I'm not sure, but I think the bow wake phenomona will not occur until the climber reaches something like 1000 miles per hour, depending partly on the tension of the ribbon just ahead of the climber. If so, not a problem as the top speed will likely be less for other reasons.   Neil

Do I understand correctly that you plan to cut the old ribbon at an altitude of 1700 kilometers? Then splice in 1700 kilometers of new ribbon, which is folded in half? A wench on the anchor ship would roll up the old ribbon on to ten ? reels of 170 kilometers each, which could be sold as salvage? What I don't understand is why do the edges need to be trimed?
The only addition I see is the fold could not be released faster than the winch wound up the old ribbon, otherwise tension on parts of the ribbon near altitude 1700 kilometers would be too low to prevent the counter weight from moving outward/more so when all but the delivery climber had reached Geo altitude and more. Climbers could not pass the fold in either direction for the ten days it would take to reel in the old ribbon? Somewhat less than 1700 kilometers of full size ribbon might be all a climber could safely deliver to 1700 kilometers, but the ribbon can be replaced in smaller instalments than 1700 kilometers? Winches may be available that can reel in more than 170 kilometers per day, which would reduce the ten days to perhaps 5 days. 340 kilometers per reel might also be practical.   Neil

You are the first word, I have heard. Does anyone have details about laser protection of the SE?  Neil

Hi jallison: At an altitude of about 100 kilometers,  a tiny bit of space junk, or a less than one millimeter meterorite will shatter a few of the nano tubes. If they contain a few hydrogen atoms, a nitrogen atom or worse a single atom of oxygen will be unlikely to enter though the gap as compared to high vaccuum inside. Perhaps this will occur too rarely to bother with making nano tubes in a one milibar hydrogen atmosphere for a few hundred kilometers of the ribbon. I'm guessing. Perhaps CNT is made in a methane = CH4 atmosphere at several bars pressure?  Neil

If we complete SE1 in 2020 SE2 in 2024, Then wait 5 years to start SE3, We could end up with no SE in 2030, because we did not start SE3 soon enough. ie SE1 and SE2 were both distroyed in a meteor shower. Completing SE4 and SE5 by 2031, greatly reduces the probability of zero SE by 2031, so perhaps four or five has more magic than three. Building follow up SEs in rapid sequence has the advantage that the construction teams are kept intact, thus minimizing training of new people, but the possible disadvantage of not enough customers to make 4 or 5 SEs profitable.   Neil

Someone posted that the electrical conductivity of a very long CNT ribbon is still open to speculation. Likely it will be a trade off with other ribbon properties. Even if it is twice as good as aluminum and several times better than copper, gold and silver by weight, losses will be worse than the lasers after 10,000 kilometers, or so. Adding thin metal wires to the ribbon to carry a small amount of electricity could double the the optimum taper ratio and greatly increase the total mass, besides adding another probable failure mechanism.
Transfering energy from pavement to moving vehicles requres the pavement to be much flatter than present pavement standards to avoid scraping the pickup device about a millimeter off the pavement. Energy losses are unsatisfactory at one centimeter, making the cost double or more that of fosil fuel.   Neil

A vastly improved energy souce likely will not make the SE obsolete, but we might stop after constructing three SEs.   Neil

I don't know how to do the math, but I will guess the total mass is about a million tons, for a taper ratio of ten. (Is ten a cross sectional area ratio of 100?) A total mass of one million tons means almost 50,000 threads need to be laid, if the average climber and thread is 20 tons. 50,000 retired climbers as a counter weight means the ribbon can be perhaps 85,000 kilometers instead of 100,000 kilometers. A shorter ribbon is not a disadvantage to building a second and third SE up to 200,000 kilometers long, but it may make a Mars mission impractical until a longer SE is completed.
Completion of the first SE takes 10,000 days = 27 years, if we can launch an average of 5 tread laying climbers per day (present thinking is about 5 per week). With bad luck, the damage rate from millimeter and smaller particles will exceed the thread laying rate, so we probably can not build the SE, unless the taper ratio is less than ten or my million ton guestimate is way high. A starter ribbon with a mass of 1000 tons would help considerably, but I don't know how to calculate how much.
The high taper ratio means half of the mass of the thread will be laid within a few thousand kilometers of GEO altitude.
 If some of the climbers reach the far end with significant left over thread, can we start construction of SE 2 and 3 long before SE 1 is complete? Will The first three SE form a triangle about 200 kilometers per side?
Top engineers and scientists are excited about long shot technology, because they are open minded to even remote possibilities.   Neil

Dr.Edwads allegedly calulated that the laser beams need to total 2.4 megawatts = 2,400,000 watts for a 20 ton elevator car.  I suggested 100 horsepower = 645,000 watts in a newer thread and was advised several million watts (likely excessive) is needed to move upward at 136 miles per hour = 63 meters per second by the motors in the climbers. That was at the lowest end of the ribbon for the smallest climbers. If so, perhaps 20 times that much is needed for the largest climbers and the elevator car. Electric motors are up to 90% effeciency according to another source. I'll guess the rollars are 30% efficient at high speed, somewhat better at low speeds. Less power is needed at higher altitudes, but more of the laser energy misses the photo cells. The direction of 'up' reverses at 36,000 kilometers, but very little power is needed for either direction between 30,000 and 50,000 kilometers. Beyond about 50,000 kilometers, nearly all the laser energy misses the solar panels, so several lasers will be needed to move back toward GEO altitude (from the far end) but we may rarely have reason to do that, on the first elevator. Beyond about 50,000 kilometers breaking will be necesary to avoid dangerous over speed. If dynamic breaking and an electricaly conductive ribbon proves practical, the climbers can provide power for other purposes, when they are moving toward the far end.
The nuclear rocket (and turbine) ideas are extrapolated from some proto types built about 1965, I think. The prototypes put dangerous amounts of radioactive particles in Earth's atmosphere, but were a modest improvement over chemical rockets in some respects. There is significant concern that the atomic rocket would heat the ribbon dangerously, in some senarios. My guess is the problem of cooling the vapor in the condencer for the turbine could easily double the gross mass of the climber in the vacuum of space, where heat can be disposed of only by radiation of infrared photons.
I agree there is a slight possibility that atomic rockets may be cost competitive, before the first SE is completed, but I doubt they can be better than the laser system to power the climbers and elevator cars.   Neil

Hi Steve : Some of us have been kicking around the possibility of another method for the first 10 or 20 miles, but I don't think there is any Liftport support for any of these ideas at present. About half of the regulars (including me) on this forum have far less applicable education than you, so we are mostly repeating what we have heard, or seems reasonable to us. My guess is the ribbon will flutter vigorously in even a light breeze (perhaps destructively at 60 meters per second). Fortunately, high winds are very rare in the planned region for the first space elevator.  It is called the Doldrums = where sailing ships were often stalled for weeks as in "The Rhyme of The Ancient Mariner." I don't know if the jet stream is ever that close to the Equator, but I believe the jet stream is usually lower than the ten miles you suggested. Perhaps some of the others have ideas on how to minimise the flutter which, I think, will interfer with the climbers moving at high speed.
The ribbon will be thicker near GEO altitude, but taper very little in the bottom ten miles, as you suggested.
The usual thinking is the ribbon will be 8 inches wide and the climbers will add theads until it is one meter wide. I have not heard that more threads will increase the thickness near GEO altitude, but I can think of no other way to produce a taper ratio between 2 and 10.
If the finished ribbon averages one milimeter thick times 1000 millimeters wide times 100,000,000,000 milimeters long = 10E14 cubic millimeters = 10E11 cubic centimeters = 10E11 grams = 10E8 kilograms = 100,000 metric tons. I think it is hoped that somewhat less mass will safely support a 20 ton payload in an elevator climber. Some have suggested an average density of 1/2 for the ribbon which would halve the mass. The nano tubes are hollow, so each can contain high vacuum for the portion outside Earth's atmosphere. The thinking is about 1/10 th millimeters thick (thinner than paper) for the 1000 miles close to Earth, but the need to protect the CNT from atomic oxygen, likely means more than 1/10 th millimeters for the portion where atomic oxygen is the worst problem.  Neil

~I can correct errors I made so please comment, refute and/or embellish~

Hi. Just curious, as I have followed the progress of this somewhat, since proposed by Clarke. I was to the understanding that as of now, no carbon nano-tube more than a very tiny size could be produced. Clearly, you have better sources than I do.

Doubt he has, but it is a fascinating idea, is it not? At this moment in time it would seem worth spending billions, if that is what it takes, to get sufficiently long tubes.

~The last I heard (year ago)many labs were making 1 to 2 centimeter tubes, but one French lab annouced they could make them kilometers long. Likely that was a fib.
I understand that very long tubes are essential as the tubes are slippery, making both cohession and adhession poor. Neil~

Probably already out of date:

Extra-long carbon nanotubes set new record
20 September 2004

Researchers at Los Alamos National Laboratory and Duke University, both in the US, have created, at four centimetres long, what they believe is the world's longest single-walled carbon nanotube. The team hopes it may ultimately be able to grow nanotubes continuously.

"Although this discovery is really only a beginning, the continued development of longer length carbon nanotubes could result in nearly endless applications," said Yuntian Zhu of Los Alamos. "Actually, the potential uses for long carbon nanotubes are probably limited only by our imagination."

According to the researchers, applications for long single-walled carbon nanotubes could include electronic devices, microelectromechanical systems, biosensors, scaffolding for the growth of neurones, robotics, space exploration, personal armour and sporting goods.

To grow the nanotubes, Zhu and colleagues used the iron-catalysed decomposition of ethanol vapour, creating the tubes on a silicon substrate. Both metallic and semiconducting nanotubes formed, lying flat on the substrate. The growth rate was extremely high - around 11 µm per second - and Raman spectroscopy indicated that the nanotubes were of a high structural quality.

The scientists believe that ethanol was critical for the growth of the ultralong nanotubes, "probably because it does not tend to form amorphous carbon on dissociation". The team reckons the long nanotubes formed by a tip-growth mechanism, with the catalytic iron particles moving as the nanotube tip grew. All the tubes had a diameter between 1.31 and 2.25 nm, suggesting that the size of the catalyst particles was important.

The researchers expect that optimizing the carrier gas flow rate and composition, the growth temperature and the initial concentration of catalyst solution (which would affect the size of the catalyst particles) would enable them to grow longer nanotubes, and possibly even carry out the process continuously.

The scientists reported their work in Nature Materials.

What length would be needed? Are there sources for this?

~I have not seen any numbers on fiber length, but my guess is kevar and CNT makes better tethers if the fibers are as long as the tether. Fibers like wool grip each other like velcro, so even one centimeter fibers make moderately strong cloth and thread. Present thinking is epoxy as a binder for CNT fibers. I wonder if anyone is researching ceramic binders for CNT. I think CNT retains it's strength to more than 1000 degrees c, which is a big plus if the binders are still working that hot. Hot CNT needs to be protected from oxygen as it burns much like charcoal or coke. Apparently atomic oxygen degrades CNT (and lots of other substances )even below room temperature. Atomic oxygen is found in Earth's upper atmosphere and is one atom to a moelecule, while ozone is three atoms per molecule and likely also degrades CNT. Neil~

I think the possiblites of CNT get interesting once the fibers start being easily produced a around an inch long.

Where I read this or even if I make it up I can't recall.02/26/05  The possiblites of CNT get interesting once the fibers start being easily produced a around an inch long.

I concur.

A space elevator rated CNT ribbon would be made of a composite. The idea behind composites is that you combine a load-bearing material (fiber) with a load-spreading material (matrix). The CNT fibers would be embedded in an "epoxy" matrix.

If one inch CNT fibers become readily available, the challenge shifts to the matrix material. It does not need to be as strong as the CNT, but it does need to be strong enough and ductile enough to distribute the load between adjacent fibers. The CNT fibers would of course overlap along their lengths, so in principle they don't have to be as long as one might think.

That being said, the longer the CNT fibers the better; this would reduce the requirements on the matrix.

Of course, the matrix has other material property requirements that add to the challenge. And it seems more than likely that a space elevator would not be the first application of this new "wonder" material.

...it seems more than likely that a space elevator would not be the first application of this new "wonder" material

I agree, I think that if CNT becomes cheap that one of its major uses will be in construction. Currently most construction materials (metal, steel, glass, concrete) are very heavy and require a large amount of machinery to move them around. If cheap composites could be used instead the weight of the materials drops substantially and therefore so does the cost of the associated machinery.

Also it’s not until some other usage drops the price of CNT that SE become realistically affordable from a materials point of view.
 
I agree. I was thinking about climber costs as well. Those babies won't come cheap. And they are climbers only. Not climber/descenders. So they are 1 use only.

Along with the other facts stated above about the maturity of CNT technology and some more plausible arguments, I must come to the conclusion that space elevators are not something for the near future.

~If we could afford to buy a million tons of CNT this year we could perhaps start building a SE this year with a taper ratio of ten or twenty. Longer CNT = stronger ribbon = smaller taper ratio = much reduced total mass. The price would go sky high if we tred to buy a million tons, as no one is yet sure of the best way to mass produce CNT.  Neil~

My guess is the SE will behave differently from a clasical pendulum: 1 It is not rigid. 2 the period of the SE is days rather than seconds 3 GEO altitude may behave more like the fixed point than either end 4 The gravity and centifugal force changes over the length.   Neil

Jallison typed "at that small level we have the material bind together on the reel" I hope not, but this effect increases in the vacuum of space = vacuum welding.
On the optimistic side, CNT allegedly adheres poorly to everything, including CNT. If high pressure improves adhesion and cohesion, the ribbon may improve as each climber squeezes it between the rollars that give the climbers traction on the slippery ribbon.
Yes, I'm thinking of traveling waves or oscillations when I type transients. Transients seem more appropriate as the period of the oscillations is very long on 36,000 kilometers or more of ribbon, and the wave may have attenuated to unimportant, by the time it is reflected at GEO or an end.   Neil

We won't know for sure if  electrically conducting tethers can significantly discharge the Van Allen belts and other radiation belts, until we try it, hopefully soon. It does apppear that protecting electrically conducting tether from over heat due to excessive current induced by a strong CME may offset most of the advantages of an electrical conducting ribbon. On the optomistic side, excellent heat conductance likely accompanies good electrical conductance, reducing hot spots at least a little.   Neil

100 foot waves occur in shallow water, but they are only about a foot tall in deep water. The SE will have a floating anchor in deep water. Typically there is some advance warning of tsamiis and a climber launch would be delayed while some ribbon is extended from the anchor temporarilly, to leave some local slack in the ribbon in case a record breaking wave occurs.
We have some operational magnetic levetation trains = electomagnetic rail? How much scale up is needed to launch vertically instead of horizontally at 5000 kilometers per hour? At what altitude would the vehicle stop rising due to air resistance and gravity, even if we had lasers to reduce the air resistance? Would ablative tiles be required to prevent burning the skin off the space craft? How many kilometers tall must the tower (that holds the maglev track) be to limit the g loading of the pay load to 20 g or less? My guess is R&D for maglev is far more costly than for the SE and mag lev gets the space craft no higher than 30 kilometers.   Neil