Continued Success for Space Elevator Tests

Jacki O writes "According to their Web site the Space Elevator company Lifport recently managed to get their platform and climbing robot to the mile-high mark over the Arizona desert." From the announcement: "A revolutionary way to send cargo into space, the LiftPort Space Elevator will consist of a carbon nanotube composite ribbon eventually stretching some 62,000 miles from earth to space. The LiftPort Space Elevator will be anchored to an offshore sea platform near the equator in the Pacific Ocean, and to a small man-made counterweight in space. Mechanical lifters are expected to move up and down the ribbon, carrying such items as people, satellites and solar power systems into space."

I can top that.

[Orrin Bloquy (898571)]

I stood outside my door this morning in Flagstaff, which is 6200 feet above the Arizona desert.

1500 feet not a mile

[babokd (857897)]

The robot only made it around 1500 feet. The cable was a mile long.

Re:1500 feet not a mile

[lucabrasi999 (585141)]

"According to their Web site the Space Elevator company Lifport recently managed to get their platform and climbing robot to the mile-high mark over the Arizona desert."

The robot only made it around 1500 feet. The cable was a mile long.

Rule Number 1: Don't let the facts ruin a good story.

Re:1500 feet not a mile

[Rei (128717)]

In other news, my Teleporation Shoes are performing extremely well in tests. The shoelaces have survived twelve straight tying tests, including one "bunny ears" test conducted by a young child. Sole durability tests are also holding up well. Teleporation will be tested at some time in the future.

Seriously, that's what this is like. The challenges of a space elevator aren't in the climber; they're in the cable. We're not even remotely close to such a cable. To be realistic, you need a mass producable cable with a tensile strength of over 100GPa at a density similar to SWNTs. That's well more than the strongest *individual* SWNT measured thusfar, let alone the strongest bundle of tubes, let alone the strongest continuous fiber producable. It may well not even be possible with physics as we know them.

Re:1500 feet not a mile

[barawn (25691)]

The challenges of a space elevator aren't in the climber; they're in the cable.

C'mon. That's not true. The main reason it seems like this is because you think you know how to build the climber, but you have no idea how to build the cable. Ask a materials scientist who's working on carbon nanotubes, and they might disagree with you.

Plus, you do not need a 100 GPa cable. You need a 100 GPa cable for a small taper. At 50 GPa the taper becomes ... well, large, but not unreasonably large. It would just cost a lot more.

There are a lot of issues with the climber design. A lot. Speed, reliability, weight, and power. Reliability in particular will take a lot of time to nail down. It makes sense to tackle that one first, because it can be done in parallel with the cable design, and in addition, the third major challenge (power delivery) can't really be done until the climber design is finalized.

So you've got three difficult tasks - the cable, the climber, and the power delivery system. The last two are coupled. What makes sense is having two separate tasks, one of which handles the cable, the other the climber, and then the power delivery system. Oh look! [liftport.com] That's exactly what they're doing.

Given our lack of experience in building cheap vehicles that can travel 100,000 km with zero failures (with low power, in vacuum) I think it's safe to say that all parts of the elevator are difficult.

Re:Heres a question

[Golias (176380)]

Why don't we just build a 500 mile high pyramid of some description?

Indeed! Then we shall be like gods!
Effettivamente! Allora saremo come i dii!
In der Tat! Dann sind wir wie Götter!
En effet! Alors nous serons comme des dieux!

Re:Heres a question

[Golias (176380)]

Got any about Hammurabi?

Are you kidding? I've got a stele full of them!

Re:Heres a question

[Moofie (22272)]

You're high, aren't you?

Re:Towers as part of space elevator

[DanielRavenNest (107550)]

IAARRS (I am a retired rocket scientist, and have participated in a NASA
Space Elevator workshop, and been on a science panel with one of the Liftport
guys - I guess that makes me a relative expert)

A tower going up from the ground meeting a cable coming down from orbit is
more efficent than a cable going all the way to the ground, if, and this is
important, the strength of the cable is substantially less than the depth
of the earth's gravity well.

Here's why: As you build a longer cable or a taller column of constant area
under gravity, the stress gets higher. In a column the maximum stress is at
the bottom, and in a cable it is at the top. Eventually you exceed the
strength of the material.

The Earth's gravity well is equal to one gee times the radius of the planet
= 6,378 km. A space elevator is centered at GEO, which is 97% of the way out
of the Earth's gravity well, so we need to span 6,167 km at one gee.

The strongest readily available carbon fiber that is not made of nanotubes
is about 1 million psi in strength. It has a density of 0.067 lb/in^3, so
if you had a cable 15 million inches long under one gee, it would be at the
limit of it's strength. 15 megainches = 381 km, which is a factor of 15
below what we need.

You can build towers or cables longer than the strength limit if you make
them progressively wider to keep the stress below the limit of the material.
Each 15 inches of length in the cable above adds one millionth to the stress,
therefore the area has to increase by one millionth. Over a 381 km length,
the area of the cable increases by a factor of e (2.718...). This length,
found by dividing strength by the density of the material, is called the
scale length. If you have 16.2 scale length to cover (6167/381), your
cable area increases by e^16.2 = ~10 million.

A graphite/epoxy composite is needed for a tower. Bare fibers are okay in
tension, but you need to stiffen them for a compression structure. Typically
using the same fibers, the composite will be 30% as strong in compression as
the bare fibers are in tension. Now assume you build a tower up and a cable
down with the same area ratios from bottom to top. The tower's scale height
is 114 km, so the combined scale heights for the tower + cable = 495 km.
Now you need 6167/495 = 12.5 scale heights. e^12.5 = ~250,000, which is
a factor of 40 improvement.

If you have carbon nanotube cable which has, say a 10 million psi strength,
your scale length is 3810 km, and your area only needs to grow by a factor
of 5 from bottom to top, so the reduction possible by using a tower is much
less helpful. Of course, we are not making 10 million psi cable in useful
quantities yet.

Daniel

Re:Towers as part of space elevator

[MickLinux (579158)]

To be more succinct,

../\
..\/
_/\_

has a lesser mass than

../\
/....\
\..../
_\/_

Aside from that, if you build the tower first, you can launch from the tower to build the rope, and start getting significant returns much sooner.

Last of all, it's easier to blow the second example free in a case of terrorist attack. It's rather hard to do much to the first. And if it does break free, it does tons less damage in the first case (the tower+rope).

Don't get me wrong here...

[Skyshadow (508)]

...but it seems like the climber is the easy-ish part of a space elevator. If they were doing work with the carbon nanotubes, I'd be much more impressed.

Re:Don't get me wrong here...

[barawn (25691)]

...but it seems like the climber is the easy-ish part of a space elevator.

Far from it. All of the components of a space elevator will be revolutionary, not just the ribbon. The climber's mechanical parts have to work flawlessly for about 100,000 km. The actual problem of gripping a cable isn't trivial, either. And it needs to be very low weight. Oh, and very low power. And just to make things even more fun, it'll need to work in vacuum as well.

If you read some of the papers on concerns for the climber at the space elevator conference, you realize that there's nothing easy about this. It's unsurprising that the climber is seeing the most progress first, but that first concern (perfect reliability over 100,000 km) will take a long time, so better to start now.

1 down, 61,999 to go!

[lannocc (568669)]

A little progress is better than no progress.

1500 feet != 1 mile

[Dynedain (141758)]

The article said that the platform (held up by baloons) at the end of the teather was a mile up. The climbing device reached 1500 feet, 500 feet further than previous attempts, but still quite a bit short of a mile.

Acme

[lbmouse (473316)]

I think the theory for this method of transportation was disproved by Wile E Coyote [wikipedia.org] a few years ago.

Ah, the first robot in the Mile High Club

[adnonsense (826530)]

For those who have not experienced this particular pleasure: the obligatory Wikipedia [wikipedia.org] reference.

If this thing snaps.....

[NDPTAL85 (260093)]

...won't it whiplash and kill people all over the world?

Worst problem

[wsanders (114993)]

A guy gets on at the bottom and punches all the buttons. For 100,000 km your're thinking, "asshole!"

Re:I'm a little confused.

[Anonymous Crowhead (577505)]

Take a string, tie a rock to it and swing it around your head. Then you'll get the picture.

Re:I'm a little confused.

[interiot (50685)]

and make a robot to move back and forth along the string...

and shoot laser beams out of your head that powers the robot...

and have safety procedures in place in case the string breaks, and the robot comes plummeting towards your head...

and have the multinational population living on the surface of your head come to some agreement about who's going to finance, maintain, and operate the thing...

Re:I'm a little confused.

[TigerNut (718742)]

The reason to run the cable out to 62000 miles (far beyond geosynchronous orbit) is to be able to hang a counterweight on the outboard end and to have that provide sufficient tension to keep the cable up.

There was an article in Analog (WAAAAY back when) on the math behind space elevator cables, and they indicated that unless a material such as carbon fibers (nanotubes and the like weren't even on the horizon then) were developed to commercial viability then the required strength to weight ratio would make the cable waaay too wide at its halfway point.

Well, you know what they say about assume...

[Skyshadow (508)]

Actually, the ribbon will be tied to a really large bird.

A space bird.

Re:I'm a little confused.

[timster (32400)]

The centripetal force is what holds it down, not what holds it up. From an inertial frame of reference, there is no force that holds it up; that's simply a function of its own inertia. If you wish to use the Earth as your reference frame (as you are doing) you must invent a force, called a centrifugal force, to account for the fact that a spinning object is not an inertial reference frame.

Re:Don't you mean 62 miles?

[RevRigel (90335)]

No. 62 miles is the completely arbitrary definition of "space", but a space elevator that ended at that altitude would simply fall back down. By necessity, the center of mass (radially from the surface of the Earth) must be at or near geosynchronous orbit, so it naturally remains centered over its ground anchor. Geosynchronous orbit is at 22,241 miles above sea level. So, by gradually tapering the cable and extending it past GEO, the center of mass ends up there. Alternatively, you can have a large mass like a captured asteroid or something as an anchor just on the far side of GEO, although you should also have some counterweights you can move around on the cable to keep the center of mass in the right place as a load moves up from the surface. Additionally, keeping the center of mass just a little bit further out that necessary ensures that the space elevator will have just enough tension to keep it taut, giving the climbers an easier job.

Re:Don't you mean 62 miles?

[barawn (25691)]

But who knows, maybe they do mean 62,000 miles? I thought the elevator's main purpose was to get things in and out of just the atmosphere, as to avoid all the problems with expensive and dangerous rocket launches and dangerous re-entries.

We don't use rocket to get above the atmosphere. Planes can pretty much do that. Balloons can (and regularly do) do that. That's the easy part.

We use rockets to get velocity, because you need a ridiculous velocity in order to actually orbit the Earth at a low height.

You do not, however, need a ridiculous velocity in order to orbit at a very, very high height. At geosynchronous orbit, you need no velocity, because you've already got the speed from the Earth's rotation.

So yes, they do mean 62,000 miles (100,000 km). And the benefits you get from a cable like that are insane. Costs/pound to launch things into space become negligible. Transit to the Moon becomes cheap and fast, because the end of the cable is actually moving faster than orbital velocity.

In fact, if you climbed all the way to the end of the cable, and let go with good timing, you'd end up past Jupiter (and on a direct trajectory, too, no mucking about in Lagrange points).

Yes, it's moderately insane. Yes, it's ridiculously difficult. But it would also end up being one of the biggest changes in human industry that has ever occurred. Space solar power plants beaming down power becomes feasible. Large-scale structures built in space become easy.

Plus, once we get the technology, we can build them on other planets as well. The Moon. Mars. It basically eliminates almost all of the serious difficulties of space flight.