and even most likely have to
master asteroid mining for the raw materials for any potential space elevator.
My bet is that it may become feasible around 2250-2500 (yes I know this is a
250 years window :)) if it's possible at all (because when all said and done
even carbon nano-tubes aren't good enough they are a good candidate and most
likely will be used but we need much stronger composites than what carbon-nano
tubes alone can offer).

------
matt-attack
What I never seem to see addressed, is the following: As the elevator ascends
the cable, it's "ground speed" must continually increase. What is the source
of the force that provides that acceleration (parallel to the ground)?

A traditional rocket expends a great deal of energy firing its rockets with a
component parallel to the surface of the earth to gain acceleration in that
direction. Where is the equivalent coming from w/ the space elevator?

~~~
Retric
The earth's rotation. Much like how your rotational velocity increases when
you climb stairs. Also, the cable is not vertical, you want a large mass past
geostationary orbit which pulls the cable fairly thought though there is some
bend.

PS: Try and calculate just how much energy is in earth rotation it's a rather
large number.

~~~
willismichael
> climb stars

I love this typo.

------
sandworm101
A space elevator only provides access to geostationary orbit. One can climb up
to LEO altitudes along an elevator, but that doesn't mean much. You wouldn't
be in orbit, but sitting stationary as if atop a tall building. So we would
still need to launch rockets for any space use in LEO (GPS and imaging sats
for example). And any such orbiting objects would of course have to be
navigated around this obstruction. Many useful orbit types would have to be
outlawed to protect the elevator.

I wonder, is easier to launch into a LEO from the ground or from a fixed point
at say 300km altitude? If you climbed a space elevator you would still need
8km/s of speed laterally. So you jump off and fire your rocket. You still fall
towards the ground, requiring some thrust to keep out of the atmosphere.
Without the arcing trajectory of a ground launch you would have to accelerate
roughly twice as quickly, requiring larger engines. Is that really any better
than starting from the ground as we do today?

Or you could climb to a near-geostationary position, burn retrograde until you
touch the atmosphere, then aerobrake down to LEO. That's still a heck of a lot
of effort.

~~~
jasonpeacock
Any height is an advantage in achieving orbit. It's an exponential problem -
you need fuel to go up, and you need more fuel to lift the fuel you need to go
up, etc.

Also, air resistance is much more at the surface than higher up.

So by starting your ascent at a high altitude you need much less fuel both
because you need less fuel, and because there is less air resistance
(friction).

Space elevators still need to use the same energy to lift something, but they
use an external power source so do not need to lift their own fuel, and they
lift more slowly and greatly reduce the effect of air resistance.

So no, a space elevator won't get you to "outer space", but it creates a
stepping stone which greatly reduces the cost of getting there.

~~~
sandworm101
Air resistance is a very minor issue for rockets. Long/thin things are very
slippery and once at 10-20-30,0000 meters the air is basically gone.

Jumping off the elevator from LEO altitudes would still require one to fight
gravity, to avoid dipping back into the atmosphere before getting to orbital
velocities. So there are still gravity-related losses to account.

~~~
enraged_camel
This isn't correct. Air resistance increases at the rate of velocity squared.
At the speed those rockets achieve, is is a big factor. Elon Musk himself
likened the atmosphere to a "thick soup" when it comes to launching rockets to
space.

~~~
sandworm101
My understanding is that atmospheric drag on a standard launch vehicle to leo
is on the order of 300-400m/s, a small fraction of the total budget.

------
Symmetry
A space elevator on Earth is very hard to build and would require exotic
materials which we can't yet synthesize in bulk. But you can make a decent
lunar space elevator with Kevlar.

[http://hopsblog-hop.blogspot.com/2012/09/beanstalks-
elevator...](http://hopsblog-hop.blogspot.com/2012/09/beanstalks-elevators-
clarke-towers.html)

------
mixedmath
I certainly believe an underthought of this article, which is that improved
capabilities with materials such as carbon nanotubes might lead to a paradigm
shift in the possibilities of what can be done with materials.

------
joshuagross
"But you’ve had civilizations rise and fall by a change in material strength
by a decimal point, and now you’re talking about orders of magnitude."

Does anyone know what he's referring to in this comment?

~~~
mattmanser
I would assume Bronze -> Iron -> Steel would be the changes he's alluding to.

------
jrcii
My understanding of the biggest challenge is that each point in the cable must
be strong enough to carry the weight of all the cable beneath it, which by the
time you reach the upper atmosphere would be tremendous even using carbon
nanotubes. The cable would also be perpetually struck and damaged by high
velocity micrometeoroids.

~~~
Fargren
Can't you have multiple stages with multiple cables? I guess acceleration and
deacceleration between stages could be costly, though.

~~~
ajmurmann
What do you connect your stages to other than the next stage?

~~~
Fargren
I would imagine the cabin could stop halfway, were it would attach to some
magnetic or mechanic lock system. There it would detach from it's cable and be
attached to another one that would pull it out the rest of the way. Actually,
the first cable could be the lock system; you just have to keep it attached
until you setup the second one.

------
cgrubb
Space elevator shadow wouldn't look like that:
[https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra](https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra)

------
Beltiras
I remember back in the early 2000's when predictions for when it would be
built was 2015-2020. 4 years to go.....

~~~
blammail
To be fair, the advances in space tech by the private sector have been nothing
short of amazing as of late. It's really an exciting time.

~~~
ZanyProgrammer
I fear we're heading into Year of Linux Desktop memes with the private sector.
I'd love to be proved wrong.

