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Thread: Living on Mars?
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2017-12-04, 11:55 AM (ISO 8601)
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Re: Living on Mars?
Yeah, as far as I'm concerned the big problem with the climbers is that we don't know if they'll hold up when we get to full scale, we can already make proof of concept climbers or scaled down versions if we need to. We don't know if the ribbon is even possible, we have theoretical materials that might be able to maintain the strength needed at the required length, but it's definitely a 'might' not a 'will'.
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2017-12-04, 12:16 PM (ISO 8601)
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Re: Living on Mars?
Last edited by Bohandas; 2017-12-04 at 12:17 PM.
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2017-12-04, 12:21 PM (ISO 8601)
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Re: Living on Mars?
Last edited by Bohandas; 2017-12-04 at 01:13 PM.
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2017-12-04, 12:39 PM (ISO 8601)
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Re: Living on Mars?
Most people would also not want to live permanently in a place with no sanitation, clean water or access to reliable sources of food, and yet over a billion people do so anyway. If being on the space station means having a job and a future for your kids, there'd be queues, no matter how bad the living conditions were, so long as they were better than the ones on Earth.
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2017-12-04, 12:49 PM (ISO 8601)
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2017-12-04, 12:50 PM (ISO 8601)
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Re: Living on Mars?
How high would that elevator reach? Generally a space elevator terminates at the "Geo"synchronous orbit, as I understand it. But for the tidally-locked Moon, that's a point roughly 385,000 km away (Earth is in a "Geo"stationary orbit around the moon). For the lunar elevator, are they looking at a tower rather than a ribbon?
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2017-12-04, 01:03 PM (ISO 8601)
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2017-12-04, 01:03 PM (ISO 8601)
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Re: Living on Mars?
Oh, yes, ludicrously long. That said, it seems I mispoke - wikipedia does not susgest steel as a construction material, so wherever I read that was probably wrong. Interestingly, I see in the wikipedia that the design calls for a double elevator, anchored (as it must) at the equator, but with a secondary ribbon going to the pole, where the lunar base is more realistically to be placed. I had not seen that design before, but it makes sense, if it is achievable.
As to ribbon vs tower, (assuming "ribbon" hangs from the planet and "tower" rests on the planet), it would still be a ribbon, held taut by the moon's 28-day long spin on its own axis. Although I suspect that to a certain degree, the elevator might also be assisted by Earth's gravity pull on its end.
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2017-12-04, 01:47 PM (ISO 8601)
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Re: Living on Mars?
So? You were arguing that we can't get more than "a few millimetres". But we never expected to make one huge molecule, it's the fibre we were always after - and it is the technology that already exists. Now we simply need to perfect it.
"2.4 GPa" demonstrates that Pasquali fibre is not some mush. We've got to 5.6 GPa by 2015 (Kumar), and will keep on improving it for years to come - despite not even spending any significant amount of money on this research. If we'll get serious, we may even have space elevator in a decade. But we can't have that, can we? Which is why "space elevator is a pipe dream" is being repeated endlessly.
Hardly anything new. Moreover, it is the _existing_ (circa 2006) technologies that are investigated.
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2017-12-04, 02:14 PM (ISO 8601)
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Re: Living on Mars?
Single walled nanotubes is not equivalent to multiwalled nanotubes. Being able to produce the latter doesn't do squat for the prospects of the space elevator, that cannot use them. Only the former count. And I stand by my statement that we have not figured that out yet. Your claim that we are now making it by the meter and that only "politics" stands in the way is particularly misdirecting if not outright wrong.
So yes, we have not produced more than a few millimeters (a few dozen, as it turns out) of a material capable of building the space elevator. You telling me that a similar, but much weaker, material also exists is irrelevant.
No, we won't. The upper theoretical limit for multi-walled carbon nanutubes is significantly below the minimum necessary for the space elevator. Just because single and multiwall nanotubes are both carbon nanotubes, the research into one does not mean we have figured both out.
And this just reads like the ravings of a conspiracy theorist, so I'm done with you.
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2017-12-04, 02:20 PM (ISO 8601)
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Re: Living on Mars?
The bolded part is an assumption, this is somewhere where we're not sure where the practical upper limits are. Maybe we can create magical 200GPa carbon nanotubes, maybe doing so takes more energy than launching 1030 rockets and high sophisticated nanofabrication, we don't actually know.
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2017-12-04, 02:58 PM (ISO 8601)
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Re: Living on Mars?
Research stations (basically like the ISS) seem perfectly reasonable, but I don't think Mars could be regarded as habitable for any permanent settlers. Microgravity does really strange and uncomfortable things to a body and even though Mars has some gravity, I don't think the human body will work properly in such an environment. But that's just for healthy adults. When you think of permanent settlement you also have to include developing children and I actually don't even want to imagine what it would do to them. Bone, muscle, and nerve development would all probably turn our very funky, likely leading to severe disabilities.
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2017-12-04, 03:00 PM (ISO 8601)
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Re: Living on Mars?
Sun rising tomorrow in the east is also an assumption. It simply happens every morning. Day after day. We aren't sure whether it will do so tomorrow. Maybe it will magically rise again, maybe not. We don't actually know, do we?
To put it another way: instead of putting the label of "assumption" on anything and pretending the each and every possible event has the same chance to happen, we need to evaluate how probable the "assumption" is - since every potential event can be called an assumption.
In this specific case, we have new technology that not only did not exhaust basic approaches (we literally get new methods every year), but didn't even perfect any of the existing. Thus, it is practically certain we will get much better at making carbon nanotubes, and we will be getting better soon. Leaps of qualitative improvement (more than doubling within 2 years) suggest that improvement will be significant.
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2017-12-04, 03:26 PM (ISO 8601)
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2017-12-04, 03:36 PM (ISO 8601)
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Re: Living on Mars?
No, it is an expectation. There are reasons it might not rise in the East (international consensus to exchange the directions of east and west, suddenly being put out by a highly advanced alien race), but it is expected it will.
To put it another way: instead of putting the label of "assumption" on anything and pretending the each and every possible event has the same chance to happen, we need to evaluate how probable the "assumption" is - since every potential event can be called an assumption.
In this specific case, we have new technology that not only did not exhaust basic approaches (we literally get new methods every year), but didn't even perfect any of the existing. Thus, it is practically certain we will get much better at making carbon nanotubes, and we will be getting better soon. Leaps of qualitative improvement (more than doubling within 2 years) suggest that improvement will be significant.
Let me put it this way, we might be able to make carbon nanotubes that strong. However, there is literally no guarantee that a) we will do it within the lifetime of any poster on this forum, and b) that we won't hit a roadblock in say 17 months that caps the tensile strength of the carbon nanotubes due to the manufacturing methods not being precise enough or some other problem. Instead of looking at things that are decades to centuries away, like space elevators and fusion plants, why don't we look at stuff that is years away, like better fission reactors?
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2017-12-04, 03:42 PM (ISO 8601)
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Re: Living on Mars?
One problem with living on Mars that I have not seen mentioned yet: Dust. It will be everyplace. And it will be a much bigger problem on Mars than it is here on Earth.
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2017-12-04, 03:53 PM (ISO 8601)
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Re: Living on Mars?
And how is it different from expectation of technological progress?
It's like saying that we should account for sun rising only during November of 2017. And that happened only a few times so far.
Why isn't expectation of improvement based on the fact that we've been getting better things we were doing for centuries?
Before making statements such as this, you need to remember the sun: is it possible to say "there is literally no guarantee that sun will rise tomorrow in the east"? If it is - then your statement is meaningless.
As I've pointed out, we have multiple approaches and none had been developed exhaustively. I.e. the technology is not mature. Consequently, chances of some critical roadblock are negligible.
What does this have to do with the topic?
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2017-12-04, 10:28 PM (ISO 8601)
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Re: Living on Mars?
Crime rates in small communities are vastly higher than they're often depicted, and corruption in general is yet more common.
The maximum material strength being lower than the necessary minimum is a critical roadblock, and their presence is hardly a negligible chance.
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2017-12-05, 12:32 PM (ISO 8601)
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Re: Living on Mars?
There is no "maximum material strength" as such. There is maximum theoretically possible (which is in low hundreds of GPa and cannot be a "critical roadblock"), and the maximum which we can do/will be able to actually achieve. The latter heavily depends on the production method used.
I.e. there is no one single maximum. For each approach the maximum will be different.
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2017-12-06, 09:24 AM (ISO 8601)
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Re: Living on Mars?
I think the point of twisted rope is more about getting the strands interconnected. If you have a long rope of a hundred strands, and each strand is broken, but each one in a different spot, the rope still has 99% of its original strength, while just a bundle of straight fibers would have been completely severed by that point. Something as tiny as carbon nanotubes, which we probably can't make long enough to individually go all the way up to geosynchronous orbit anyway, would most likely benefit quite a lot from some sort of twisting/braiding/webbing.
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2017-12-06, 10:07 AM (ISO 8601)
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Re: Living on Mars?
...
You quoted me to talk about this, but not sure why. I was talking about conditions on Earth, not on Mars, and how some people would find life in a space station an upgrade to their conditions here.
I can't comment on the generating water from permafrost - would need to know how much of it is present in likely landing sites (I'm aware one of the poles has plenty of frozen brine, but poles make for very poor base locations). We are also quite proficient at this point at water recycling, so it's not usually a concern (and it might be that any ship that takes humans outside the magnetosphere for any amount of time will use water as radiation shielding anyway, so you'd end up with plenty of water when you got to Mars).
As I understand it, it's not any "stronger" by MPa measures. Braiding means you need a longer thread to cover the same distance, which means that it is overall heavier, which if anything reduces its ability to be a space elevator tether.
However, as Lvl 2 Expert points out, you braid because real life is a bitch, and braiding allows a form of redundancy and safety that means any stress due to breaking is kinda shared by all the threads at once, which leads to an overall stronger cord by the measure that matters (likelihood of snapping). It also may be the only way to create the tether. I doubt we will ever create strands of anything 100,000 km long, so braiding is the only way we will get tethers that long.
So, returning to your question: yes, braiding carbon nanotubes is being done, whenever the practical applications of them are discussed, vs. the single-strand properties.
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2017-12-06, 05:46 PM (ISO 8601)
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2017-12-07, 03:01 AM (ISO 8601)
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2017-12-07, 09:18 AM (ISO 8601)
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Re: Living on Mars?
Visible at the north pole, present but under CO2 ice at the south pole:
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2017-12-07, 10:12 AM (ISO 8601)
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Re: Living on Mars?
... they don't? The tether is absurdly light. That's the point, and the problem of why we can't build it. It's like being hit with a feather in freefall... except it is much, much, much lighter than a feather.
Yes, the whole thing will weight tons, but stretched out over 100,000 km. The scenarios I have seen for collapse suggest that it will mostly burn up in the atmosphere, or get blown all over the place by the winds. But it's not going to hurt much, because it doesn't have the density. Admitedly, I haven't seen similar scenarios modeled for, say, Mar's thin atmosphere or the Moon's no atmosphere, but I can't imagine that even in vacuum freefall a feather would hurt that much.
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2017-12-07, 10:48 AM (ISO 8601)
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Re: Living on Mars?
Depends how long it has to accelerate in vacuum freefall. Given sufficient distance, a featherweight object left to fall on the Moon would reach a speed of 2.38km/sec (Lunar escape velocity) or nearly so. A typical feather might mass 0.01g, and travelling at 2380m/s would have a kinetic energy of about 56J. Doesn't sound like much, but it's in the same ballpark as an arrow fired from a short bow, and since we're not talking about an actual feather but a broken fragment of the space elevator, it'll probably be quite sharp as well, and may also be heavier than that 0.01g figure I mentioned above--we only have to increase that to 0.1g to have an object with the same kinetic energy as a .45 ACP round fired from a pistol.
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2017-12-07, 11:01 AM (ISO 8601)
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Re: Living on Mars?
To put it bluntly, human civilization is based on massive agricultural investment in narrow bands of prime land and then sent to large population centers. Almost the entire population is located within subtropical and temperate zones with arable land, all major nations require major ports to be economically viable, and the ecological fertility of Earth is at the boiling point in many places despite those places being little more then camps for people to live in while receiving grain out of more fertile zones.
Civilization, in other words, cannot be exported to other planets because grain shipments from Kansas can't reach there. If we want to make Mars habitable we might at least try settling the Sahara desert first.
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2017-12-07, 11:32 AM (ISO 8601)
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Re: Living on Mars?
Fair enough. I haven't double checked your math, but it sounds reasonable. Now, on the moon that wouldn't concern me much (since th tether would be unlikely to hit anything), but I do wonder how much the thin atmosphere of Mars would manage to slow down a Mars tether.
I don't disagree with any of this, except in a general "we really should stop taking over ecosystems and turning them into our private farms"... but I make an explicit exception to the Sahara, because It'd be nice to turn its expansion around.
That said, do you have an opinion on the development of urban vertical farms? A recent article went through the history of the approach, saying that it looks like tech is almost there to make them economically viable*. We may soon have the ability to grow food at the population centers, which would be an interesting development in the nature of human civilization, although I'm ambivalent of how big the consequences would be.
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*It also admits to having said so 5 years ago, but the cost curve is definitely trending in the right direction, so they should be viable in our lifetimes, even if this particular one also failsLast edited by Grey_Wolf_c; 2017-12-07 at 11:33 AM.
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2017-12-07, 11:35 AM (ISO 8601)
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Re: Living on Mars?
I will add one observation;
If humans don't colonize space; we will die.
We (the human species) have a choice, die on Earth when Sol dies, or, travel into space to colonize elsewhere and live on as a species when Sol dies.
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2017-12-07, 11:41 AM (ISO 8601)
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Re: Living on Mars?
Humans will die whether or not we colonize space.
If all we are worried is about the death of the Sun, I think we can push of the issue for several orders of magnitude longer than humans have existed, and let technological innovation continue to make the problem easier.
Now, I am sympathetic to the reality that civilization-killing asteroids and other single-planet dangers do exist, but if one of those happens, and the Mars colony depends on Earth for survival, we haven't actually put our eggs in more than one basket. And the bottom line right now is that Mars does not sound independently viable.
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