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Thread: Dangling a rope from orbit.... (Is this a stupid question?)

  1. #1
    As a kid, I always wondered why "if you had the space shuttle already in orbit why couldn't you dangle a rope down and pull up supplies....(or even another person)?"

    Answering my own question years later,
    three obvious things occur to me.
    1. A normal rope would snap under its own weight.
    2. It would pull the object out of orbit.(?)
    3. Logistically, it would be very hard to control(weather/wind etc).

    Hypothesising on a solution:
    Create a rope that is of very little mass and almost infinitely strong, and assuming we can deal with (3) above by only using the rope in the right conditions, does my childhood concept have any plausibility at all?

    I have some very long rope NASA can borrow if they want to give it a go... Comments and solutions please...?????

  2. #2
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    This is a variation on the space elevator concept. It's been discussed here before.

    However, in addition to the problems you mentioned, there is an additional one if you use the shuttle. The shuttle operates in low Earth orbit, which means it orbits the Earth very quickly. There's no way it can stay over one point long enough for anything to be hauled up. In order for any tether/elevator scheme to work, it would have to reach all the way up to geosynchronous orbit, some 37.000km up.

  3. #3
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    On 2002-06-24 10:13, sadprince wrote:
    As a kid, I always wondered why "if you had the space shuttle already in orbit why couldn't you dangle a rope down and pull up supplies....(or even another person)?"

    Answering my own question years later,
    three obvious things occur to me.
    1. A normal rope would snap under its own weight.
    2. It would pull the object out of orbit.(?)
    3. Logistically, it would be very hard to control(weather/wind etc).

    Hypothesising on a solution:
    Create a rope that is of very little mass and almost infinitely strong, and assuming we can deal with (3) above by only using the rope in the right conditions, does my childhood concept have any plausibility at all?

    I have some very long rope NASA can borrow if they want to give it a go... Comments and solutions please...?????
    Actually, you've hit upon something that is a neat idea and has been thought of before, sort of. I believe Arthur C. Clarke had this basic idea and envisioned a "space elevator". Make a "rope" strong enough (say out of graphic or diamond) and hang it down from a satellite in geosychronous orbit. Then run elevator cars up and down it. Cheap way to get mass into and out of orbit. Many stories have been written about this (I recently read "Jumping Off the Planet" by David Gerrold which explores exactly this concept).

    As for your answers:
    1. Yes, the "rope" would need to be made of a very strong material. Graphite might work.
    2. A satellite in geosychronous orbit made from say an appropriately sized asteriod would do.
    3. Strong rope again (or 'cable'). Likely the whole thing would cause it's own weather down where it was tethered on Earth. Also, just the cables reaching up through the atmostphere would generate electricity.
    Other things you can do like this: There was a recent experiment about dragging a line behind the space shuttle to try and generate energy. Not sure of any of the details on this though.

    [Fixed spelling]



    <font size=-1>[ This Message was edited by: honestmonkey on 2002-06-24 15:57 ]</font>

  4. #4
    OK, I've read the space elevator bits now. No duping intended. So in which case assuming we are in geo-stationary orbit and we aim our little rope downwards towards the earth, are we able to control it's desent without it pulling us out of orbit, and prevent the 'rope' burning up on re-entry. Indeed, how fast or slow do you have to go to not burn up????

  5. #5
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    If you're interested in this subject, you should read Arthur C. Clarke's novel "The Fountains of Paradise", where he discusses it thoroughly.
    The idea isn't his. It was first thought up by a Russian engineer named Yuri Artsutanov.

    [Added later:
    Well, the idea is fairly simple. I'm sure many people have thought of it. The tricky part is how to make it work...]

    <font size=-1>[ This Message was edited by: informant on 2002-06-24 10:48 ]</font>

  6. #6
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    On 2002-06-24 10:41, sadprince wrote:
    OK, I've read the space elevator bits now. No duping intended. So in which case assuming we are in geo-stationary orbit and we aim our little rope downwards towards the earth, are we able to control it's desent without it pulling us out of orbit, and prevent the 'rope' burning up on re-entry. Indeed, how fast or slow do you have to go to not burn up????
    -We would be pulled down. The usual counter-measure is to simultaniously unwind another rope "upwards", which will be carried out by the centrifugal force. If you unwind both ropes at the right rates, you'll stay in geosynchronous orbit.
    -If you let the rope down from geosynchronous orbit, it will enter the atmosphere with (ideally) no relative speed. That's the point of the geosynchronous orbit, a satellite in it seems not to move relative to a fixed point on earth.

  7. #7
    On 2002-06-24 10:53, kucharek wrote:
    -We would be pulled down. The usual counter-measure is to simultaniously unwind another rope "upwards", which will be carried out by the centrifugal force. If you unwind both ropes at the right rates, you'll stay in geosynchronous orbit.
    -If you let the rope down from geosynchronous orbit, it will enter the atmosphere with (ideally) no relative speed. That's the point of the geosynchronous orbit, a satellite in it seems not to move relative to a fixed point on earth.
    Ok. Winding makes sense, but I'm missing the bit on how we even get to this point. In order to lower the first 'rope' (which would be a loop of rope that we could wind) I'm imagining we could thrust increasingly against the lowering rope so as not to pull us down. Now please forgive the untechnical writing below - I'm having some fun here as I realise the whole thing is kind of dumb:

    Once the rope has been lowered all the way assuming the above is ok, Questions remain:

    1) Do we not get continually tugged down and have to provide perpetual thrust to maintain our rope?

    2) Let's assume our "space station" with the rope attached is a 5 ton object. What can I theoretically attach in terms of weight to pull (wind) back up?

    3) Would a few drunk guys from the local pub be able to pull our space station down if they started pulling the end? Surely it does not now weigh it's earthly five tons, but it IS connected directly



  8. #8
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    We could use asteroids in geosynchronous orbits to dangle satellites into lower orbits. In effect, we could have geosynchronous satellites in lower orbits which would be good for communications.





  9. #9
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    On 2002-06-24 11:22, sadprince wrote:
    On 2002-06-24 10:53, kucharek wrote:
    -We would be pulled down. The usual counter-measure is to simultaniously unwind another rope "upwards", which will be carried out by the centrifugal force. If you unwind both ropes at the right rates, you'll stay in geosynchronous orbit.
    -If you let the rope down from geosynchronous orbit, it will enter the atmosphere with (ideally) no relative speed. That's the point of the geosynchronous orbit, a satellite in it seems not to move relative to a fixed point on earth.
    Ok. Winding makes sense, but I'm missing the bit on how we even get to this point. In order to lower the first 'rope' (which would be a loop of rope that we could wind) I'm imagining we could thrust increasingly against the lowering rope so as not to pull us down. Now please forgive the untechnical writing below - I'm having some fun here as I realise the whole thing is kind of dumb:

    Once the rope has been lowered all the way assuming the above is ok, Questions remain:

    1) Do we not get continually tugged down and have to provide perpetual thrust to maintain our rope?

    2) Let's assume our "space station" with the rope attached is a 5 ton object. What can I theoretically attach in terms of weight to pull (wind) back up?

    3) Would a few drunk guys from the local pub be able to pull our space station down if they started pulling the end? Surely it does not now weigh it's earthly five tons, but it IS connected directly
    I believe you are forgetting the contribution that the rope extending OUTWARDS from teh geostationary satellite would have. The weight of this rope would counter the weight of the dropped rope as the centrifugal force would be trying to pull the sattelite to a higher orbit.

    By the way the best proposal so far for the material that the rope would be made from is the "tube" version of the carbon 60 molecule or "BuckyBall". Surprisingly the theoretical calculations have show that buckytubes would be strong enough to withstand their own weight if used in this manner.

    One possible problem could be what would happen if the rope was struck by lightening, but no doubt there are pleanty of other technical problems that would need to be addressed before we are ready to make such things.

    Phobos

  10. #10
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    As has been mentioned, check out "The Fountains of Paradise" by Arthur C. Clarke. Not only is it a "good read", but the science in it is accurate. He also touched on the subject in "The Songs of Distant Earth"

  11. #11
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    It's a long time since I read Clarke's Fountains of Earth, so I can't remember what he did or didn't say. But there is one other problem I haven't seen mentioned here.

    kucharek: if you let the rope down from geosynchronous orbit, it will enter the atmosphere with (ideally) no relative speed. That's the point of the geosynchronous orbit, a satellite in it seems not to move relative to a fixed point on earth.

    True enough for the satellite, at the far end of the rope. But not so true for the rope itself. You want the rope to stay "rigid", as it hangs down from the satellite fixed in geosynchronous orbit, to a point fixed relative to that, on the surface of Earth. But, each little piece of the rope "wants" to move at the orbital velocity of a Keplerian orbit at that radial distance from Earth.

    So, aside from its own dead weight, you have to worry about a strong shear induced by this mismatch between the "fixed" rope, and the "natural" rope, which would wind up around the Earth, as each piece trys to move at its local orbital velocity.

    <font size=-1>[ This Message was edited by: Tim Thompson on 2002-06-24 15:34 ]</font>

  12. #12
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    On 2002-06-24 15:32, Tim Thompson wrote:

    kucharek: if you let the rope down from geosynchronous orbit, it will enter the atmosphere with (ideally) no relative speed. That's the point of the geosynchronous orbit, a satellite in it seems not to move relative to a fixed point on earth.

    True enough for the satellite, at the far end of the rope. But not so true for the rope itself. You want the rope to stay "rigid", as it hangs down from the satellite fixed in geosynchronous orbit, to a point fixed relative to that, on the surface of Earth. But, each little piece of the rope "wants" to move at the orbital velocity of a Keplerian orbit at that radial distance from Earth.
    Not exactly. Each molecule on the cable under the asteroid would be moving too slow to maintain the Keplerian orbit, resulting in an unbalanced force directly towards the Earth's center of mass. But... there would be a solar and lunar effect, causing the rope to sway back and forth with each orbit.

    A few more complications:
    1. Lunar tidal forces will make the asteroid move slightly up and down relative to the equator as the moon orbits the earth. We would probably want to anchor it in such a length that there is always a little tension between the top of the cable and the asteroid regardless of the moon's position.

    2. I wouldn't want to be under the rope when a tiny piece of space junk knocks out a chunk of it somewhere in space. The severed piece is gonna HURT anything it falls on. Need to have several strands and link them at various positions for redundancy.

    3. Add the weight of the lights you will need to place along the cable to satisfy FAA for airplane safety. [img]/phpBB/images/smiles/icon_smile.gif[/img]

    4. This thing would attract the wrath of terrorists who believe it to be a modern "Tower of Babel".
    --Tommy

  13. #13
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    Here are some links for tethers and space elevators.

    Space Elevator
    This has info on the classic ground to geo-
    orbit space elevator.
    http://www.space.com/businesstechnol...or_001226.html

    Tethers
    This link has a lot of info about tethers.
    http://www.tethers.com/

    Space hotel
    Here is a cool link proposing a space hotel.
    http://www.space.com/businesstechnol...or_001226.html

    Kizarvexis

  14. #14
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    Weight of the material, orbit and drag problems..... And one more important flaw, the inefficient use of energy to get things up and down. Somehow I think rocket fuel gets more oomph for your buck than anything you could use to run the winch.

  15. #15
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    On 2002-06-25 01:02, beskeptical wrote:
    Weight of the material, orbit and drag problems..... And one more important flaw, the inefficient use of energy to get things up and down. Somehow I think rocket fuel gets more oomph for your buck than anything you could use to run the winch.
    Well in the elevator's favor: you don't have to carry the fuel with you. Perhaps the car could crawl to the top using power delivered within the cable or transmitted via microwave . Therefore the weight of the car is mostly payload.

    In the rocket's favor: Imagine how much energy it would take to capture an asteroid and bring it to earth and place it into geosyncronous orbit. Imagine the time, materials, and energy needed to build cables 37000 km. Imagine the time it would take the elevator car to climb 37000 km! Do you wait for the elevator to come back down before starting the next payload, or do you send another car up before the 1st reaches the top?

    Yes, I see what you mean about "oomph for the buck" [img]/phpBB/images/smiles/icon_smile.gif[/img]

  16. #16
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    On 2002-06-24 18:27, traztx wrote:
    A few more complications:
    1. Lunar tidal forces will make the asteroid move slightly up and down relative to the equator as the moon orbits the earth. We would probably want to anchor it in such a length that there is always a little tension between the top of the cable and the asteroid regardless of the moon's position.
    I've no figures about the influence of tidal forces on geostationary satellites, but they seem to be small, otherwise it would be pretty fuel-consuming to keep a satellite on position for so many years as they do.
    I also guess that deviations in the distance between the satellite and the anchor point on the earth are caught by the elasticity of the rope.
    As we have seen during experiments with relatively short tethers on Gemini 11 and 12 and STS-46 and STS-75, strange things happen.

    Harald

    PS: And there are many excuses [img]/phpBB/images/smiles/icon_wink.gif[/img]
    http://www.brouhaha.com/~eric/nasa_excuses.html

  17. #17
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    On 2002-06-25 01:02, beskeptical wrote:
    Weight of the material, orbit and drag problems..... And one more important flaw, the inefficient use of energy to get things up and down. Somehow I think rocket fuel gets more oomph for your buck than anything you could use to run the winch.
    The problem with rockets are, that you not only have to carry energy with you, but also mass that you can throw behind you (with the energy) so you move forward. And all the mass you need for your final push have to be pushed with you until this moment, so most of your fuel is used to accelerate the other fuel.
    IIRC, it needs only some 15kWh of energy to get a mass of 1kg out of the gravity funnel of the Earth. I guess, if you buy large amounts of energy, you get these 15kWh for one buck.
    So, if your space elevator is built, it's pretty cheap to get stuff up there. And imagine, if you extend a rope upwards, stretched by the centrifugal forces, you can slide outside there and if you detach at the right moment, you can get a spacecraft onto any interplanetary trajectory you want (as long as it is within the equatorial plane of the Earth).
    Another thing one has to keep in mind are the Coriolis forces when the elevator goes up or down, but these can be controlled by the speed at which you travel.

  18. #18
    I've got to say - finding the debate fascinating.

    Most of the scenarios dealt with involve semi-permenant solutions. It's fairly obvious the nature of our environment would destroy our rope. eg: Lightning/Storms/Meteorites etc.

    So what about something 'temporary' which can be lowered / raised when conditions allow? Surely this is a more feasible solution? How fast could we lower or raise the object/rope without it being destroyed etc?

  19. #19
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    I've got to say - finding the debate fascinating.
    See? No dumb question at all.
    So what about something 'temporary' which can be lowered / raised when conditions allow? Surely this is a more feasible solution? How fast could we lower or raise the object/rope without it being destroyed etc?
    Well, I guess the last 20 km should not be too difficult. But maybe a better solution would be to built some 20 km high tower (if we can do that rope, I'm sure we can do such a tower).

    Harald

  20. #20
    I've been reading some of the various linked pages left by the writers here. Interesting...

    But we're talking some major hi-tech leaps to access space hotels 22,000 kms out using the elevator technique, and I have serious doubts that something like this would last structurally as pointed out by traztx.

    This tether concept seems more plausible. But surely there's an easier way...

    Now forgive my schoolyard thinking here:

    High altitude balloons. Get's us pretty far up right? Co-ordinate with our orbiting spaceshuttle with long 'rope' dangling with some navigational control at the bottom of the it, now snare the balloon and its contents (just like fishing), and hoist away upwards!


    Here's a balloon to get us started...
    http://www.cosmiverse.com/news/space/space05060205.html

    Again maybe I'm missing some huge logic here, but could someone tell me what's wrong with this scenario?

    Thanks!

  21. #21
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    Wouldn't a baloon be very unstable due to the wind?

    (Warning: this is schoolyard thinking too.)

  22. #22
    Well at 13 to 15 Kms I'm assuming we should have cleared all our turbulent atmospheric conditions...?

  23. #23
    It gets better...

    40Kms/25miles (and this is a manned balloon).

    http://news.bbc.co.uk/hi/english/uk/...00/1645195.stm

  24. #24
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    *BZZZZZZZZZZT*
    "Hello, security desk"
    "Uh, Hello, security? We're stuck here in the space elevator on the 19,234th floor.
    "Don't touch any buttons, we'll get you out.'
    "What if we climb out the top escape hatch?"
    "Not a good idea. It's -200F and zero air pressure. But we have a fireman starting the climb now."
    "WHAT???"
    "In emergencies, the elevators are locked in position. If you look out the porthole you can see the Space Emergency Staircase next to the Space Elevator Cable"
    "You mean a fireman is going to climb all the way up to the elevator car???"
    "Well yes, that's what they're trained for. Special high-rise unit of FDNY."
    "How long will it take?"
    "Well, figure 30 seconds a floor times 19,234 floors."
    "BUT I GOTTA PEE NOW!!!!!!"


    (:raig

  25. #25
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    The current issue of Popular Science (I guess the June 2002 issue?) has an article on just this topic: Space Elevators. It's the cover story. Check it out.

  26. #26
    Another question.

    If it was built, where is the best place to anchor a space elevator. Surely North / South poles make a lot of sense, even with the wobble?

  27. #27
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    On 2002-06-25 10:37, sadprince wrote:
    Another question.

    If it was built, where is the best place to anchor a space elevator. Surely North / South poles make a lot of sense, even with the wobble?
    I think it would have to be on the equator, which is the only place where satellites can hover over the same spot.
    Everything I need to know I learned through Googling.

  28. #28
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    Several thoughts on this subject:

    Buckeytubes (or if you prefer, carbon nanotubes) break down when they transmit large currents. Lightning strikes could and likely would destroy such a cable. A system to draw the current away from the cable (such as several lightning-rod cables) would alleviate this problem, but would add considerable wieght to the system. However, that system would only have to go above the altitude at which the cable would be subject to lightning.

    Aside from lightning and terrorist activity, the only other hazard to the cable would be space debris in low Earth orbit. Meteorites would have a tiny chance of hitting the cable, but any cable strong enough to hold a space elevator would have to be stong enough to deal with micro-meteorite strikes. Larger meteorites will be so unlikely to strike the cable that they aren't worth dealing with.

    Convervation of angular momentum means that an elevator ascending/descending will cause the cable to sway somewhat, as will lowering the cable. However, the Earth's gravitation will serve to dampen this effect.

    We don't need an asteroid to start the whole process. A large satellite in geosynch orbit over the equator is all you need, provided that the satellite can lower a tiny cable to the ground, and at the same time raise a tiny cable the other way to provide a counterweight. The stress on this cable will be tremendous, but it is within our ability to solve in the near future, especially given the fact that we are almost ready to mass produce carbon nanotube fibers, which would allow us to build such a large cable system.

    Once the thin cable is lowered, a small machine could be attached to raise more cable fibers, eventually allowing large payloads.

    <hr>

    All of these problems can be solved in the next 20 years or so, except one: debris in low Earth orbit. If we ever intend to build a space elevator, we have to clean up the orbiting bolts, wrenches, paint flecks, frozen human wastes as well as the dead satellites, booster rockets and whatever the ISS will produce. Whether we build the space elevator 10 or 20 years from now, or we do it 10,000 years from now, we have to clear the Earth of orbiting junk first.

    _________________
    If E = MC<sup>2</sup>, why do I have less energy the more mass my body acquires?
    That is all.

    --Azpod... Formerly known as James Justin

    <font size=-1>[ This Message was edited by: Azpod on 2002-06-26 15:58 ]</font>

  29. #29
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    On 2002-06-25 08:53, Mespo_Man wrote:
    But we have a fireman starting the climb now."
    "You mean a fireman is going to climb all the way up to the elevator car???"
    "How long will it take?"
    "Well, figure 30 seconds a floor times 19,234 floors."
    (:raig
    Wow, that would change the fire fighters' annual rodeo time schedule.

  30. #30
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    I wonder... How much tension would you get on this rope, relative to the rope material's mass-density? Probably way way too much. Sounds like an interesting calculation to do, though. [img]/phpBB/images/smiles/icon_smile.gif[/img]

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