(no subject)
2003-09-13 10:05![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
blufiveThe Guardian reports on a conference on space elevators being held in Santa Fe. There's at least one wonderful howler in the report:
While I'm not up to doing the maths to work out how strong the cable would need to be, I have seen figures from people whose mathematical skills I trust, and my engineering training tells me that this stuff is still pure Unobtainium. Thanks to everyone's favourite buzzword, "carbon nanotubes", we can just about predict the possible development of a material that might just be strong enough. Right now, the main ingredient for this material costs about a zillion dollars per gramme, and is only available in minute quantities. Which also have poor quality control. In short, we still can't make pieces of this material big enough to do sensible mechanical testing to work out if it's as strong as we think it will be.
Of course, you're going to need at least 50,000km (probably more) of cable, which is probably going to be several metres thick, minimum. It's going to mass hundreds of thousands of tonnes. You also need to get this cable into geostationary orbit. At this point I will just say "launch capacity" and leave it at that.
Finally, if the material is only just strong enough, there's alwasy the risk it will break. You do not want a space elevator cable to break. It won't land gently in a nice neat little pile around the ground end. Remember, this thing will be long enough to wrap around the planet with cable left over. In any case, the higher parts of the cable will hit pretty hard when they land. How many cities are there within, say, 250km of the equator?
So, while the basic science is sound, it's still in la-la land from an engineering perspective. I'd love to see one, but I'm sceptical that we'll have the engineering capacity in my lifetime. From the Guardian again:
At [...] 36,000km from Earth [...] objects take a year to complete a full orbitAhem. Yes. Try "24 hours". Apart from that, it's mostly on-the-ball.
While I'm not up to doing the maths to work out how strong the cable would need to be, I have seen figures from people whose mathematical skills I trust, and my engineering training tells me that this stuff is still pure Unobtainium. Thanks to everyone's favourite buzzword, "carbon nanotubes", we can just about predict the possible development of a material that might just be strong enough. Right now, the main ingredient for this material costs about a zillion dollars per gramme, and is only available in minute quantities. Which also have poor quality control. In short, we still can't make pieces of this material big enough to do sensible mechanical testing to work out if it's as strong as we think it will be.
Of course, you're going to need at least 50,000km (probably more) of cable, which is probably going to be several metres thick, minimum. It's going to mass hundreds of thousands of tonnes. You also need to get this cable into geostationary orbit. At this point I will just say "launch capacity" and leave it at that.
Finally, if the material is only just strong enough, there's alwasy the risk it will break. You do not want a space elevator cable to break. It won't land gently in a nice neat little pile around the ground end. Remember, this thing will be long enough to wrap around the planet with cable left over. In any case, the higher parts of the cable will hit pretty hard when they land. How many cities are there within, say, 250km of the equator?
So, while the basic science is sound, it's still in la-la land from an engineering perspective. I'd love to see one, but I'm sceptical that we'll have the engineering capacity in my lifetime. From the Guardian again:
[Arthur C] Clarke [...] once said a space elevator would only be built "about 50 years after everyone stops laughing"Well, on Sky News' "tomorrow's front pages" thing last night, they had a grand old giggle.
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no subject
Date: 2003-09-13 07:31 (UTC)The numbers KSR uses for the elevator collapse in Red Mars seem to show that one collapsing on earth, no matter how thin, would dump a lot of energy into the atmosphere.
Engineeringwise, we're actually not that far off. We could actually build one today, using current materials. It would be big, and bulky, but it can be done. It's the smaller, dropped from orbit, versions that require more exotic materials. Oh, and an asteroid sized counterweight...
There is an interesting alternative, which is a lot cheaper, requires much lower tensile strengths, and that's the rotating skyhook. Imagine a rotating 2500 km cable in a Molniya orbit that dips the end of the cable in for a few minutes every few hours... and then hook stuff onto it as it passes through the atmosphere. It'll be moving quite slowly, so wouldn't even require complex supersonic pickups...
no subject
Date: 2003-09-14 05:06 (UTC)There's another kind?
Elsewhere:
Yes, the less ambitious skyhooks look more feasible from an engineering perspective, though hooking something onto the end of even a subsonic cable-end in mid-air would still be lively.