Space Elevator Even Theoretically Possible?

[tdamskov]

Not mooring the space elevator to the ground is akin to having a container ship waiting 30 kms off the coast, with each item needing to be carried by a human swimmer .. If you can build the nanotubes with the strength to withstand 35580 km of tension, I suspect those last 20 km of atmosphere won't make much difference.<br />

 

[ariesr]

That's the crux of it I would think.<br /><br />Material strong enough hasnt been invented yet.

 

[billslugg]

The problems with the last 20km to the ground are legion. Tension is the least of the problems. In fact the tension is less and less as you reach the ground where it is zero.<br /><br />Problems include airplanes running into it, terrorists bombing it, lightning strikes, wind moving it about, and don't forget bird droppings. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[kelvinzero]

Anyone considered lighter than air sky scrapers? Im thinking something huge, like 10km wide and 25 high, consisting of almost nothing.<br /><br />Im thinking that if you scale them large enough they will be able to resist huge winds because the volume will grow faster than the surface area. So even if the volume is only filled with a wisp of cables, if built large enough the structural strength of the volume will far outmatch the force of the wind against the surface.

 

[tdamskov]

I think those risks are manageable. Let's assume the cable has a diameter of 4 meters at ground level. Attached to the cable exterior are probably guide rails and sensors but not much else.<br /><br />Impacting an airplane into a massive 4 meter cable would pretty much just split the plane in two. There's nowhere for the fuel to linger; it will explode and burn very quickly. Exterior attachments might be damaged. However, all damage is at an altitude which is easy to reach and fix from the ground. Not sure how carbon nanotubes are affected by the heat or impact itself, but compared to buildings the solid cable present a completely different kind of structure.<br /><br />Okay, so what about other kinds of terrorism... Shaped charges at ground level? It's a risk, but security should be able to handle it. Actually, I think the biggest risk here is if a group of terrorists decide to disrupt cable services - in whatever way possible. That might be very costly for the companies/governments that run it.<br /><br />Weather. Hmm.. Someone will need to do the calculations on how much stress the cable will be able to handle. Lightning probably won't be much of a problem - we know how to divert the energy. Ice and rain could be troublesome in terms of corrosion and weight but those are factors we handle with bridges even today.<br /><br />Space debris might be the worst threat to the cable.

 

[alokmohan]

It is possible only by nanotechnology.Am I correct?

 

[billslugg]

tdamskov<br />I notice that you have conveniently avoided the bird dropping issue. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[Mee_n_Mac]

<font color="yellow">I notice that you have conveniently avoided the bird dropping issue.</font><br /><br />I'd have thought that given the lightning strikes the answer to the bird dropping issue would have been obvious ... it's like a self cleaning oven ! I'll boldly go when no one has so far and predict that the base stations of the tethers will have KFC franchises .... serving new courses such as fried sparrow, fried robin, fried ....<br /><br /><br /><br /><img src="/images/icons/wink.gif" /><br /><br /><br /><br />More seriously .... given that the Earth's magnetic field flucuates vs time, wouldn't having a big conductor stuck into it, and ground, pose a larger problem than lightning ? <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>

 

[usn_skwerl]

bird dropping issue<br />resolved by adding high frequency bird repellant devices around the perimeter of the base, similar to what you find in aircraft hangars, but focused upwards along the length.<br /><br />aircraft avoidance is simple; warning like TCAS, solar or wind powered rotating HID beacons or, the more efficient and reliable LED strobe lights (like aircraft have) every few hundred or couple thousand feet. The additional weight of batteries shouldn't be much of an issue by the time we get around to building the elevator (the technology should be there), and if it is, a clean (soloar?) power supply plant at the base of the elevator (on earth's surface) to power the aircraft avoidance system, lighting, and bird repellant. <div class="Discussion_UserSignature"> </div>

 

[nexium]

Most of the wrong ideas got corrected somewhere in this thread, but most readers must be confused. There is lots of correct info at www.liftport.com There is also a forum which has some errors at www.liftport.com look for word forum about 80% of the way down the main page.<br />Let's focus on the Edwards space elevator in this thread and a separate thread about a bolo = rotating tether and rotovator.<br />Edwards proposed 91,000 kilometers = 60,000 miles of ribbon. 60% of the ribbon is above GEO altitude, and a sizeable counter-weight is still needed at the far end. This is because Earth's gravity decreases with altitude. Edwards starts with a ribbon that can only lift one ton with a breaking strength of two tons. The climber = lifter has pinch rollars powered by electric motors to climb the ribbon. The electricity is delivered by laser beams to two photovoltaic panels. Other methods of propelling the climber leave no payload. The payload is a reel of very thin CNT thread, 60,000 miles long, which the climber attaches to the ribbon to increase the strength of the ribbon. Several hundred of these threads are needed to increase the ribbon strength to 20 tons = break at 40 tons. Climbers that lay thread are stored at the far end to serve as the counter- weight.<br />If the CNT has a working strength of 60 GPA. the cross sectional area at GEO altitude needs to be about double the cross sectional area at the top and bottom end = the ribbon is tapered. The required taper ratio increases rapidly at slight weaker material, quickly making the ribbon too costly, and the number of strengthening threads required increases rapidly until the construction time exceeds the 10 or 20 years before the ribbon is excesssive lumpy from patches due to space junk damage. It is thought that the ribbon can dodge the pieces of space junk which are large enough to have known orbits, by moving t

 

[nexium]

CNT has a tensile modus of 1000 GPa and several other materials are almost as good. So far, the macro strength of actual ribbon has been much less, but hopes are still high for 60GPa working strength or more. Funding is needed to advance several other possible show stoppers. <br />DSS = darkskystation or equivent kites such as www.skywindpower.com are also short of funding. Generally an anchor at 20 to 40 kilometers is not thought to be enough help to justify the extra complications, but that thinking could change, if a long term demonstration of a an upper atmosphere station actually flew. Neil

 

[R1]

I'm glad you mentioned the airplane, I was thinking about the dangers myself.<br /><br />I'm thinking a bird would definitely be cut in two by flying into it, a nanotube is a lot thinner and stronger than a razor blade,<br />and dangerously invisible, is it not ?! <br /><br />as for airplanes, I think it's true that the airspace can simply be restricted, but hopfully over a really large area,<br />if the cable is subject to some erratic movement a robot may have to be the one loading and unloading the cable, due to<br />the danger of being instantly sliced in half by something that strong and only a few atoms thick !<br /><br />I wonder if laws are being planned to make nanotubes illegal, or for government use only, or something as strange.<br /><br />Can you imagine if people buy needles and rods of thin nanotubes? It's hard enough to find a needle in a haystack, but<br />theoretically you can, but what if you misplace some nanotubes you just bought somewhere in your furniture or just<br />somewhere in your house?<br /> <div class="Discussion_UserSignature"> </div>

 

[tdamskov]

Although the tensile strength of CNT is high, like most other materials it will happily bend and break if it's very thin. I would be more worried about inhaling fragments than cutting myself on the stuff.<br /><br />A space elevator would definitely need to be thicker than just a few atoms, I reckon at least several centimeters. Not just for strength, but also for your spider to have something to grab and climb.

 

[R1]

thanks tdamskov, that's another good precaution for scientists to pre-plan<br /> <div class="Discussion_UserSignature"> </div>

 

[billslugg]

Mee-n-Mac<br /><br />Fried sparrow is OK, but fried robin more closely approximates Whooping Crane. Yes, having a 20,000 km conductor hanging around when a major solar event squashes the earth's magnetic field might cause some problems. There will be a current induced in the cable that will charge whatever is at the far end. Sitting there with a charge is not a problem as long as no other spacecraft comes up to you and touches. A giant spark would ensue. The end of the cable at Earth's surface would simply discharge to ground. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[nexium]

It does take some delta v to get from the Space Elevator to a circular low earth orbit. The least energy is to drop off the ribbon at an altitude of about 22,000 kilometers. You drop like a rock, use some delta v to miss Earth's atmosphere by a few kilometers then some more delta v to circularize the orbit at the desired LEO altitude.<br />GEO and solar orbits are easier and safer from the Space Elevator, so LEO will rarely be used, if we get a Space Elevator. <br />64,000 miles is the correct length with a modest counterweight near 64,000 kilometers altitude. The space Elevator can be much longer with very little counterweight. Neil

 

[usn_skwerl]

here's a video of a 1,000 deal...space elevator test <div class="Discussion_UserSignature"> </div>

 

[bguth]

"Space Elevator Even Theoretically Possible?"<br /><br />Why of course it is, at least on behalf of going to/from from the surface of our physically dark moon, as headed directly towards good old mother Earth (perhaps getting its dipole tether element safely as close to Earth as 2r).<br /><br />LSE-CM/ISS is a moon L1 kind of super/mega Clark Station on a tether. <br />-- Brad Guth

 

[habue6]

NOT Possible, practical, or probable in theory or in practice.<br />We did have a great cheap way of delivering objects into space, but the SR-71 Program was canceled by a democrat president- Mr. &%$#@! Cigar in the oral office.<br />They were working on putting up a global satellite com system when he X it. So now were still using crappie cell phones 12 years later.<br />

 

[drwayne]

Uhhh, my understanding differs from yours:<br /><br />The Blackbird was shut down during the first Bush administration (Dick Cheney was a big factor in the decision in his role as SOD) - the Air Force did not like running the program for the benefit of other services when those services were not paying for them. And the SR-71 is quite expensive to fly.<br /><br />The Blackbird was actually brought back on a limited basis by Clinton some years later. <br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[killium]

(replying to the whole thread)<br /><br />Hi all, it's been a long time since i didn't write but i read a lot....<br /><br />I think something is wrong with the whole concept of space elevator. If i understand this right, there would be a cable between the surface (or near it) and that 'above geosynch terminal'. The whole thing beeing geosynch means it would sweep around the earth every 24 hours. Like a giant "weed eater" lol!<br /><br />The problem with this is that ANY orbit you can think of intersect this plane, or follows it. Since that thing is not a compact object but a long, uninterrupted cable, ANYTHING in ANY orbit will inevitably smash on it soon or later (and i'm talking about a couple days only here....). In order to built it you have to be sure there is nothing left in orbits (old satellites, debris etc....) and launching anything else is out of the question.....<br /><br /><br /><br /> <div class="Discussion_UserSignature"> </div>

 

[Pooua]

What did the SR-71 have to do with delivering objects to space?