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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 stood outside my door this morning in Flagstaff, which is 6200 feet above the Arizona desert.
"Made up/misattributed quote that makes me look smart. I am on
The robot only made it around 1500 feet. The cable was a mile long.
...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.
Every year during my review, I just pray the words "slashdot.org" aren't mentioned.
A little progress is better than no progress.
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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.
I'm out of my mind right now, but feel free to leave a message.....
I think the theory for this method of transportation was disproved by Wile E Coyote a few years ago.
I'm just wondering, won't these things become a lightning magnet? You say it can be grounded, but what happens when these things stretch into higher parts of the atmosphere with more ions flying around?
For those who have not experienced this particular pleasure: the obligatory Wikipedia reference.
Take a string, tie a rock to it and swing it around your head. Then you'll get the picture.
A space bird.
Every year during my review, I just pray the words "slashdot.org" aren't mentioned.
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 of those associated with current means.
The platform, a proprietary system that the company has named "HALE"
Oh come on, they're just asking for it.
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.
Less is more.
...won't it whiplash and kill people all over the world?
Mac OS X and Windows XP working side by side to fight back the night.
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.
I have seen the future, and it is inconvenient.
...when they extend that thing if the moon gets nervous?
The race isn't always to the swift... but that's the way to bet!
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.
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.
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.
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.
What he can't kill, he has sex on. Trent.
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...
Do the maths: taking the earth as 6,000,000m across and an average density of 2t/m^3:
Volume ~ 4/3 * 3 * (3,000,000)^3 ~ 115,000,000,000,000,000,000 m^3
Mass ~2xvolume tons: ~300,000,000,000,000,000,000 t
To take a billionth part out would be 300 billion tons.
Much of a problem?
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.
Really? Are you sure? Can you build a bearing for a 20-cm wheel that will be able to turn 500 million times with zero chance of failure? And can you do it lightly? And in vacuum?
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".
Does the firm have any ideas on how to avoid tremendous death and destruction if this immensely long cable were to fall to the Earth, possibly hitting certain areas twice as badly if it were long enough to wrap more than once around?
Yes. They're going to deploy a massive cushion 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.
A guy gets on at the bottom and punches all the buttons. For 100,000 km your're thinking, "asshole!"
Give a man a fish and you have fed him for today. Teach a man to fish, and he'll say "WHERE'S MY FISH, YOU IDIOT?"
The point is that the cable is by far the hardest part. We aren't even close. When we are 75% of the way to producing an adequate cable we can start the other parts. I bet we would still finish those other components before the cable is ready.
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!
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
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.
Hell, you don't even need to reach escape velocity - just build a pyramid 36000km high, hoist stuff slowly up the side, then give it a gentle push!
Alien tourists would come to see the only planet in the galaxy that looks like an ice cream cone...
What part of "a well regulated militia" do you not understand?
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has a lesser mass than
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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).
Correct Horse Battery Staple: 72 bits of entropy. Enter "Correct H" into google. When it generates the phrase, that's
Your post makes me incredibly glad I learned physics using only metric units.
Megainches??? Do real scientists seriously use such a measurment?
-- If you try to fail and succeed, which have you done? - Uli's moose