wreck@fmsrl7.UUCP (Ron Carter) (06/18/91)
In article <FeJc41w164w@w-dnes.guild.org>, w-dnes.guild.org!waltdnes (Walter Dnes) of "Ye Greate Calkulatinge Machine Hoaxe" writes: >wreck@fmsrl7.UUCP (Ron Carter) writes: > TV transmitters and microwave relay towers aren't *DESIGNED* >to "do work on the air" (pun not intended). Yet occasional >failures/collapses do happen. Because loads on the structure exceed its strength. However, you've not shown a single calculation to test the proposition that this is likely in the case of a beanstalk. Why not? Is expressing your ignorance your best tactic? > In the general case, you will *NOT* find wind blowing at the >same direction and speed from ground level to the top of the >stratosphere. Wind at 10,000 feet can be one speed and direction, >another at 20,000 feet and yet another at 30,000 feet, etc. Wonderful. The smaller the net force on the beanstalk, the smaller the net offset it will assume from vertical. The worst-case situation is all winds in the same direction. >>Any flex in the beanstalk, or vehicles moving up and down, >>will cause it to shed ice. Also, it can be heated electrically >>if icing is a difficulty. > > Structural icing simply makes loading worse. It adds weight >to the whole structure, and increases the cross-section area that >the wind sees. Don't expect heating elements to keep the >beanstalk 100% ice-free 100% of the time. If it's hot enough to >do so, I'd hate to see what it does to the graphite beanstalk >itself. Of course, you didn't bother to consider the possibility of thermostatic control. Nor did you calculate the power required to keep ice thickness to less than some arbitrary value. Graphite is very refractory; it gets stronger with increasing temperature. Again, the argument from ignorance: "If I don't know that it won't be a problem without doing any work to see if it might not be, it is." Very poor technique. > Heavy rime icing in cloud is a lot worse than the worst >freezing-rainstorm you have ever seen. It is one of the worst >nightmares for a pilot. Don't tell me about pilot's nightmares. I've lived a few. >A falling >beanstalk can wrap around most of the equator and cause damage in >lots of countries. Not unless it breaks far, far above the surface. The portion of the beanstalk above the break remains in orbit; only the portion below will fall anywhere. If the portion below is large enough, breaking it further will allow the upper parts of that to remain in orbit as well. The terminal velocity of a cable of density 1.7 must be considered. If the cable is only an inch or two in diameter and the lengths are not long enough to whip the ends up to high speed ("range-safety" equipment is indicated!), terminal velocity will not be high, and damage will be small. > Electrical heating is one anti-icing system. You'd need >power fed from the surface up to a height of 10 - 15 km. A couple >of insulated cables power to worry about. What does this do to >the weight of the whole system ? Why didn't you calculate this yourself? Are you incapable? How do you know it is an issue at all? >Does the whole beanstalk need to be made thicker ? How much ? Why didn't you calculate this yourself? Are you incapable? How do you know it is an issue at all? >Your other alternatives are to pump >de-icing fluid several km uphill against gravity, or encase >several km of the beanstalk in a flexible airtight sleeve (in >short manageable sections) and inflate/deflate it in cycles to >dislodge icing as it accumulates. Those are the three main types >of anti-icing systems used on aircraft. Of course, you never considered systems not in use on aircraft. Alternatives include piezoelectric flexors to deform the beanstalk's cross-section and flake ice off, flash heaters to evaporate ice into steam and blow overlying ice off, and other devices not compatible with bent sheet metal structures. Use some imagination! > In summary, wind and ice loading is an important real world >problem that no amount of hand-waving will make go away. Again, how do you know it is an issue at all? Have you calculated the loadings and found them excessive, or are you just hand-waving? > As far as weight is concerned, I would be much more worried >about the weight of several km of heating cable wrapped around >near the bottom of the beanstalk. How much cable do you need? If you don't know, how do you know it is an issue? > The thread title says "Beanstalk reprise". Beanstalks are a class of tether. Weren't you here for the lecture? > More to the point is... 40,000 km worth of the stuff put >together as one piece. Ever consider that it might NOT be one piece? That it might have joints and connectors? That individual strands might be testable and replacable while in use, like a suspension bridge? Where's your imagination? > Beanstalks aren't possible given today's technology. I >agree with you... again !! Agreed. However, they are possible given MATERIALS known today. This is a crucial distinction; we know what to shoot for, and even many of the physical processes required. As for ice loading and wind loading, I'm not going to lecture for free to address your misconceptions any longer. If you want to continue responding to my data with hand-waving, you can pay for the priviledge. Ergo, I offer you this deal. I bet that I can do the following: 1.) Refute the contention that ice loading on a beanstalk of design chosen by me (within reason) presents any structural difficulties, given the use of known de-icing technology, and 2.) Refute the contention that wind loading at a wind speed of 250 KPH could bring a beanstalk of design chosen by me (within reason) down, given ice loads limited by de-icing equipment a la 1.) above. I assume that you will bet that I cannot refute these contentions. I offer the sum of $100 American on each of these two assertions. We must agree on a judge. This has advantages for you: you get the lecture, and YOU get paid if it is wrong. You only have to lay out money if you are truly getting educated. What a deal! So, are you ready to put your money where your mouth is?
jmc@DEC-Lite.Stanford.EDU (John McCarthy) (06/18/91)
I didn't get in on the beginning of this argument, but I want to make one general point. While all inventions are subject to the laws of physics, arguments that the laws of physics forbid some achievement often have holes. Moreover, it is invention that finds these holes. Arguments that beanstalks can't work have holes too. Here's one. Suppose we build the beanstalk from the bottom up to the top of the atmosphere, and hang the upper part from synchronous orbit down to the top of the atmosphere. That way the part built up from Baker Island can be thick and strong where the winds are and can also be dynamically stabilized. -- John McCarthy "The people of the antipodes, gazing at the moon when for us it is only a small crescent, remark, 'What a splendid brightness! It's nearly full moon'" - Stendhal, Memoirs of an Egotist
carl@sol1.gps.caltech.edu (Carl J Lydick) (06/18/91)
In article <43882@fmsrl7.UUCP>, wreck@fmsrl7.UUCP (Ron Carter) writes: >The terminal velocity of a cable of density 1.7 must be >considered. If the cable is only an inch or two in diameter >and the lengths are not long enough to whip the ends up to >high speed ("range-safety" equipment is indicated!), terminal >velocity will not be high, and damage will be small. I don't think I've heard of any beanstalk proposal that has a cable "only an inch or two in diameter". On another note: A couple of years ago, somebody (Robert Forward, maybe?) published a fairly detailed study of what it would take to make a beanstalk in a fact article in Analog Science Fiction/Science Fact. As I recall, the conclusion was that if our knowledge of how chemical bonds work is correct, there is theoretically no material strong enough for a beanstalk anchored to the Earth (to Mars or the Moon, yes; to the Earth, no), but that pinwheels would be possible. Anybody out there with that issue of Analog? -------------------------------------------------------------------------------- Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL
carl@sol1.gps.caltech.edu (Carl J Lydick) (06/18/91)
In article <43882@fmsrl7.UUCP>, wreck@fmsrl7.UUCP (Ron Carter) writes: >The terminal velocity of a cable of density 1.7 must be >considered. If the cable is only an inch or two in diameter >and the lengths are not long enough to whip the ends up to >high speed ("range-safety" equipment is indicated!), terminal >velocity will not be high, and damage will be small. I've never seen a proposed beanstalk with that small a cross-section. >> The thread title says "Beanstalk reprise". > >Beanstalks are a class of tether. Weren't you here for the lecture? >> Beanstalks aren't possible given today's technology. I >>agree with you... again !! > >Agreed. However, they are possible given MATERIALS known >today. This is a crucial distinction; we know what to shoot >for, and even many of the physical processes required. A couple of years ago there was a science fact article in Analog Science Fiction/Science Fact that concluded that if we properly understand the mechanisms of chemical bonds, there is no material theoretically capable of the strength needed for a beanstalk on Earth (on the Moon or Mars, yes; on the Earth, no). However, the article concluded that pinwheels would be feasible. Anybody out there got that issue of Analog (or about as good, the issues with the indices in them) and willing to let us know which article I'm talking about? -------------------------------------------------------------------------------- Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL
carl@sol1.gps.caltech.edu (Carl J Lydick) (06/18/91)
In article <43882@fmsrl7.UUCP>, wreck@fmsrl7.UUCP (Ron Carter) writes: >The terminal velocity of a cable of density 1.7 must be >considered. If the cable is only an inch or two in diameter >and the lengths are not long enough to whip the ends up to >high speed ("range-safety" equipment is indicated!), terminal >velocity will not be high, and damage will be small. I've never seen any proposal for a beanstalk that thin. >> The thread title says "Beanstalk reprise". > >Beanstalks are a class of tether. Weren't you here for the lecture? > >> Beanstalks aren't possible given today's technology. I >>agree with you... again !! > >Agreed. However, they are possible given MATERIALS known >today. This is a crucial distinction; we know what to shoot >for, and even many of the physical processes required. There was a science fact article in ANALOG Science Fiction/Science Fact a couple of years ago that concluded that, given our understanding of chemical bonds, there was no material theoretically strong enough to build a beanstalk on Earth (on Mars or the Moon, yes; on Earth, no), but that pinwheels would be feasible. Anybody out there who can point us to the appropriate issue of Analog? -------------------------------------------------------------------------------- Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL