Highlift Systems' Space Elevator In The News Again 618
Kris_J writes "Highlift Systems may have found a second location for the anchor of their space elevator -- Perth, Western Australia. Apparently we have the calm waters and international airport that it needs, amongst other things. Slashdot has covered this company's efforts before: Oct 9, 2002 and, earlier, August 13, 2002, but it's worth discussing again since '[recent funding] has been given momentum by the Columbia shuttle disaster.'"
But what about? (Score:4, Funny)
Re:But what about? (Score:3, Funny)
Comment removed (Score:4, Funny)
Coming down (Score:4, Funny)
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Re:But what about? (Score:4, Funny)
Can you hear me now?
Okay (Score:3)
Re:Okay (Score:2, Informative)
Obviously, there has to be a pretty good anchor in the ground for it not to go flying into space.
Re:Okay (Score:3, Interesting)
Question: The article mentions having a cable some 100,000 kms long. Uh, wouldn't that lap the planet a few times? What would keep (or cause) a Gary Larsonesque tragedy from occuring?
Granted I'm being leight hearted with my question, but in light of the recent shuttle tragedy one has to weigh the potential risk of something like this happening.
Re:Okay (Score:4, Insightful)
Re:Okay (Score:3, Informative)
If this is built out of carbon nanotubes, like people suggest, then its possible they could be woven together in such a way that if any point broke, the chain would come apart in many places, so that a lot of little pieces would fall, however the extra length/weight of tubing required for this might make it prohibitive.
Re:Okay (Score:3, Interesting)
Something like this happens in 'Red Mars' - the cable snaps after the end-point in space is blown up, and wraps itself aroung the planet, with huge destructive force, making a giant trench. KSR prides himself on being as scientifically accurate as possible, is this an error?
Re:Okay (Score:3, Informative)
The cable simply lacks the required strength to do this. It's made of carbon nanotubes, which are incredibly strong and ligthweigth. Those tubes would however burn up on reentry in the atmosphere.
If some low pieces should somehow *not* burn up, then they would fall very slowly, this is due to the low density of such a cable. Think along the lines of a 5cm wide strip of paper falling. It would not make a huge mess on impact exactly...
Re:Okay (Score:3)
This is a job for.... International Rescue!
mod parent down science is wrong (Score:5, Informative)
Re:Okay (Score:4, Informative)
This is a bit of a simplification, but here goes. In a space elevator, the object at the other end of the cable is in geosynchronous orbit. The cable's purpose is purely for the elevator to traverse. You could take the cable away and the object at the end would still be there*. It is not holding the object in it's orbit - that's what gravity is for.
* Technically, that's not true. Because the cable and cargo have some weight, you have to figure it into the calculations on where the object at the end will rest. It will actually be slightly farther than geosynchronous orbit.
Re:Okay (Score:2, Insightful)
Rotational velocity. The rotation of the earth imposes an outward force on the elevator, keeping it in place. The elevator would be anchored to the earth, not anchored to the sky.
Re:Okay (Score:3, Informative)
What's that sound? Why, it's just Isaac Newton, spinning in his grave fast enough to power a city...
Velocity exerts no force. The orbital anchor will "want" to fly off straight at high speed. The (currently wundertech) carbon nanotube cable, attached to it, suffers a tension. The Newton III complement to this tension pulls the anchor toward the Earth. This imparts an acceleration exactly balanced so as to cause the anchor to execute a circle about the center of the Earth.
It's only been 320 years since the Principia. Maybe someday soon we'll catch up to Newton.
Re:Okay (Score:5, Informative)
will SOMEONE explain to me how such a thing is supposed to work?
In a nutshell, the center of mass of the whole elevator, including ribbon and cargo, is at (or near enough) the radius which provides geosynchronous orbit. This can be achieved and maintained in a number of ways, all of which are irrelevant details once you grok what 'geosynchrony' and 'orbit' really mean.
Carbon funicular (Score:3, Informative)
Weeeell, yes, just not for very long. I suppose you could build tracks around a meridian and put up with trains constantly hurtling around the planet at over 1000km/h, but it would hardly be economical.
Assuming the original poster was not just practicing rectal ventriloquism, `connected' doesn't mean literally bolted together. You would slingshot a load off the end of the elevator and catch it again on the end of another elevator at the destination. You could also use elevators (even just spinning tethers in free space) to accelerate and decelerate traffic out- and in-bound.
Translation: `I have no sense of scale'. (-:
On top of this, since the elevators are in orbit, they don't make the planet wobble at all (caveat: the mass of the elevators would move the center of mass of Earth, perhaps by a measurable amount).
Re:Okay (Score:2, Informative)
To give you an idea, get a weight and tie a rope to it. Spin in a circle. Notice the weight pulls away from you and stays steady? Now, you could build a little robot to move up and down that rope (while you are spinning it). That's how it works. The forces are astronomical though, and the materials science problem is why it hasn't been attempted before.
Re:Okay (Score:3, Informative)
The other possibility sometimes mentioned is electrical charge. The differential over a long length of conductor inserted into the Van Allen belt could provide enough charge to suspend it.
Re:Okay (Score:5, Informative)
Re:Okay (Score:5, Informative)
The first cable would be 1 micron thick, and taper from 5cm wide at Earth to 11.5cm in space. This would be added to each climb. By the 107th addition it would be capable of holding a climber of 22tons with a 14 ton payload.
Of course it would be made of Carbon nanotubes (the only thing that could possibly be strong enough and light enough).
Now I'm not saying I believe it can or will be done. I'm only quoting Bradley C. Edward's paper.
Re:Okay (Score:5, Informative)
It's like this...a car pulls a trailer. The car is pulling the trailer! There is a force acting backwards on the trailer hitch on the car, but it is actually the car pulling the trailer, not the other way around. The anchor is not pulled by the swung object, the anchor PULLS the swung object.
If the string is cut, the object does not accelerate away from the anchor because of some centrifugal force; the object will STOP accelerating and continue along in a straight tangential line.
Centripetal force is real, centrifugal force is apparent.
Re:Okay (Score:5, Funny)
I hope the clears it all up (or down as the case may be) for you.
Re:Okay (Score:3, Informative)
Re:Okay (Score:3, Informative)
you slack or stupid? (Score:5, Insightful)
Which just goes to show, if you're asking on Slashdot, then you're either too lazy or too stupid to find out yourself.
As long as you're talking how it works (Score:2)
Re:Okay (Score:3, Insightful)
Centrifugal force pulls the moon away from us.
Gravity (both from the Earth and Moon) pull them towards each other.
Kind of like if you swing a weight on a string. But gravity is the string. That's why the moon can be not in a geosynchronous orbit. It's string moves.
With a heavy weight (platform) on the end of their carbon nanotube string, far enough away from the Earth, the platform should be pulling on the string, so the fact that you're pulling a bit on the string back down isn't much.. You'd be as significant as an ant on top of a mountain.
That'll be an interesting place to visit..
I wonder how long after the build it, that someone will build a solar sail craft.. It's not a hard concept.. Make "sails" big enough to create a small force from the solar winds. Then it would be a simple matter of riding the winds and gravational forces of the bodies encountered. Mars may be a lot closer than we thought.. You could fly the solar system with almost no fuel.
I volunteer to take a fast run to Pluto. The course should be pretty easy. It'll just take a little math to figure out..
Leave the platform, "falling" towards the moon. Pass the moon, and change your vector towards the sun (ok, a little fuel). Now "fall" towards the sun.. It's a good sized object, it should have a little pull. (hehe).
Use Venus and it's moons your next turning point. Sails out, then pick and choose your planets to use to manuver..
With a bit of good navigation other solar systems aren't quite as unreachable as they are now..
You angle the sail, and/or you tack. (Score:3, Insightful)
Re:Okay (Score:4, Informative)
Speare's giving the basic idea: You keep the entire Load-Cable-Station system as a whole at (or near) geosync.
There are a couple different methods that have been tossed around, some more elegant or wasteful than others.
One method involves building a massive offloading station and using rockets to automatically maintain the orbit. You basically ignore the orbital decay induced by lifting the elevator, as the load is probably much smaller than the space platform and won't have an effect the already necessary constant correction wouldn't take care of in it's normal course of duty. This method is relatively easy to initially set up, but lifting heavier loads would require A) more propellant AND/OR B) a more massive end station.
Another plan is to have mobile weight(s) attached along the cable. As a load advances along the cable the weight(s) adjust position (and so the effect on the station-cable system's orbit) to counterbalance the drag of the load. Basically you turn the whole thing into a huge counter-beam balance. The really kinda groovy thing about this system is that you can automate the weights and skip the whole business of a far-end station altogether and just have the load slip off the end of the cable.
A third option involves launching a counterweight into a higher orbit and then reeling it back in while the load is climbing.
Incidentally, as seductively simple as the swing-a-rock-around-your-head description sounds, there should be almost no tension/load at the Earth-Cable and Station-Cable connections (except perhaps during operation, and not necessarily even then depending on how you choose to compensate for the load).
A clarifying question would probably be to ask what's resisting the downward force of *the cable*.
The Actual Physics: (Score:5, Informative)
E =
(m = mass of object, r = distance between centers of mass, dr/dt = rate of change of distance between centers of mass, L = angular momentum, G = gravitational constant, M = the mass of the Earth) The first two terms are kinetic energy, and the third is potential. It is possible, however, to group the angular momentum term with the actual potential energy, and what you get looks like a centrifugal force.
You're right to be concerned, though, because angular momentum looks like this:
L = m*(omega)*r^2
( omega = angular frequency) The object is climbing outward with a constant angular frequency (the cable gaurantees that the object will sweep the same angle in the same amount of time), but the distance between the object and the Earth is increasing, thus the angular momentum of the object is increasing. The exact size of the effect depends on the how the length of the cable compares with the radius of the Earth (change in angular momentum: L - Lo = m*(omega)*(C^2 + 2*C*R) where C = cable length and R = radius of earth), but even if the change isn't big, the angular momentum has to come from somewhere. And it comes from the rock and the cabel (effectively dragging it in a bit). It will probably be massive enough that a single load won't bring it crashing down. Plus, anyone returning to Earth is going to have to, in effect, return the angular momentum they took from the elevator as they climb down.
So, long story short, there are two things that will keep the thing up over the long haul: one, inbound and outbound traffic will tend to balance each other out; two, we can use vastly more efficient ion thrusters to keep it in orbit. Ion thrusters don't work for launching things, because they are incapable of overcoming the force due to gravity directly. What they excell at, is increasing or decreasing angular momentum once the object is in a frictionless environment, because they use small forces for extremely long firing times (chemical rockest last minutes and have millions of pounds of thrust, ion thrusters can go for weeks or months non-stop and push about as hard as a piece of paper on the palm of your hand; the ion thruster still wins out in terms of amount of fuel used to get the same effect, it just takes longer to do it). Granted, we couldn't have everyone rushing a non-returning payload out to the top at once, so it has its drawbacks, but it would still be vastly more efficient than the present system. If it is even feasible, that is.
BlackGriffen
Re:The Actual Physics: (Score:3, Informative)
Taking an irrotational center of mass frame, things get even more interesting. For starters, the position of the center of mass of the system cannot change. So, when you move a payload out to the asteroid, you change the position of the center of mass relative to the center of mass of the Earth (moving it out a bit). Since this is a closed system, Ltot cannot change. Ltot = I*(omega), and I (the rotational inertia) is increasing, omega, which is both the rotational speed of the earth and the orbital speed of the platform, has to change. So, even though it is still geosynch without help, you still want to get omega back up to keep the thing from falling down.
So, going back in to the reference frame I originally considered. the energy of the object is approximately (to within several orders of magnitude):
E =
The angular momentum of the parts of the system are:
Lp = mp(omega)rp^2 (mp = mass of platform, rp = orbital distance of the platform)
Le = Ie*omega (Ie = rotational inertia of earth about its center, a constant)
Lc = mc(omega)(d+R)^2 (mc = mass of cargo, d = distance climbed, R = radius of earth)
The angular momentum of the climbing object is increasing because (d + R)^2 dominates changes in omega, but that angular momentum is coming at the expense of both the earth (which is losing omega but not changing shape) and the platform (which is losing omega and not changing its orbital distance). That is, assuming that the platform is geosynchronous, which does not have to be the case.
The system I originally described, though, pretty much assumed no significant attatchment to the Earth's crust, which would be cheaper (less of an anchor to the earth needed) and far more feasible (Earth's crust not something good to anchor to for something as big as I'm thinking of).
It's bad enough that I had to teach the professor of my advanced mechanics class how to do orbital mechanics properly, I really shouldn't be wasting my time expaining everything to some know-it-all on Slashdot.
BlackGriffen
Question (Score:4, Insightful)
Also, could this possible create drag in the solar wind and slow the Earth's rotation? (most likely another stupid question)
Re:Question (Score:5, Informative)
Good article, nice website, fantastic project. As Arthur C Clarke said (I think, loosely), we'll be using a space elevator about twenty years after everyone stops laughing at the idea.
Re:Question (Score:5, Informative)
Not stupid at all, accurate actually. See their FAQ [highliftsystems.com] .
The second paragraph ends with:
It's kinda neat that they used Australia as an example (I read their FAQ a few days ago, before this decision about putting it near Australia was published; they didn't change the example for this recent news).
OT: the fortune at the bottom of the page is very amusing: "Mr. Spock succumbs to a powerful mating urge and nearly kills Captain Kirk." -- TV Guide, describing the Star Trek episode _Amok_Time_
Re:Question (Score:5, Informative)
P.S. Yes, technically the orbit of the top of the elevator/upper anchor is not geosync, but rather slightly above geosync to allow for the center of mass of the contraption to be geosync in its orbit, (and the bottom anchor then serves to maintain the proper orientation).
Re:Question (Score:5, Informative)
There's also no reason why the top would "lag behind a bit". In fact the orbital speed of the counterweight will tend to increase, not decrease, if the orbit decays below geosynchronous orbit. So it would tend to lag forward, not behind. It would definitely need a transport system to carry rocket fuel up to the counterweight for corrective thrust.
The real reason why one hasn't been built is the extreme material strength required. Nobody has yet developed a material that can hang suspended for a length of 30,000 miles without breaking. This is why most designs count on the bottom of the elevator touching the ground, so that a significant portion of the elevator's weight can be supported by contact with the earth instead of tension in the elevator. Another mitigating factor is the weightlessness of the material at high altitudes- the parts up near the counterweight hardly contribute any tension at all and can be built especially thick. Even with these two caveats, the required tensile strength is so high that people still talk about exotic materials like buckytubes and single-crystal metals whenever the topic of the space elevator comes up. Without some breakthrough in materials engineering, the project is essentially hopeless.
Re:Question (Score:5, Funny)
For technical reasons this only works when the bottom of the elevator ribbon is suspended a few feet about a small wicker basket; however, the idea is sound.
This also alludes to the second problem in keeping the elevator vertical - once the material strength issues are solved, you still need to find someone who can play the flute indefinitely without stopping. The Perth placement is partly designed to take advantage of the circular breathing techniques developed and perfected by the local didgeridoo players.
Just the opposite (Score:5, Insightful)
First of all, the tendency to buckle makes it vastly more difficult to build a long structure under compression than one under tension. Building a structure to support the elevator from below would be just like building any other skyscraper; you wouldn't get the top of the section under compression to be more than a mile off the ground, and after that you'd still have 25,000 miles to go.
But perhaps just as importantly, the bottom of a geosynchronous elevator design needs to touch the ground because it needs the base to be pulling down on it, not lifting up. If you want to take a 20 ton payload up the elevator without pulling it down, then the elevator is going to need to be under at least 20 tons of tension at the ground when there is no payload on it.
Re:Just the opposite (Score:3, Insightful)
Naah, not necessarily.
Say (for simplicity of argument) we have a free-floating design, with a basket hanging a few feet off the ground. In equilibrium, the center of mass of the entire elevator (basket, cable, counterweight) is in geosynchronous orbit.
You put a 20 ton payload into the basket. This shifts the CM downward by an amount. So you pump (weightless) hydrazine up the elevator to corrective rockets sitting on the counterweight, and the rockets push the CM back up into geosynchrous orbit. They do this by pushing the counterweight into a realm above geosync orbit where it experiences a centrifugal force of 20 tons in the upward direction, and this equilibrates with the 20 tons pulling down on the ground. Of course the centrifugal force isn't a "real" force, it's really just an artifact of inertial effects within a rotating coordinate system.
Once the CM is in stable orbit again it doesn't matter what you do with forces internal to the orbiting assembly, i.e. between the counterweight and the basket. Pulling the basket up to the level of the counterweight won't alter the CM placement. (Although sideways Coriolis forces on the rising 20 tons will start complicating things on the way up.) Still, the amount of rocket fuel spent raising the payload into orbit this way is much less than with a conventional rocket.
Your design is slightly different in that you have the CM sitting outside geosynchronous orbit in the realm where it experiences the outward centrifugal force all the time. So you've got the other end attached to the ground, pulling up on it. This is conceptually a little bit simpler to grasp, but it puts increased tension in the cable, and after lifting a certain amount of stuff into orbit, the CM of the system will reach geosynchronous orbit anyway- and all the tension at the ground will be gone.
But there is hope (Score:5, Informative)
While there is no current material that yields the necessary strength/mass required in order to built a space elevator, realistic possibilities are on the horizon. Quite simply, with the advent of nanotechnology, we are nearing the technological feasibility of creating a material composed of intertwined nanotubes. This is theoretically the strongest material that can ever be created. Carbon-Carbon bonds are extremely strong and would be extremely densely packed in a nanotube pole. It would be an order of magnitude stronger than steel, as well as significantly lighter.
While nanotubes can already be readily produced (Dr. Smalley of buckyball fame operates a production facility), strong nanotubes rods have yet to be produced. This is due to a variety of technical hurdles that must still be overcome. Perhaps the foremost obstacle is getting the produced nanotubes to lie parallel to each other. The current production method has the nanotubes forming from a catalyst and then becoming intertwined in a jumbled mess. When tension is applies to the mesh, the rope breaks not within the nanotubes (which would require a great deal of energy), but between the nanotubes, unraveling them from each other. Attempts to get the nanotubes to align properly have failed. Nanotubes are not an easy molecule to work with. They have extremely strong cohesion forces and are very difficult to pull apart from one another. The obvious approach of functionalizing each nanotube in order to orient it correctly doesn't work as doing so causes the nanotube to lose much of its mechanical and electrical promising properties.
In addition, when nanotubes are put under extreme mechanical stress, the bonds within the nanotube shift. For example, I've seen simulations where the bonds separating two polygons disappears, creating what appears to be a bonding who in the nanotube. The hole then resonates through the nanotube causing significant weakening in the structure.
At a talk I attended, the most promising idea I heard discussed was a steel/nanotube alloy. The nanotubes would run vertically through the steel, reinforcing the structure in the same way steel rods are often used to reinforce concrete. This would alleviate the risk of the nanotubes becoming unraveled intermolecular while at the same time using their large intermolecular strength to reinforce the structure.
Of course, without any physical models, this is mere speculation. However, it suffices to say that a there are real possibilities of breakthroughs that would allow for the construction of such a space elevator.
Re:Question (Score:3, Interesting)
Re:Question (Score:2)
Re:Question (Score:2)
Seriously, my guess is that there's going to be enough money floating around this operation for a mathematician to be engaged just to sort this stuff out.
Great Glass (Score:5, Funny)
Fortunately (Score:5, Funny)
Off-topic? OFF-TOPIC??? (Score:2, Funny)
Muzak == Craziness
Moderators == On Crack
Clark's Fountains of Paradise (Score:5, Informative)
Arthur C. Clark wrote a novel, Fountains of Paradise, where the whole premise of the story revolved around the creation of the first space elevator. It's worth a read for anyone who wants to understand the basics of the concept.
Re:Clark's Fountains of Paradise (Score:2)
Re:Clark's Fountains of Paradise (Score:2)
Re:Clark's Fountains of Paradise (Score:2)
Monorail (Score:5, Funny)
Lyle Lanley: Well, sir, there's nothing on earth
Like a genuine,
Bona fide,
Electrified,
Six-car
Monorail!
What'd I say?
Ned Flanders: Monorail!
Lyle Lanley: What's it called?
Patty+Selma: Monorail!
Lyle Lanley: That's right! Monorail!
Get the earth elevators right first! (Score:5, Funny)
Just like the usual, the mechanics are off for today. It would sure suck to hang up there held by a f...ng thread
Re:Get the earth elevators right first! (Score:2)
Don't worry. They have a backup-plan: stairs. You can leave the luggage- it will be delivered when (if) you reach the top.
Ya know ... (Score:5, Funny)
Although, it would make for a REALLY good tv-movie.
Re:Ya know ... (Score:4, Informative)
It seems like.. (Score:4, Interesting)
Basically, it would take some sort of War or space race with China for this to even be the slightest possiblity. Tax payers will not vote for a 17 billion dollar project unless it was under dire circumstances or felt threatened [alla China]
Think about all the previous advances in the human culture. So many were spawned from war. For instance, I doubt the common 747 jet airliner would be such a popular mode of transportation today if the Nazi's weren't looking for a plane that could run circles around the allied air force.
This post is going off in a tangent. I guess what I'm trying to say is that with war comes advancement in technology. Without war, technology is backed by monetary gain. What is to gain by building a space elevator? Unless they can mine diamonds or gold from the upper atmosphere...
Quite the contrary (Score:2)
KFG
Re:It seems like.. (Score:3, Insightful)
WRT the anecdotal comment regarding mining diamonds: Potential diamond yield is unlikely to encourage anything, since diamond production is artificially stymied by a cartel. I'm pretty sure you didn't mean it seriously, but it does elucidate the enigma of incentive, which is really the core of this converse.
I think your comments on a China space race, and allusion to Nazi induced innovation, are right on the money. Let us hope that, with respect to the latter, it is not a price we should have to ever again pay for innovation.
100,000 *km* tall? (Score:2)
100,000km would be almost a third of the way to the moon, right?
Maybe the plan is much more ambitious than I thought...
Crud. Guess I'm stupid. (Score:2)
I always thought this thing was going to just tickle the atmosphere. I was off by a factor of 1000.
Wow.
When can I get a ride?
Re:Crud. Guess I'm stupid. (Score:2)
Just the base tower is going to be 30 miles high, the cable itself is going to be collosal.
By the time the carriage reaches the end it should be doing about 7 miles per second.
Perth people, prompt the Premier page (Score:5, Informative)
Re:Perth people, prompt the Premier page (Score:2)
Australia? (Score:5, Interesting)
Re:Australia? (Score:5, Funny)
No, Sri Lanka was to get it as close to Arthur C. Clarke as possible.
Re:Australia? (Score:3, Insightful)
Though they may be good at cricket, I wouldn't call Sri Lanka politically stable.
Re:Australia? (Score:2)
- in
- near
- economically advanced
- politically stable country
I might not argue, but SR may have something to feedback. Some could argue that ANZ fails a point or two from that list...joke.Why Bother? (Score:2, Insightful)
If you ask me, we put altogether too much emphasis on putting stuff in orbit these days. Manned space exploration has been stalled since the end of the Apollo program; putting people into orbit has become the be-all and end-all. Our focus should be beyond orbit; we should head back to the moon, and then on to Mars. Right now, we are doing fine using disposable rockets to put satellites into orbit, and assuming that the investigation into the Columbia disaster comes up with substantive results and recommendations, the shuttle program can continue to put people into orbit (and we end up grounding the shuttles, I don't see why we can't use Soyuz-like capsules to send people to orbit). If we're planning new space technologies (and major space-related capital commitments) I think we must literally aim higher than Earth orbit. While a space elevator would be an incredible technical achievement, it should wait until we have enough in the way of manned orbital stations to justify the cost, or until private companies want to pay for it as a satellite delivery system.
If we're going to spend that much money on space, we should spend it on space exploration.
Re:Why Bother? (Score:2)
Re:Why Bother? (Score:3, Insightful)
Re:Why Bother? (Score:3, Insightful)
Don't take this as flamebait, but this sort of thinking is exactly why things have stalled: A penchant for the flashy combined with essentially no understanding of what's actually involved in space exploration, nor of what's needed.
If you want to settle the Moon or explore Mars or any other grandiose thing, you're going to absolutely need cheap Earth-to-orbit capability. Right now it's about $10,000 per pound that we lift -- that means almost nothing can be profitably put into orbit. Bring that down, and the rest follows.
To stretch a historical analogy, while exploration of North America occured since 1500, massive settlement of it awaited the railroads and cheap transport. (And put down those flamethrowers
Re:Why Bother? (Score:3, Interesting)
it should wait until we have enough in the way of manned orbital stations to justify the cost
Transportation systems come first, then comes money making. If we wated to have a global system of communications satellites before launching rockets, we wouldnt have any system. In the rainforest, roads come first then the settlers and lumberjacks. If you ever fly across america you can see little strings of towns founded along sometimes now extinct railroad lines. Urban sprawl is a result of increased roadbuilding and major interstates. When the first interstates were built they were mostly empty. Theres a story i heard about some family that was lost on the Washington DC beltway and just made a U-turn in the middle of it because there was no traffic. Try that today. Transportation systems are the ultimate "if you build it, they will come" phenomenon. Private companies wont pay for it, private companies want a 5 year break even with a 30% rate of return. Good luck on even getting the thing built in 5 years, let alone getting it to break even. There are some things only govt can do because buisness is always looking at next quarters bottom line and not the bottom line 10 years from now.
Doesn’t the anchor need to be on the equator? (Score:3, Insightful)
geo-synchronous elevator (Score:2, Interesting)
Tow hook for the earth (Score:2)
Kim Stanley Robinson's 'Mars' Trilogy (Score:2, Informative)
when i think of a space hook i think of (Score:4, Insightful)
How's it get up? (Score:2)
I can imagine a 100,000km elevator coiled up in the australian desert, then a shuttle launched with it tied to the back. The huge coil slowly unwinds, only to be dragged across Australia, levelling perth!
Not on the equator? (Score:5, Interesting)
In more detail:
In a reference frame rotating with the Earth, the counterweight has three forces on it:
Gravity: G m M_earth / r^2
towards the center of the earth
'Centrifugal' force (because we are in a rotating frame): v^2 / r cos l (l = latitude) directed perpendicular to and away from the earth's axis
Tension on the cable.
We want these three forces to cancel out, so that the counterweight is stationary (in the rotating frame.) The problem is that the gravity force has a north/south component unless the counterweight is on the equator. The centrifugal force can't have a north/south component, so the balancing force has to come from the cable tension.
The cable will have be at a small angle to vertical, and the north/south component of the tension is proportional to the sine of this angle, so that component can't be big.
Aha! I think I have the solution.I was thinking of the counterweight being above the tether point.
In the 1st approximation, put the counterweight in geostationary orbit (i.e. on the equator). Run the cable to it.
If the cable had no tension, we would done - but it does. The major component of the tension is towards the earth. We compensate for this by moving the counterweight into a higher orbit. (Decreases gravity, increases centrifugal force, to balance the tension.) There is nothing new here - the Highlift Systems website talks about this.
If the cable was anchored south of the equator, it will have a slight angle to vertical, which will give a southwards force component. If we now modify the orbit of the counterweight to be slightly south of the equator, there will be a northward component to the gravity vector. We can adjust to balance.
From the point of view of the tether point, the cable (if it is straight) will be pointing almost towards the geostationary point. From 30 degrees south, that would be a point about 3000 km north and about 35 km up, so it would be about 5 degrees off vertical.
Energy generation? (Score:5, Interesting)
Would it be feasible to create a tether to low-earth orbit for the express purpose of generating electricity? I wonder how the cost would compare over the long-term to other low-cost sources like wind and nuclear.
Um, reality check anyone? (Score:5, Informative)
One, if the elevator is to remain in a fixed place above the Earth, the radial force (tension) must balance the inertia. For this to happen, a quick calculation shows that at that latitude, the center of mass of the elevator must be 18% higher than the geosync height over the equator. You'll have to put a massive asteroid into orbit at roughly 30k miles up going thousands of miles an hour to anchor this sucker.
Two, that asteroid will orbit with a 32 degree angle of inclination until it's actually connected to the elevator. I pity the poor fool that has to play catch with that thing in orbit and actually link it to the elevator. If anything goes wrong, the asteroid drops to Earth, bringing devastation on a global scale. All of the previous discussion assumes that the elevator remains perfectly vertical, which brings me to...
Three, if you anchor a space elevator to the Earth at any latitude but 0 degrees (the equator), you're going to have a lateral inertial component, perpendicular to the radial, that'll bend that rope like a taut bow string. Another calculation shows that the shear force on that rope will be almost 53% of the tension. (This is simple trig.) Carbon nanotubes may have a hella strong tensile strength, but has anyone looked at their shear strength? I wouldn't want the thing to snap like a twig just after they get Mr. Doomsday Rock into position to fuck us worse than the dinosaurs...
Unobtainium (Score:3, Informative)
When you can buy spools of this stuff, it's time to take this seriously. But not yet.
Lack of Imagination? (Score:5, Insightful)
First off if you read the PDF (15M) report [usra.edu] to Nasa [usra.edu] prepared by Bradley C. Edwards to satisfy the requirements of his $500 000 grant you will readily see that this is totally feasible.
Next check out the website [highliftsystems.com] - where they are calling for people to express interest in working on this project. They expect to be hiring in the next year or so. You'll also see that serious people are taking this seriously. Do you want a job?
Next understand that $17B is not very much money. Considering that BP just spent [rferl.org] $6.7B on a oil company in Russia and has plans for more purchases.
I meantion BP because they have a plan to move beyond oil.... BP Solar [bpsolar.com] is BP's attempt to become a broader energy company (check out their new sun logo) instead of an oil company. The High Lift systems news page says: -
BP Solar - a subsidiary of British Petroleum, currently doing $300M in annual sales. Our discussions have focused on BP's interest in using the SE for deployment of a solar energy satellite. Several items that came up included possible collaborative efforts, the performance of our system and the possibility of BP using our system. They are considering writing a letter of endorsement
If BP with the cash they have can throw $6.75 B at Russia they could, over 5 years, finance a large share of the Space Elevator. Who needs the Government? In fact Nasa would make sure it costs more to build than it should. Nasa is a bureaucracy, not a business, and is ill-suited to the sort of cost control required of economically viable business decision. Only communists would argue that a Space Elevator should be built and controlled by government.
What would BP Solar do? Build Power Sats [powersat.com]....
These are High Lift's vision for the main use for the Space Elevator. Imagine a fleet of these beaming power to anywhere on earth. Every country on the planet could get cheap electricity without the huge national grid infrastructure required now. Without the huge investments in time and resources to build power stations - and without the fossil fuel use.
Use your imagination.
These ideas have been the subject of SF for decades - but the Space Elevator is now possible due to those nifty Carbon Nano-tubes.
When your imagination focussed by the reality of this thing actually being built in the near term (5 years) everything changes - and it'll change for us not our children. It'll change our careers.
Imagine this - an electric airplane that is powered by a Powersat beaming microwaves to it. No fuel to carry, super efficient travel - and at what speeds?
These guys are planning for the Space Elevator to be operational SOON - they have realistic timelines.
What I want to see here is some discussion of the uses that could realistically be made of a space elevator. We're the generation that will built it, use it and be changed by it. I like the parallel to be made with electricity, or flight, or the steam engine - in the early stages everyone probably dismissed it - and the world changed despite them.
What would you realistically (with a nod towards economic viability) do with the low launch costs they're projecting - $10/LB...
Ideas anyone?
Re:But Why on the Ocean? (Score:2)
Re:But Why on the Ocean? (Score:3, Informative)
Re:But Why on the Ocean? (Score:4, Interesting)
Re:But Why on the Ocean? (Score:2, Insightful)
The Mars Trilogy's elevator is on a smaller planet with much less atmosphere, and it's apparently also ridiculously over-engineered. (Or maybe it was built with more commonplace materials, instead of carbon nanotubes as is being explored today... anybody who's read the books more recently than I have care to comment?)
In short, don't worry about cable breaks, unless you're on the cable at the time, or you have stock in the elevator company.
Re:Cost (Score:2)
see the shuttle faq [geocities.com] for that info.
Arthur C. Clark said 'The space elevator will be built 50 years after everyone stops laughing."
You have to be kidding... (Score:2)
Re:Come to Perth - meet crooked cops (Score:2, Funny)
Re:Am I missing something? (Score:2)
Re:impossible (Score:5, Informative)
Re:which end first? (Score:4, Interesting)
The ease of replacement, more than anything, is what is going to keep the thing off any terrorist's a-list of targets.
Re:Perth not compatible with a geosync orbit (Score:5, Interesting)
Would a physicist please correct the following?!
I picture a tether at the equator going out at 90 degrees. If you move down to Perth, the tether will still go out at 90 degrees to the axis of rotation wouldn't it? That is, it would go out parallel to the tether at the equator. See diagram.
X
XX
XXX
XXXX
XXXX---------O equator
XXX
XX---------O perth
X
So, does that mean that it wouldn't be vertical at perth but would go out at an apparent 31 degrees?
Also, does that mean that the thing actually goes over all of the airspace between 31 degrees and just south of the equator? That is, because of the angle, would it actually go over, say, Indonesia's airspace.
Parts of Indonesia are nearly 10 degrees south. Does a line drawn vertically from Indonesia intersect with the ribbon?
Re:Perth not compatible with a geosync orbit (Score:4, Informative)
The cable would trace out a cone if it were straight, if that helps you visualize it.
Justin Dubs
Re:I'm Skeptical (Score:3, Informative)
Launching it requires a rocket launch to past geosynch orbit, reeling out the tether (1mm^2 cross-sectional area) as it launches, the rocket doesn't have to go much past 35k km (geosynch), well at least not the full 65k km, more like 10-25k km before the cable will self unwind to the full extension.
Then a tiny robot (likely solar powered) will crawl up this tiny thread and stick another layer on. And another, and another until it has counterweight capability and strength to lift a 22 tonne lift car and 14 tonnes of cargo. The initial launch is difficult, BUT after that it is just materials and robots... 3 days a piece, after a year it'll be ready... Each robot can haul slightly more cable than the previous robot, which in turn increases its loadbearing capability, and thus more heavier cable... etc...
Z.
Re:Terrorist Target? (Score:3, Insightful)
This would significantly reduce the appeal for attack that a single space elevator would have.
That assumes that the only reason why the terrorists would attack the ribbon would be to disrupt its operation. However, in reality, terrorists would attack the ribbon for its potential to wreak havoc. If a terrorist blows up a dam, he doesn't do it to deprive nearby cities of drinking water or electricity. He does it to provoke a flooding catastrophe!
Although Highlift's website downplays the effects of a ribbon rupture, somehow I've trouble believing them. If the cable is strong enough to hold up, wouldn't it also be strong enough to slice everything in half that it encounters on its way down? As anybody having worked on a ship can attest, a rope under tension packs a helluva lot of destructive energy, which is released all at once when it snaps. It'll certainly do much more damage than "loose sheets of newspapers".