Because let's face it, if you *have* to eat nuclear lunches, you want them to be clean. Coworkers might not be so understanding about your expelling radioactive gas.
I don't see that kind of strength-to-weight ratio being produced any time in the near future.
Pure carbon nanotubes have the required strength-to-weight ratio. The only question is how long before we can develop a composite that binds CNTs together into a material that retains enough of the strength of pure CNTs. Steady progress is being made. Keep an eye on LiftWatch.org for regular updates on this and related techs.
...this neglects the fact that you need to go to geosync orbit rather than LEO, and also that you need to grab an asteroid for the counterweight, and that you need to do on-orbit fabrication of a material barely out of the laboratory right now...
You need to read about more recent deployment plans for the space elevator. Start here.
Things you got wrong:
There are viable deployment plans wherein we only need to launch 100-200 tons to GEO... and these can be divided between several payloads.
No in-orbit fabrication of anything is required. The ribbon is manufactured on Earth.
An asteroid is not required for a couterweight. The initial counterweight will be on the order of perhaps 100 tons, which is feasible to launch, as you point out.
Unless they plan on catching everything they launch again, then we will slowly be slowing the earth down.
True, but very misleading. We will be slowing the Earth down by a NEGLIGIBLE amount.
You know, when you drive a heavy truck East, you are actually slowing the Earth's rotation by a small amount due to the same law of conservation of (angular) momentum.
The Earth is VERY heavy, however. 6.6x10^21 tons. So you would have to move many billions of tons of mass in order to have a measurable effect on the Earth's rotation.
Also, building the space elevator involves moving insane amounts of mass around.... There's no reasonable way to build a space elevator without nuclear propulsion.
We're not talking thousands of tons to launch a space elevator.
We're talking 100-200 tons. And it could be divided into several payloads.
I'm not trying to argue against the idea of nuclear powered rockets here... but they would not be REQUIRED in order to raise a space elevator because the amounts of mass we're talking about are really not 'insane'.
Wrong: a disasterous shockwave is IMPOSSIBLE
on
Clean Nuclear Launches?
·
· Score: 2, Informative
A shockwave that destroys significant amounts of life on Earth isn't impossible.
Sorry to disappont the Kim Stanley Robinson fans, but this simply isn't the case.
Even if the SE breaks at halfway, we're not going to get a catastrophic shockwave. You have to consider the material to know how it's going to behave. First, this thing is VERY light weight. It's also VERY thin. Not much displacement means not much shockwave. Not much weight means it will be easily dampened by the atmostphere.
After a break, yes, the end near the break will start off at a pretty high velocity because of the tension that it was under. But -- and this is part of the design -- carbon is combustible and will BURN UP in the atmosphere if it's travelling too fast.
There is NO WAY that a falling CNT ribbon will be catastrophic, even to those right underneath it.
You'd be better advised to worry about payloads that might fall off it. But even these would be engineered to have re-entry systems for just such an eventuality.
As another poster has pointed out, you are arguing on out-dated information. Let's look at each point in turn.
Even if they could make carbon nanotube strands longer than 10 microns
Individual CNTs have been manufactured up to lengths of several centimeters at least. This article is from May of last year, and progress has been made since then. This is not thousands of kilometers, of course, but it does not need to be, since we're going to be using CNT composite materials rather than pure CNTs.
and even if they could braid them in a fashion where they wouldn't slip
We have been able to manufacture CNT composite materials on the order of meters in length with strengths on the order of several GPa's now for a couple of years. Currently, steady progress is being made to increase the strength of the composites to the required ~100 GPa.
they'd still have to launch a few thousand tons worth of stuff into geosynch orbit
Try about 100 metric tons placed in LEO. (Here's a reference for an older deployment strategy that comes in at 122,000kg.) Hubble weighs 11. Mir was more...
And then they'd have to figure out how to avoid getting the tether cut by space debris
This is the hardest problem, but not insurmountable even within a couple of decades. The ribbon will be made very resilient to micrometeorite damage. (Not saying it won't take damage... just that it will continue to work fine in spite of some damage.) For larger debris, it becomes considerably less likely to collide with the ribbon, but active avoidance will be used to move the ribbon out of the path of larger pieces of junk. Also note that once one ribbon is
up, the cost of raising a second one lowers dramatically. The first order of business for SE1 will be to raise the components for SE2...
There is some serious research going on here, and it's looking very encouraging. See LiftWatch.org for regular news, links to research and companies, discussion forums, images, etc.
Carbon nanotubes and the idea of using lasers to do work both hearken to another up-and-coming scientific advancement destined to save humankind: the Space Elevator!
We've got links to this story and many more... plus reports on the recent SE conference in Santa Fe, discussion forums, image galleries, etc. Check it out!
I've put in a request... hopefully our headlines will be added as a slashbox here soon.
It sounds like the conference was a success. Critics were given some podium time, and Arthur C. Clarke updated his now famous prediction to a bolder "10 years after everybody stops laughing". (He originally said "50 years after everyone stops laughing".)
At LiftWatch we're putting up reports by people who attended, as they become available. Blaise Gassend, one of the speakers, posted some good notes on the first two days of the conference.
The article mentions that Disney has contributed the enhancements back to the community. So unless we want to pay $60 for Crossover Office, where do we get our hands on the source code?
Slashdot Mirror
Here's Chapter 5 of Bradley Edwards' phase-I, NASA-funded study, which details such a low-initial-payload deployment strategy.
Because let's face it, if you *have* to eat nuclear lunches, you want them to be clean. Coworkers might not be so understanding about your expelling radioactive gas.
Pure carbon nanotubes have the required strength-to-weight ratio. The only question is how long before we can develop a composite that binds CNTs together into a material that retains enough of the strength of pure CNTs. Steady progress is being made. Keep an eye on LiftWatch.org for regular updates on this and related techs.
You need to read about more recent deployment plans for the space elevator. Start here.
Things you got wrong:
--
LiftWatch.org - Space Elevator News
True, but very misleading. We will be slowing the Earth down by a NEGLIGIBLE amount.
You know, when you drive a heavy truck East, you are actually slowing the Earth's rotation by a small amount due to the same law of conservation of (angular) momentum.
The Earth is VERY heavy, however. 6.6x10^21 tons. So you would have to move many billions of tons of mass in order to have a measurable effect on the Earth's rotation.
Not to worry.
--
LiftWatch.org - Space Elevator News
LiftWatch.org - regular news updates, links directory, etc. All about space elevators and related techs.
We're not talking thousands of tons to launch a space elevator.
We're talking 100-200 tons. And it could be divided into several payloads.
I'm not trying to argue against the idea of nuclear powered rockets here... but they would not be REQUIRED in order to raise a space elevator because the amounts of mass we're talking about are really not 'insane'.
--
LiftWatch.org - Space Elevator News
Sorry to disappont the Kim Stanley Robinson fans, but this simply isn't the case.
Even if the SE breaks at halfway, we're not going to get a catastrophic shockwave. You have to consider the material to know how it's going to behave. First, this thing is VERY light weight. It's also VERY thin. Not much displacement means not much shockwave. Not much weight means it will be easily dampened by the atmostphere.
After a break, yes, the end near the break will start off at a pretty high velocity because of the tension that it was under. But -- and this is part of the design -- carbon is combustible and will BURN UP in the atmosphere if it's travelling too fast.
There is NO WAY that a falling CNT ribbon will be catastrophic, even to those right underneath it.
You'd be better advised to worry about payloads that might fall off it. But even these would be engineered to have re-entry systems for just such an eventuality.
--
LiftWatch.org - Space Elevator News
As another poster has pointed out, you are arguing on out-dated information. Let's look at each point in turn.
Individual CNTs have been manufactured up to lengths of several centimeters at least. This article is from May of last year, and progress has been made since then. This is not thousands of kilometers, of course, but it does not need to be, since we're going to be using CNT composite materials rather than pure CNTs.
We have been able to manufacture CNT composite materials on the order of meters in length with strengths on the order of several GPa's now for a couple of years. Currently, steady progress is being made to increase the strength of the composites to the required ~100 GPa.
Try about 100 metric tons placed in LEO. (Here's a reference for an older deployment strategy that comes in at 122,000kg.) Hubble weighs 11. Mir was more...
This is the hardest problem, but not insurmountable even within a couple of decades. The ribbon will be made very resilient to micrometeorite damage. (Not saying it won't take damage... just that it will continue to work fine in spite of some damage.) For larger debris, it becomes considerably less likely to collide with the ribbon, but active avoidance will be used to move the ribbon out of the path of larger pieces of junk. Also note that once one ribbon is up, the cost of raising a second one lowers dramatically. The first order of business for SE1 will be to raise the components for SE2...
There is some serious research going on here, and it's looking very encouraging. See LiftWatch.org for regular news, links to research and companies, discussion forums, images, etc.
Carbon nanotubes and the idea of using lasers to do work both hearken to another up-and-coming scientific advancement destined to save humankind: the Space Elevator!
I've put in a request... hopefully our headlines will be added as a slashbox here soon.
It sounds like the conference was a success. Critics were given some podium time, and Arthur C. Clarke updated his now famous prediction to a bolder "10 years after everybody stops laughing". (He originally said "50 years after everyone stops laughing".)
At LiftWatch we're putting up reports by people who attended, as they become available. Blaise Gassend, one of the speakers, posted some good notes on the first two days of the conference.
Also check out LiftWatch.
A shameless plug for my new hobby site:
LiftWatch
A friend and I started this site a week ago because we noticed an apparent lack of a centralized news source for space elevators and related concepts.
Please check out the site and contribute!
We're hoping to turn it into the defacto space elevator portal site.
The article mentions that Disney has contributed the enhancements back to the community. So unless we want to pay $60 for Crossover Office, where do we get our hands on the source code?
Anyone got a link?
I don't know if it would classify as an allergy, but I'd certainly have a strong sensitivity to having a nut transplant.