Carbon Nano Technology Thread

[chris_in_space]

I have not yet said what material the wire would be made of... <img src="/images/icons/wink.gif" /><br /><br />How about a wire made of carbon nanotubes as well. Current chemistry knowledge shows that molecules made out of 6 carbon atoms in a hexagone are very good conducters in the plane of the hexagone. Carbon nanotubes also have this configuration. Unfortunately I havn't been able yet to find reliable sources for the conductivity of a single carbon nanotube in the direction of the tube. Also the high conductivity would be there only if the carbon nanotube is made out of a single piece and not incorporated in a composite epoxy matrix as for the mechanical CNT cable. It means you'd have to build a single CNT long of more than 36000km. We're not yet there, but still I carry on with my hopes that in a couple of decades it will be availible... <br />

 

[barrykirk]

Well, assume that the CNT material is just as conductive as pure copper. <br /><br />First problem is that you need two conductors minium to carry power. I'm assuming that it will be DC and not 3 phase AC.<br /><br />So, assuming that the conductors are as good as copper and the intervening material is a really good insulator.<br /><br />What is the cross sectional area of the elevator cable. Remember that you have to divide by two because of two conductors and then subtract out the insulator section.<br /><br />The insulator section will have to be pretty good to support any voltage difference. Arcing would be a major problem since that would probably destroy the elevator cable.<br /><br />There is also the problem of coupling the car to the cable in a way that doesn't scratch or damage the cable in any fashion. That isn't necessarilly a trival problem.<br /><br />Look at the electrical coupling for a electric rail car, and you see sparks as it goes down the track . On a space elevator those sparks would be very damaging to the cable.<br /><br />Any case, assuming you solve all of those problems. Look at the cross sectional area of the conductor. Remember that you have to transmit the current tens of thousands of miles. To transmit any significant power is going to require significant voltage or your ohmic losses are going to eat up all of the power.<br /><br />If your transmitting power on the ground for hundreds of miles. The typical voltage is 115KV Three phase AC.<br /><br />At 115KV you need monster large insulators. The climber car is going to have to deal with that huge voltage. Very few motors are built at that voltage, because the insulation requirements are huge. <br /><br />Even at that voltage, there are significant power loses over a couple of hundred miles. At 10,000 plus miles, the power losses would be staggering.

 

[chris_in_space]

Most of the problems you mentioned can be solved.<br /><br />Still don't forget I didn't said the concept is absolutely feasible. I still have to get values for the conductivity of a single carbon nanotube. It could be lower or higher than that of copper. It's still open to question. So until I get reliable values for this conductivity everything is still open. It could work as it could be unfeasable. I just don't know right now...<br />

 

[barrykirk]

fair enough

 

[jatslo]

<font face="verdana">Spider Web Products? Much stronger than steel, and...<blockquote><font class="small">In reply to:</font><hr /><p><font color="yellow">The carbon nanotube fibers do not yet have enough tensile strength to support a space elevator off the earth. At least 70 GPa's is needed and many consider 100 to be far more realistic. No mention of this in your posts, or the articles. However, it's still a thread (grin) which is the most likely to become practical, in time. Altho not certain.</font>p><hr /></p></blockquote>...some of these strands are stronger than steel strands of the same thickness; the microstructure of this material is under investigation for potential applications in industry (Space Elevators?).</font>

 

[barrykirk]

bump, <br /><br />well most of the stuff here is devoted to CNT for use in space elevators.<br /><br />With Space tethers the web sites I've visted seem to think that you can really enhance your rocket performance with a tether that reduces your required velocity to reach orbit by 2.5 Km/sec.<br /><br />And that velocity can be reached fairly easily with commercially available products, Spectra 2000 which is about 3.5 GPa and fairly low density, less than water. I saw Ti Va fibers mentioned in this thread with 5 to 6 GPa, but it is much higher density than Spectra 2000 and it's strength to weight that is more important than total strength.<br /><br />Any case, the talk is that about 100GPa CNT would be required for a space elevator.<br /><br />No this is pure conjecture on my part. But it would seem to me that 40 to 50 GPa CNT will be available and much cheaper than 100 GPa CNT.<br /><br />At 40 to 50 GPa, a space elevator is still not possible because the equation for taper ratio is really unforgiving. But what kind of tether could you build with 40 to 50 GPa?<br /><br />LEO has an orbital velocity of 7.8 Km/sec<br /><br />Would a tip velocity of 7.8Km/sec be possible with 40 to 50 GPa tether with a reasonable taper ratio.<br /><br />I would think so. Is anybody who understands how to do those calculations listening? I'm just guessing on the numbers.

 

[publiusr]

Bump

 

[jmilsom]

What's happening in Carbon Nanotech these days? I keep up to date with the major science mags, but have not seen anything. After all the fanfare with the continuous threads it seems they've all hit a wall. Anyone got anything new? <div class="Discussion_UserSignature"> </div>

 

[nexium]

Several claims by promoters, maufactures and scientists are encouraging, but perhaps not reality. www.liftport.com click on forums near the bottom of the page. Neil

 

[jmilsom]

Thanks Neil, that's a great site - a lot to read. <div class="Discussion_UserSignature"> </div>