Talk:Space elevator/Archive 3

Metadiscussion:this whole talk page is not as messy as it used to be.
Metadiscussion:this whole talk page has become a colossal mess. (User:Bryan Derksen)

Boy, hasn't it. How about wiping archiving the whole thing and starting over, with a set of disputed topics, e.g., ==marginal_cost/kg via an Edwards skyhook==, ==... via an advanced elevator==, ==what is the minimum traffic level needed to justify an elevator?== How about taking longer turns, with sceptics and boosters posting on alternate days?

But it seems to me that webpages are suboptimal for presenting multiple involved discussions with multiple participants. People insert and/or append responses, and the ::: thing is quickly overloaded. How about moving the discussion to  sci.space.tech  or some such? I'd be much easier to keep the threads and subthreads straight, and we could get some new participants, with maybe some new perspectives. It's not true that all knowledge is contained in wikipedia (not yet, anyway). --wwoods 08:06, 12 May 2004 (UTC)


 * I very nearly did that yesterday, I had the page nearly cleaned off into /Archive 2 in edit windows but I chickened out before pressing "save page" because I didn't want to be quite that bold. :) However, since I take this as a "seconding" of the idea, I think I feel more confident in doing that now. I'm going to move the bulk of this talk into Archive 2, and if there are unresolved issues that get moved with it I suggest that the proponents of those issues please restate them in a more organized way. Also, in future when this page gets too long let's be more careful about how it gets trimmed down; we shouldn't be snipping out bits and pieces of discussions, instead leaving or removing them whole-cloth. Bryan 15:27, 12 May 2004 (UTC)


 * By all means include a general comparison with rockets here. But don't spend whole paragraphs exploring the details of rocketry economics behind those general figures, instead say "for a detailed breakdown of these costs, see rocketry" and put them over there. If there's disputes over those details, then talk:rocket would be the appropriate place to work them out. Bryan 00:26, 13 May 2004 (UTC)

I moved stuff relevant to rockets over to Talk:Rocket, as suggested by Bryan. I hope some of it might be useful enough to move to the Rocket article. -- DavidCary 14:50, 13 May 2004 (UTC)

I moved stuff relevant to rockets over to Talk:Rocket. Again. I moved stuff relevant to the Van Allen radiation belt over to Talk:Van Allen radiation belt. Please edit those talk pages and move the facts out into the articles where they belong. Thank you. -- DavidCary 10:22, 27 May 2004 (UTC)

Economics: Where did these numbers come from?
I moved all the discussion of economics to Talk:Space elevator economics. -- DavidCary 18:51, 1 Jun 2004 (UTC)

Rocketry Capital Costs
(moved to Talk:Rocket)

Reversions of Wolfkeeper's Contributions
I have read Wolfkeeper's references and they seem as authoritative as any produced here. Certainly a lot has been said by others without references being produced. It seems to me profoundly wrong to remove information from the page which is backed up by references. Not only wrong but against NPOV Wikipedia policy. Rei you must find another way than just reverting back past info that does not agree with your POV. Read NPOV. Paul Beardsell 00:26, 25 May 2004 (UTC)

Rei, you have now reverted 4 times - against Wikipedia policy - and this is the last comment provided: ''It's not a POV, it's false "facts" which have not been defended on talk. Until they are defended, it is information that has been challenged without rebuttal.'' What seems to qualify as a "false fact" is something not said by you. Wolfkeeper has provided references. Your so-called rebuttal, in the above section, is without a citation to back it up. There is nothing for Wolfkeeper to defend - he has provided references. You have supplied some text which may or may not be true. References please. Paul Beardsell 00:41, 25 May 2004 (UTC)


 * False information is not a POV. It is false information.  Should I go over to the page on the Moon and take the "Point of View" that it is actually an alien space ship plotting to destroy the world, and then start reverting it when people say that it isn't?


 * No. But you would be asked to provide a reference.  The reference would be subject to scrutiny.  And your moon POV is plainly false and would be very much a minority POV, whereas here, in this dispute, you must think there is a conspiracy against your POV:  How can so many be so wrong, you must be thinking.  Paul Beardsell 01:21, 25 May 2004 (UTC)


 * Yes, I think the correct wikipedian way is to include both POV. Deleting other people's opinions is considered gauche at best. It also says you are insecure enough in your own arguments that you don't think your arguments will be believed, it's a sign of immaturity (IMHO). Rei is actually holding it up here as if it is a good thing... small wonder she failed the admin vote I think; she isn't feeling the wiki, she so isn't.


 * His reference uses outdated dollar and payload figures in many cases. Some of the new rocket systems which should be considered "under development" (such as the Long March 2E, which is still struggling with a lousy 71% success rate) currently are cheaper than 10k$, but the shuttle would be that cheap also if we didn't inspect the tiles each turnaround  ;)


 * Here we have you admitting a lower cost than you will allow in the article: Make the reliability point in the article if you will.  But it seems you are not being consistent.  Paul Beardsell 01:09, 25 May 2004 (UTC)


 * As for citations, for God's sake, Psb, learn to use google and site:astronautix.com. I'll do your work for you this time , but you have to do it yourself next time.   And you're hardly one to talk about wikipedia reversion policy. Rei 00:48, 25 May 2004 (UTC)


 * Rei, it is your job to backup your own argument. I cannot see how your refs back up your POV.  Perhaps a page or a line number?  Or a quote.  Paul Beardsell 01:14, 25 May 2004 (UTC)

I have once broken the reversion policy but once it was pointed out to me I never did it again. How long have you been aware of the policy, Rei? Paul Beardsell 01:04, 25 May 2004 (UTC)

That the information is or is not false is the question. Your argument is circular. Paul Beardsell 01:04, 25 May 2004 (UTC)

I refer you to the Third Commandment. Paul Beardsell 01:04, 25 May 2004 (UTC)

LEO transfer orbit
One of the candidate versions of the article now says that an orbital launch to 180km at 51 degrees inclination is a "LEO transfer orbit" - an unusual term! An orbit at 180km altitude is a good LEO. If any part of it is higher than 180km then that is even better. But the 51 degrees refers to the angle at which the satellite crosses the equator - it does not make the orbit elliptical. Paul Beardsell 00:54, 25 May 2004 (UTC)

It's gone now, but for clarity: If 180km altitude can be attained at 51 degrees then, given a better launch site a higher altitude can be attained (or more payload lifted) for the same cost. Paul Beardsell 01:50, 25 May 2004 (UTC)

More than that: reducing the payload size slightly raises the orbit, and only slightly worsens the cost/kg ratio.

Basically this term 'leo transfer orbit' is spurious unless it's at seriously low altitude (like 100km). Any orbit that goes around the earth atleast once is LEO by definition. Wolfkeeper

Van Allan belt problem
What's the solution to this? On the face of it we have mutually exclusive solutions. The focus in the Economics section is the Edwards proposal, an up-only elevator, but the proposed solution (in this article) to the Van Allan belt problem is portable shielding shifted about on an up-down elevator. An up-down elevator reduces by a large factor the payload capacity (it seems difficult or impossible to have multiple climbers and decenders simultaneously - difficult enough that Edwards did not want to solve it) and thereby the economics are significantly affected. Maybe we send cargo only and the astronauts go by rocket? Paul Beardsell 13:49, 25 May 2004 (UTC)

Yes, my understanding is that the Edwards plan for the first space elevator is a up-only, cargo-only elevator, without any shielding. -- DavidCary 10:22, 27 May 2004 (UTC)

(details moved to Talk:Van Allen radiation belt)

General Editing Principles
Look, houserules. You can stick more or less anything you want in the Space Elevator section; but you'd sure as heck better have a citation; no citation and I'm unilaterally editing it out again. The point of a wikipedia is you don't 'make shit up'. Some people appear to be doing this.

So I'm currently expecting a citation to Rei's scheme for sheilding the cars- if she can't produce it I'm removing it. (I don't actually think this scheme works- the worst of the belts are at low altitude anyway, where the cable is weakest).

As for deleting other people's contributions; if you have a *well* respected source, then it's barely ok, but you're better off adding in the contrary citation. And it had better be a primary source, not some airy-fairy 'rockets are all so inefficient and expensive opinion piece' or 'space elevators are impossible' or some such. Got it? Wolfkeeper

Meaning of "reality"
Recently the 2nd para was changed to say the SE "might become a reality in a little over a decade". This calls into question the meaning of the word "reality": It does not mean "realistic proposition". I reverted to "might become a reality in decades to come". Paul Beardsell 20:25, 26 May 2004 (UTC)

Actually that was me; I had neglected to log on. Apologies.

Let me explain. The only known showstopper for the space elevator is the cable.

This is a fierce research area for a whole host of reasons, not just for space elevators, but suspension bridges and a massive list of other possible uses of carbon nanotubes; including better and cheaper rockets :-)

If the cable technology was to appear in the next two years; that would not particularly surprise me; the current record of 10 cm at 63 GPa is *incredibly* close to being enough; the theoretical strength estimates are about 120 Gpa right now. OTOH if it didn't turn up for a decade or ever; that wouldn't surprise either.

Brad Edwards has a project plan that shows going from zero to elevator in (IRC) 14 years. It seems reasonable that it won't take much less than this, even if some sort of space race happened, but of course could take a lot longer.

So this is not necessarily decades off. So I think this language is justified.

Besides it's only the opening paragraph, having a few 'could's and 'maybe's and 'might's is fine. I don't agree with 'would's and 'will's though. --Wolfkeeper 22:39, 26 May 2004 (UTC)

C'mon now: Let's at least say something in the introduction with which we all can agree. If we are not going to have the bland version I propose then, Wolfkeeper, at least you mustn't delete Rei's references as this is something of which you yourself complain. Paul Beardsell 20:22, 27 May 2004 (UTC)

Yes, I certainly can see why you are complaining, and I'm not terribly unwilling to change it back, but I think that the opening paragraph *must* be positive, we want the reader to read the rest of the article; rather than just instantly dismissing the idea as silly. I made it clear that the people who think that are optimistic, and I personally do believe that the seed elevator might become a reality in a little over a decade. It probably won't; but it might; I'd be betting on 20 years even if the cable popped up tomorrow by the time it was financed; even the channel tunnel took 200 years to complete. It really critically only depends on the cable technology; the rest looks doable. Whether it stays up; more than 5 minutes I don't know. The one thing financially in it's favour is that people *love* the idea of a elevator; so financing might well be twisted out of the scrouge-like politicians or some rich entrepreneur.--Wolfkeeper 21:13, 27 May 2004 (UTC)

The showstoppers are not currently limited to just the cable. We have to be able to move LEO satellites. Paul Beardsell 20:22, 27 May 2004 (UTC)


 * Huh? What satellites? What are you talking about? Please explain--Wolfkeeper 21:13, 27 May 2004 (UTC)


 * Have you not even read the article that you're editing? (It would make a lot of sense, since you've been adding in a lot of redundancy in places).


 * You seem to take everything very personally and then you insult people- whilst assuming that other people do not take your insulting and offensive behaviours personally. Given that; you are likely to find your time in wikipedia very frustrating and annoying I think.--Wolfkeeper 01:07, 28 May 2004 (UTC)


 * Let me sum up: Every object in orbit between LEO and GEO has an orbit that will *eventually* intercept the space elevator.


 * Oh that. But, because the elevator moves, this doesn't constitute a show stopper; does anyone have a showstopper?--Wolfkeeper 01:07, 28 May 2004 (UTC)


 * While this collision will be a relatively rare event, the number of objects in space is quite high, and has been constantly increasing. Consequently, either the elevator has to move (as per Edwards), or all of the aforementioned objects must have maneuvering capability (of which many don't, especially defunct satellites and debris). Rei 21:23, 27 May 2004 (UTC)


 * Yes, yes, it moves; and sometimes it falls down anyway; which incidentally makes the economics worse, since it becomes maintenance not capital costs.


 * Incidentally some research I've read shows that the type of lasers for powering elevator cars can do double duty for clearing away space junk- if you can target it; and if it isn't cloudy that day.


 * Sorry that you find it insulting when people have to explain to you the parts of the article that you didn't bother to read before editing.


 * Sorry if you think that's what happened.


 * I hope it bothers you that other people are having to read for you.


 * Obviously that's what would happen when I asked what he meant when he said: "We have to be able to move LEO satellites.". I hope you didn't do any totally unnecessary reading Rei, that would be too sad. Everytime Rei does unnecessary reading... an Angel in heaven... dies.


 * Not every elevator design is designed to move; many are stationary.


 * And it's unclear why they would be practical; hoytethers are not a panacea.


 * Edwards' design happens to move. As per lasers, a space broom has notably different requirements,


 * No, not really.


 * and the elevator needs its power (that's what the laser is there for).

These objects won't be over the horizon for long; and if it is predicted to hit another object you'd do much better to take it out early than try to dodge the tiny fragments.


 * And your "sometimes it falls down" remark is just silly;


 * Not so; a sufficiently large micrometeorite will cut the cable entirely; also upon being struck the cable will tend to explode; some of the shrapnel will cause secondary damage.


 * all designs call for engineering within a tolerance so that this doesn't occur.


 * Not so. At best you can design it not to happen more often than every 100 years on average; or some such number. Same way they design buildings for a hundred year storm.


 * You might as well argue against building bridges because "sometimes they fall down". Rei 16:37, 28 May 2004 (UTC)


 * Amazing how you managed to make it sound as if we weren't on agreement on this point.

Economics detached from main article
I moved the economics section to space elevator economics and replaced the section in this article with a short summary. This is not an attempt to get rid of the current dispute by hiding it in some obscure place. I moved it because 1) the section was getting very detailed, and 2) this article is too long and should preferrably be partitioned even further. The fact that the economics dispute can now get a talk page of its own is merely a fortunate side effect :)

Feel free to improve my summary. It was a quick work and doesn't do as good a job as it should do. But try to keep excessive details out of it. The separate article can now be expanded to include every conceivable cost detail, this summary should be kept brief and abstract so a casual reader can get a good overview without getting confused. I find the current economics article rather confusing to read myself. Fredrik 22:46, 27 May 2004 (UTC)

Incorrigible optimists
See what the incorrigible optimists have been reading. Paul Beardsell 00:50, 29 May 2004 (UTC)


 * Perhaps you could point out what the relevance of this link to space elevators is? There doesn't seem to be any. Bryan 05:56, 29 May 2004 (UTC)

Well, it seemed to me that there is a certain parallel between the naive optimism which is being gently but appreciatively poked at that web site and the barely-a-decade optimism here. Failing which I hoped that the web site would be appreciated for its own sake by those who have a sense of humour, regardless of their position on the optimism scale. It can't be that a defining attribute of the space elevator enthusiast is a lack of a sense of humour? Paul Beardsell 00:45, 30 May 2004 (UTC)


 * Perhaps my sense of humor is worn thin on this particular topic, but my sense of irony isn't. I note that most of the "incorrigibly optimistic" methods portrayed here are rocket-related. :) Bryan 03:02, 30 May 2004 (UTC)


 * The link doesn't even appear to work... 404?


 * Works for me. You are clicking on "reading" in the 1st para of this section?  Paul Beardsell 01:31, 30 May 2004 (UTC)


 * Ah got it- Mozilla gives 404, but Internet Explorer gives a cheesey 1950's style page. Kinda weird that the two browsers give different results to that extent.


 * Works on Mozilla (1.6) for me. Paul Beardsell 16:06, 30 May 2004 (UTC)


 * FWIW I'm using Mozilla (1.7b)- don't know why that would matter. Reproducibly works with IE version 6. Reproducibly not working with Mozilla 1.7b under windows XP.

carbon nanotubes

 * Hmm. In all fairness you'll note that space elevator designs currently rely on currently non existent [ carbon nanotube ] cables, whereas rocket cost reductions mainly rely on launching more often, using better engineering and architectures, using actual past experience; and avoiding being part of a national program as they usually don't care so much about money. Wolfkeeper

I moved discussion of carbon nanotubes to the Talk:carbon nanotube article -- DavidCary 18:51, 1 Jun 2004 (UTC)

characteristic length
Someone needs to fix the engineering discussion in the Cable section. The feasability of constructing a space elevator isn't determined by the material's tensile strength, it's determined by the ratio between the material's tensile strength and density. If someone discovers 120 GPa Unobtanium tomorrow, it'll still be useless for a beanstalk if it's as dense as gold. One of the reasons people are so excited about carbon nanotubes is the combination of low density with high tensile strength.


 * Yes, I agree. Since the "strength/density ratio" is the critical number, that's what we should be comparing between these materials. Another name for this number is the "characteristic length". Is it OK if I quote http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/1982.articles/skymes in the article ? -- DavidCary

A nice intuitive way to express the strength to weight ratio of a material is called "characteristic length". It is the length of material fashioned into a constant cross-section rope that can just support itself when hung from one end in a uniform one earth gravity field. (The formula is tensile-strength/(density*1g)). Graphite, with its strong covalent carbon-carbon bonds is the best actually existing material. Its theoretical characteristic length is several thousand km. A metastable metallic version of hydrogen that can exist at room temperature might be quite a bit better because hydrogen has much less dead weight, but its existence is only conjectured. . Later editions of the CRC handbook have a NASA originated table labelled "Mechanical and Physical Properties of Whiskers". The indicated whiskers are actual laboratory grown, millimeter length, single crystal rods of various substances, whose strength and density can be measured. The measured properties give the following characteristic lengths: . Graphite whiskers	961 km Al2O3 whiskers		527 km Iron whiskers		162 km Si3N4 whiskers		455 km SiC whiskers		704 km Si whiskers		337 km. These numbers are about 1/5 to 1/10 of the theoretical limits for the substances. . By comparison we have todays engineering materials: .       Bulk aluminum		  10 km        Bulk iron		  11 km        Bulk steel		  40 km        Nylon			  88 km        Fiberglass		  98 km        Kevlar			 195 km. As stated in my previous message, a strength five times that of Kevlar would make earth elevator cables of varoius varieties possible. This means a characteristic length of about 1000 km; a bulk material with the graphite whisker strength above would do fine.

-- http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/1982.articles/skymes


 * It would be really, really nice if the above materials: aluminum, iron, steel, nylon, fiberglass, kevlar, silicon (Si), graphite, sapphire (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC) -- as well as nanotubes -- had both the numbers we need for this calculation (tensile strength and density) in their respective articles. Unfortunately, most of them *only* list density; and nanotubes only lists tensile strength. -- DavidCary


 * Tensile strength has a table. Assuming tensile strength of 60 GPa and a density of 1.5 g/cm&sup3; gives a characteristic length of about 4,000 km. Another figure of merit is the characteristic velocity, sqrt(strength/density), which is not intuitive, but isn't tied to Earth's gravity either. Other refs:  --wwoods 23:00, 12 Jun 2004 (UTC)

Why, in the quoted material above, is a characteristic length of 1000km good enough for a cable much, much longer than that? The first few thousand km of which will be in a gravity close to what we experience here on the ground. Paul Beardsell 04:40, 14 Jun 2004 (UTC) From your last reference I quote:

The support lengths assume no tapering. He figures tapering would be used, but a safety margin is also required, so they cancel out. The necessary support length for a Terran beanstalk is about 4,940 km.. He mentions that graphite whisker is already strong enough for a Martian beanstalk, where the support length is 975 km.

Paul Beardsell 04:44, 14 Jun 2004 (UTC)


 * The optimal taper (ignoring saftey margin) is exponential; the characteristic length is the length over which the diameter must increase by a factor of e. So even with constant gravity, you can get away with a few characteristic lengths before your cable becomes outrageously huge.  (I assume this is part of what went into the 4940 km above; at such lengths decreasing effective gravity can help too.) --Andrew 04:51, 14 Jun 2004 (UTC)

Drag
The "Launching into outer space" describes drag on the cable (west ward0 when mass climbs. But it doesn't explain how the cable katches up after imparting orbit velocity to the payload. Pud 23:59, 25 Jun 2004 (UTC)


 * Yes it does. "This angular momentum is taken from Earth's own rotation." and "The horizontal component of the tension in the cable applies a tangental pull on the payload, accelerating it eastward. Conversely, the cable pulls on Earth's surface, insignificantly slowing it." - basically, the rotation of Earth pulls the elevator back up to its original momentum again, infinitesimally slowing down Earth's rotation in the process. I'll add the direction of the pull to the article, hopefully clarifying this. Bryan 00:29, 26 Jun 2004 (UTC)


 * What is to keep the cable from being continually pulled back as more and more mass is lifted, what acts to straigenten it out and keep it verticle? Pud 00:38, 26 Jun 2004 (UTC)


 * The centrifugal force acting on the counterweight at the end of the tether. Since the elevator's center of gravity is slightly farther out than geostationary orbit, the elevator acts a lot like a rope being held onto by a spinning figure skater; it "wants" to stick straight outward, and if it gets nudged to the side it will swing back out again on its own. Bryan 02:46, 26 Jun 2004 (UTC)


 * How about; "the verticle componant of the cable tension causes the cable to return to verticle after accelerating the launch mass" ? Pud 00:45, 26 Jun 2004 (UTC)


 * Sounds good, I'll work that in. Bryan 02:46, 26 Jun 2004 (UTC)


 * It won't necessarily return to the vertical--if there's a constant (net) flow of mass along the cable, the Coriolis force'll impose a permanent incline to the cable. Not much--it's like a rope being held by a spinning skater, along which ants are crawling. The tilt sets one limit on the throughput of the system, but it's not a problem, as long as the center of gravity isn't pulled down below GEO. Of course, by varying the movement of mass along the cable you can make it swing and shimmy; that's the way proposed to avoid some collisions. --wwoods 08:45, 26 Jun 2004 (UTC)


 * Another good point to work in :) Bryan 16:52, 26 Jun 2004 (UTC)

Clarification requested
Moved discussion of various types of tethers, and what to name each one, to Talk:tether propulsion. --DavidCary 08:52, 11 Jul 2004 (UTC)

it seems the whole article uses metric, except for the "Building an elevator" section. i wanted to change it, but i realized i have no clue which ton is used. can somebody try to find out, and then change it to fit the rest of the article?

Economics article factual dispute still ongoing?
There's been a factual accuracy dispute tag over at Space elevator economics for two months without any editing being done on either the article or the talk: page, does anyone know whether the dispute is still ongoing? I asked in that article's talk page too, but I figured this page was more likely to be bookmarked by interested people. Bryan 18:34, 25 Sep 2004 (UTC)

I think pretty much everyone got bored by the bickering and people claiming that white was black, or that only orange is important. I know I got bored. -WolfKeeper