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Crow T Robot
2003-Feb-05, 05:29 PM
I was wondering what everyones thoughts were on the viability of the space elevator.

I know this pops up once in a while and while it seems to work on paper, from an actual engineering standpoint it looks daunting to say the least.

Recent Article in Wired:
Wired Magazine" (http://www.wired.com/news/technology/0,1282,57536,00.html)

and an interesting report from NASA:
Space Elevator (http://www.niac.usra.edu/files/studies/final_report/pdf/472Edwards.pdf)

SpacedOut
2003-Feb-05, 05:36 PM
Interesting Stuff - but my guess is that the $10 Billion estimate is probably off by at least a factor of 10. It will probably cost at least $10 Billion just to do all the feasability studies.

Lexx_Luthor
2003-Feb-05, 05:51 PM
Thanks!!! A friend would like to see that.

Now he can. !!!

Feasability. How many Feasability Studies did Kennedy's administration conduct before he "mooned" America in his 1961 speech?

Eirik
2003-Feb-05, 07:21 PM
The space elevator popped up on the local news here in Seattle last night (KING-5) as if it were a reletivly new thing, but I recall that a couple Seattle companies were talking about getting some funding for research months ago. I'm not sure if the Columbia disaster caused them to issue some new press releases or what.

From what I understand, though, if it could be done it would drop the cost of going into orbit rather condsiderably...

Rich
2003-Feb-05, 08:09 PM
Well, it would drop the one-time launch cost, but what about the cost per launch over the life of the system? If it cost $10 trillion (an admittedly far-out and unsubstantiated guess) to build when would you even reach a break even point? I know they said ten billion, but that's just laughable (are they calculating that budget in 1945 dollars?).

There are still many, many technical hurdles to overcome. No one can yet manufacture carbon nano-tubes, the preferred building material, on a large scale. No one knows, for sure, how to bond such a large nano-tube construction. There is no sure fire way and no cost estimate for an anchor. No one knows exactly how upper atmosphere weather, especially poorly understood electrical phenomena, would affect such a structure. No one knows how safe a carbon nano-tube structure would be if it gathered a large charge from electrical phenomena or friction from the atmosphere. No one knows how to protect such a structure against electrical discharges or sources of fire (carbon nano-tubes are highly conductive and eminently combustible).

In short there are a lot of unresolved issues. Decades worth of technical work remains to be done, even then I'm sure we'll run into interesting problems we never even thought of. Barring massive political/industrial/commercial backing on the scale of the Manhattan Project I wouldn't plan on riding on a space elevator even in your children's lifetime. I'd love to be wrong, but I just don't see it.

Doodler
2003-Feb-05, 08:14 PM
I think the recent issues with the shuttles may bring the idea (at a small scale) closer to the forefront. Even if they aren't building it within a human lifetime, they can at least start developing the infastructure. Think nanotubes make a great elevator cable for satellites, how many bridge builders would sell offspring and internal organs for access to this stuff? Material applications need not only work in space. If they can market the potential, they could indirectly accelerate industry towards their goal. Its just a matter of schmoozing the right people.

Simon
2003-Feb-05, 08:43 PM
On 2003-02-05 15:09, Rich wrote:
Well, it would drop the one-time launch cost, but what about the cost per launch over the life of the system? If it cost $10 trillion (an admittedly far-out and unsubstantiated guess) to build when would you even reach a break even point?

Well, call it $50 trillion for the cost of the system, and say it reduces lift costs from $22,000 to $50 (not impossible by any means; all it'd cost is electricity and maintainance). So it'd have to lift 2,278 tons to pay for itself. I think that's roughly equivilant to the mass of all the payloads lifted into orbit by the Space Shuttles to date. Of course, it could probably lift that mass in relatively short order.

Someone double-check my math, willya? /phpBB/images/smiles/icon_wink.gif And rustle up some investors while you're at it.

Rich
2003-Feb-05, 08:50 PM
Depends what's the $50 for, per ton or per pound?

Even if it's $50/ton that's still $50,000,000,000,000.00/($50/ton)
= 1 trillion tons...

That's a lot...

Rich
2003-Feb-05, 08:58 PM
On 2003-02-05 15:50, Rich wrote:
Depends what's the $50 for, per ton or per pound?

Even if it's $50/ton that's still $50,000,000,000,000.00/($50/ton)
= 1 trillion tons...

That's a lot...


The flip side is that you could put some very large payloads into space. I would think the pay-off would be directly proportional to the lift capacity. If you could built the entire ISS on the ground and lift it, assembled, in one shot... Whoa!

I'm sure that would significantly increase the building cost while driving down a one-time lift cost independent of construction costs and overhead (no pun intended).

[Edit: Damn my spelling]

<font size=-1>[ This Message was edited by: Rich on 2003-02-05 16:00 ]</font>

Doodler
2003-Feb-05, 09:05 PM
Is that unreasonable considering the potential operational lifespan of the elevator? Aside from replacing worn out cars, the cable itself should be EXTREMELY long lived, if its designed properly.

SeanF
2003-Feb-05, 09:11 PM
On 2003-02-05 15:43, Simon wrote:

Well, call it $50 trillion for the cost of the system, and say it reduces lift costs from $22,000 to $50 (not impossible by any means; all it'd cost is electricity and maintainance). So it'd have to lift 2,278 tons to pay for itself. I think that's roughly equivilant to the mass of all the payloads lifted into orbit by the Space Shuttles to date. Of course, it could probably lift that mass in relatively short order.

Someone double-check my math, willya? /phpBB/images/smiles/icon_wink.gif And rustle up some investors while you're at it.


At a savings of $21,950 per unit, you'd have to lift 2.278 billion units, not 2.278 thousand, to save $50 trillion dollars.

RafaelAustin
2003-Feb-05, 10:06 PM
I've always loved this concept since reading about it Foutains of Paradise, but admittedly it's a technology still 100 years in the future. And I think that's more because of the magnitude of the project, not necessarily the technical aspects.

Here's a previous disscusion (http://www.badastronomy.com/phpBB/viewtopic.php?topic=2980&forum=2) on BABB about this with some links.

And I think I remember that the lifting capacity wouldn't be greater than that of the Shuttle, but the frequency would multiply (2-4 lifts per day??). There are all sorts of ideas about using the platforms built on it for satellite stations, observation decks and hotels, etc.

In addition to the problems mentioned before, the harmonics aren't well understood and I believe someone on this board claimed that it's not stable at all.

Regardless, it's a concept to dream and plan for and who knows, maybe someone eventually will have the manufacturing and public relations expertice to get it done.

Crow T Robot
2003-Feb-05, 10:39 PM
Apart from engineering.....
It seems to me that the cost to orbit drives the whole thing. It seems to me the way to calculate payback on investment is to compare the new way with the old way.

Current cto is, what, around $20,000/lb.
At a $50/lb cto the payback is $19950/lb
Which works out to $100,000/ton vs. $40Million/ton with the Shuttle, a savings of $39,900,000/ton.

Now assume a $50T cost to build the Space Elevator.

With a cto of $50/lb you would need to launch about 1.253M tons of stuff to break even on the project based on previous cto vs new cto. This works out to about 39,782 Shuttle launches.

By the way if launch costs were cut to $50/ton you would still need to launch 1.250M tons or 39,682 Shuttle launches.

If the cost to build is $1T then we're looking at about 795 Shuttle launches worth.

At $100B 79.5 Shuttle launches and
at $10B 7.95 Shuttle launches.

If costs are in the $50T range it would be pretty difficult to justify but at $1T and lower I think a good case can be made to spend the money if the engineering is there.
If you bring launch costs down to $50/lb - $50/ton you'll have more business than you can handle even with a launch window every hour or two.

Ex. At $50/lb my big butt could get into orbit for about $15,000 that's less than I paid for my Jeep, and at $50/ton it works out to $7.50, a normal sized person would be @ $4.25. I spend more than driving to work each day.

If they can get cto to $50/lb most people can afford to head to orbit at least once if not several times, and I can prety much guarantee millions would sign up. At $50/ton anyone that wants to go can afford it, even the beggers on the street corner can scrounge up 4 bucks.

traztx
2003-Feb-05, 11:11 PM
Is the current shuttle a good comparison? How does Soyuz compare to Shuttle for cost? What about Atlas?

How fast can an elevator ascend? Remember, it has 35,786 km. Imagine lifting cargo at even 100 km/hour (I don't know any elevators that fast)... will take 15 days to reach geosync.

Is the elevator useful for any other orbit lower than geosync?

Still seems to me like something way far out of my lifetime, but who knows, technology sometimes takes a leap!

sacrelicious
2003-Feb-05, 11:14 PM
how can it work though?

1) the top of the ribbon would be anchored to nothing but microgravity space. the lower portion would have the burdon of more and more gravity the lower it goes. it reminds me of the old cartoon cliche of someone trying to climb a rope that has been severed from what it was tied to, each pull only bringing the rope down more.

now you might argue that the top platform would have rockets to provide a counterforce when things are being brought up. not having any concept of fuel weight/thrust ratios, I would be unable to debunk that, so I will assume that it is reasonable. however, the ribbon itself, no matter what ultra-light material it is made of, would likely exert more force by itself than even the largest cargo that it would carry. this means that you would have to be burning rockets to counter the force, not only when you are lifting, but 24 hours a day, seven days a week! now I'm no mathmetician, not by a longshot, but it would seem to me that burning that burning any fuel nonstop like that would have to cost a hell of a lot more than our current shuttle system, and likely multiplied a few times over!

2) fragility: it would not take much for a terrorist, or even a rather skilled prankster, to sever the ribbon. one homemade missile could do the trick nicely, and considering the rather large target area presented, it seems to me that fighter cover (another added expense, btw) could only even dream of 75% effectivness in such a situation.

then there is weather to worry about. all you need is one hurricane to destroy the whole thing. even regular winds could force the top platform into an entry trajectory.

now please tell me how I might be wrong about these things, cause I can't figure out how profesional scientists could actually deem this reasonable.

daver
2003-Feb-06, 01:32 AM
On 2003-02-05 18:14, sacrelicious wrote:
how can it work though?

1) the top of the ribbon would be anchored to nothing but microgravity space. the lower portion would have the burdon of more and more gravity the lower it goes. it reminds me of the old cartoon cliche of someone trying to climb a rope that has been severed from what it was tied to, each pull only bringing the rope down more.


Imagine a rope that goes from some spot on the equator up about 60,000 km or so. Now, imagine you're on a spot at geosynchronous altitude. You experience no net force--you're in orbit. Head "down" (towards earth). The further down you go, the more weight you feel (pulling you towards the earth). OK, climb back up to geosync. Now, head "up" (away from earth). The further up you go, the more weight you fell pushing you away from earth (as you head towards the earth, the gravitational force increases and the centrifugal force decreases; contrariwise for heading in the other direction).

So the trick is to put enough mass on the far end of geosynchronous orbit to overcome the weight on the nearside.



[some speculation deleted]

2) fragility: it would not take much for a terrorist, or even a rather skilled prankster, to sever the ribbon. one homemade missile could do the trick nicely, and considering the rather large target area presented, it seems to me that fighter cover (another added expense, btw) could only even dream of 75% effectivness in such a situation.



Yep, this is a problem. The proposed site is a long way from anywhere; it would be difficult for a terrorist to launch a missile at it. However, it would be possible for them to put a bomb in a cargo container and have it sent up the tether




then there is weather to worry about. all you need is one hurricane to destroy the whole thing. even regular winds could force the top platform into an entry trajectory.



A hurricane wouldn't destroy the whole thing; it might blast the very bottom. The rest of it would go into a higher orbit, they'd have to repair the bottom few miles and go for a reattachment.

One of the criteria for the proposed base station site was its freedom from bad weather, but there will always be flukes.



now please tell me how I might be wrong about these things, cause I can't figure out how profesional scientists could actually deem this reasonable.


Thank you for asking (i'm serious here. I've seen plenty of postings that claim flat out that it is impossible (usually for pretty bogus reasons) and call everyone involved with such a thing charlatans and con men. It's refreshing seeing somebody actually ask if it's reasonable). There is a website (i don't have it handy, but it's been posted, both here and on some Yahoo boards on this topic).

logicboy
2003-Feb-06, 02:41 PM
Come and get your Carbon Nanotubes only $50 - $100 per gram

MERCORP (http://www.opus1.com/~mercorp/index.htmlx)

Carbolex (http://carbolex.com)

CNI (http://www.cnanotech.com)

Mainframes
2003-Feb-06, 04:06 PM
On 2003-02-06 09:41, logicboy wrote:
Come and get your Carbon Nanotubes only $50 - $100 per gram

MERCORP (http://www.opus1.com/~mercorp/index.htmlx)

Carbolex (http://carbolex.com)

CNI (http://www.cnanotech.com)



What's the quality of those nanotubes though? Did an undergraduate project on Carbon Nanotubes a couple of years ago and the price varied greatly with the production methods.

The production methods determined the quality of the nanotubes and physical properties such as orientation of tubes ie lined up or random, overall length, no. of imperfections (a chain is as strong as it's weakest link) plus whether they were multi-walled or single-walled, and chirality(affaects electrical conductivity).

Anyway i'll shut up now....

logicboy
2003-Feb-06, 05:17 PM
What's the quality of those nanotubes though? Did an undergraduate project on Carbon Nanotubes a couple of years ago and the price varied greatly with the production methods.

The production methods determined the quality of the nanotubes and physical properties such as orientation of tubes ie lined up or random, overall length, no. of imperfections (a chain is as strong as it's weakest link) plus whether they were multi-walled or single-walled, and chirality(affaects electrical conductivity).

Anyway i'll shut up now....

What you just said is over my head
but i will try to figure it out

Kaptain K
2003-Feb-07, 01:15 PM
Then there is weather to worry about. All you need is one hurricane to destroy the whole thing.
A space elevator would have to be over the equator (The only place where a geosynchronus orbit is also geostationary.) Hurricanes are a temperate zone weather phenomenon. There are no hurricanes in the tropics.

Argos
2003-Feb-07, 02:22 PM
On 2003-02-07 08:15, Kaptain K wrote:

Then there is weather to worry about. All you need is one hurricane to destroy the whole thing.
A space elevator would have to be over the equator (The only place where a geosynchronus orbit is also geostationary.) Hurricanes are a temperate zone weather phenomenon. There are no hurricanes in the tropics.


I don´t think a hurricane could threaten such a huge structure as the base of the space elevator.

Anyway, the whole idea lacks elegance. Space elevator would be a monster; an ecologist´s nightmare. It would always hurt some important bioma, regardless of where it were located (especially at the equator). It would degrade the landscape, since it could be seen from a vast area around. It would interfere with local [perhaps global] weather and other human affairs as transport, communications and so on. It has the potential for hindering people´s activities in a large scale. On the other hand the space elevator could be used to generate energy, as it drags across the magnetic field of Earth. This could balance (at least partially, by a small fraction) the environmental debt it would generate. The environmental impact [as well as the cost/benefit ratio] is something that will be carefully addressed in this question.

I would prefer something better to take us to the stars, although I´m not against the project by the wholesale. But I´m trying to point out its severe downsides.

<font size=-1>[ This Message was edited by: Argos on 2003-02-08 07:33 ]</font>

Argos
2003-Feb-07, 02:36 PM
And from "Wired"

Edwards said a space elevator could transport materials into the cosmos for about $100 a kilogram. He estimated that sending materials on a shuttle costs $10,000 to $40,000 per kilogram. That could make it affordable, for example, to build huge solar-energy gatherers and send them into space on the elevator.

"African countries could send up a solar satellite, and use that energy to build wells, and pump water and develop their economies," Edwards said.

I don´t thing the environmental impact of sending a microwave beam down to Earth has been correctly adressed either,

Eirik
2003-Feb-07, 07:00 PM
I'm not sure that this would be a huge problem. My understanding is that mircrowaves are pretty narrow and can be focused very tightly. A few large, high capacity solar panels might be able to generate a great deal more energy with less overall environmental effect than a large coal burning powerplant, for example.

On a flip side, I've heard of the proposal for large orbiting mirrors to focus light on specific points of the earth 24/7 for either energy production or greater growing seasons. Not sure how viable that is, either.

logicboy
2003-Feb-07, 07:43 PM
On a flip side, I've heard of the proposal for large orbiting mirrors to focus light on specific points of the earth 24/7 for either energy production or greater growing seasons. Not sure how viable that is, either.

Die Another Day?

I would think it would have to be a very big mirror + how much could it do for growing? unless the plants were genetically altered somehow to handle 24 hour sunlight. Light is like water to plants too much can kill.

Eirik
2003-Feb-07, 07:58 PM
The concept existed before the doomsday weapon of that movie. I understood that a small scale test was done a few years ago, in which an orbiting mirror was used to shine sunlight on a small area of land. Beyond that, I've not heard anything about it.

And you're right, my understanding of plant biology is that there is a needed dark cycle as part of their growth cycle, but that you might improve yeilds by increasing the amount of time that they spend in spring and summer conditions, such as occurs naturally in places like California or central America.

Eirik
2003-Feb-07, 08:01 PM
Did a quick search for information and this was the first site that I found, giving information on a failed Russian venture along these lines:

http://www.space-frontier.org/Events/Znamya/

Argos
2003-Feb-08, 12:32 PM
I have on more thing on this matter.

During the evolution of space exploration, space industry was always regarded as a continuum to the aircraft industry. The space was an extension of the sky. With SE we’ll have to opt. Once the SE is built we can never send satellites to orbit by aerodynamic means anymore. Given the obstacle represented by the elevator tower, it will not be possible to orbit Earth bellow the altitude of the elevator. This will have an impact on astronautic science. SE will cause a cleavage in the aerospace industry. The synergy between aircraft and spacecraft will cease, or lose momentum, since we’ll go to the space by land! [Will the traditional Air Force influence in space issues slowly turn to the Army?].

The problem is that, as we’ll still need to work in other atmospheres elsewhere, we can’t afford to forget aerodynamics as applied to space vehicles. As result, we’ll have two technologies to deal with space affairs: the elevator to put satellites in Earth orbit, and the common aerospace vehicles to work elsewhere. This introduces a complication in our space system, and, therefore, a rise in the costs.

Also, during the construction of the tower all the low orbit satellites will have to be deorbited (And there’s a lot of them up there). All our needs will have to be satisfied by high orbit satellites, which imposes a considerable hike in costs.

There’s more to the project Space Elevator than meets the eye.

darkhunter
2003-Feb-08, 08:27 PM
On 2003-02-08 07:32, Argos wrote:
I have on more thing on this matter.

Also, during the construction of the tower all the low orbit satellites will have to be deorbited (And there’s a lot of them up there). All our needs will have to be satisfied by high orbit satellites, which imposes a considerable hike in costs.

There’s more to the project Space Elevator than meets the eye.



Not to mention the utter loss of access to space should we decommision our launch platforms, the have some catastrophe that destroys the space elevator.

In todays world, I would hesitate to build one due to the fact it is a rather large target, and there will always be the chance some Bad Guy (Tm) decides it has to go...

edit: WOOHOO!!! not a newbie anymore....I'm an apprentice (though still got a ways to go...)
_________________
Words define reality, but they can't alter it.

<font size=-1>[ This Message was edited by: darkhunter on 2003-02-08 15:29 ]</font>

g99
2003-Feb-08, 08:35 PM
On 2003-02-08 15:27, darkhunter wrote:

edit: WOOHOO!!! not a newbie anymore....I'm an apprentice (though still got a ways to go...)
_________________
Words define reality, but they can't alter it.


What a coincidence, i hit 1000 just a few minutes ago. Congradulations!!!!!!!. Just promise to make your posts alot more informative than mine are. /phpBB/images/smiles/icon_smile.gif

And believe me it will not be long till you reach 1000. It will sneak up on you very fast.

DaveC
2003-Feb-08, 08:38 PM
Congrats, g99. I'm looking forward to the day when I get there too, although at the rate I'm going I have a long road ahead.

darkhunter
2003-Feb-08, 08:53 PM
On 2003-02-08 15:35, g99 wrote:

What a coincidence, i hit 1000 just a few minutes ago. Congradulations!!!!!!!. Just promise to make your posts alot more informative than mine are. /phpBB/images/smiles/icon_smile.gif

And believe me it will not be long till you reach 1000. It will sneak up on you very fast.




Thanks for the support! Congradulations for your accomplishment as well!! /phpBB/images/smiles/icon_smile.gif

I try to learn wherever I can, and this board is one that has taught me a lot (I used to think I knew quite a bit about space, but now my horizons have expanded and I will be learning more /phpBB/images/smiles/icon_smile.gif )

g99
2003-Feb-08, 09:11 PM
Thanks /phpBB/images/smiles/icon_smile.gif

ToSeek
2003-Aug-13, 04:12 PM
New website devoted to the Space Elevator concept:

http://www.spaceelevator.com/

Pinemarten
2003-Aug-13, 10:23 PM
I am still curious as to whether the tether would need to reach earth. If the centre of gravity is in orbit, couldn't we just 'dip' one end into the atmosphere, and lift cargo from that point?
Edited for stupid typo.

daver
2003-Aug-14, 12:24 AM
I am still curious as to whether the tether would need to reach earth. If the centre of gravity is in orbit, couldn't we just 'dip' on end into the atmosphere, and lift cargo from that point?

No, it doesn't have to, but it probably would.

Ground transportation is cheaper than air transportation--it'd be cheaper to ship your stuff to the terminal and hook it on to the tether. Ground transportation costs could actually become a significant fraction of the price to put something in space.

At least one company has proposed jiggling the ground station in order to send waves up the tether in order to dodge any satellites.

Having a ground station should give a way of adding angular momentum to the tether, to make up for all the mass you send up it.

Having a ground station forces one end of the tether to remain over a given position on the earth. This should simplify details such as powering the elevator cars on the way up and down the tether.

The only reason i can see not to put in a ground station would be if some atmospheric phenomenon (lightning, stratospheric winds) turned out to be bad for the tether. The advantages of going all the way to the ground would give a good incentive to solve this problem.

Donnie B.
2003-Aug-14, 01:01 AM
Asimov (I think) once described a space elevator that wasn't stationary... its two tethers constantly rotated, dipping into the atmosphere where they coupled to a vehicle at the ground station, then continued their rotation (taking the vehicle up with them). The cables had enough flexibility to spend 15 minutes or so at the ground station, allowing the vehicle to hook up. Vehicles could return to Earth by reversing the process, hooking on at the top of the arc, I think.

One big advantage was that the vehicle wound up getting accelerated to fair speed on the way up. Of course, the technical problems would be massive: making an even stronger cable, controlling such a huge dynamic system to keep it stable, figuring out how to couple and uncouple the vehicles...

daver
2003-Aug-14, 06:23 PM
Asimov (I think) once described a space elevator that wasn't stationary... its two tethers constantly rotated, dipping into the atmosphere where they coupled to a vehicle at the ground station, then continued their rotation (taking the vehicle up with them). The cables had enough flexibility to spend 15 minutes or so at the ground station, allowing the vehicle to hook up. Vehicles could return to Earth by reversing the process, hooking on at the top of the arc, I think.

One big advantage was that the vehicle wound up getting accelerated to fair speed on the way up. Of course, the technical problems would be massive: making an even stronger cable, controlling such a huge dynamic system to keep it stable, figuring out how to couple and uncouple the vehicles...

There have been two general types of tethers proposed--rotating tethers and nonrotating tethers. The nonrotating tethers are tidally locked, their dynamics are a lot simpler to compute. The beanstalk is a special case of a non-rotating tether; other, smaller non-rotating tethers might be a useful interrim step (they reduce somewhat the delta-V required to get to orbit, which might make a SSTO craft practical).

Rotating tethers seem to have significant advantages--you can tweak the rotating speed so the end of the tether nearest the earth approaches with approximately zero velocity--it would be like a trapeze descending from the sky, and then climbing back up. My guess is that docking would be done in mid-air (this can compensate for variances in the tether orbit, and reduces somewhat the effect of the atmosphere on the tether), and would probably be at a few hundred miles an hour. However, the dynamics of a rotating tether would seem to be quite a bit more complicated--it might be restricted to an equatorial plane. It might not be stable, regardless--i haven't checked to see if anyone has done the math.

A rotating tether with a 15 minute docking window would be huge; i'd think it's more likely to be measured in seconds.

Payloads on non-rotating tethers need to climb the tether; payloads on rotating tethers just need to hang on (and release at the proper time).

Both tethers would need some sort of a lift system. The rotating tether would need thrusters on both ends, the non-rotating tether could get by with thrusters in just the middle section. The beanstalk wouldn't need one--if the beanstalk started to sag, you could just send more mass up and out to the far end.

Pinemarten
2003-Aug-14, 10:36 PM
How are we doing with 'strong fiber' technology? Is it still in theory stage or have we built one?

Kizarvexis
2003-Aug-14, 10:40 PM
How are we doing with 'strong fiber' technology? Is it still in theory stage or have we built one?

Carbon Nanotubes theoritically are strong enough to support a ground-to-geo elevator. They can make tubes that are around a meter long, IIRC. Now they need to connect the tubes together and make them much longer.

Kizarvexis

daver
2003-Aug-15, 12:49 AM
How are we doing with 'strong fiber' technology? Is it still in theory stage or have we built one?

Carbon Nanotubes theoritically are strong enough to support a ground-to-geo elevator. They can make tubes that are around a meter long, IIRC. Now they need to connect the tubes together and make them much longer.

Kizarvexis

I don't know how they survive in a space setting (UV, atomic oxygen, radiation). Most of the beanstalk will be in near-continuous sunshine, but the parts near the earth are going to have day-night cycles to deal with as well.

Kizarvexis
2003-Aug-15, 01:02 AM
How are we doing with 'strong fiber' technology? Is it still in theory stage or have we built one?

Carbon Nanotubes theoritically are strong enough to support a ground-to-geo elevator. They can make tubes that are around a meter long, IIRC. Now they need to connect the tubes together and make them much longer.

Kizarvexis

I don't know how they survive in a space setting (UV, atomic oxygen, radiation). Most of the beanstalk will be in near-continuous sunshine, but the parts near the earth are going to have day-night cycles to deal with as well.

Also, since the nanotube cables will be almost or pure carbon, they will be conductive as well. (They can make nanotubes with other atoms added in as well to give the tube different properties.)

Kizarvexis

Pinemarten
2003-Aug-15, 02:28 AM
Is there a reasonable budget on the research; or is it suffering?

daver
2003-Aug-15, 04:48 PM
Is there a reasonable budget on the research; or is it suffering?
I don't think that large sums of money are being poured into research on these. I'm not sure that it would help much. Regardless, i'd like to see nanotubes used on terrestrial applications before we tried space applications (cheaper, and more immediate feedback).

eburacum45
2003-Aug-17, 05:25 AM
originally posted by Daver
There have been two general types of tethers proposed--rotating tethers and nonrotating tethers. The nonrotating tethers are tidally locked, their dynamics are a lot simpler to compute. The beanstalk is a special case of a non-rotating tether; other, smaller non-rotating tethers might be a useful interrim step (they reduce somewhat the delta-V required to get to orbit, which might make a SSTO craft practical).


Tell me, if you will, about the smaller non-rotating tethers
shorter than Geostationary ...
- are they the ones associated with dynamically supported rings, or is there a cheaper solution?

russ_watters
2003-Aug-17, 06:44 AM
They can make tubes that are around a meter long... For some reason people tend to overlook the difference between a meter and orbital distance. Theoretically possible or not (I have my doubts on even that), there still isn't a way to manufacture these things on anywhere near the scale needed to make such a large structure.

Kizarvexis
2003-Aug-17, 09:03 PM
They can make tubes that are around a meter long... For some reason people tend to overlook the difference between a meter and orbital distance. Theoretically possible or not (I have my doubts on even that), there still isn't a way to manufacture these things on anywhere near the scale needed to make such a large structure.

Well, I was off by a lot. As of 2003, individual nanotubes have been made that are as long as 4 millimeters. And nanotube strands have been made which are as long a 20 centimeters. in any case, this is a big jump from the original tubes that were only a few hundred carbon atoms long.

There is still a lot of research to be done, but carbon nanotubes are the only thing so far that even have the potential to be strong enough for an elevator. (rant)It's not like I said that we would have a space elevator next year.(/rant) 8)

Kizarvexis
(I must have misremembered a researcher predicting meter long nanotubes in the near future, rather than that they have already made them. :oops: Sorry about that.)

daver
2003-Aug-18, 08:40 PM
Tell me, if you will, about the smaller non-rotating tethers
shorter than Geostationary ...
- are they the ones associated with dynamically supported rings, or is there a cheaper solution?

There's not much to tell. Launch a tether a couple of thousand miles long so the close end is just above the effective atmosphere. The close end will be moving at less than orbital velocity, the far end at greater than orbital velocity. How much of a difference depends on the mass distribution of the tether. Anyway, now, instead of requiring 9.5 km/sec delta V to orbit, it may only need 8 km/sec to latch onto the near end of the tether. Since the rocket equation is logarithmic, this may be sufficient to make SSTO (well, SSTT) practical. Once you have the tether in orbit, you can launch up a few things (like a power supply and booster) to maintain the orbit, and you can start launching payloads to bootstrap the tether.

Locke
2003-Aug-22, 05:56 AM
Has anyone heard about the "space elevator" they have been talking about? They were planning on collecting carbon-nanno tubes from the bottom of the ocean, and making them into a cable that will hang from a certain point in space, and will allow people to ride the elevotor up into null-0 gravity. Sounds interesting to me.

Locke

Qayyim
2003-Aug-23, 08:08 PM
So when a visitor is in this elevator, they&#39;d sit there for a few hours just going up (it better be air conditioned). Wait&#33; But what if, when the visitor in the 0-G environment and they elevator goes back down, they&#39;ll be pushed to the top and when they are back where gravity is an "effective force", they would slam down.

Furthermore, the physics of the contraption don&#39;t really add up. Also, it sounds expensive.

Fraser
2003-Aug-23, 08:32 PM
There&#39;s a new website called the Space Elevator Reference that looks pretty cool. Check it out at:
http://www.spaceelevator.com/

Locke
2003-Aug-24, 03:38 AM
Where do you find all these websites fraser? :D

Emspak
2003-Aug-30, 06:32 PM
FOr those of a literary bent, see Arthur C. Clarke's book The Fountains of Paradise for a treatment of a space elevator.

He talks of using carbon filaments of some kinf I think, tho in the book there is no mention of the conductivity problem.

Tuckerfan
2003-Sep-01, 09:05 AM
Highlift Systems (http://www.highliftsystems.com/) is working on building a space elevator. They estimate the cost for construction at $15 billion. (They've stripped their site down to the bare bones, so I can't find the price tag.) And Motorola (http://www.motorola.com/mediacenter/news/detail/0,1958,2981_2436_23,00.html)'s just announced that they've discovered an economical method of producing nanotubes.

ToSeek
2003-Sep-17, 03:05 PM
Space Elevator: High Hopes, Lofty Goals (http://www.space.com/businesstechnology/technology/space_elevator_030917.html)

Space.com article on the subject.

NubiWan
2003-Sep-17, 09:02 PM
The 86-year-old Clarke recounted an earlier prediction about when the space elevator might be up and operating. "It’ll be built 10 years after everybody stops laughing … and I think they have stopped laughing."
8)

BubbleGum
2003-Sep-18, 07:07 AM
Twenty years ago I actually thought of this idea all be myself. I called it Jacobs Ladder.

After 20 years of thinking about it, I decided it was just a pipe dream.

Carbon Nanotubes, Asteroid Capture, Zero G Manufacturing, Astronot Life Support.

Sorry, hate to be a Killjoy. But the ants under my house have a better chance at building the Great Wall of China then we have of building The Elevator.



But I must admit, it is a great topic.

Here's a tiny side topic.... How much voltage would there be between the top of the tower and Earth. ??? Would there be current to back it up ? It could turn out to be a giant power station.

~Bub

eburacum45
2003-Sep-18, 02:39 PM
it seems a good idea to look at alternative methods of getting to orbit;
Some of these tether and or mass pellet concepts that might bear some looking at; however they tend to require either
materials which cannot be manufactured in large quantities at the moment
or
unfeasibly strong and well behaved magnetic fields.

This said, at least they do not involve teleportation or antigravity.

rotating tethers
http://www.space.com/businesstechnology/technology/tether_tech_030618-1.html
---------
mass pellet driven space towers
http://www.islandone.org/APC/Tethers/03.html
---------
dynamic orbital rings
(ok this one is mine, and it's sf, but based on an idea by Paul Birch of the British Interplanetary Society
http://www.orionsarm.com/eg/d/Du-Dz.html#dynamic_orbital_rings
---------
lofstrom loop-
http://www.islandone.org/LEOBiblio/SPBI116.HTM
---------
rotavator
http://members.aol.com/Nathan2go/lunavat.htm
---------
skyramp
http://www.skyramp.org/
---------
mooncable
http://home.earthlink.net/~jedcline/mcbl2.html
--------

mike alexander
2003-Sep-18, 07:45 PM
Re: Carbon nanotubes or similar

While it's not feasable (I really think) to create contiguous nanotubes 40,000 km long, how long would the individual tubes have to be to get the necessary strength? I'm thinking that even noncovalent attractive forces on a nanotube bundle with a centimeter overlap would really add up. But this ain't my area of expertise.

samarth269
2003-Sep-19, 03:25 PM
Do you think we can make the space elevator? We have got through the hurdle of choosing the rope&#39;s material :Carbon Nanotubes .But there are many problems like storms ,earthquakes,meteors,etc.
Can some expert elobarate on this...

Great Satan
2003-Sep-20, 02:46 AM
http://www.halfbakery.com/idea/Elevator_20to_20Space#1063967947

blanking@bellsouth.net
2003-Sep-21, 07:05 PM
Gee, wouldn&#39;t it be great if such a thing could be built?&#33; What an achievement that would be.

CyberJIT
2003-Sep-22, 01:18 PM
The space elevator had long been dismissed as a science fiction concept
perhaps centuries away from actually being built, but new studies
suggest a space elevator could be built in the near future for a modest
cost. The first in a two-part report on the prospects and challenges a
space elevator faces.

The space elevator: going up? (part 1) (http://www.thespacereview.com/article/47/1)


About 75 people gathered in New Mexico earlier this month to discuss the
research into, and the hazards threatening, a space elevator. The second
in a two-part report on the prospects and challenges a space elevator
faces.

The space elevator: going up? (part 2) (http://www.thespacereview.com/article/48/1)

i don&#39;t know if it explains everything about it. but it should be the latest news about space elevators.

hope it helps :)

ccampbell
2003-Sep-23, 04:04 AM
[Disclaimer: I&#39;m plugging my own site here... ;-) ]

I help run a new space elevator news site:

LiftWatch.org (http://liftwatch.org)

We&#39;ve got regular news updates, discussion forums, a good directory of relevant websites, image galleries and more...

Please check it out&#33;

ccampbell
2003-Sep-23, 04:14 AM
Please see my site, which is all about this topic:

LiftWatch.org (http://liftwatch.org/)

We&#39;ve got regularly updated news, discussion forums, image galleries, and more...

Locke
2003-Sep-23, 04:25 AM
The link to your website didn&#39;t work. But it sounds very interesting.

-Locke

ccampbell
2003-Sep-23, 04:29 AM
Really?

It&#39;s working for me... albeit a wee bit slow right now. Are you getting an error message or is it just timing out?

supermarket
2003-Sep-23, 08:12 AM
23.09.03

Greetings, fellow elevator freaks&#33;

Please excuse my lack of or mis-information, but how on earth can it be desirable to have some kind of static inter-panetary travelling vehicle? What is the point of not being able to move freely in space? What about high-speed dust particle collisions or asteroids, for that matter? What kind of propulsion mechanism would be useful and surviveable by humans, given the huge distances involved in travelling even to our near neighbours in space?

Don&#39;t tell me: I need to read a book or five.

Best wishes,

Supermarket.

Greg
2004-Apr-30, 05:48 PM
I recently read a very interesting article regarding the feasibility of building a space elevator. If one could be made it would radically lower the cost of parking tonnage in orbit, opening the way to very rapid development and exploration of the inner solar system by making numerous economic ventures potentially profitable.
The gist of the article is that currently no material made is capable of withstanding the load of tension placed on it from such an elevation as an orbital space platform. Any wires or cables passed down will simply snap under the enormous tension. A scientist calculated the tensile strength of carbon nanotubules and stated that cable made of nanotubules would be resilient enough to withstand the stess. The article suggested that if a serious effort was placed into developing an elevator that it would be feasible to build one within 10 years.
To me it sounds too good to be true, but I tend to suspect that unforseen problems would hinder such a device or make it impossible to bring to reality. Moreover it is likely to be a prohibitively expensive venture to build one. More importantly I doubt the technology is available anyway to build it within 10 years. I have not heard of any company advertising its capable of building 80 mile long nanotuble cables as of yet.
I am not a materials scientist or an engineer, so I was curious to see what others might have to say on the subject.

antoniseb
2004-Apr-30, 06:13 PM
I am also interested in this idea, and agree with you that we are a lot more than ten years away from being able to build this. BTW, the cables would have to be 19,000 miles long [or more] since it would need to descend from a geosynchronous orbit. A similar cable would have to extend away from Earth from that orbit.

One of the difficulties is that the Earth end would have to be above the tops of thunderstorms, as Carbon nanotubes are supposed to be easy to set on fire. I&#39;m not sure whether the best solution is to leave a gondola free-swinging at 60,000 feet or to build a tower that tall.

Greg
2004-May-02, 05:42 AM
Another concern I have is the effects of atmospheric drag and wind on the cables slowly affecting their position (making it unstable). I would think that problem would be worse with an elevated platoform. I have imagined the elevator to be ground based with a ground based power station supplying the motion to the cables. A space based (solar) power generator would be incredibly expensive to build. Also delivering cargo from an elevated platform would be impractical unless you used a zeppelin to get it up there. As far as lightning strikes go, the nanotubules would provide the support, a conducting wire or perhaps an insulator coat would protect the cables from lightning strikes, I suppose.

John
2004-May-03, 02:52 PM
The group Liftport Space (http://www.liftport.com/index.php) is already working on building the first Space Elevator, and you can get all of the information you need at their site.

First of all, the cable will be a carbon nanotube composite, and it will stretch to at least 60,000 miles above the surface of the Earth. The extra distance beyond geosynchronous orbit is for counter weight, and the sling shot effect. The sling shot effect allows a payload to use the orbital energy of the Earth to launch to other destinations in the solar systems. Just like a ball on a string being spun around your head, when the ball separate from the stirng it takes off, and so would a space probe at the end of the elevator cable.

Also, the cable will be extended down from orbit (luanched first by the shuttle or another heavy lifter) to a sea-based platform on the equator. The equatorial Pacific has been chosen specifically for the extremely low occurance of electrical storms and typhoons/hurricanes. The bigger problem is atomic oxygen ions in the upper atmosphere coroding the cable, but they&#39;re working on that, too.

If you have further questions I recommend going to this site (http://www.isr.us/SEHome.asp), or to the Liftport site at the top of this post. Both have great info on the technical plans and required technologies to complete one.

John
2004-May-03, 09:34 PM
Popular Science (http://www.popsci.com/popsci/science/article/0,12543,599827-4,00.html) has a recent story regarding the current plans to build a Sapce Elevator.

ToSeek
2004-Jun-25, 07:52 PM
Scientist Sees Space Elevator in 15 Years (http://story.news.yahoo.com/news?tmpl=story&amp;cid=1894&amp;e=1&amp;u=/ap/20040625/ap_on_he_me/space_elevator)

orangeSCT
2004-Jun-25, 10:00 PM
Here is a great paper on space elevator research (http://www.niac.usra.edu/files/studies/final_report/pdf/521Edwards.pdf). I've posted this on another thread related to space elevators so I apologise if its repetative but I think it is a good source of info.

George
2004-Jun-25, 10:03 PM
If anyone sees materials data, I would enjoy seeing it.

For what it's worth, I truly doubt this will get built in 50 years, regretfully. Paper thin walls being pounded by storms, deterioation by lightning strikes (a guess), space debris and meteor impacts, joint weights and weaknesses, thermal stresses (night/day), etc. Not to mention.....1 terrorist.

orangeSCT
2004-Jun-25, 10:16 PM
I had forgotten about this until just recently, but there is actually a space elevator conference going on next week in Washinton DC. Hopefully some new information will be released regarding research for the past year. The information in my last link (http://www.niac.usra.edu/files/studies/final_report/pdf/521Edwards.pdf) is about a year (or more) old and I will be curious to see if there are any new thoughts.

Pinemarten
2004-Jun-26, 08:25 AM
I am wondering which more feasible/popular at this time; a tethered/stationary elevator or a "floating tail' ?

Excelsior
2004-Jun-26, 10:00 AM
I am not sure we have the materials strong enough to withstand the stresses required by a space elevator.

milli360
2004-Jun-26, 03:18 PM
Scientist Sees Space Elevator in 15 Years (http://story.news.yahoo.com/news?tmpl=story&amp;cid=1894&amp;e=1&amp;u=/ap/20040625/ap_on_he_me/space_elevator)
This appeared in my local paper this morning, and I figured you'd already have a link to it. :)

He's figuring to have it built and operating by 2019.

And it's going to cost $10 billion dollars, an amount that the article calls "a pittance compared with other space endeavors". I'd have to agree. Since it is going to be 62,000 out into space, that's $10,000,000,000 / (62,000 * 5,280 feet), or $30 per foot. Construction of our local jogging trail (ten foot wide asphalt), not counting land acquisition, cost $70 per foot. I'll bet that figure gets revised in the next couple days.

Candy
2004-Jun-26, 04:26 PM
I am not sure we have the materials strong enough to withstand the stresses required by a space elevator.

Edwards (http://dailynews.att.net/cgi-bin/news?e=pub&amp;dt=040626&amp;cat=science&amp;st=scienced83ejbh 00&amp;src=ap) said he probably needs about two more years of development on the carbon nanotubes to obtain the strength needed. After that, he believes work on the project can begin.
I'm more concerned with how it would be possible to carry explorers such a distance safely? 8-[

eburacum45
2004-Jun-26, 05:07 PM
This is a good page about the difficulties in creating a material with enough strength;

http://www.isr.us/Downloads/niac_pdf/chapter2.html
when that page was written, nanofibres were being produced with a tensile strength of 63 Gpa-
the theoretical maximum strength of nanofibres has been calculated to be 300 Gpa, and a space elevator becomes feasible at 130 Gpa.

I think we have a long way to go; if anything can do it, a max strength nanotube is going to be best produced by nanotech matter compiler, IMO.

Tuckerfan
2004-Jun-27, 05:38 AM
There's a conference on it in a couple of days. (http://isr.us/Spaceelevatorconference/) The biggest issue I see is the funding. I say we mug Bill Gates.

George
2004-Jun-28, 01:11 PM
Has any major structure been built yet with this material? A 1/2 mile bridge or something?

orangeSCT
2004-Jun-28, 01:30 PM
No, nothings been built with it yet that I am aware of. I think the problem is that it is still insanely expensive to produce. For a major construction project like a bridge or the space elevator tons of the material will be needed not grams (which is how production is measured now). But like anything else, the ability to mass produce will come eventually.

George
2004-Jun-28, 02:04 PM
Are they planning to build something conventional with it and test it for 10 years or so?

Philippe
2004-Jun-28, 05:15 PM
The biggest issue I see is the funding. I say we mug Bill Gates.

hear hear!
=D>

Tacitus
2004-Jun-28, 10:23 PM
How about this for progress...

100-metre nanotube thread pulled from furnace (http://www.newscientist.com/news/news.jsp?id=ns99994769)

Admittedly the thread they produced is no stronger than regular yarn, but this is still an impressive step forward and is likely to be improved upon significantly.

Mike

Excelsior
2004-Jun-29, 06:45 AM
So what are the challenges preventing us from building a space elevator today ?

ToSeek
2004-Jun-29, 01:11 PM
So what are the challenged preventing us from building a space elevator today ?

Technologically, developing the materials to build it from. Practically, getting sufficient funding.

daver
2004-Jun-29, 05:16 PM
"Developing the materials" consists of more than just being able to spin thousands of km of ridiculously high tensile strength material. You also have to answer questions about how it survives in a space environment, how it survives in a terrestrial environment, how it survives wear and tear from the trolleys, how to build it so that it is resistant to degradation from micrometeorites.

After all that, you'll have some legal issues. An annoying number of people say "terrorists", and think that that is sufficient reason not to build it. You will have to convince people that (1) it is robust in the face of terrorist attacks with an airplane, (2) it is robust in the face of terrorists sending up explosive cargos, (3) even if there is a failure (terrorists sending up a nuke, meteor strike, space junk strike, terrorists taking over the control cabin and steering it into ISS, whatever) that the resulting thread won't wrap around the equator, taking out Nairobi or something. The legal issues may prove tougher than the technical issues.

orangeSCT
2004-Jun-29, 06:20 PM
Another big hurdle beyond development of materials of sufficient strength and the obvious political issues, are the potential public health concerns (http://online.sfsu.edu/~rone/GEessays/nanobraindamage.htm)
This actually worries me more than figuring out how to build the thing. Some groups are actually calling for a moratorium on nanoparticle production until further study on health implications are done. I agree more safety studies need to be done, but I hope it doesn't end up slowing down research on developing these materials.

Avatar28
2004-Jun-29, 07:38 PM
After all that, you'll have some legal issues. An annoying number of people say "terrorists", and think that that is sufficient reason not to build it. You will have to convince people that (1) it is robust in the face of terrorist attacks with an airplane, (2) it is robust in the face of terrorists sending up explosive cargos, (3) even if there is a failure (terrorists sending up a nuke, meteor strike, space junk strike, terrorists taking over the control cabin and steering it into ISS, whatever) that the resulting thread won't wrap around the equator, taking out Nairobi or something. The legal issues may prove tougher than the technical issues.

1) is easy enough. Since you're going to have it offshore anyways, just set up a 50 mile (or whatever) no fly zone around it. If you try to fly an airplane at it, you get a warning. If you persist in flying towards it, you get shot down. Period.

2) You would have a relatively small amount of cargo. Sufficient checks on the cargo ought to be sufficient. When's the last time terrorists smuggled explosive cargo aboard a rocket

Not sure about 3, though I would expect it to be relatively lightweight. They're talking about a ribbon 3 feet wide and paper thin.

Tacitus
2004-Jun-29, 08:46 PM
So what are the challenges preventing us from building a space elevator today ?

The key is that you need to get to the point where one or more companies/governments can be convinced that investing in a space elevator is worth the investment risk.

If the $5bn-$10bn estimate is correct, the project is well within the budget of a number of corporations/agencies, but currently the risk is too high - we simply don't have the technology to do it yet.

My guess is that once it can be proved you could spin a 100,000km long ribbon with the required tensile strength and at manageable cost, investment will start in earnest.

Money talks - they'll find a way to resolve political and legal objections.

Mike

Swift
2004-Jun-29, 09:04 PM
1) is easy enough. Since you're going to have it offshore anyways, just set up a 50 mile (or whatever) no fly zone around it. If you try to fly an airplane at it, you get a warning. If you persist in flying towards it, you get shot down. Period.

Ok, then how do you get to it. I can't imagine people are going to want to take a boat to get to the space elevator.

I agree with the general consensus that materials are the fundamental problem. There are, within about the last year, some lab scale concepts to spin macro-sized threads (cm to meter length and fractions of a mm thick) of a fraction of theoretical strength. That is orders of magnitude away from hundreds of kilometers of meter thick cable of enough strength.

tofu
2004-Jun-29, 09:09 PM
Not sure about 3, though I would expect it to be relatively lightweight. They're talking about a ribbon 3 feet wide and paper thin.


If the ribbon is cut, anything above the cut will fly off into space, although it would probably remain in high Earth orbit. Anything below the cut will fall to Earth. However, it's not like we are talking about giant steel cables falling from the sky and killing people! It should have about the same terminal velocity as a newspaper. If you were lucky enough to know that pieces are coming your way, you could walk outside and catch them and then of course you'd sell them on ebay. :)

More than likely, it would be cut in low Earth orbit since that's where most of the hazards are. If the base station is several miles offshore, the individual pieces would never reach land, they'd just fall into the sea. There wouldn't be enough cable from the ground to LEO to wrap all the way around the planet.

And the reason I say "individual pieces" is that the portion of the cable below the cut will fall toward Earth on a ballistic trajectory and very likely have enough velocity when it hits the atmosphere to burn up and therefore further fragment.

The benefits of a space elevator so enormously outweigh the potential hazards that I think it's safe to say if we don't build one nature should definitely select us for extinction – because we'd be crazy!

Consider this: what is the value of oil? Think about all the amazing things that are possible because of cheap oil. Jet travel makes organ transplants possible. Millions of people have fresh food to eat because it can be delivered quickly. Plastics have revolutionized medicine. The benefits to our society are really just too many to count.

Now imagine that you could go back in time 150 years. If you tried to tell someone from that era that they should really invest research into a movable platform that could stay afloat in the rough north atlantic, could sink a pipe all the way to the sea floor, could then drill down through the sea floor for oil, and could offload the oil to a ship, they'd most definitely laugh you out of town. They wouldn't be able to imagine the benefits to be gained from the oil. They'd just focus on how impossible it seems to build an offshore oil rig. I mean, have you ever seen one of those things? They are amazing!

I think the space elevator is very similar. Average people (not us astronomy nerds, the average person on the street) will invariably focus on the elevator's size and cost. They'll worry about potential problems. They'll think the whole thing is a pipe dream. Many of them will probably laugh outright. But the truth is, we can't even begin to imagine the kinds of things that an elevator will make possible for us, and the benefits it will bring to average people everywhere.

Imagine if we could cover the Moon with solar panels (and no, you wouldn't be able to see them from Earth any more than you can see Earth cities from the moon). We could beam the power back to Earth and never have to burn another lump of coal or put another drop of CO2 in our atmosphere. A space elevator makes going to the moon virtually free. Once you climb the elevator past geosynchronous, you can just let a payload go and it will fly off into space. Projects that you wouldn't even consider before become almost trivial with an elevator. It really will revolutionize society.

Avatar28
2004-Jun-29, 09:20 PM
1) is easy enough. Since you're going to have it offshore anyways, just set up a 50 mile (or whatever) no fly zone around it. If you try to fly an airplane at it, you get a warning. If you persist in flying towards it, you get shot down. Period.

Ok, then how do you get to it. I can't imagine people are going to want to take a boat to get to the space elevator.


Why not? It's not like we're talking a multi day trip. Even 50 miles would probably be not significantly longer than an hour or so to cross. You could use hovercraft or hydrofoil and probably do it faster yet. People take ferrys across the ocean all the time and many of those rides can be an hour or more. You would just fly to an airport or whatever near the closest coast to the elevator, then take a ferry from that point out.

Besides, let's face it. It would probably be awhile before you get any sort of commuter traffic going up and down. Perhaps with cheap access to orbit, though, we could build a REAL space city near the geosync point.

daver
2004-Jun-29, 11:37 PM
1) is easy enough. Since you're going to have it offshore anyways, just set up a 50 mile (or whatever) no fly zone around it. If you try to fly an airplane at it, you get a warning. If you persist in flying towards it, you get shot down. Period.

You have an airport at the terminal (or the space elevator is worthless). Airplanes have to take off from the terminal; that's the most reasonable spot to stage a hijacking.



2) You would have a relatively small amount of cargo. Sufficient checks on the cargo ought to be sufficient. When's the last time terrorists smuggled explosive cargo aboard a rocket

How much explosive do you need to sever the cable? The trolley car is securely attached to it. And the elevator would be carrying tons of cargo at a time.

Terrorists haven't tried smuggling cargo aboard a rocket because there hasn't been much point--people don't ship cargo by rocket. With the space elevator, shipping things to orbit will be routine.


Not sure about 3, though I would expect it to be relatively lightweight. They're talking about a ribbon 3 feet wide and paper thin.

I'm more or less parrotting problems that have been raised on other boards; the problem is that the problems sound legitimate to the uninformed. Even after you get approval from governments, you'll have to fight the boatloads of Rainbow Warriors convinced that space lightning is going to render all the tofu in the world radioactive or something (governments can be convinced by experts or political pressure or bribes; converts are much less subject to reason).

tofu
2004-Jun-30, 12:26 AM
Even after you get approval from governments, you'll have to fight the boatloads of Rainbow Warriors convinced that space lightning is going to render all the tofu in the world radioactive or something

It's true you know.

daver
2004-Jun-30, 01:03 AM
Even after you get approval from governments, you'll have to fight the boatloads of Rainbow Warriors convinced that space lightning is going to render all the tofu in the world radioactive or something

It's true you know.

I know. This is all part of a disinformation campaign--we want to associate the data with an obvious lunatic so that it will not be taken seriously until it is TOO LATE.



.

ChaosInc
2004-Jun-30, 01:45 AM
A few questions for the unenlightened such as myself: How do we put it in position? Does a large spool get placed in Geostat and then pay out a long spool as the counterweight moves higher? The other one is how do you power the elevating cargo? I think I read something about lasers, but that seems like something out of a sci-fi novel. One final question is where does the momentum come from? Won't coriolus (spelling?) acceleration tug on the orbiting weight?

Pinemarten
2004-Jun-30, 04:37 AM
According to my thinking the elevator is more simple than some perceive.

Mass must be counterweighted as the tether is built. This can be attained by adding length to an upward arm or adding mass. Adding length would be easier.

The energy needed to raise payloads could be counterweighted by lowering 'space junk' back to Earth.

Wally
2004-Jun-30, 01:53 PM
One final question is where does the momentum come from? Won't coriolus (spelling?) acceleration tug on the orbiting weight?

The earth's rotation provides the momentum, just like swinging a yoyo around your head. The base would be anchored on the equator, thus corriolus (sp as well) wouldn't be a factor.

milli360
2004-Jun-30, 03:25 PM
One final question is where does the momentum come from? Won't coriolus (spelling?) acceleration tug on the orbiting weight?

The earth's rotation provides the momentum, just like swinging a yoyo around your head. The base would be anchored on the equator, thus corriolus (sp as well) wouldn't be a factor.
I think they are including a vertical coriolis effect--objects at different heights along the elevator would have different linear velocities.

Avatar28
2004-Jun-30, 05:00 PM
1) is easy enough. Since you're going to have it offshore anyways, just set up a 50 mile (or whatever) no fly zone around it. If you try to fly an airplane at it, you get a warning. If you persist in flying towards it, you get shot down. Period.

You have an airport at the terminal (or the space elevator is worthless). Airplanes have to take off from the terminal; that's the most reasonable spot to stage a hijacking.


Why would the airport HAVE to be at the terminal end? It's not like it's expensive to ship cargo out to it. Not to mention that you're likely talking about having a floating or anchored platform. What are you going to do, make a floating runway? No, if it's in the ocean then you just take a ship/boat/hovercraft/whatever out to it.




2) You would have a relatively small amount of cargo. Sufficient checks on the cargo ought to be sufficient. When's the last time terrorists smuggled explosive cargo aboard a rocket

How much explosive do you need to sever the cable? The trolley car is securely attached to it. And the elevator would be carrying tons of cargo at a time.

Terrorists haven't tried smuggling cargo aboard a rocket because there hasn't been much point--people don't ship cargo by rocket. With the space elevator, shipping things to orbit will be routine.
[/quote]

Again, I think that having sufficient checks on all cargo being shipped would be sufficient to guard against that.



Not sure about 3, though I would expect it to be relatively lightweight. They're talking about a ribbon 3 feet wide and paper thin.

I'm more or less parrotting problems that have been raised on other boards; the problem is that the problems sound legitimate to the uninformed. Even after you get approval from governments, you'll have to fight the boatloads of Rainbow Warriors convinced that space lightning is going to render all the tofu in the world radioactive or something (governments can be convinced by experts or political pressure or bribes; converts are much less subject to reason).[/quote]

Fair enough then.

daver
2004-Jun-30, 05:20 PM
No, if it's in the ocean then you just take a ship/boat/hovercraft/whatever out to it.

Then you hijack the boat and crash it into the terminal. Maybe not as dramatic as the airplane, but it takes the elevator out for a year or so.

In this case, the only damage is to the terminal and the beanstalk--the UN (or whoever ends up regulating this) won't be too concerned. The millions of people who live on the beanstalk or in colonies in orbit whose lives depend on the beanstalk might be a bit more worried.



Again, I think that having sufficient checks on all cargo being shipped would be sufficient to guard against that.

But some of the cargo is supposed to be explosive--rocket fuel will be needed for interplanetary probes, oxygen, fertilizer for hydroponics or decorative gardens, hydraulic fluid, whatever. It wouldn't take much to plausibly hide an explosive.

So the question is what is the worst case damage from someone succeeding in hiding an explosive on board--it might not be easy, but it could be done, and the more damage that would be done, the more likely it is that someone would try it. If worst case it's the total destruction of the beanstalk, that's not too bad. If it's the loss of every city on the equator, that's unacceptable. And again, there's the problem of perceived danger as opposed to the actual danger.

orangeSCT
2004-Jun-30, 06:19 PM
One thing I think that needs to be realized is that the initial space elevator is not going to be servicing an orbital city. It will simplify access to space, but it will not immediately increase the volume of cargo to the point of universal access. As the use of the space elevator increases, so will the complexety of the structure. I would imagine redundancy of main structural elements so that if one cable is "taken out" the elevator itself would not be lost.

Emspak
2004-Jun-30, 07:29 PM
While I like the idea of a space elevator using carbon nanotubes as a base material, judging by the article linked earlier in the thread I have my doubts about their viability anytime soon. Not that it can't happen, but I have my doubts.

Before anyone jumps on me for being a luddite, think about all the new technologies that haven't panned out over the centuries, or proved impractical. Some examples: Da Vinci's human-powered screw-type helicopter, firing a gun into space to launch space vehicles (Verne), and using heating ducts to melt snow in the streets of New York (see Scientific American -- this one appeared as an idea 150 years ago and was published in the magazine at the time), and pneumatically-powered mass transit. They weren't bad ideas, by the way. They just weren't feasible withthe technology at the time, or other, better ways of doing the same thing became available. Even the vaunted Bell Labs, which produced many of the technoogies we find familiar now, hit a lot of duds on the way.

I hope there is a way to do it. I think there may be. But until the issue of a material strong enoguh to handle the stresses is solved, I'll invest my pension fund money elsewhere, thanks.

Tuckerfan
2004-Jun-30, 07:32 PM
Before anyone jumps on me for being a luddite, think about all the new technologies that haven't panned out over the centuries, or proved impractical. Some examples: Da Vinci's human-powered screw-type helicopter, firing a gun into space to launch space vehicles (Verne), and using heating ducts to melt snow in the streets of New York (see Scientific American -- this one appeared as an idea 150 years ago and was published in the magazine at the time)You do know, that there's a city in Japan which uses this to melt the snow on their streets? They're able to do it because there's a handy source of geothermal energy nearby.

ChaosInc
2004-Jun-30, 09:47 PM
Milli addressed my question (thanks!), but I never got a complete answer to the coriolis acceleration question. I suppose that we could mount small rockets on the lifting vessel to provide a force counteracting the acceleration as the body rises. It seems counterproductive to add rockets to something as simple as this. I understand the idea about lowering space junk/debris, but would we always have the right mass of junk available when we lifted a new cargo?

One problem I would see with a meter wide strip that is paper thin is vortex shedding would tend to rip it apart or at the very least cause excessive vibrations that I am not sure would be predictable. Has anyone ever tried to hang a happy birthday banner on a windy day?

Sam5
2004-Jun-30, 10:56 PM
I think this is a hoax, designed to get more government (taxpayer) dollars for “research”.

milli360
2004-Jun-30, 11:03 PM
One problem I would see with a meter wide strip that is paper thin is vortex shedding would tend to rip it apart or at the very least cause excessive vibrations that I am not sure would be predictable. Has anyone ever tried to hang a happy birthday banner on a windy day?
Now try to hang a happy birthday banner made from kevlar, with a five ton weight attached to the bottom of it. I bet the wind goes crying to Mariah.

Brady Yoon
2004-Jun-30, 11:33 PM
[Sam5 wrote]I think this is a hoax, designed to get more government (taxpayer) dollars for "research".[/Sam 5 wrote]

Why do you think so? It was in Discover magazine, a science magazine. There are better ways to con the public...

Sam5
2004-Jul-01, 12:05 AM
I think this is a hoax, designed to get more government (taxpayer) dollars for "research".

Why do you think so? It was in Discover magazine, a science magazine. There are better ways to con the public...

Over the years I’ve heard all kinds of wild ideas from government agencies, and they always needed more “research and development” money to test new ideas. This sounds like a long drawn out R &amp; D project.

I also worked with TV towers. The bottom few feet have to support the weight of the entire rest of the tower. Think of how much a several hundred mile tower would weigh, before they got it up high enough to supposedly support itself.

Back in the old days, the mass media science magazines used to publish all sorts of articles about “jet flying wings” for TWA and American Airlines, “US flying saucers” that would carry thousands of people at super-sonic speed, "tourist space ships to Mars", etc., etc. These articles are just designed to sell magazines to a gullible public.

Tuckerfan
2004-Jul-01, 12:32 AM
I think this is a hoax, designed to get more government (taxpayer) dollars for “research”."Why, fer cryin' out loud..research physicists need Porsches, TOO!!" Opus. Well, NASA wasn't the first to come up with the idea (it dates back to the turn of the last century, and Clarke used it as the central premise in his Fountains of Paradise novel [you might have heard of him, in addition to being a science fiction writer, he came up with the idea of the communications satellite]), but NASA's been doing some research, studying the concept. (http://trs.nis.nasa.gov/archive/00000535/)

Sam5
2004-Jul-01, 12:43 AM
I think this is a hoax, designed to get more government (taxpayer) dollars for “research”."Why, fer cryin' out loud..research physicists need Porsches, TOO!!" Opus. Well, NASA wasn't the first to come up with the idea (it dates back to the turn of the last century, and Clarke used it as the central premise in his Fountains of Paradise novel [you might have heard of him, in addition to being a science fiction writer, he came up with the idea of the communications satellite]), but NASA's been doing some research, studying the concept. (http://trs.nis.nasa.gov/archive/00000535/)


Yep, that’s what I said. Tax dollars for research and studies for an “elevator” into space. Oh boy, we really need to spend our tax dollars on that!

Tuckerfan
2004-Jul-01, 12:51 AM
I think this is a hoax, designed to get more government (taxpayer) dollars for “research”."Why, fer cryin' out loud..research physicists need Porsches, TOO!!" Opus. Well, NASA wasn't the first to come up with the idea (it dates back to the turn of the last century, and Clarke used it as the central premise in his Fountains of Paradise novel [you might have heard of him, in addition to being a science fiction writer, he came up with the idea of the communications satellite]), but NASA's been doing some research, studying the concept. (http://trs.nis.nasa.gov/archive/00000535/)


Yep, that’s what I said. Tax dollars for research and studies for an “elevator” into space. Oh boy, we really need to spend our tax dollars on that!So what would you propose we spend the money on?

Sam5
2004-Jul-01, 01:02 AM
So what would you propose we spend the money on?

Well, doh. The feds could let us keep more of our own money. I’d like to decide where I spend my own research money. I’d like to spend my portion on a vacation to Yucatan.

Also, we need a new source of power for our cars, other than oil.

Back in the ‘50s, the income tax rate was about 10%-20%. We spent the money on our families, not on space elevators or putting some guys on Mars

Tuckerfan
2004-Jul-01, 01:14 AM
So what would you propose we spend the money on?

Well, doh. The feds could let us keep more of our own money. I’d like to decide where I spend my own research money. I’d like to spend my portion on a vacation to Yucatan.

Also, we need a new source of power for our cars, other than oil.

Back in the ‘50s, the income tax rate was about 10%-20%. We spent the money on our families, not on space elevators or putting some guys on MarsYou really don't understand how government works, then. NASA gets less than $.01 of every tax dollar (http://www.tennessean.com/opinion/nashville-eye/archives/04/04/50017937.shtml), try taking your family to the Yucatan on that. If NASA didn't get the money, it'd go to some other branch of the government, like the military, so they could try and find WMDs in Iraq. As for finding a replacement for oil in cars, you do know that NASA pioneered research into fuel cells (http://www.nasa.gov/vision/earth/technologies/18mar_fuelcell.html), don't you? And that fuel cells are the most talked about replacement for gasoline powered vehicles at the moment? And that Housing and Ubran Developement gets twice the budget (http://www.hud.gov/news/release.cfm?content=pr03-014.cfm) that NASA does?

Or that NASA research in the areas of manned spaceflight has led to medical devices for the family pet? (http://www.nasa.gov/missions/science/f_analyzer.html)

wedgebert
2004-Jul-01, 01:27 AM
I know it's been said before, but our space program helps everybody. From obvious things like GPS, weather satellites and communication satellites, to less obvious things like increasing the coordination between airliners (and thus increasing saftey), laser angioplasty, self-righting life rafts and more. (see this page (http://www.thespaceplace.com/nasa/spinoffs.html) for more spinoffs)

Lower cost to orbit means satellites will be cheaper. Cheaper satellites means cheaper telecommunications. Cheaper satellites means more weather satellites and improved weather forecasting.

You want a new source of energy for your car? NASA was one of the pioneers in photovoltaic power systems. And we can't have clean fusion until we have a large source of Helium-3, something not found on Earth in more than trace quantities.

Spend the money of families? Aside from the too numerous to mention medical spinoffs from NASA technology, what about household smoke detectors? Those were developed for Skylab in the 1970's. Another NASA derived techology designed to measure the attention span of pilots is being used to help kids with A.D.D.

I'd say that dollar for dollar, money spent on research for the space program has produced a wider range of advancements to our daily lives than any other research. Remember that next time you're grocery shopping, because the barcodes they scan at the register, saving both time and money, were developed by NASA as well.

Sam5
2004-Jul-01, 01:28 AM
So what would you propose we spend the money on?

Well, doh. The feds could let us keep more of our own money. I’d like to decide where I spend my own research money. I’d like to spend my portion on a vacation to Yucatan.

Also, we need a new source of power for our cars, other than oil.

Back in the ‘50s, the income tax rate was about 10%-20%. We spent the money on our families, not on space elevators or putting some guys on MarsYou really don't understand how government works, then. NASA gets less than $.01 of every tax dollar (http://www.tennessean.com/opinion/nashville-eye/archives/04/04/50017937.shtml), try taking your family to the Yucatan on that. If NASA didn't get the money, it'd go to some other branch of the government, like the military, so they could try and find WMDs in Iraq. As for finding a replacement for oil in cars, you do know that NASA pioneered research into fuel cells (http://www.nasa.gov/vision/earth/technologies/18mar_fuelcell.html), don't you? And that fuel cells are the most talked about replacement for gasoline powered vehicles at the moment? And that Housing and Ubran Developement gets twice the budget (http://www.hud.gov/news/release.cfm?content=pr03-014.cfm) that NASA does?


Hey, I’m not against NASA. NASA isn’t the problem. The problem is multi-million dollar research projects for space elevators.

If I had my way, I’d give NASA a bigger budget and shut down some other agencies altogether. I think NASA should work on many other science research projects instead of some of the other agencies working on them, but a “space elevator” is about the most ridiculous government research project I’ve ever heard about.

As far as the war goes.... I agree.



Or that NASA research in the areas of manned spaceflight has led to medical devices for the family pet? (http://www.nasa.gov/missions/science/f_analyzer.html)

That's just great.

milli360
2004-Jul-01, 03:43 AM
Sam5:
I also worked with TV towers. The bottom few feet have to support the weight of the entire rest of the tower. Think of how much a several hundred mile tower would weigh, before they got it up high enough to supposedly support itself.
I thought someone said that it might not even touch the ground. :)

eburacum45
2004-Jul-01, 04:18 AM
Sam5:
I also worked with TV towers. The bottom few feet have to support the weight of the entire rest of the tower. Think of how much a several hundred mile tower would weigh, before they got it up high enough to supposedly support itself.
I thought someone said that it might not even touch the ground. :)

Many proposals for the design of the space elevator do not touch the ground.
Dani Eder has investigated the idea of a ground based tower, whigh rises above the bulk of the atmosphere to meet the descending space elevator; he says the tallest man-made structure using known materials is likely to be fifteen kilometers tall.
By building upwards as well as downwards the problems with windspeed and lightning are avoided.

Sam5 is right in another way too; the tower has to support the weight of the cable from geostationary orbit, so should be much thicker there.


Despite having used these constructs in OA (http://www.orionsarm.com/historical/space_elevators.html) I think the threat of terrorism might deter any builders in the foreseeable future. If the entire Earth became a closely watched, security obsessed crime-free society then it might one day be built. But that world would be quite different to, and more restrictive than the one we live in.

orangeSCT
2004-Jul-01, 01:50 PM
Ummm.... the worlds problems are because of "multi-million dollar research projects for space elevators"?????

IIRC only $500,000 has been spent so far on the research. There is another $2.5 million earmarked for the next few years. A pittance in the overall picture of research dollars. How much money is spent on research on reusable launch vehicles? How much does each Space Shuttle launch cost? If the space elevator concept turns out to be feasable, the cost of access to space will plummet ($100 per pound to orbit vs. $10,000). That alone is worth an initial investment.

The concept that is being studied has pretty solid research, not just some woo-woo trying to steal your money. ISR is actually looking for people to tell them why this concept won't work. All they ask is for people to review the research that has been done so far. Thislink is a little outdated but is the most current I know of (http://www.niac.usra.edu/files/studies/final_report/pdf/521Edwards.pdf) on what has been studied so far.

As far as the base needing to support the entire weight of the elevator, thats not how it works. There will be no "weight" that will have to be supported. The ribbon will be lowered from orbit with a counterweight extended in the opposite direction until the ribbon reaches earth. True the ribbon does need to be very strong, but the stress will come from tension not compression as we are not builing up but hanging down.

wedgebert
2004-Jul-01, 02:07 PM
Don't forget that the ribbon is very likely to be tapered as well. The closer to the ground the ribbon gets, the less each portion has to support, so the thinner it can be. The material strength determines the taper factor.

Also, high-winds would not be much of a problem. The ribbon has a very narrow crosssection and is quite strong, plus most of it is in portions of the atmosphere that aren't as dense as near ground level.

eburacum45
2004-Jul-01, 04:59 PM
Eder's reasoning for building a fifteen mile (sorry not kilometers) high base tower was to avoid any wind shear on the frail tape - and to earth the cloudlayer;
plenty of electrical charge could run through the last fifteen miles because of atmospheric conditions-

it is easier to earth a solid structure than a tape.


http://www.popularmechanics.com/science/space/2002/7/going_up/print.phtml

Saorsa
2004-Jul-01, 05:18 PM
Hello. Long time reader, first time poster, etc.

Space.com has a new article about the space elevator today and I was struck by the size they claimed researchers were aiming for:


Anchored in space a ribbon 62,000 miles (100,000 kilometers) long would be made of carbon nanotubes. A "climber" would haul cargo, as well as passenger modules up and down the length of ribbon. Those are the basics. Of course, money is a key lubricant in this high-wire balancing act of technology.

My first assumption was that someone misplaced their decimal point since those numbers look like they should be 62 miles and 100km, which would make sense for a space elevator. But, I thought, maybe some lunatic really does want to stretch it 1/4 of the way to the moon.

Avatar28
2004-Jul-01, 05:35 PM
Hello. Long time reader, first time poster, etc.

Space.com has a new article about the space elevator today and I was struck by the size they claimed researchers were aiming for:


Anchored in space a ribbon 62,000 miles (100,000 kilometers) long would be made of carbon nanotubes. A "climber" would haul cargo, as well as passenger modules up and down the length of ribbon. Those are the basics. Of course, money is a key lubricant in this high-wire balancing act of technology.

My first assumption was that someone misplaced their decimal point since those numbers look like they should be 62 miles and 100km, which would make sense for a space elevator. But, I thought, maybe some lunatic really does want to stretch it 1/4 of the way to the moon.

Those numbers are roughly correct. The midpoint of the cable would be in geosyncronous orbit. Though I thought that geosync was closer to 26,000 miles which would make the cable 52,000 miles long.

Pretty mind boggling when you think about it, eh? If you're going up in it, though, better pack a lunch. It will take a few days for it to reach that altitude. Even assuming the climber could reach an average vertical speed of 500 mph (which I would be skeptical of), you're talking 52 hours to reach geosync orbit.

Saorsa
2004-Jul-01, 05:51 PM
Those numbers are roughly correct. The midpoint of the cable would be in geosyncronous orbit. Though I thought that geosync was closer to 26,000 miles which would make the cable 52,000 miles long.

Pretty mind boggling when you think about it, eh?

Absolutely. And that only magnifies the confusion generated by another of the article's claims that, once the necessary materials are gathered, the elevator would take only 15 years to build. I thought that was reasonably optimistic for 62 miles, given the engineering difficulties, but that sounds impossible for a 52,000 mile elevator. I'm not sure that could be built in a century.

ToSeek
2004-Jul-01, 05:52 PM
Those numbers are roughly correct. The midpoint of the cable would be in geosyncronous orbit. Though I thought that geosync was closer to 26,000 miles which would make the cable 52,000 miles long.

Geosync is 22,300 miles from the surface of the Earth, about 26,000 miles from the center.

wedgebert
2004-Jul-01, 06:13 PM
The cable has to extend out to about 100,000 km though to properly balance the elevator. It's not just a 1 to 1 ratio for cable above and below the geo-sync point.

Pinemarten
2004-Jul-02, 05:42 AM
I'm curious.

Does the tether have to have equal length extending out from GC orbit, or would a heavier counterweight on a shorter tether serve the same purpose?

eburacum45
2004-Jul-02, 07:19 AM
Most of the older designs use a small asteroid as counterweight; but it seems someone has calculated that the energy required to capture an asteroid is larger than that involved in shipping up material from Earth.

I have my doubts; a million tonnes of dumb rock versus a million tonnes of buckytube? I would bet on the rock myself.

Emspak
2004-Jul-02, 03:14 PM
As people talk about where to spend research money, I think research money is always well spent, IMO, even if it shows something isn't possible. Negative results are fine -- they are part of science.

Before people start dumping on government bureaucracies, remember that almost every piece of fancy dan technology we use now was developed in a government-sponsored lab (much of the time for the military) or at Bell Labs. The latter didn't have to worry about making money as it was supported by AT&amp;T, a protected monopoly at the time. Basic research is almost always unprofitale. After all, lasers were made possible by quantum theory, but nobody in 1930 envisioned them, or using quantum-based devices (a shout out to solid state electronics!) to make anything people would buy.

By the way, something that is a bit OT -- Sam5 I think wrote that in the 50s the income tax rates were 10-20%. This is not the case-- tax rates hit 90% at the upper brackets. (There are several good histories on the subject -- i'll go get the authors and titles if you want, I can't recall them right now).

If someone were to tell me "I can build a space elevator in 20 years" I would be reluctant to hand over my cash because I think the likelihood of success is too small for me (a private investor). Governments can afford to take a longer view, if they so choose, as could Bell Labs. (Which, by the way, ran into very serious financial problems when it renamed itself Tellabs and tried to do what it did under AT&amp;T after the parent was broken up).

I still think the space elevator is a cool idea, and I hope someone can find a material to make it out of. Carbon-based materials seem a good bet in that regard, as they outperform metals. Most of the problems people cite are minor, in the scheme of things, though that does not mean others won't come up we haven't thought of (remember the Tacoma Narrows Bridge?)

On the other hand, sometimes you have spectacular successes, like Moon landings or the Hoover Dam.

orangeSCT
2004-Jul-03, 03:06 AM
Just curious, has anyone heard anything about how the Space Elevator conference went? I figured some of my usual astronomy related websites would have a summary, but I have not seen any new info as of yet. If anyone has a link I would appreciate it.

Armilus
2004-Jul-03, 02:30 PM
Is the Space Elevator as insane as this article claims, or are the problems surmountable?
http://www.rense.com/general54/wef.htm

Tuckerfan
2004-Jul-03, 04:43 PM
Is the Space Elevator as insane as this article claims, or are the problems surmountable?
http://www.rense.com/general54/wef.htmOkay, I'm not even going to bother to look at the site, simply because I've seen articles on that site before that were all skewed heavily to the "woo woo" side of things. Rense believes (or at least he's posted numerous articles claiming) that the events of 9/11 were part of a plot by the US Gov't. He's had articles on UFOs which have made various claims that they were extraterrestials/time travellers who were in contact with a secret government, which was really running the world, and the insanity gets worse from there.

Yeah, I know, I shouldn't simply dismiss the claims out of hand simply because of the source, but I have limited time and resources in my life, and when I see someone spouting stuff that's garbage 99% of the time, I'm not going to waste my time investigating anything they say on the off-chance that it might be the 1 time they're right.

If there is a secret government, which has alien technology, we'd never know about it. Standard theories hold that if you've got FTL, you've got time travel, so it'd be very easy for the secret government to travel back in time and whack whomever it was who started spewing out secrets, long before any of us ever heard of them.

ToSeek
2004-Jul-09, 05:49 PM
Elevator to space my way to travel (http://www.coloradoan.com/news/stories/20040709/news/811192.html)


It sounds like a civilized way to travel -- I'm not big on sitting atop giant tubes of explosives, either.

I'm ready to go. Just point me toward the "up" button.

ToSeek
2004-Aug-30, 05:47 PM
Space Elevator Climber Competition (http://www.elevator2010.org/site/competitionClimber.html)


Showcasing the first representative prototypes of the Space Elevator, this event will re-define public perception of the Space Elevator project by taking the first step away from mathematical models and drawing boards and into the world of real working hardware.
By participating, you get the opportunity to partner in writing this unique chapter of history.

Avatar28
2004-Aug-30, 08:25 PM
Out of curiosity, anybody know what the vertical speed would be on the climbers? Even if you figure an average speed of 1000 mph, you're talking over a day to reach geosync orbit. Obviously if you just want LEO you wouldn't have to wait nearly as long, though you'll still need a good supply of rocket fuel to get your speed up to orbital velocities.

logicboy
2004-Aug-30, 08:37 PM
You don’t necessarily need fuel to get up to speed http://www.space.com/businesstechnology/technology/tether_tech_030618-1.html

Tuckerfan
2004-Aug-30, 08:46 PM
Out of curiosity, anybody know what the vertical speed would be on the climbers? Even if you figure an average speed of 1000 mph, you're talking over a day to reach geosync orbit. Obviously if you just want LEO you wouldn't have to wait nearly as long, though you'll still need a good supply of rocket fuel to get your speed up to orbital velocities.I've seen estimates of up to a week to get from the surface to LEO.

Avatar28
2004-Aug-30, 10:18 PM
Out of curiosity, anybody know what the vertical speed would be on the climbers? Even if you figure an average speed of 1000 mph, you're talking over a day to reach geosync orbit. Obviously if you just want LEO you wouldn't have to wait nearly as long, though you'll still need a good supply of rocket fuel to get your speed up to orbital velocities.I've seen estimates of up to a week to get from the surface to LEO.

Hmm, better pack a lunch then. Still, I have to seriously question how usable it will be to get people into space if it's that slow. If you figure a week to LEO then you're talking probably about 6-7 months to reach the station at the geosync midpoint. And that's assuming that they're referring to the higher extremes of LEO. If you're talking lower altitudes of, say, 300 miles for that week then you're looking at about 20 months. Pack a lunch indeed!

ToSeek
2004-Aug-31, 01:00 AM
Out of curiosity, anybody know what the vertical speed would be on the climbers? Even if you figure an average speed of 1000 mph, you're talking over a day to reach geosync orbit. Obviously if you just want LEO you wouldn't have to wait nearly as long, though you'll still need a good supply of rocket fuel to get your speed up to orbital velocities.I've seen estimates of up to a week to get from the surface to LEO.

That doesn't sound right - you can walk faster than that! Are you sure you don't mean geosync?

Tuckerfan
2004-Aug-31, 01:18 AM
Out of curiosity, anybody know what the vertical speed would be on the climbers? Even if you figure an average speed of 1000 mph, you're talking over a day to reach geosync orbit. Obviously if you just want LEO you wouldn't have to wait nearly as long, though you'll still need a good supply of rocket fuel to get your speed up to orbital velocities.I've seen estimates of up to a week to get from the surface to LEO.

That doesn't sound right - you can walk faster than that! Are you sure you don't mean geosync?Could be. It's been a while since I read the article and I can't find it at the moment.

daver
2004-Aug-31, 05:34 PM
Out of curiosity, anybody know what the vertical speed would be on the climbers? Even if you figure an average speed of 1000 mph, you're talking over a day to reach geosync orbit. Obviously if you just want LEO you wouldn't have to wait nearly as long, though you'll still need a good supply of rocket fuel to get your speed up to orbital velocities.I've seen estimates of up to a week to get from the surface to LEO.

That doesn't sound right - you can walk faster than that! Are you sure you don't mean geosync?Could be. It's been a while since I read the article and I can't find it at the moment.

It's almost certainly time to geosynch--there's no particular advantage to LEO from a beanstalk--it takes a lot of fuel to launch to an orbit from there, and nearly any orbit will eventually intersect the beanstalk (about the only applications that would make sense would be molniya orbits or sun-synchronous orbits for spysats. Even they would more likely be dropped from higher up, and aerobrake followed by a small boost to their final orbit).

ToSeek
2004-Sep-21, 10:28 PM
Space Elevator Now the Subject of Research By Cadets at the United States Air Force Academy (http://home.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view&amp;newsId=2004092100508 2&amp;newsLang=en)


"My students are fascinated with the concept of the space elevator," said Major Tom Joslyn, instructor of Astronautical Engineering at USAFA and mentor for cadets conducting research on the space elevator. "They are young enough to see such a program come to fruition and many of them see it as a next generation launch system that could revolutionize access to space. Interest in the scientific and engineering objectives of the space elevator will undoubtedly motivate them to learn more than we require them to and hopefully make some discoveries that will help overcome roadblocks to the space elevator."

Tacitus
2004-Sep-21, 11:53 PM
Space Elevator Now the Subject of Research By Cadets at the United States Air Force Academy (http://home.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view&amp;newsId=2004092100508 2&amp;newsLang=en)

I guess it makes a change from studying wormhole physics for their Stargate program. :D

ToSeek
2004-Oct-12, 05:39 PM
Space visionaries aiming high

ELEVATOR WOULD CARRY SUPPLIES INTO ORBIT (http://www.mercurynews.com/mld/mercurynews/9897548.htm?1c)


Yes, some laugh or giggle or just lose it, but that's not stopping Ben and Meekk Shelef from spreading the word.

What we really need, they say, is a gigantic freight elevator to carry supplies from Earth into outer space.

``Kooks,'' is the reaction Ben says they get. ``Kooks in space.''

The pair are hardly pioneers with the space-elevator idea, but they are among its biggest backers. The two Shelefs, who are divorced, and a handful of true believers are forming a Mountain View non-profit and organizing a series of contests to foster space-elevator buzz.

And now they might be getting some traction.

ToSeek
2005-Aug-24, 04:19 PM
Space Elevator Update (http://www.spaceref.com/news/viewsr.html?pid=17844)


We now have 7 teams that have climber hardware and are intending to show up for the 2005 competition. The competition date has been pushed back 3 weeks - we will start accepting hardware on the original Sept 30th date, but will spend 3 weeks debugging both our infrastructure and the team's hardware - this is the first time this hardware is being brought together, and we expect integration to require some extra time and attention.

publiusr
2005-Aug-24, 05:33 PM
I saw that.

www.elevator2010.org/site/index.html
www.liftport.com

JHotz
2005-Aug-27, 12:18 AM
Wouldn’t things pulling on the cable pull the entire elevator down?

Faultline
2005-Aug-27, 05:28 AM
Wouldn’t things pulling on the cable pull the entire elevator down?

I think you're right. There's nothing to "anchor" a space elevator's upper end orbiter.

Van Rijn
2005-Aug-27, 06:07 AM
A decent reference on the subject:

http://en.wikipedia.org/wiki/Space_elevator

The center of mass for a tensile space elevator is at geostationary orbit, with the cable extending beyond that, probably topped with a counterweight that reduces the amount of cable required.

The elevator cab would have a small mass relative to the total structural mass. It wouldn't bring the cable down. There are technical issues - a key issue is the large amount of near-theoretical strength carbon nanotube cable required - but the concept is technically sound.

There are other designs that would only go up to geostationary orbit, but are technically more difficult. There are designs for non-geosynchronous tethers that would be easier to build but would also be very useful. I suspect we'll see those first.

imran
2005-Aug-27, 07:45 PM
A new space elevator article in IEEE's latest issue (made the cover page!).

A Hoist to the Heavens (http://www.spectrum.ieee.org/WEBONLY/publicfeature/aug05/0805spac.html)

eburacum45
2005-Aug-28, 01:02 AM
Wouldn’t things pulling on the cable pull the entire elevator down?

I think you're right. There's nothing to "anchor" a space elevator's upper end orbiter.

If the elevator has a lot of weight pulling on it in the Earthward direction you can in theory counteract that by moving ballast outwards from thr geostationary point towards the outer end; centrifugal 'force' will act to pull the elevator outwards, and compensate for extra mass on the earthwards portion.

Astronot
2005-Aug-28, 01:55 AM
What about the rotational energy needed to get the cab to the orbital speed of the station? Do you just borrow that from the station and the on the way up and repay it on the way down?

eburacum45
2005-Aug-28, 03:40 AM
What about the rotational energy needed to get the cab to the orbital speed of the station? Do you just borrow that from the station and the on the way up and repay it on the way down?

You gain this energy by climbing the elevator; climbing the elevator obviously requires energy, and as you rise up the elevator you are gaining momentum all the time.

I don't know how difficult it would be to have two way traffic on a single elevator cable; but if you have cars constantly going down as well as up the net effect on angular momentum should be almost nil.

(here is a little graphic I have done of two cars passing each other on a two -way elevator- perhaps the car going down could contribute power to the one coming up in some way...
http://img66.imageshack.us/img66/9678/elevator7tj.jpg

this model isn't finished yet by the way- I am working on adding some more interior furnishings etcetera...)

The Supreme Canuck
2005-Aug-28, 05:12 PM
Here's a question: say you get some sort of impact on the cable that severs a number of nanotube fibres. How do you repair that? Seems to me that you'd have to remove the damaged fibres and replace them. And that's hard to do. Any ideas?

Van Rijn
2005-Aug-28, 09:58 PM
If the elevator has a lot of weight pulling on it in the Earthward direction you can in theory counteract that by moving ballast outwards from thr geostationary point towards the outer end; centrifugal 'force' will act to pull the elevator outwards, and compensate for extra mass on the earthwards portion.

While you could do things that finely, in a tensile elevator, normally you would have a static counterweight past the geostationary point. Given that the structure is under tension, as long as you don't overload it, you won't drag it down or break it.

In theory, an actively stabilized structure in compression would only need to go up to geostationary orbit and all forces would be downward. Again, the point would be not to overload it. A space fountain also would only need to go up to geostationary orbit, with support supplied dynamically. Of course, these are technically more difficult than a tensile structure.

Van Rijn
2005-Aug-28, 10:07 PM
Here's a question: say you get some sort of impact on the cable that severs a number of nanotube fibres. How do you repair that? Seems to me that you'd have to remove the damaged fibres and replace them. And that's hard to do. Any ideas?

You would want multiple redundant support cables, so individual ones can be replaced or repaired. Also, there is the concept of the hoytether:

http://www.tethers.com/Hoytether.html

that can suffer significant damage without complete failure. We're just on the edge of being able to make materials strong enough for an earth based geostationary space elevator, and it is certain we will see many earth based applications when we can make this stuff. For that matter, it probably would find applications in spacecraft design. We're going to get a lot of experience with this stuff before we build a space elevator.

The Supreme Canuck
2005-Aug-29, 07:48 PM
Hey, that hoyteher thing looks like it has promise. But that doesn't solve my problem entirely. Just how long are the individual cables supposed to be? And could they be repaired or would they have to be replaced entirely? It would be pretty annoying to have to replace a 35 000 km-long cable everytime it was hit by something.

PatKelley
2005-Aug-29, 07:55 PM
If the "Hoytether" is hollow in profile, as it appears, one could have a climber on the outside (or inside) with a repairer on the other face of the tether, responding to problems as they occur.

PatKelley
2005-Aug-29, 07:58 PM
Here's a question: say you get some sort of impact on the cable that severs a number of nanotube fibres. How do you repair that? Seems to me that you'd have to remove the damaged fibres and replace them. And that's hard to do. Any ideas?

As far as carbon nanotubes, it might be possible to "solder" new fibers in place. There was a trial before demonstrating how with proper application of microwaves, I believe, a "mat" of intersecting nanotubes could be coaxed into a coherent set of crossing but chemically attached (single topology) nanotubes.

Van Rijn
2005-Aug-29, 08:53 PM
Right, you don't need absolute theoretical strength for the cable, though it does have to have an extremely impressive strength to weight ratio by present standards. So you don't need thousand mile long unbroken carbon nanofibers. I've seen a number of reports saying it should be possible to make composites strong enough that don't use continuous fibers and aren't carbon nanotubes only. There are a number of potential methods to join the material together with high strength. The key is to keep the average strength high and the average mass low.

The Supreme Canuck
2005-Aug-29, 10:07 PM
Thanks, you two. Answers me perfectly. :)

genebujold
2005-Aug-30, 11:43 AM
The BEST website on space tethers and all other options can be found here: http://www.islandone.org/LEOBiblio/. It's written by an engineer, not a marketing staff, or worse, a wild-eyed enthusiast trying to hawk his wares.

I'm not too thrilled with the Skyramp model, for the following reason:

"The Space Shuttle burns half its fuel just to reach 1000 mph (Mach 1.3) because it struggles to push through the dense lower atmosphere with a full fuel load."

Ummm, no. This comment alone tells me that the individual writing it understands very little about the physics behind surface to orbit rocketry. The shuttle burns half it's fuel just to reach 1000 mph because it's lifting the top half of it's weight from sea level to somewhere between 60,000 and 70,000 feet, depending on the mission (payload, authorized burn, etc.).

The energy required to overcome the atmospheric drag is actually a very small percentage of the total energy expended during ascent, primarily because the velocity profile is slowest in the most dense atmosphere, and fastest in the least dense atmosphere.

This same profile is even more pronounced for rotating space tethers, as well. Lift-off begins with just a slight percentage agove 1G, with the velocity the slowest near the Earth's surface, minimal throughout most of the atmosphere, and building rapidly after the end has left the atmosphere.

Before we start moving toward's space tethers, we need to employ a vastly different approach. Skyramp is one such approach: http://www.skyramp.org/

However, the problem with Skyramp is that it seeks to generate significant velocities at low altitudes where the parasitic drag is the worst.

The most efficient approach by far is to use winged aircraft to lift the orbital payload to the highest elevation and most velocity as possible. It's simply capitalizing on the fact that Oxygen weighs far more than Hydrogen, and the Earth supplies it in abundance between sea level and the upper limits of most winged aircraft, around 40,000 feet. Therefore, it makes little sense for a rocket to carry it's own oxygen to that altitude/elevation. Second, the most energy expended by the shuttle occurs in the atmosphere, both fighting gravity as well as accelerating the shuttle.

I think it's interesting to note that "the minimum mass of a buckytube skyhook (for 1-ton cargo) is 10^4 tons." (http://www.islandone.org/LEOBiblio/). That's 20 million pounds. While it sounds like a lot, it's not, as most skyscrapers weight many times more. A fully-loaded 747 cargo plane, for example, is just a little more than 800,000 pounds. Air Force One's max takeoff weight, is 833,000 pounds.

It's also interesting to note that if the skyhook were made of the highest-strength steel, it's weight would be more than the mass of the entire Earth! That's how much stronger and lighter buckytube technology is than steel!

Even better than a skyhook, however, is a rotovator, which would be smaller and therefore lighter than a skyhook.

The grappling problem isn't a problem at all. We've had good technical solutions for attaching the end of a rotovator to a shuttle car for perhaps 100 years. No worries there.

One of the biggest problems is dealing with the conductivity of the skyhook, but as someone mentioned, the signficant research being done with buckytubes has shown that, when properly doped, their conductivity can be very well controlled.

The most significant obstacle, however, is getting the thing built, and providing for the possibility of collision with space junk. If no provision is made, the liklihood of catastrophic failure due to collision with space junk during a 10-year period of use is greater than 50%. Separating the strands would be advisable, such as in a 3, 4, or even 5-cable design would work, provided if one of the strands were severed, the others could hold the load.

The beauty of the skyhook is that you can move a small asteroid into orbit at it's center of rotation for an anchor and to provide "descent mass." The descent mass, if slightly greater than the ascent mass, would be enough to power the rotorvator, overcoming the slight atmospheric friction effects working to slow the thing down. Varying the length of the cable would also conserve energy, as it would allow the rotorvator to keep the ends out of the atmosphere until needed for ascent or descent of a load.

imran
2005-Sep-03, 04:47 AM
Some new articles:

Trading Rockets for Space Elevators (http://news.nationalgeographic.com/news/2005/08/0825_050825_spaceelevator.html)

Space Program: Looking Up (http://www.techcentralstation.com/083105C.html)

publiusr
2005-Sep-07, 05:18 PM
You are still going to need HLLVs to put the ribbon/spinner up there.

People need to quit bashing rockets and learn to love them.

ToSeek
2005-Sep-26, 05:00 PM
Space Elevator Concept Undergoes “Reel” World Testing (http://www.space.com/businesstechnology/050923_spaceelevator_test.html)


A private group has taken one small step toward the prospect of building a futuristic space elevator.

LiftPort Group Inc., of Bremerton, Washington, has successfully tested a robot climber – a novel piece of hardware that reeled itself up and down a lengthy ribbon dangling from a high-altitude balloon.

The test run, conducted earlier this week, is seen as a precursor experiment intended to flight validate equipment and methods to construct a space elevator. This visionary concept would make use of an ultra-strong carbon nanotube composite ribbon stretching some 62,000 miles (100,000 kilometers) from Earth into space.

GOURDHEAD
2005-Sep-27, 02:35 AM
The test run, conducted earlier this week, is seen as a precursor experiment intended to flight validate equipment and methods to construct a space elevator. This visionary concept would make use of an ultra-strong carbon nanotube composite ribbon stretching some 62,000 miles (100,000 kilometers) from Earth into space. To avoid crashing into lotsa objects including mountains, trees, high buildings, etc., the rotovator/elevator is required to have its center of mass, whether loaded or not, at approximately 22,420 miles above sealevel and with semi-major and semi-minor axes approximately equal (very circular) to avoid bobbing up and down straining at its anchor, and the plane of its orbit must be very closely aligned with that of the Earth's equator. In order to keep its center of mass at 22,420 miles above sealevel as a significant load is hoisted, there must be a counterballancing load that moves through variable locations above 22,420 miles above sealevel.

Current nanotube technology has not produced CNT cables, ropes, nor ribbons of sufficient tensile strength and are not likely to for 50 years. Earth's atmosphere is too dynamic and lightning infested and the sun/moon gravitational tugging is too variable for a space elevator to be installed and working prior to 200 years from now.

Here (http://www.universetoday.com/forum/index.php?showtopic=7355&st=0&#entry71549entry71549) (fairly deep in the thread) is an earlier discussion with more detail about design challenges applicable to the space elevator.

GOURDHEAD
2005-Oct-03, 12:28 AM
I'm still looking for general details for constructing a ribbon out of CNT fibers and the characteristics listed below.
Maximum length of the ribbon sections.
Minimum mass of the adhesives, protective coating, and splicing devices.
Minimum tare weight of the climbers.
Maximum tensile strength per square meter of ribbon cross section.
Minimum safety factors to be incorporated into the design and rationale.


As the center of mass of the assembly, with load, bobs in and out of the exact EGO altitude from the effects of accelerating loads, do the corresponding changes in velocity apply significant changes in ribbon loading due to the torque applied from this variation?

Has any one been able to calculate the current that will flow through the ribbon when it is first connected to whatever anchors it to the Earth.

jkmccrann
2005-Dec-05, 06:47 PM
Please see my site, which is all about this topic:

LiftWatch.org (http://liftwatch.org/)

We've got regularly updated news, discussion forums, image galleries, and more...

Nice website cc, but I can't believe that around 50% of people responding to your poll think that the first private space station will be serviced by a space elevator rather than more conventional means!

Not a chance in my view.

Wina
2005-Dec-06, 08:33 AM
Supermarket, I'm still waiting to see someone blow up a soup can filled with BB's in the upper atmosphere lol. If anyone wanted to commit a serious terrorist action there's the way to go. Byebye to them cell phones and GPS satellites lol.

BANG

..... (random thought)

01101001
2005-Dec-06, 08:40 AM
Hello?

ccampbell (http://www.bautforum.com/member.php?u=6907)'s last activiy: 31-October-2003

supermarket (http://www.bautforum.com/member.php?u=6869)'s last activity: 14-July-2004

five_distinct
2005-Dec-07, 05:18 PM
Is necroposting a regular thing here?

Kaptain K
2005-Dec-07, 06:47 PM
Is necroposting a regular thing here?
Only for jkmccrann and despite numerous requests, including PMs from moderators, he ignores all requests for an explanation. :(

publiusr
2005-Dec-09, 11:50 PM
Please see my site, which is all about this topic:

LiftWatch.org (http://liftwatch.org/)

We've got regularly updated news, discussion forums, image galleries, and more...

Also visit www.liftport.com

mugaliens
2005-Dec-11, 11:44 PM
I remember reading that even with buckytubes it's all but impossible, cost way too much.

Isn't there a rotating lift system that works better, rather than a static, counterbalance system?

Cugel
2006-May-23, 08:11 AM
http://www.nature.com/news/2006/060522/full/060522-1.html

Bad news, actually. But at least it proofs that people are working on it.

Warren Platts
2006-May-23, 09:24 AM
Arthur C. Clarke said in his book that the space elevator cable could be constructed out of chewing gum if the cable was tapered.

And why make the cable in the form of ribbon? Isn't there a reason that practically every rope or cable from parachute cord to suspension bridge cables are cylindrical in shape? Wouldn't a ribbon be statistically more likely to get hit by micrometeors than a cylinder due the higher surface to weight ratio?

To me, the most practical design would be a giant hollow tube formed from woven cylindrical cables rather like the inside of a coax cable. The inside of the the tube would house a maglev system so that the elevators can get to GEO in a reasonable amount of time with no friction.

I'm worried about other showstoppers, however. Isn't it the case that nanotubes are great transmitters of electricity? And isn't it the case that when you move a wire through a magnetic field, an electric current is set up in the wire? If so, then as the space elevator moves through Earth's magnetic field, huge currents would be set up that would cause a giant short-circuit and fry the nanotube cables. I haven't scene this possibility dicussed much in the literature, despite that the one major tether experiment that's been tryed failed because the tether shorted out.

Van Rijn
2006-May-23, 10:09 AM
http://www.nature.com/news/2006/060522/full/060522-1.html

Bad news, actually. But at least it proofs that people are working on it.

That's a questionable argument. He isn't arguing the theoretical strength of carbon nanotube cable, but arguing that there are too many defects in cable when using known methods for making the stuff. That's hardly a surprise. Even with his argument, the strength could be nearly 30 GPa which is substantially more than enough for non-synchronous skyhooks.

I do expect it will be awhile before we can make extremely low defect carbon nanotube cable, but I have little doubt we will see it eventually.

Count Zero
2006-May-23, 10:37 AM
I'm worried about other showstoppers, however. Isn't it the case that nanotubes are great transmitters of electricity? And isn't it the case that when you move a wire through a magnetic field, an electric current is set up in the wire? If so, then as the space elevator moves through Earth's magnetic field, huge currents would be set up that would cause a giant short-circuit and fry the nanotube cables.
The space elevator would not moving through the Earth's magnetic field. They are both physically connected to the Earth and revolve with it.

Cugel
2006-May-23, 11:34 AM
A skyhook actually is dragged through the upper layers of the atmosphere. Well, maybe it could act as a generator and provide its own power?
As for the shape of the cable, I think (speculation alert!) that a ribbon would be easier to handle at deployment. Remember, you still have to figure out a way to handle 100.000 km of the thing.

Warren Platts
2006-May-23, 03:25 PM
The space elevator would not moving through the Earth's magnetic field. They are both physically connected to the Earth and revolve with it.

You raise an interesting philosophical point about the meaning of "physical connection." However, the Earth's magnetic field is offset from the axis of rotation by 11 degrees, and the magnetosphere is not symetrical in shape, rather it's shaped kind of like a comet's tail due to pressure from the solar wind, and therefore aligned around the ecliptic, so that a space elevator necessarily connected to Earth's equator must move through the magnetic field, thereby generating electric currents. Indeed, measureable voltage potentials occur right here at the surface on large radio antennas.

Whether such currents would be a significant concern, I can't say for sure, but because of the distances and the diameters of the cable that would be involved, they might very well be.

Relmuis
2006-May-23, 03:34 PM
As long as the magnetic poles don't sweep across the landscape every 24 hours, their excentric position doesn't matter. The space elevator is stationary with respect to the magnetic field.

Warren Platts
2006-May-23, 03:43 PM
A skyhook actually is dragged through the upper layers of the atmosphere. Well, maybe it could act as a generator and provide its own power?
As for the shape of the cable, I think (speculation alert!) that a ribbon would be easier to handle at deployment. Remember, you still have to figure out a way to handle 100.000 km of the thing.

Who knows? Maybe space elevators could solve the world's power shortage if the cables could handle the juice.

As for handling ribbons, think of handling long lengths of sticky tape: it gets twisted and then gummed up. Or imagine fishing in 60 fathoms with a ribbon, or a suspension bridge constructed of ribbons. Also, how do you splice a ribbon? In a movie, you use a piece of tape, but how do you tape a meter wide nanotube ribbon and yet retain its strength?

There's a reason that no one on Earth uses ribbon for construction projects involving long cable lengths.

Warren Platts
2006-May-23, 04:30 PM
As long as the magnetic poles don't sweep across the landscape every 24 hours, their excentric position doesn't matter. The space elevator is stationary with respect to the magnetic field.

At low altitudes, the Earth's magnetic field roughly obeys Gauss's equations. But higher up, where the space elevator would mostly be, electrical fields in the ionosphere and the solar wind predominate in shaping the magnetic field, and these are constantly moving and chaotic. Here, the shape of the magnetosphere is dominated by the sun; that is, the average flux lines are aligned with the sun. Moreover, the magnetosphere has a long tail pointing away from the Sun, and this tail most emphatically does not rotate with the Earth. Since the Earth is tilted with respect to the Sun, and the tail does not rotate, it would seem a logical necessity that the space elevator would sweep through these flux lines, thus generating electrical currents in the carbon nanotubes.

This is a problem that has not been discussed much if at all in the literature:

Wikipedia (http://en.wikipedia.org/wiki/Space_elevator)

NASA (http://www.affordablespaceflight.com/spaceelevator.html)

Doodler
2006-May-23, 04:51 PM
Heh, before you even get to the magnetosphere, I would love to see the effects of lightning strikes and hail on this stuff.

loglo
2006-May-24, 05:04 AM
There's a reason that no one on Earth uses ribbon for construction projects involving long cable lengths.


Here's one for using a ribbon in space. http://www.tethers.com/Hoytether.html

As usual weight vs strength vs reliability is the overriding issue.

Warren Platts
2006-May-24, 02:43 PM
Your link to what you call a "ribbon" is actually a lot like what I originally proposed, a braided cylindrical tube (what they call a "hoytube").

Again, why use flat ribbons????

loglo
2006-May-27, 02:06 PM
Your link to what you call a "ribbon" is actually a lot like what I originally proposed, a braided cylindrical tube (what they call a "hoytube").

Again, why use flat ribbons????

Hmm, now that I look again I see you are right. I thought the 2nd and 3rd diagram were showing ribbons but they are in fact just section views.

This is from a paper by Blaise Glassend:-
"The tether is ribbon shaped to allow the climber to climb up it, and to protect
it from space debris."

Apart from that I can't find any paper that actually comes to this conclusion. Suspect that it is due to the tapering that is required but I can't see why that couldn't be done with a cord just as well.

Good question, wish I could find an decent answer.

antoniseb
2006-May-27, 06:38 PM
I think part of the issue in the original post was that flawed CNTs have insufficient strength to hold their own weight for the whole cable, let alone maintain the stresses of a climber.

The hoytube makes sense. I visualize it being collapsed as the climber climbs it, and re-circularized after it goes passed. But even so, a project like this as the space elevator will require some technology we don't yet possess, which I imagine will be machine that can produce long quantities of perfect woven CNT made of pure Carbon 12. I think we are almost a century from being able to do this. I'm sure less robust Hoytubes will find uses as tethers long before that.

RGClark
2006-May-28, 05:30 PM
http://www.nature.com/news/2006/060522/full/060522-1.html

Bad news, actually. But at least it proofs that people are working on it.

This article from doing actual measurements found a highest strength of 63 GPa:

Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load.
SCIENCE, VOL 287, p. 637-640, 28 JANUARY 2000
http://bucky-central.mech.northwestern.edu/RuoffsPDFs/science-9.pdf

This report showed actual measured tensile strengths up to 150 GPa:

Direct mechanical measurement of the tensile strength and elastic modulus of multiwalled carbon nanotubes.
B.G. Demczyk et al.
Materials Science and Engineering A334 (2002), 174, 173-178.
http://www.glue.umd.edu/~cumings/PDF%20Publications/16.MSE%20A334demczyk.pdf

Both of these studies were done on multiwalled tubes since they are larger and it's easier to make attachments with them.
In the earlier study in Science, the authors from SEM imaging noted that it was actually the outer single-walled nanotube that broke first therefore it was carrying the load. This would make sense from the way the attachments were formed which could only form a bond with the outer surface of the multiwalled tube. Therefore the numbers quoted were for the strength of this outer single-walled nanotube using as thickness only that of this single-walled nanotube.
However, in the later study in Materials Science and Engineering, the authors believed the attachments were made to all the layers of the multi-layered nanotube, which would explain their higher measured strength.
The prevailing theory is that the range of strengths is due to the number of imperfections in the nanotubes. So we should be able to look at the nanotubes at the nanoscale using SEM,'s, STM's or AFM's and find which ones have the least imperfections. These should be the strongest tubes.
In the Science study, 1 out of 21 of them, 5%, have the best strength, 63 GPa. At a production of millions of tubes at a time this should still be feasible economically and technically.
The lengths of the nanotubes in these studies were however, were at the micron scale though. Nanotubes have been created at the centimeter length scale, but as far as I know the strength of these have not been tested.
Note that the reported strengths of centimeter long or longer "fibers" made of nanotubes being less than 1 GPA are not measuring the strength of individual nanotubes at these lengths. This is because the fibers are composed of the nanotubes stuck together end to end by weaker Van der Waals forces, rather than the much stronger carbon-carbon bonds that prevail in individual nanotubes.
Here is one study that detects, characterizes defects in the nanotubes at the nanoscale:

Resonant Electron Scattering by Defects in Single-Walled Carbon Nanotubes.
Science 12 January 2001, Vol. 291. no. 5502, pp. 283 - 285.
http://www.sciencemag.org/cgi/content/abstract/291/5502/283

Methods such as this might make it possible to find the nanotubes with the least defects beforehand and therefore automatically select those of the highest strengths.


Bob Clark

tofu
2006-May-30, 03:46 PM
This is a problem that has not been discussed much if at all in the literature:

Could that be because the engineers have looked into it and determined that it's really not as much of a problem as you think??

http://www.isr.us/SEScienceFAQs.asp#6

If you add up all of these currents and voltages, you end up with nothing that will be problematic with the exception of the lightning. So as long as we avoid lightning and the storms associated with it, we will get very little current flow or trouble from this area. You can think of most of this in terms of a conventional TV tower. Related to most of the topics discussed above (1 and 3a) we will experience the same voltages and millions times less (due to the relative sizes) current as a TV tower. Several colleagues had hoped that we might produce electric power from the ribbon but from what we have found power generation from the ribbon will take a lot of work and design modifications to produce much of anything.

-Dr. Brad Edwards

Warren Platts
2006-May-31, 09:51 PM
Could that be because the engineers have looked into it and determined that it's really not as much of a problem as you think??

http://www.isr.us/SEScienceFAQs.asp#6

If you add up all of these currents and voltages, you end up with nothing that will be problematic with the exception of the lightning. So as long as we avoid lightning and the storms associated with it, we will get very little current flow or trouble from this area. You can think of most of this in terms of a conventional TV tower. Related to most of the topics discussed above (1 and 3a) we will experience the same voltages and millions times less (due to the relative sizes) current as a TV tower. Several colleagues had hoped that we might produce electric power from the ribbon but from what we have found power generation from the ribbon will take a lot of work and design modifications to produce much of anything.

-Dr. Brad Edwards
The design on your website (http://www.isr.us/SEScienceFAQs.asp#3) calls for a 1 cm width below 10km. This is an unrealistically small cross section. The real space elevator will be made of massive cables capable of supporting a maglev railway. I mean a real railroad. Something capable of moving some serious cargo.

Since the current that can be sent through a wire is proportional to its cross section, the total current that could be delivered will be higher than suggested.

Also there remains the fact that the Earth's magnetosphere does not rotate along with the Earth. There are two zones: (1) the low elevation zone that rotates with the Earth, and (2) the high elevation zone that does not. Therefore, a 60,000km cable will be well extended into this higher zone, where movement through the magnetic flux will not be a mere matter of vibration, but will be faster than 4km per second, based on my own back of the envelope calculations. I call that a fast rate of speed--far faster than any Earth-bound generator achieves--that might generate some serious current even in a weak magnetic field.

Van Rijn
2006-May-31, 11:49 PM
The design on your website (http://www.isr.us/SEScienceFAQs.asp#3) calls for a 1 cm width below 10km. This is an unrealistically small cross section. The real space elevator will be made of massive cables capable of supporting a maglev railway. I mean a real railroad. Something capable of moving some serious cargo.


For a starter cable, used for bootstrapping, you want to start small. The massive system you mention would come much later.



Also there remains the fact that the Earth's magnetosphere does not rotate along with the Earth. There are two zones: (1) the low elevation zone that rotates with the Earth, and (2) the high elevation zone that does not. Therefore, a 60,000km cable will be well extended into this higher zone, where movement through the magnetic flux will not be a mere matter of vibration, but will be faster than 4km per second, based on my own back of the envelope calculations. I call that a fast rate of speed--far faster than any Earth-bound generator achieves--that might generate some serious current even in a weak magnetic field.

But how does the current flow? As I mentioned here:

http://www.bautforum.com/showpost.php?p=750443&postcount=8

this is only an issue at relatively low altitude. This is where there is significant plasma and the Earth's magnetic field is relatively strong. At 60,000km, it would be a non issue. And, the cable needs to be an efficient conductor, but there is no requirement for that in the design.

mugaliens
2006-Jun-04, 07:06 AM
http://www.nature.com/news/2006/060522/full/060522-1.html

Bad news, actually. But at least it proofs that people are working on it.

Requires subscription.

Please do not create threads and post links to which most of us do not have access. It's annoying.

Thanks.

As for the space elevators "going down," perhaps you could post the gist of what's in the link so we might intelligibly comment.

Again, thanks.

Cugel
2006-Jun-04, 12:01 PM
Sorry Mugs!

You're not gonna believe it but I don't have access to it myself! It was publicly there the first time I posted it and apparently now it isn't.

In short: when you mass produce CNT's some small errors will creep into it. It turns out that these fabrication errors greatly reduce the strength of the material. So much that it falls below the required strength for a space elevator. I believe to remember it drops below 1 GPa, according to the author.

IMHO it is all pretty much a theoretical discussion. As others have remarked: let's wait untill we/they come up with cables 10 or 100 meters long and see what happens. Maybe then we can scale up things a bit from there.

mugaliens
2006-Jun-04, 10:52 PM
Why does everyone continue to persist with the idea that a stationary elevator is the way to go? Such an elevator requires many times the strength of a rotovator, which dips down, picks up the cargo, and rotates it to a higher orbit. Said rotovator could easily be solar powered, a large mass (captured asteroid?) that's given additional energy via solar panels and ion rockets until it trades that energy for a pickup. Letdowns would restore most of the energy involved in the original transportation.

Far less strength required, only rudimentary (by current standards) math and physics.

Consider it, folks, as it may be just years away, instead of decades away.

ToSeek
2006-Jun-05, 03:31 PM
Sorry Mugs!

You're not gonna believe it but I don't have access to it myself! It was publicly there the first time I posted it and apparently now it isn't.



Often an article will be generally available when it's fresh, but after a short time period it's archived and is then available only to subscribers or for a fee. That's probably what happened here.

publiusr
2006-Jun-28, 06:20 PM
I wonder if tethers of modest length could discharge the Van Allen belts and remove them.

ToSeek
2006-Sep-04, 02:00 AM
Nasa hopes to catch an elevator to space (http://observer.guardian.co.uk/world/story/0,,1863755,00.html)


n a few weeks, scientists from across the world will gather in the New Mexico desert to compete for one of the strangest - and most ambitious - technological competitions ever devised.

Some researchers will unveil robots, powered by solar panels, that will climb long lengths of cable. Others will demonstrate materials so light and strong that mile-long stretches of the stuff could be hung in the air without snapping. And some will highlight their plans to launch satellites carrying sets of mini-probes tethered together, to discover how they behave in space.

All these different projects are united by one extraordinary goal: to build a stairway to heaven. Each of the groups that will gather in New Mexico is competing to win a Nasa prize set up to encourage entrepreneurs to start development work on the technology needed to create a space elevator. Such a device would involve constructing a 23,000-mile cable that could pull men and goods into orbit without blasting them there on top of expensive, and dangerous, rockets.

Ronald Brak
2006-Sep-04, 03:26 AM
Most cable designs I've seen suggested wouldn't last 24 hours when deployed. The cable is under so much tension that a collision with a tiny fleck of paint would bring the whole thing crashing down. Perhaps some kind of holly tether would be able to survive minor impacts, but this would increase the weight of the cable and require stronger material than other designs. The ability to repair inevitable damage in site would also be required.

I think that once we have the ability to make material for a space elevator that will stay up for a decent amount of time we'll have the ability to construct whatever we need from materials already in space and so a space elevator will not be redundant. They're not very well suited for passengers so they are unlikely to be used to transport humans.

Cugel
2006-Sep-04, 08:04 AM
Wouldn't it be possible to use a protective coating on the cable? I mean, if we can build a cable from mono Sinclair filament (or whatever) I would think some sort of super protective shielding should be easy. For bigger pieces of space debris the cable could use an active defense mechanism, simply swinging out of the way when something is on a collision course.

Ronald Brak
2006-Sep-04, 08:13 AM
Wouldn't it be possible to use a protective coating on the cable? I mean, if we can build a cable from mono Sinclair filament (or whatever) I would think some sort of super protective shielding should be easy. For bigger pieces of space debris the cable could use an active defense mechanism, simply swinging out of the way when something is on a collision course.


A protective coating strong enough to protect against minor collisions would weigh a heck of a lot over 36,000 kilometers. A holly tube or tether or whatever design that can withstand some damage makes better design sense. Also it shouldn't kill millions if it happens to fall down.

But even with a holly tube design I don't see how you can protect against a single impact generating shrapnel that snaps multiple strands in a localized area, bringing the whole thing down.

Cugel
2006-Sep-04, 09:57 AM
It wouldn't have to weight that much if you use a double skin design. The problem just reminded me of the protection needed for interstellar craft. Travelling at very high speed makes every speckle of dust the craft encounters a potential danger. For some time this was regarded as a showstopper for high speed (0.4C or so) spaceflight until somebody came up with the double protection system. Two thin layers of material interspaced with vacuum turned out to be a very effective protective device. The first layer is punctured by the object but it is vaporised in the process. The second layer just has to stop the gas and debris that remains of the intruder.

For our cable this means you would have to cover it with an inch of foam (as placeholder) with a thin layer of cable material on top of that. Of course, I'm not claiming that this is the ultimate solution but I think that in the grand scheme of things worrying about space debris is kind of micro management.

We're talking about 100.000 km of cable here. By the time you've worked out the technology to do that I really don't think space debris can be a showstopper.

It's just as with terraforming Mars. Think big! There are no small problems because you have to face a couple of really big mega problems.

Ronald Brak
2006-Sep-04, 11:21 AM
Assuming we build high power radar that allows us to track and avoid objects larger than one centimeter, the cable protective layer will still have to stop a 1cm meteroite or piece of space junk travelling in excess of 10,000 meters a second without damaging the actual load bearing cable at all. Even if this armour had an average weight of only 100 grams per meter it would still add 3,600 tons to the weight of the cable and would have to be in place from the beginning. This makes things difficult for people who were hoping to start a cable with a mass of only 80 tons.

Cugel
2006-Sep-04, 09:24 PM
Yes, that is true. But do you really believe that this specific reason is why we will not succeed in building a space elevator? You think mass procuction of mono filament covered with unobtanium is just around the corner? Dangling 100.000 km of cable from a small asteroid is just another day at the office? I think that when we succeed in doing these things in 472 years from now, the problem of space debris will be left to some junior engineer.

Ronald Brak
2006-Sep-05, 03:50 AM
Well some people think suitable elevator cable is just around the corner. I'm sure we'll have a material that is technically strong enough to be suspended from geosynchronous orbit before too long, but making something that is impact proof is much much more difficult. For this reason I don't think a space elevator will be built. I think people will come up with a better alternative before it become practical. I imagine in the future we will be able to build whatever we want from materials already in space so an elevator won't be needed and humans will travel into space in high speed flying vehicles, although I won't try to guess how they'll be powered. As unlikely as it sounds, perhaps in 472 years we will beam up down from orbit Star Trek style.

Cugel
2006-Sep-05, 09:08 AM
Maybe you just touched on another intrinsic problem of every mega structure: the danger of becoming obsolete before return on investment is sufficient.
With such huge investments required, that could be a serious problem for the space elevator.

GOURDHEAD
2006-Oct-06, 02:49 AM
http://physorg.com/news79026480.html is bad news of sea anchors for space elevators.

tofu
2006-Oct-06, 03:10 AM
huh? Do we get many icebergs at the equator?

Ronald Brak
2006-Oct-06, 03:11 AM
http://physorg.com/news79026480.html is bad news of sea anchors for space elevators.

Oh well, at least if the icecaps melt and the sea levels rises then the cable can be a little bit shorter.

Always look on the bright side of life...

GOURDHEAD
2006-Oct-06, 01:24 PM
The space elevator enthusiasts have stated that there are places in the pacific ocean along the equator relatively free from surface disturbances. The point I was stressing is that disturbances at either pole will generate waves that can change the elevation of the anchor as the waves go by adding complexity to the design of the ribbon-to-anchor attachment device. Then there are the randomly occurring rogue waves generated by inphase summing of "normal" surface waves that NASA has been monitoring.

tofu
2006-Oct-06, 04:34 PM
I seriously doubt that waves are going to be much of a problem. There significant practical experience with the design of stationary platforms, in the form of offshore oil rigs. Those things don't bob up and down like corks.

publiusr
2006-Oct-06, 05:54 PM
www.liftport.com

I think icing loads will most likely be a problem--with "hailstones" always hitting the roof of the elevator.

This will have to be stationed along the ITCZ--a band of low pressure (and squalls) along the equator. Hurricanes generally have to be further north--or south.

I want to see the station at 0 lat and 0 long. Just south of the hump of Africa. Sao Tome is nearby.

GOURDHEAD
2006-Oct-07, 02:53 PM
Those things don't bob up and down like corks.Do you have a reference that describes that bobing up and down can be avoided? The elevator folks want to be able to maneuver the anchor to avoid orbiting stuff. Are we looking at submarine type anchors?

mugaliens
2006-Oct-14, 04:43 PM
Every time I mention the word "rotovator," there's no response. Almost like it's been broadcast to a complete vaccuum. Is it because people don't understand the concept, and how that would greatly differ from Clark's stationary vision?

Rotovators and their anchoring points aren't geostationary, and they require 1/10th (perhaps less) the strength of a geostationary design.

DaveC426913
2006-Oct-14, 07:50 PM
if we can build a cable from mono Sinclair filament (or whatever)
Somebody's been reading Larry Niven...

DaveC426913
2006-Oct-14, 07:51 PM
Every time I mention the word "rotovator," there's no response. Almost like it's been broadcast to a complete vaccuum.
{Shh. He's on to us...}

loglo
2006-Oct-14, 07:53 PM
I've always had the impression that rotovators would be hard to do on a planet with an atmosphere, especially one as thick as Earth's. For the Moon I can see them being useful, same goes for Earth orbit, Mars etc.

Why do you think rotovators would be so much easier to do on Earth, apart from a shorter length of cable? Has anyone seriously proposed one? I'm all for tether technolgy, don't know why more money isn't being directed there. I am just having trouble seeing rotovators being used on Earth.

Cugel
2006-Oct-14, 07:54 PM
Somebody's been reading Larry Niven...

From ringworld I think. Sinclair monofilament.

mugaliens
2006-Oct-15, 05:49 PM
I've always had the impression that rotovators would be hard to do on a planet with an atmosphere, especially one as thick as Earth's. For the Moon I can see them being useful, same goes for Earth orbit, Mars etc.

Why do you think rotovators would be so much easier to do on Earth, apart from a shorter length of cable? Has anyone seriously proposed one? I'm all for tether technolgy, don't know why more money isn't being directed there. I am just having trouble seeing rotovators being used on Earth.

Actually, it's not hard at all, as the least velocity for the rotovator occurs only in the most dense atmosphere. The transfer pod would encounter far less atmospheric effects of your typical shuttle launch and recovery. Typical protections for heat shielding for upper atmospheric effects, but it wouldn't require anywhere near the shielding of a Mercury/Gemini/Apollo/Shuttle reentry.

Quite a mild ride, actually.

Van Rijn
2006-Oct-16, 09:10 AM
I've always had the impression that rotovators would be hard to do on a planet with an atmosphere, especially one as thick as Earth's. For the Moon I can see them being useful, same goes for Earth orbit, Mars etc.

Why do you think rotovators would be so much easier to do on Earth, apart from a shorter length of cable? Has anyone seriously proposed one? I'm all for tether technolgy, don't know why more money isn't being directed there. I am just having trouble seeing rotovators being used on Earth.

There's no real reason to have a rotovator tip dip much below about 50 miles altitude. A rotovator doesn't need to be as massive as a full synchronous tether, but it also doesn't need to handle the full velocity change to orbit to still be very useful. This allows further reductions in mass. The space elevator gets the press because it is "neat." However, I expect that rotovators or other non-synchronous tether schemes will be used long before a space elevator is built (if it ever is).

loglo
2006-Oct-20, 06:51 AM
Actually, it's not hard at all, as the least velocity for the rotovator occurs only in the most dense atmosphere.

I don't understand that, isn't the speed of the ends generally constant on a rotovator?


However, I expect that rotovators or other non-synchronous tether schemes will be used long before a space elevator is built (if it ever is).

Well, you would hope so. I can't think of a single good reason why these technologies aren't being developed right now. They are a lot more do-able than some of the fairyfloss I read coming from the space tourism developers.

Van Rijn
2006-Oct-20, 08:00 AM
I don't understand that, isn't the speed of the ends generally constant on a rotovator?


Pretty much (there might be some cable stretching as it goes vertical), but the trick is a little like the way a geostationary satellite works. Assuming you have material with a sufficient strength to weight ratio, you could match the earth's rotation with the tip velocity such that relative ground velocity would be zero or at least fairly low. The tip would seem to come down and go back almost vertically. But in practice, I would expect early tethers to have a high ground velocity. [edited to correct sentence. Also, I'll add that it wouldn't get that close to the ground. Early tethers would only handle a fraction of the velocity change needed for a spacecraft to reach orbit.]




Well, you would hope so. I can't think of a single good reason why these technologies aren't being developed right now. They are a lot more do-able than some of the fairyfloss I read coming from the space tourism developers.

High strength to weight ratio materials are a major research area now. I think tether research will get a lot more serious when the materials have improved a bit. At a guess, we might be looking at 15-20 years before it gets really serious. Meanwhile we should be developing rockets. I'm not sure what you mean by "fairyfloss" but reuseable rockets could do very nicely (not horribly expensive) if flown regularly. And, suborbital rockets are just the thing for flying to and from early rotovators.

parallaxicality
2006-Oct-22, 10:02 AM
My biggest issue with the space elevator concept is the counterbalance. Where would we get it, how would we get it into place, and most importantly, how would we ensure that it stayed in place and didn't crash into the Earth?

tofu
2006-Oct-22, 01:56 PM
My biggest issue with the space elevator concept is the counterbalance. Where would we get it, how would we get it into place,

The initial counterbalance is just the spool from the first strand. It's more than enough to allow robots with additional strands to climb the elevator. As each one makes it to the top, the ribbon gets stronger and the counterbalance gains mass.


and most importantly, how would we ensure that it stayed in place and didn't crash into the Earth?

huh? If you cut the elevator the counterbalance would fly off into (at least) a higher orbit - more likely it would leave Earth orbit alltogether. It's not going to crash into the Earth. Climbing the elevator does pull down on the counterbalance - but because the counterbalance is beyond geostationary orbit, it is constantly pulling up, straightening the cable, and countering this. There's no way to accidently overload the counterbalance.

parallaxicality
2006-Oct-23, 09:08 AM
But how would you get it into place in the first place without it crashing into the Earth?

the_shaggy_one
2006-Oct-23, 10:14 AM
But how would you get it into place in the first place without it crashing into the Earth?

put the spool of wire for the space elevator in geosync. As you lower the wire towards earth, the spool will move outwards to keep the center of mass at geosync. Action -> reaction, it's as simple as that.

NEOWatcher
2006-Oct-23, 01:00 PM
put the spool of wire for the space elevator in geosync. As you lower the wire towards earth, the spool will move outwards to keep the center of mass at geosync. Action -> reaction, it's as simple as that.
And how much would that weigh [for launching]?
Either the entire spool with counterbalance would have to be launched. Or the factory would have to be built in space.
I wouldn't want that wire to be spliced anywhere.
Although the counterbalance would not come crashing down, the cable would. Again; how much weight is that?

parallaxicality
2006-Oct-23, 01:59 PM
and how would you stop a 9/11-style attack on such a conspicuous target? Or even a simple plane collision? Is there anywhere on Earth so off the flightpaths of commerical aviation that such a construction would be viable?

the_shaggy_one
2006-Oct-23, 08:21 PM
And how much would that weigh [for launching]?
Either the entire spool with counterbalance would have to be launched. Or the factory would have to be built in space.
I wouldn't want that wire to be spliced anywhere.
Although the counterbalance would not come crashing down, the cable would. Again; how much weight is that?

I forget the exact numbers, but I think current plans call for a cable that weighs about 18,000 kg. Lifting 18 metric tons to geosync would be difficult and require a heavy launch vehicle, but it could be accomplished - something like the Ares V would be able to do this easily. The rest of the cable would be pulled up from the ground strand by strand, untill the elevator was completed. This is very similar to the way the cables are made for suspension bridges.

NEOWatcher
2006-Oct-23, 08:32 PM
I forget the exact numbers, but I think current plans call for a cable that weighs about 18,000 kg..
That statement implies that it is the cable only. What about the counterweight?

The rest of the cable would be pulled up from the ground strand by strand, untill the elevator was completed. This is very similar to the way the cables are made for suspension bridges.
But that's where I see a problem. Most of the strength of the cable is only to hold itself up. So, to pull a strand up, most of the cable needs to be in place. Sounds like a catch-22 to me.
The cable of a suspension bridge has strength designed to carry the bridge not itself. The weight of the cable in a suspension bridge is somewhat insignificant.

the_shaggy_one
2006-Oct-23, 09:26 PM
That statement implies that it is the cable only. What about the counterweight?

The spool becomes the original counterweight. The robots that climb up the cable with further strands add to the mass of the counterweight. For some designs, the counterweight is simply another 42,000 km of cable, swinging out in space.


But that's where I see a problem. Most of the strength of the cable is only to hold itself up. So, to pull a strand up, most of the cable needs to be in place. Sounds like a catch-22 to me.
The cable of a suspension bridge has strength designed to carry the bridge not itself. The weight of the cable in a suspension bridge is somewhat insignificant.

The cable will be strong enough to hold itself up, and the weight of at least a second cable. If each strand is only capable of holding itself up, there's no point to building a space elevator, as the whole thing would have a capacity of zero. Each strand would have to be strong enough to actually add to the total capacity of the elevator.

Even if a single strand is not capable of holding up another strand on it's own, you would just launch, say, 5 or 10 or however many strands into orbit, and gather them together into the initial cable. Either way, there is a point at which you can begin sending strands up from the surface to complete the elevator.

Besides, I said it was similar, not identical, to the way a suspension bridge is built. I was referring specifically to the way a guide strand is used, and how the many strands are individually laid down, one after the other, to create the finished cable.

Most of the cost of building a space elevator comes from the cost of the initial launch(es). But realize, as soon as you have a cable capable of pulling an 18 thousand kilogram strand into geosync, you have a cable capable of putting a 5,000 kg communications sattelite into whatever sort of orbit it needs to be in, for a much smaller cost than a rocket launch. The cable would not have to be very large before you would start to see it used as an alternative for rocket launches.

Eoanthropus Dawsoni
2006-Oct-24, 02:36 AM
How will the weight and drag problems of ice be dealt with?

Ronald Brak
2006-Oct-24, 06:29 AM
How will the weight and drag problems of ice be dealt with?

A de-icing/demoulding unit will go ahead of every robot climber and will climb down over the robot climber once it's high enough for the cable to be clear. Since it stays in the atmosphere, theoretically it could use helium or hydrogen to reduce its weight. Of course, you will need a cable that is capable of staying up without being destroyed by impacts before you need to worry about ice.

tofu
2006-Oct-24, 04:59 PM
and how would you stop a 9/11-style attack on such a conspicuous target?

By your logic, we shouldn't construct buildings or launch the shuttle. Cassini had plutonium. How are we going to prevent a 9/11-style attack on it?? That plutonium could kill thousands of people!

Anyway, what do you think would happen if the cable was cut? I bet you think that the elevator would crash down on the Earth in horrible fiery destruction, right? Well, it doesn't work that way. If a terrorist walked up to the cable with a pair of scissors and cut it, the whole thing would float away into space - costly, but not deadly.

In fact, anywhere that you cut the cable, the part above the cut goes off into space. So if a high-flying aircraft cut it at say, 70,000 feet, you would have 70,000 feet of cable fall to Earth, and the rest would go off into space. If it was cut by space debris hundreds of miles up, the part that fell to Earth would burn up in the atmosphere. We keep saying cable - it's really a ribbon. If any of it survived reentry, it would flutter to the ground like paper. The only way it would kill anyone would be if they were stupid enough to collect it and eat it, and even then they would probably just throw up.

NEOWatcher
2006-Oct-24, 05:40 PM
...If it was cut by space debris hundreds of miles up, the part that fell to Earth would burn up in the atmosphere...
Huh? How do you figure? Where is the pressure buildup, and from what?

the_shaggy_one
2006-Oct-25, 12:47 AM
Huh? How do you figure? Where is the pressure buildup, and from what?

the cable is under tension. if it broke anywhere, the portion with a center of mass below geosync would have insufficient velocity to remain in orbit, and fall to the surface. only the first few miles of the cable would be moving slow enough to survive (this is why a sea-based platform is the most likely anchor point), and this portion closest to the ground is the thinnest. Anything above a certain height would have enough speed by the time it hit the atmosphere to burn up. Because the cable is much thinner closer to the earth, this is the most likely area for failure, and also the least likey to survive re-entry.

The elevator will be built as a ribbon. A metor impact would puncture the ribbon, but it would only sever a very limited number of strands. A meteor punching through (or into) a round cable would be much more destructive, and would do many times more damage. Also, the ribbon will be much easier to climb, de-ice, and repair.

WE're only concerned about very small, difficult to detect objects here. larger objects could be detected via radar, etc, and the cable would be moved out of the way.

Ronald Brak
2006-Oct-25, 01:12 AM
The elevator will be built as a ribbon. A metorite impact would puncture the ribbon, but it would only sever a very limited number of strands. A meteor punching through (or into) a round cable would be much more destructive, and would do many times more damage. Also, the ribbon will be much easier to climb, de-ice, and repair.

I don't think a ribbon will work. The cable will be under immense tension. If a steel cable that's being used to tow a car snaps it can whip about with enough force to kill someone. A broken space elevator strand will release much more energy and will destroy ajacent strands setting off a chain reaction. It has been suggested that a hollytether design that looks something like this:

><><><><><><><><><><><><><
><><><><><><><><><><><><><

might be able to survive this destructive process but this seems unlikely as the shock waves would travel up and down the snapped strand and destroy strands at the closest nexus. Even if it could be made to survive this process, shrapnel from the initial impact could still destroy other strands. The design also increases the weight of the cable and makes it harder to deploy.

So far we have no way to overcome this problem and the space elevator project is dead in the water in an area of low lightning incidence off South America until it is solved.

Van Rijn
2006-Oct-25, 01:39 AM
I don't think a ribbon will work.


Okay, fair enough. You're speculating that it might not work.



The cable will be under immense tension. If a steel cable that's being used to tow a car snaps it can whip about with enough force to kill someone. A broken space elevator strand will release much more energy and will destroy ajacent strands setting off a chain reaction.


And you did the design analysis to demonstrate this?




It has been suggested that a hollytether design that looks something like this:

><><><><><><><><><><><><><
><><><><><><><><><><><><><

might be able to survive this destructive process but this seems unlikely as the shock waves would travel up and down the snapped strand and destroy strands at the closest nexus. Even if it could be made to survive this process, shrapnel from the initial impact could still destroy other strands.


Again, based on what analysis?




The design also increases the weight of the cable and makes it harder to deploy.


If you mean that there would be more mass than for a theoretical minimum mass cable, well certainly there would. There would obviously be some redundancy in any real-world design. However, it is not clear that a hoytether design would mass more than competing designs. Also, why would it be harder to deploy?



So far we have no way to overcome this problem and the space elevator project is dead in the water in an area of low lightning incidence off South America until it is solved.

How did you get from your speculation to a problem "we have no way to overcome"?

Ronald Brak
2006-Oct-25, 01:57 AM
Me, I'm just remebering what I've read in Wikipedia and stuff. It could all be lies. Here is the relevent bit from Wikipedia:


...Far worse than meteoroids are micrometeorites; tiny high-speed particles found in high concentrations at certain altitudes. Avoiding micrometeorites is essentially impossible, and they will ensure that strands of the elevator are continuously being cut. Most methods designed to deal with this involve a design similar to a hoytether or to a network of strands in a cylindrical or planar arrangement with two or more helical strands. Constructing the cable as a mesh instead of a ribbon helps prevent collateral damage from each micrometeorite impact.

It is not enough, however, that other fibers be able to take over the load of a failed strand — the system must also survive the immediate, dynamical effects of fiber failure, which generates projectiles aimed at the cable itself. For example, if the cable has a working stress of 50 GPa and a Young's modulus of 1000 GPa, its strain will be 0.05 and its stored elastic energy will be 1/2 &#215; 0.05 &#215; 50 GPa = 1.25&#215;109 joules per cubic meter. Breaking a fiber will result in a pair of de-tensioning waves moving apart at the speed of sound in the fiber, with the fiber segments behind each wave moving at over 1,000 m/s (more than the muzzle velocity of an M16 rifle). Unless these fast-moving projectiles can be stopped safely, they will break yet other fibers, initiating a failure cascade capable of severing the cable. The challenge of preventing fiber breakage from initiating a catastrophic failure cascade seems to be unaddressed in the current (January, 2005) literature on terrestrial space elevators. Problems of this sort would be easier to solve in lower-tension applications (e.g., lunar elevators).


How did you get from your speculation to a problem "we have no way to overcome"?

My friend and I have been totally unable to get around this problem.

the_shaggy_one
2006-Oct-25, 03:19 AM
That looks like the sort of back-of-the-envelope unsourced speculation that wikipedia is riddled with. Redundancy in the design, and the bootstrapped nature of the elevator itself, leads me to believe that this won't be as much of a problem as the author of that particular section makes it out to be.

I know this is mostly just a friendly discussion and not a rigorous debate, but using such sources is misleading. I would be extremely interested if you could find an authorative source on catastrophic failures of a space elevator due to a micrometeor severing a carbon nanotube rope.

Ronald Brak
2006-Oct-25, 05:54 AM
I don't read technical stuff on space elevators. I'm not saying it's beyond me, it's just usually written for the small subset of humans who have the specialized ability to do math without using their fingers. But here is a clearly written page by Blaise Gassend who is pretty smart. Go to thoughts on space elevators and then problems.

http://gassend.com/

Personally I think a space elevator is a really cool idea. Unfortunately, cool is not the same as practical. While I am certain that we will eventually be able to make cables of such strength they could theoretically be suspended from orbit, I'm far from sure we can make a space elevator cable that will be able to withstand the inevitable damage it will sustain.

Any cable that is put under tension stores up energy. If a steel cable that is being used to tow a truck snaps, it can whip around with enough force to kill someone. The cable of a space elevator will be under incredible tension. If a single fibre breaks perhaps the shockwave of energy released will destroy adjacent fibres and set off a chain reaction that will snap the entire cable. Currently we don't know how big a problem this is or how to avoid this problem. It is possible that a cable that consists of many, very thin, load bearing, strands, interconnected by material that absorbs and redistributes energy when any one strand snaps, may be able to avoid a destructive chain reaction. But even if a cable can be protected in this way, the extra weight it would entail may render a space elevator impractical. It would certainly make manufacturing and deploying the cable much more difficult.

Even if we can make a cable robust enough to survive if one fibre snaps, it might not take long for it to be severely damaged or destroyed by impacts with space junk or meteorites.

A space elevator cable can be moved to avoid collisions with larger objects that can be tracked by radar. However there is no way to avoid the many smaller pieces of junk ranging from centimetres across down to particles the size of a speck of dust. Dangerous impacts don’t happen all the time, otherwise satellites wouldn’t last as long as they do, however the space shuttle suffers numerous impacts with tiny pieces of space junk and tiny meteorites on every mission, which typically lasts less than two weeks. Space shuttle windows are replaced on average every other mission as a result of impacts. One impact left a hole about half a centimetre deep. If the space shuttle windows which are only about a couple of square meters in area are hit so often, then a space elevator cable, which in a popular design is a thin ribbon about a metre across, can expect to be hit often as well.

Although only about 2,000 kilometres of cable will pass through areas with significant space junk, a square meter of cable can expect to be hit more often and with particles travelling at greater velocities than a square meter of space shuttle. When the space shuttle orbits there will be a portion of space junk that will be in a similar orbit and so will have a low relative velocity. However, only the part of the space elevator cable at 36,000 km will actually be in orbit. In lower orbit, the cable will almost be standing still compared to the space junk, and many pieces will collide with it at speeds in excess of 10,000 kilometres per hour (2.8 kilometres per second). I'm sure these impact speeds are fast enough to pit or chip diamond (a gemcutters chisel doesn't move that fast, although I am unsure of what the exact effects would be, as I lack a small bore rifle with which to take pot shots at my store of diamonds.

If we can’t make a cable that won’t destroy itself if even one fibre breaks, then I don't think it will be possible to build a space elevator. Impacts would soon destroy it even if it could be deployed intact. I would expect a ribbon like, meter wide cable could receive an impact like the one that put a half centimetre deep hole in the space shuttle window every day. A significantly larger impact could be expected every week a larger on every month and so on.

If such a cable avoid impacts that would be large enough to destroy it at once, then it would still need to be regularly repaired or replaced as a result of damage from smaller impacts. If it is to be replaced that will greatly increase the cost of using space elevators. Repair would be difficult unless we had robot climbers that could manipulate carbon molecules in such a way as to perform flawless repairs in material under incredible amounts of tension. However, if we had robots that could do that, we probably wouldn’t need a space elevator to haul cargos up from earth as these robots should have the ability to make whatever we want from materials already in space.

NEOWatcher
2006-Oct-25, 12:25 PM
the cable is under tension. if it broke anywhere, the portion with a center of mass below geosync would have insufficient velocity to remain in orbit, and fall to the surface. only the first few miles of the cable would be moving slow enough to survive (this is why a sea-based platform is the most likely anchor point), and this portion closest to the ground is the thinnest. Anything above a certain height would have enough speed by the time it hit the atmosphere to burn up. Because the cable is much thinner closer to the earth, this is the most likely area for failure, and also the least likey to survive re-entry.
Try the first hundred or so miles that is in the atmosphere which will not gain enough velocity for burning up.
As the lower parts of the cable are hitting the atmosphere, they are slowing down, so the only effect on acceleration toward the Earth is that portion that is still above the atmosphere, so I'm fairly certain that would leave a considerable portion (not a lot, but enough for a problem) that would not be burned up.

I'm not trying to imply that it can't be done. But, to force it into early development with so many unknowns would potentially drain costs from other projects. I personally would love to see it, but it's not time, let's work on the individual technologies before looking at the big picture.

tofu
2006-Oct-25, 02:29 PM
to force it into early development with so many unknowns

These are not unknowns to engineers. The same people who are able to design and build huge buildings that can withstand earthquakes and hurricanes are able to do the math to figure out what is possible and what is not possible with regard to a space elevator.

If you and I had never seen a skyscrapper, and someone was talking about building one, then you and I might be having a conversation like this, "whoa whoa, what happens when a hurricane hits New York? It's going to blow the building right over! There are just too many unknowns here!"

But we would be wrong, wouldn't we.

NEOWatcher
2006-Oct-25, 04:30 PM
These are not unknowns to engineers. The same people who are able to design and build huge buildings that can withstand earthquakes and hurricanes are able to do the math to figure out what is possible and what is not possible with regard to a space elevator.
The unknown is how long it will take for technology to be able to make the tether. And after the technology is discovered, then, and only then, can the costs be determined.
Skyscrapers were not built with future materials.

RBG
2006-Oct-26, 04:56 AM
Is there any theoretical provision for an escape pod or some such thing should the cable break while in use? And what kind of physical repercussions would there be from a breaking cable anyway? On board a ship, a breaking mooring line goes off practically like dynamite in its destructiveness.

RBG

Ronald Brak
2006-Oct-26, 06:32 AM
On board a ship, a breaking mooring line goes off practically like dynamite in its destructiveness.

I wrote above about the explosive effects of a snapping cable above and I just fixed a link so you can read what a smart person says about it. Basically it's a big problem that makes the space elevator a really difficult to construct. It will be very hard to build an elevator cable that doesn't destroy itself when one strand snaps. Since it will be hit by small debris and meterorites all the time there are lots of opportunities for snappage.

A robot climber might carry an explosive charge to blow it to pieces in case it falls. A parachute might be another option. Or to save on climber weight some sort of interceptor could take out a falling one if it's a threat to human life. A climber would presumably need some sort of propulsion system to move it away from the cable to prevent damageing it. Above about 24,000 km a falling climber will enter orbit.

People are unlikely to use climbers as they take a long time to get to orbit and spend a lot of time in the Van Allen radiation belts. Generally current designs couldn't lift a human plus life support and shielding and are for cargo only.