
Space Elevators Are Possible - cyphersanctus
http://www.techblog.co/space-elevators-are-totally-possible-and-will-make-rockets-seem-dumb/
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avmich
The main problem with the elevator, in my opinion, for many years already is
not in the strength of the material. After all, nanotubes are known for many
years, and their properties are sufficient for the tether, so in principle it
can be done. No, the main problem is with satellites. In fact, asking many
times - what to do with existing or future satellites - I never heard a
workable answer, even in principle.

Just a reminder - every satellite crosses the equatorial plane twice for every
rotation around the Earth. Majority of satellites are below the geostationary
orbit. So, given enough time every satellite will hit the tether - and even if
tether is near-zero width, the satellite isn't.

One of ideas was to dynamically move the tether - from the Earth, making
propagating wave along the tether, which would avoid the satellites. This
means we need the good means of watching the space and predicting satellites
movements - even small satellites can bring trouble. But that's not enough, we
might get a situation when we need to perform conflicting movements,
considering the current state of the wave.

This problem is well known for decades. Attempts to launch satellites from the
elevator - and the elevator makes it tantalizingly cheap, so we'll want to
launch many - will exacerbate the problem. The whole world astronautics will
have to adjust to accomodate the elevator - and nobody knows how it is going
to look like.

~~~
User8712
1\. How fast can a satellite travel up the tether? Let's say 50km/h, and it's
going to an altitude of 35,000km. That's a month just in travel time. Using
the tether for that period of time would be extremely costly. Currently,
around 125 satellites launch a year, so they would need to be going up the
tether at 500km/h, one after the other, day and night. And if we need to wait
for a platform to descend, they need to be moving at 1,000km/h. Otherwise, we
need multiple space elevators, or multiple shipments climbing at once and
passing one another to meet current demand.

2\. What's the cost of building and maintaining a space elevator?

3\. What's the cost of having a satellite climb the tether to an altitude of
35,000km? That's a lot of energy.

Taking this into consideration, is it _tantalizingly cheap_ compared to
strapping on a rocket? SpaceX has run tests with a reusable Falcon 9 rocket.
Cost of fuel for a launch is $200,000. I'm skeptical the space elevator would
be much cheaper.

The magic of SpaceX...

[http://www.youtube.com/watch?v=9ZDkItO-0a4](http://www.youtube.com/watch?v=9ZDkItO-0a4)

Downside of a rocket, it's heavy, and most of the energy is wasted lifting the
rocket, and not the payload. Advantage, you don't have to pay to maintain
cables that are long enough to wrap around the entire Earth.

~~~
percentcer
Couldn't you launch multiple satellites at a time?

~~~
Schwolop
Seems legit to me - a bunch of robots on the elevator that are each
responsible for perhaps ten kilometres of travel, and they pass the parcel to
the next one in line then move back down. You could launch way more things in
pseudo-parallel that way.

Or just an up line and a down line like most cable cars.

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ericd
If we can make one, it seems pretty obvious from the studies I've seen that it
will be the major enabling technology for getting into space in a large way.
Unfortunately, I don't think we've hit the carbon nanotube lengths that we'd
need (on the order of meters).

Here's a great book that came out of a NASA funded study that breaks the
issues down well, including costs, necessary tech, and methods for dealing
with potential issues like cable breakage: [http://www.amazon.com/Space-
Elevator-Earth-Space-Transportat...](http://www.amazon.com/Space-Elevator-
Earth-Space-Transportation/dp/0974651710)

Their conclusion was that it would be much more cost effective than most
people think, and that it would enable an incredible reduction in cost to
orbit due to not needing to use a pyramid of fuel to carry other fuel for
later, or enormous one-time-use precision machinery, and instead using simple
containers with electric motors and transmitted electricity.

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ars
This kinda glosses over the hard part: Making that tether!

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kornork
Great! What does the paper say about overcoming some of the problems that seem
to make it tough, like the radiation that humans will receive riding up, or
avoiding space debris? I'm assuming problems like building a rope strong
enough to hold its own weight will be overcome, as well as developing the
technology to climb the elevator.

~~~
mahranch
Radiation is only a minor concern, astronauts in the space station experience
similar radiation doses. I assume if it's cheaper to get things into orbit
[with the elevator], it's also cheaper to shield the entire contraption.
Climbing isn't much of a concern either, they've already run a bunch of tests
and NASA has already awarded their prizes out for the challenge. The real
issue is mass producing the carbon nanotubes.

It's like saying "Warp drive is possible" then saying all you need to do is
build a ship that can manipulate the fabric of spacetime. Well of course
that's all you need to do.

Sure, producing carbon nanotubes is easy. I've seen them make the it in a lab.
It's making the tubes to spec and making thousands of miles of the stuff that
is the hurdle. It's the equivalent of asking computer engineers in the 60s to
mass produce 22nm CPUs with billions of transistors. Can it be done? Sure. In
about 50 years.

~~~
mcv
> Radiation is only a minor concern, astronauts in the space station
> experience similar radiation doses.

Why would they be similar? The space station is only in LEO. That's not
remotely comparable to geostationary orbit, or the Van Allen belts.

Fortunately, shielding is a lot cheaper than on anything a rocket carries.

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nmc
Why does this seem like a shamelessly unacknowledged copy-paste from [1]?

Is it the other way around? Where is the original post?

[1] [http://motherboard.vice.com/blog/space-elevators-are-
totally...](http://motherboard.vice.com/blog/space-elevators-are-totally-
possible-and-will-make-rockets-seem-dumb)

~~~
vesinisa
To me, it seems like this site Techblog copied Vice without giving any credit.
Vice credits the original story to their in-house journalist, while
Techblog.co seems like a news aggregation service. I am cool with news
aggregation (think Google News), but they should definitely always credit the
original source.

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kamaal
At the risk of appearing stupid, I just have few simple questions

1\. What exactly holds the counter weight in position?

2\. Such a long rope, which the article says is around 62000 miles, won't it
function more like rubber band than function like a rope? Due to mere
stretching/elastic effect?

3\. I'm sure traveling 62000 miles is nothing like fuel efficient especially
when you travel in the direction of highest friction(Up). So how do you store
the fuel and of what weight that would be? Will such a vehicle be even
practical?

~~~
jccooper
1\. The counterweight is in geosynchronous orbit. It is "held up" by its
absurd speed like any other satellite.

2\. One of the reasons you need a very strong material. The tether will be in
tension, but probably will have quite a bit of movement to it. The tether
dynamics are not a solved problem.

3\. Most plans suggest that power will be beamed from the ground to the
climber, either as microwaves or visible light. Some plans might use a paired
tether to carry electricity. In either case, no onboard fuel is needed, which
us pretty nice, as that's a lot of weight you don't have to pull against
gravity. There have been several competitions in this area already.

~~~
kamaal
Yes, sorry the centripetal-centrifugal force balance thing was completely off
my mind when I asked that question.

But with all the remaining two points look in the domain of SciFi to me. I'm
sure tether dynamics are going to a materials engineering problem like never
seen in history of mankind.

Plus the energy problem is still by and large a very problem. Sending
electricity down the tether looks very inefficient give the article says it
will 62K miles long.

In short we are still may be what, say 50 years away from this?

~~~
jccooper
Quite possibly. I'm not concerned with power transmission so much; that's just
engineering, and the tiny Centennial Challenge teams were doing well enough
over a few years that it seems quite soluble. We will probably have UAVs
flying on beamed power regularly within a few years.

The tether materials are obviously the long pile in this tent. We have
theoretical materials that will work, which is great, but we really need
practical materials. The day you can go buy nano tube thread you can formulate
an actual timeline for a space elevator. Until then, its only a dream.

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placeybordeaux
This article did almost nothing to aleviate the real concerns.

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mehwoot
What happens if something hits the cable and it breaks? Does the whole thing
drift off into space?

~~~
ars
Depends where it hits.

On the tether there is a "zero" point. Below that point things fall toward the
Earth, above that point things "fall" away from the Earth.

So it depends on where it broke and how much weight there is above vs below
that point. (To keep the tether in the air they put lots of weight above the
point, which falls away from the Earth and pulls the tether taught.)

If I were making one of these I'd make several tethers, spaced such that a
single object can not break more than one at once. Then tie the tethers
together periodically.

This object is about max:
[https://en.wikipedia.org/wiki/Tunguska_event](https://en.wikipedia.org/wiki/Tunguska_event)
so I'd make the multiple tethers at least 200m apart. That's pretty far apart,
so I'd invest in better detection technology to reduce the size maximum
undetected object. (Although that raises the question of what to do if you do
find a big one and it's headed right toward you.)

~~~
atgm
> If I were making one of these I'd make several tethers, spaced such that a
> single object can not break more than one at once.

What I'd worry about is security, honestly.

What if some nation decides that the space elevator existing isn't in the best
interest of their national security, or some paramilitary group wants to make
a point?

Bombing the base station would hurt the elevator. But of course, we should
expect that to be secured. That still leaves the entire length of cable
running up and down the elevator -- that's a huge volume of space to secure
against anything explosive or fragmentary.

~~~
manicdee
And indeed the scenario of "terrorists sever the tether from its geostationary
anchor" was part of the story in Red Mars.

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

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maxharris
How do you keep space junk (which can include larger objects as well as small
as bolts and the like, all of which may have considerable momentum) from
tearing through the cable?

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oldmantaiter
All these comments about space junk, Spaceballs had it right with the giant
cleaning lady in orbit. I think we should switch our focus to that instead.

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frozenport
First build the hyperloop, then we will talk.

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elktea
The animated icon on this site is terrible

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thrownaway2424
The writing isn't too hot, either.

~~~
frozenport
This HN needs a downvote button or an embargo on upvotes. For example, you can
only upvote 5 minutes after you have read the link. Having been away for a
year I am shocked by the number of upvotes everything is getting.

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sgt
"The rotation keeps the cable taut, to counter the gravitational pull as
robotic, electric “climbers” ride the line up into space carrying the payload.
Boom."

Let's just hope he didn't mean that literally. But early attempts may include
some disasters, as often is the case.

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SlowButEffectiv
That's an awful long way to have to stare uncomfortably at the doors.

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panacea
No they're not.

