Talk:Space elevator/Archive 1

message: In the first History paragraph, the last line says, "His notes were sent behind the Iron Curtain after his death." The context implies "he" is Nikola Tesla, who was a naturalized American citizen at the time of his death and had his papers seized by the FBI for national security reasons. I doubt they went behind the Iron Curtain. Was it instead Russian Konstantin Tsiolkovsky's papers that "were sent behind the Iron Curtain"? If so, it should say so explicitly. -- Jeff Q 05:59, 30 Apr 2004 (UTC)
thread_title:  History: Whose notes were sent behind the Iron Curtain? 

message: I read on the Internet a while back of a proposal for an untethered elevator. The bottom of the elevator would be in low earth orbit, above wind and lightning. But I can't find my source now. If anyone knows more perhaps they could write something.
Zeimusu 12:20, 2004 May 1 (UTC)
It does not work:  The lower orbit has a shorter period than the upper.  The lower station races ahead of the upper.  They rotate about each other making the whole assembly useless.  Paul Beardsell 13:57, 1 May 2004 (UTC)
replies: text: Not so. There are proposed tether systems which rotate, and others which don't. See tether propulsion for some info. Being much shorter than the space elevator, they are much more likely to be built. --wwoods 16:43, 1 May 2004 (UTC)

text: I don't know which proposal in particular Zeimusu is talking about, but he may simply be talking about a space elevator that doesn't quite reach the ground. The lower end would be reached instead by a suborbital spacecraft, or if it's low enough perhaps a high-flying aircraft, either of which would be much cheaper than a spacecraft that had to attain orbit on its own. Bryan 20:45, 1 May 2004 (UTC)

text: A low earth orbit space elevator is discussed in this conference publication from the external links section. Fredrik 20:58, 1 May 2004 (UTC)

text: In the case of an untethered elevator, yes, it would need to be dynamically rebalanced and the momentum restored. This could be done by high-efficiency thrusters such as ion drives, though, so there's still some benefit there over conventional rockets (hypersonic skyhooks have similar station-keeping requirements). As for the tethered version, the tower would be kept in tension by having its center of mass slightly beyond geostationary orbit. This means it's stable against minor perturbations and the angular momentum can be taken directly from Earth's rotation. No problem there, this is a basic issue that I'm sure pretty much every space elevator study would check before going on to other details. Bryan 06:13, 2 May 2004 (UTC)
replies: text: OK.  I have removed some stuff here I got wrong.  It's in the log if you're interested.  Paul Beardsell 08:09, 2 May 2004 (UTC)
replies: text: It happens to the best of us, and if nothing else it lets us know what sorts of misunderstandings may need to be addressed in the article itself. It's too late at night for me to do it now, but tomorrow I'm going to go through the article and see if any of the explanations I used here in talk: need to be inserted there. Bryan 09:11, 2 May 2004 (UTC)
replies: text: I think you need to do some more basic learning at this point. Ion drives do exist, and indeed have been used in various space missions - Deep Space 1, most famously. Ion drives cannot launch things into space, however, as they don't have sufficient thrust; they're only useful once they've been launched by other means. The cable doesn't need to be rigid to transfer angular momentum to and from Earth; when a payload goes up or down it the elevator tilts very slightly to the east or west, and as a result the tension gains a tangental component that pulls Earth's surface in that direction until everything balances out again. This doesn't apply to untethered elevators because they aren't connected to the ground. Bryan 07:06, 2 May 2004 (UTC)

text: Wrong way around, if the center of mass is beyond geostationary then it will be moving too fast to be orbiting there. It will want to move outward. Bryan 06:43, 2 May 2004 (UTC)
replies: text: The further away the slower the angular velocity of the orbit.  But if you were right then the result would be the same:  Your second favorite holiday destination would be decimated by a lump of useless scrap complete with ion drives.  Paul Beardsell 06:52, 2 May 2004 (UTC)
replies: text: You seem to have a very basic misunderstanding of how orbits work, here. The elevator is moving too fast for its orbit, so it will be thrown outward. Since it's tethered to the ground, this provides tension in the cable. It's just like twirling a weight attached to a string. Bryan 07:06, 2 May 2004 (UTC)
replies: text: I was (wrongly) referring to the natural, untethered speed of a satellite at that altitude.  Paul Beardsell 08:05, 2 May 2004 (UTC)
thread_title: Untethered Space Elevators

message: That other low earth satellites' orbits will have to be adjusted from time to time so that they do not collide with the cable is discussed in the article.  That the same techniques will be used to adjust the orbits of some asteroids is also presumed.  But now we have a cable which is being bent side to side by the ascending/descending cars to provide the force to accelerate/decelerate them as they move to/from the geostationary position.  Over 38000km I reckon the cable will be deflected by 100m at least - possibly a lot more.  How will this all be taken into account when deciding which satellite orbits need adjusting.  No longer do we have to worry about a swathe being cut through the sky which is 2m wide but one which is 200m wide.  What if there is a glitch of some description and a car is stopped for a few minutes?  The deflected cable will swish gently from side to side over 200m.  This will be unexpected!  What about all those satellites we nudged?  Paul Beardsell 19:02, 4 May 2004 (UTC)
replies: text: A reasonably broad margin of error will be called for, I imagine. Arrange it so that no satellite comes within a kilometer of the predicted position of the elevator, and then you're fairly safe against both unexpected swaying of the elevator and unexpected course deviations by the satellite (within that margin, that is). Air traffic control does this sort of thing all the time; nobody would normally plan a trajectory that only barely misses some obstacle, they'll always try to leave room to be on the safe side. Bryan 01:10, 5 May 2004 (UTC)
thread_title:  Avoiding other satellites 

message: Bryan, first I ought to thank you for taking so much time to explain things to me.  I apologise that on one or two occasions some explanations may not have been necessary if I had read the article more carefully.  However this is not true for many of the points I have raised:  The answers may be obvious to you but not to many otherwise scientifically literate readers of the article.  When I make an ill-informed observation this is an opportunity to improve the article.  When I make a good observation, likewise.
In my view (but I would say that wouldn't I) the bias is the other way.  There seems to be a tendency here to sweep problems under the carpet.  Supporters of the concept refrain from criticising points made by other supporters that they disagree with.  In the article itself and here on the talk page the choice is presented as if it were uncontroversial:  For reasons of the weather either the base must be movable or it must be untethered.  Avoiding satellites make the movable base problematic so now it is no longer required.
It seems to me supporters of the concept seem to me to feel free to swap from one set of mutually exclusive proposals to another as they seem fit.  This might not be true for any one individual but as a group you are remarkably uncritical of one another.  I know there is no group per se!
This is a highly speculative proposal that should be presented in an encyclopedia as such.  An introductory sentence does not compensate for the overall tone.  This otherwise excellent and highly interesting article needs to be moderated.
Paul Beardsell 12:11, 5 May 2004 (UTC)
replies: text: But this is simply not true. There's no good reason to move the base or leave it untethered, so the tradeoff that you claim is required simply doesn't exist. Look, I have no problem at all with putting cons in this article as well as pros. I practically wrote the entire "failure modes" section of the article when someone mentioned here that there wasn't anything in here discussing problems the system had. But if you want to talk intelligibly about the problems a space elevator might have then you have to have at least some basic knowledge about how the idea works. Your questions have been useful, they've resulted in some new material being added to the article in answer to them, but your constant harangueing about how we're all being foolish by overlooking "obvious" flaws and that the concept won't work for nonsensical reasons is making me feel quite frustrated and adversarial. If you don't know how this concept works, ask questions to learn about it instead of starting out by trying to lecture people on how you imagine it works. Then perhaps you'll be able to come up with some objections that can't be dismissed by anyone who knows a bit about this stuff out of hand. Bryan 15:32, 5 May 2004 (UTC)

text: I do thank you for confining this argument to talk:, if it had been taking place in the article itself I would have lost my temper long ago. Even as it is I've let my frustration get to me more than I should, sorry about that. Perhaps you could try making a list of the details that you feel the article still doesn't go into enough detail about, and we could go from there? Bryan 01:52, 6 May 2004 (UTC)
thread_title: Article moderation required