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Continued Success for Space Elevator Tests
Posted by
ScuttleMonkey
on Wed Feb 15, 2006 03:13 PM
from the world's-highest-kite dept.
from the world's-highest-kite dept.
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."
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Space Elevator An Impossible Dream? 448 comments
bj8rn writes "Three months ago, the dreams of a space elevator finally seemed to be coming true after a successful test. An article in Nature, however, suggests that there's reason to be pessimistic. Ever since carbon nanotubes were discovered, many have been hoping that this discovery would turn the dream into reality. Pugno, however, argues that inevitable defects in the nanotubes mean that such a cable simply wouldn't be strong enough. Even if flawless nanotubes could be made for the space elevator, damage from micrometeorites and even erosion by oxygen atoms would render them weak. It would seem that sci-fi will never be anything other than what it is: a fiction."
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I can top that. (Score:5, Funny)
1500 feet not a mile (Score:5, Informative)
Re:1500 feet not a mile (Score:5, Funny)
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.
Parent
Heres a question (Score:4, Funny)
Why don't we just build a 500 mile high pyramid of some description? And maybe run a ramp up it, and a pulley system maybe so we can use very simple earthbound techniques to get projectiles to an incredible speed before liftoff? Alternately, its surely easier and cheaper to get a launch from 500 miles up, or put the tail end of a space elevator there. And we could do it with existing technology easily. Its like the question, if there were stairs going to the moon, could you walk it... the answer to that one is yes.
Parent
Re:Heres a question (Score:5, Funny)
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!
Parent
Re:Heres a question (Score:5, Funny)
Are you kidding? I've got a stele full of them!
Parent
Re:Heres a question (Score:5, Funny)
Parent
Re:Towers as part of space elevator (Score:5, Informative)
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
Parent
Re:Towers as part of space elevator (Score:5, Informative)
..\/
_/\_
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).
Parent
Re:Towers as part of space elevator (Score:4, Insightful)
Megainches??? Do real scientists seriously use such a measurment?
Parent
Even more musings (Score:4, Funny)
Alien tourists would come to see the only planet in the galaxy that looks like an ice cream cone...
Parent
Re:Heres a question (Score:4, Informative)
v[f]^2 = v[i]^2 + 2ad
So, from a standing start, taking optimistic values for acceleration (say 10 G's), and the length of the ramp (say 100 km):
v^2 = 2*10g*d
v^2 = 2*10*9.81*100000
v^2 = 19620000
v = 4425 m/s
Which isn't even close to what you need for orbit, so you still need a significant rocket. Except now, you need a rocket that can handle your launch ramp, which isn't trivial.
You'd end up spending a lot of money for not much gain. You'd save some fuel, but complexity is already the expensive part and you're increasing that quite a bit.
Parent
Re:1500 feet not a mile (Score:5, Informative)
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.
Parent
Re:1500 feet not a mile (Score:5, Insightful)
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
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.
Parent
Re:1500 feet not a mile (Score:4, Interesting)
Wait, so you do know how to build the cable? You should get in touch with these people!
You took that comment the wrong way - it wasn't meant as "you don't know what you're talking about" it was meant as "since we don't know how to build it, we don't know how hard it is going to eventually be." Unfortunately the two have the same wording.
I encourage you to check out spelsim or the gizmonics calculator. A 50GPa elevator weighs ten times as much as Edwards' calculation, and Edwards' calculation wasn't cheap.
Edwards's calculation was feasible for a business. A 50 GPa elevator would be feasible for a government. And I have checked out spelsim. I know the deal. I just have different views on "feasible" than you do. What was the estimated total cost of Apollo in modern dollars? $200B or so? And the US GDP is 4 times larger than it was then (adjusted for inflation). Feasible for the US, today, is roughly $1 trillion dollars. (*)
*: Now, whether or not it's sane to invest $1T in a space elevator - that's a different matter. Many people would argue that it wasn't sane to invest in Apollo either. I also know if you use percentage of GNP for Apollo - ~3%, and the years it took - ~10, you get about oh, half a trillion or so in current dollars. Close enough for me. And I know the reason we invested in Apollo was for military reasons. Don't shatter my deepfelt optimism that one day we'll invest as much money in exploration as we did in a giant pissing match.
The climbers are.
The climbers are not realistic present-day. Did you read the presentations from the Space Elevator conference on climber design? There were concerns that they might be impossible from power dissapation concerns. And the reliability requirements were way, way above what exists anywhere else.
You can't go out and buy the climbers off the shelf. Therefore it makes sense to figure out exactly how much work they'll need to get working. Which... is what they're doing.
Plus, as I said, the climbers block the development of the power system, since the power system needs to know how much power the climbers need.
Frankly, I'm really baffled by the derision. If it takes 20 years to figure out the cable, then they have 20 years to develop the climber. Which means it costs less per year, so it can be funded via simpler methods - including volunteer time.
Parent
Re:1500 feet not a mile (Score:4, Insightful)
Liftport doesn't have a "get out of physics free" pass.
Parent
Don't get me wrong here... (Score:5, Interesting)
Re:Don't get me wrong here... (Score:5, Insightful)
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.
Parent
Re:Don't get me wrong here... (Score:4, Interesting)
Parent
Re:Don't get me wrong here... (Score:4, Insightful)
Oh, and I didn't see this. Fundamentally, this is a bad idea. First off, the idea of a modified Howitzer? That's just explosive propulsion. This is fundamentally the same idea as a rocket - it's just that a rocket is far, far more effective in terms of thrust per unit mass.
You could imagine electromotive propulsion - a rail gun - but the problem with that is that you're imparting all of your momentum in the thickest part of the atmosphere, at which point it would just be bled away as air resistance. You'd need to supply a ridiculous amount of energy to do it, and the craft would have to have a ridiculous amount of stress support and heat resistant material. It gets to the point where there is no way that it would ever be economically feasible.
On an atmosphere-free planet, though, it does become pretty feasible, though a space elevator is likely to be more generically useful for large cargo.
Parent
1 down, 61,999 to go! (Score:5, Insightful)
Re:1 down, 61,999 to go! (Score:3, Funny)
1500 feet != 1 mile (Score:5, Informative)
Re:1500 feet != 1 mile (Score:3, Insightful)
One issue I have yet to see addressed is the issue of speed. Rockets make it up to geosynchronous orbit (22,240 miles) very quickly by moving really, really fast. Somehow, I don't think a robot climbing a ribbon will be very fast. Even at 1,000 mph, it'll take almost an entire day to get there. I don't know what the actual expected speeds will be, but I don't think
Re:1500 feet != 1 mile (Score:3, Interesting)
Acme (Score:5, Funny)
Lightning Rod? (Score:3, Interesting)
Re:Lightning Rod? (Score:3, Interesting)
It's probably too diffuse to conduct well enough into the elevator tether easily, but I wouldn't be surprised if the tether is differentially charged to significant potentials, which could create interesting problems.
On the other hand, it could be an interesting way to generate power for lifters, if you could find a way to have two strands with different potentials along them run the length of the e
Ah, the first robot in the Mile High Club (Score:4, Informative)
For those who have not experienced this particular pleasure: the obligatory Wikipedia [wikipedia.org] reference.
Lifter didn't climb one mile (Score:3, Informative)
I'm afraid I can't do that Dave (Score:3, Funny)
Oh come on, they're just asking for it.
If this thing snaps..... (Score:5, Funny)
I wonder... (Score:4, Funny)
in other news (Score:4, Funny)
In other news today, Denver-based Space Elevator company Black Shaft Industries have succeeded in achieving a height of 35 feet with their platform and climber, still easily besting their rivals Lifport. "We had a head start," acknowledges Chief Engineer, Michael Wesznick, "but our elevator didn't really need it. Plus, it has a cooler name." Wesznick went on to claim, that the elevator in question (named "Darth-Vator" to those of you who were wondering) will be the "father of all other space elevators", and, adding to this reporter's confustion, will at some point in the future "betray the Emperor to save it's son's life." Personally, I'm rooting for Lifport.
Worst problem (Score:5, Funny)
Re:I'm a little confused. (Score:4, Informative)
Parent
Re:I'm a little confused. (Score:5, Funny)
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...
Parent
Re:I'm a little confused. (Score:3, Informative)
Re:I'm a little confused. (Score:3, Informative)
The most common proposal is a tether, usually in the form of a cable or ribbon, that spans from the surface to a point beyond geosynchronous orbit. As the planet rotates, the inertia at the end of the tether counteracts gravity and keeps the tether taut. Vehicles can then climb the tether and escape the planet's gravity without the use of rockets. Such a structure could eventually permit delivery of great quantities of cargo and people to orbit, and at costs only a fraction o
Re:I'm a little confused. (Score:4, Informative)
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.
Parent
Well, you know what they say about assume... (Score:4, Funny)
A space bird.
Parent
Re:I'm a little confused. (Score:5, Informative)
Parent
Re:1 mile down.... (Score:3, Insightful)
Re:1 mile down.... (Score:3, Insightful)
> significantly more difficult than the next 61,999?
Er...except it's not. As you leave the atmosphere there's temperature extremes...radiation...vacuum. Not to mention every mile you extend the elevator increases the strain the structure must support. The first mile is the *easiest*.
Chris Mattern
Re:Don't you mean 62 miles? (Score:5, Informative)
Parent
Re:Don't you mean 62 miles? (Score:5, Informative)
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.
Parent
Re:Don't you mean 62 miles? (Score:4, Insightful)
I word things very carefully. Read it again. I said "planes can pretty much do that." I was actually thinking about commercial airlines, which fly above 72% of the atmosphere.
But, of course, there's this nugget from Wikipedia:
Balloons typically reach altitudes of 100K feet, which is above all but a fraction of a percent (it's a few Torr).
simply by building our velocity high enough to escape velocity while in the atmosphere and letting inertia take us out.
Ignoring that whole "air resistance" and "speed of sound" thing.
And curiously, if it wasn't for those two things, we could do that right now.
We use rockets for velocity, not altitude. If you doubt me, consider that the Space Shuttle's two solid rocket boosters shut off at lower altitudes than the X-15. Why don't we use a jet to boost the Shuttle to that altitude? Because the SRBs get the Shuttle to a much, much higher speed.
There's nothing "special" about Geosynchronous orbit which means you can "get the velocity from the Earth".
I get velocity from the Earth all the time. It's called standing on the ground. (Curiously enough, if I didn't, I would start flowing in these little circly patterns, called Hadley cells, which are what happens when you have a viscous medium gravitationally sitting on top of a rotating sphere. If the atmosphere extended enough, it essentially wouldn't be rotating.)
That's what special about geosynchronous orbit. Orbital velocity is slow enough that I can use the Earth's rotation to supply it.
You DO have velocity.
Which I got... from the Earth. Like, when a plane lands, after heading west, how the Earth speeds it up in a matter of seconds?
The idea is at that height, escape velocity is negligable.
It's not "negligible" - it's two thousand miles an hour (curiously, roughly 1 km/s). It's just neglible in the rotating frame of the Earth.
Parent
Re:So what? (Score:4, Insightful)
While we don't have the ribbon yet, we don't have the climber, and we don't have the power delivery system either. That's why it's called inventing. They're doing something that hasn't been done before.
And when you've got multiple independent difficult problems, you might as well work on all of them at once. Which they are doing.
Go and read the talks on building the climber at the last space elevator conference before you call it "trivial".
Parent
Re:So what? (Score:4, Interesting)
It's just a bit silly really... like building the lunar lander for Apollo but having boosters no larger than a bottle rocket.
Get closer to the Saturn V THEN build the lander!
Parent
Re:And if it falls? (Score:4, Funny)
Yes. They're going to deploy a massive cushion [wikipedia.org] around the Earth, consisting of a total of about 5000 trillion metric tons of gas. Roughly 78% will be nitrogen, and 21% will be oxygen.
If the cable breaks, the lower half will encounter this cushion at extremely high velocities, ripping it apart and causing it to flutter harmlessly to the ground.
No news about whether or not they'll patent the idea.
Parent