Living on Mars?

[hamishspence]

This is no different from saying "Isaac Asimov had FTL drives. Therefore, eventually, they would need to exist, to support a thriving space industry."

Clarke, Asimov et al are not constrained by physical realities. Clarke was able to assume a material capable of holding up its own weight even when it weighted megatons.

As he pointed out:

With a stepped, or tapered, cable it would be theoretically possible to construct the space elevator from any material, however weak. You could build it of chewing gum, though the total mass required would probably be larger than that of the entire universe. For the scheme to be practical we need materials with a breaking length a very substantial fraction of escape length.

Presumably, the super-massive cable would have a similar density to the tiny cable, but be the tiny cable, scaled up (many tiny cables, making up one immense one).

The first stage, would be much lighter, than the final cable:

The space elevator may be regarded as a kind of bridge, and many bridges begin with the establishment of a light initial cable -- sometimes, indeed, no more than a string towed across a canyon by a kite. It seems likely that the space elevator will start in the same way with the laying of a cable between geo stationary orbit and the point on the equator immediately below.

This operation is not as simple as it sounds, because of the varying forces and velocities involved, not to mention the matter of air resistance after atmospheric entry. But there are two existing technologies which may provide a few answers, or at least hints at them.

The first is that of submarine cable laying, now considerably more than a century old. Perhaps one day we may see in space something analogous to the triumphs and disasters of the Great Eastern, which laid the first successful transatlantic telegraph cable -- the Apollo Project of its age.

But a much closer parallel, both in time and sophistication, lies in the development of wire-guided missiles. These lethal insects can spin out their metallic gossamer at several hundred kilometres an hour. They may provide the prototype of the vehicle that lays a thread from stationary orbit down to earth.

Imagine a spool, or bobbin, carrying some 40000 km of filament, a few tenths of a millimetre thick at the outer layers, and tapering down to a tenth of this at the core -- the end that finally reaches Earth. Its mass would be a few tons, and the problem would be to play it out evenly at an average velocity of a kilometre a second along the desired trajectory. Moreover, an equivalent mass has to be sent outwards at the same time, to ensure that the system remains in balance at the stationary orbit.

My perspective, is that an industrial-size space elevator might be dangerous if broken - but that this potential danger simply has to be accepted, and planned for - not just assuming "whole thing will burn up harmlessly".

[Grey_Wolf_c]

Presumably, the super-massive cable would have a similar density to the tiny cable, but scaled up.

No, that does not follow. The length is the same and the width and depth are about the same, but one is heavier than the other by multiple orders of magnitude. Therefore, its density is equally larger by multiple orders of magnitude.

Edit: also, I'm done with you until you stop quoting sci-fi writers as if they were authoritative.

GW

[hamishspence]

No, that does not follow. The length is the same and the width and depth are about the same, but one is heavier than the other by multiple orders of magnitude.

Length is the same - but width and depth are vastly higher.

[Grey_Wolf_c]

Length is the same - but width and depth are vastly higher.

So then they are not comparable, and I'm still waiting for you to substantiate your assertion that the collapse of any space elevator (including those that DON'T weight megatons) would be dangerous.

GW

[hamishspence]

So then they are not comparable, and I'm still waiting for you to substantiate your assertion that the collapse of any space elevator (including those that DON'T weight megatons) would be dangerous.

I'm not sure how dangerous the 750 ton one would be if it broke. Probably not very.

I could see the middle of the collapsing cable moving faster than the terminal velocity of a feather, but slow enough not to have burned up before it hits something in its path though.

There's also the question of what scales in between 750 tons and 1 million tons, are worth taking into consideration, when it comes to "possible space elevators that might be constructed in the future".

[Bohandas]

If he talks about "megatons" of material, then he too, like Nova, is wrong. NASA designs calls for a 750 ton cable. Now, taking actual engineer's word for it, it would have less density than a feather. The terminal velocity of a feather in Earth atmosphere is not sufficient for it to cause any kind of damage, no matter how many feathers you dump at once from high orbit, nor how it wraps around the Earth.

What if they were all stuffed into a 30 foot wide, 100 foot tall conical pillow made of flame-retardant material

[hamishspence]

Regarding the possibility of many small elevators, rather than one big one - it should be noted that if there's a break in one, the collapsing elevator may hit the others:

http://gassend.net/spaceelevator/problems/index.html

[Grey_Wolf_c]

What if they were all stuffed into a 30 foot wide, 100 foot tall conical pillow made of flame-retardant material

That'd be an impressive feat of sabotage, I'll grant you that. Imagine if they also added boosters and covered it in frictionless paint.

GW

[Lord Torath]

I was answering a post who claimed that we had to leave Earth before the death of the Sun. With a seven billion year deadline, I really don't think that leaving "right now" is at all a concern.

We actually only have 2-3 billion years. In that time, the sun will have heated up enough to fry all life on Earth. So we only have half of forever to figure out how to leave.

A feather-density object, even if very massive, will hit terminal velocity almost immediately. First, there is the issue of air drag. Then there is the issue of bouyancy. These forces will contribute to a very low terminal velocity, and a huge deceleration. How massive an elevator are we realistically considering, 750 tons, + car? ROund it up to a thousand tons.

The Chelybinsk meteor was 65 feet in diameter and had a mass or 12,000 - 13,000 metric tons. It did not reach the surface, but exploded at high altitude. Our elevator fragments are likely to have an initial velocity much lower than that of the meteor. After all, the elevator is at rest at 22,000 km up, while the much more massive meteor was already moving along very quickly. It's estimated to have been moving at 60 -70,000 km/h. our cable would be lucky to accelerate to 6,000 km/h.

The Chelybinsk meteor had a mass an order of magnitude larger than our elevator cable, and a velocity another order higher than the cable. Energy goes by mass and square of velocity, so our cable will have three orders of magnitude less energy than the Chelybinsk Meteor. To my knowledge, there were no fatalities from the meteor (although a couple thousand were injured by flying glass). Reducing the damage by 3 orders of magnitude means under ten people will be injured by our falling tether.

[LordEntrails]

Simple answer: transhumanism.

...

In terms of making human life beyond the earth viable you cannot avoid considering changing the 'human life' part of the equation and it may in fact be the part the most amenable to change.

You're supporting my statement, not contradicting it. We need to develop technologies. I'm not argueing which ones.

I was answering a post who claimed that we had to leave Earth before the death of the Sun. With a seven billion year deadline, I really don't think that leaving "right now" is at all a concern.

I think you are caught up in defending your other ideas without considering what I am trying (poorly?) to communicate. My statement was not about exo-colonization prior to the end of Sol (though agreed that is the final issue to deal with), or when it gets too hot, or when an asteroid hit, or any other single possible event. The point I'm making is that as some time in the future, some event will happen that will end life on Earth. I could care less about debating which event or when. Such doesn't matter to the single point, that at some time, life on Earth will end.

You are engaging in a fallacy that the only way to develop the technology needed is colonize other planets. Such argument is, in a word, nonsense. Like multiple people have pointed out, we'd be better served colonizing the deserts/poles/sea bottoms of the Earth first. It will teach us far more, far safely, far cheaper, with far more immediate benefits.

Thanks for trying to politely insult me. Again, you misunderstand me. I am not argueing. I'm also not stating a preference for any one technology or effort/project except to say that at some point the human race must figure out a way to live outside of our solar system or die. I'm not saying it should be this century or in the next billion years. It just needs to happen before the human race becomes extinct (or else we will be extinct).

Seriously, stop relying on sci fi writers, and maybe start looking at the actual engineering designs by NASA and others. The current design for the space elevator tapers at both end, not just the ground, with the widest point midway.

Agree with this. Though many sci-fi writers have great imaginations and try to be potentially feasible, they are not engineers or scientists. I will second the request to please stop trying to present fiction as scientific or technical theory.

A. C. Clarke knows more about what would be needed than most sci-fi writers, at least - being virtually "the father of the space elevator".

Which is to say, not much.

Unless he also somehow knew more about it 50 years ago than NASA engineers today, I'm still not going to take his word over theirs.

Agreed. 50+ year old fictional or theoretical notions are beyond obsolete.

[halfeye]

Your math is wrong, because you don't account for the atmospheric friction, which is crucial when dealing with an object with the density and air resistance of a feather.

I think Bova was exaggerating, for drama, cities are actually pretty rare in terms of land use, the probability of hitting one at random is slight.

However, I really doubt that a space elevator can be as light as 750 tonnes.

As well as that, this thing would be coming in at orbital speeds, and the atmosphere is only 100 miles thin. Down here, 100 miles is a long way to walk, but in terms of the distance to London from New York, it's a very small fraction, and the length of a space elevator is about seven or eight times that.

[hamishspence]

I think Bova was exaggerating, for drama, cities are actually pretty rare in terms of land use, the probability of hitting one at random is slight.

However, I really doubt that a space elevator can be as light as 750 tonnes.

The 750 ton one is a ribbon rather than a circular-cross-section one. 16mm wide at its widest point:

https://en.wikipedia.org/wiki/Space_elevator

One plan for construction uses conventional rockets to place a "minimum size" initial seed cable of only 19,800 kg.[2] This first very small ribbon would be adequate to support the first 619 kg climber. The first 207 climbers would carry up and attach more cable to the original, increasing its cross section area and widening the initial ribbon to about 160 mm wide at its widest point. The result would be a 750-ton cable with a lift capacity of 20 tons per climber.

IMO this was not intended to be "the biggest space elevator that will ever be built" but a prototype - a testbed - a way of proving that space elevators work. Once done, I think, if successful, NASA will plan bigger ones.

[halfeye]

IMO this was not intended to be "the biggest space elevator that will ever be built" but a prototype - a testbed - a way of proving that space elevators work. Once done, I think, if successful, NASA will plan bigger ones.

They have a rocket that can lift 750 tonnes to orbit?

[hamishspence]

They have a rocket that can lift 750 tonnes to orbit?

The 750 ton elevator's built a little at a time, the first component being only 20 tons. It's 750 tons in its final configuration.

The FAQ here:

http://www.pbs.org/wgbh/nova/space/e...-elevator.html

mentions that while the first one would only be able to lift 13 tons, future ones might be able to lift 1000 tons.

Q: How big can the elevator get? What I mean is, what is the maximum amount of cargo that a theoretical elevator could take up into orbit at once?
Anonymous

Edwards: An upper limit is difficult to state, but we have already considered possible systems that could carry up to 1,000 tons. These are very large and require massive engineering but should be viable.

[Rockphed]

The 750 ton one is a ribbon rather than a circular-cross-section one. 16mm wide at its widest point:

https://en.wikipedia.org/wiki/Space_elevator



IMO this was not intended to be "the biggest space elevator that will ever be built" but a prototype - a testbed - a way of proving that space elevators work. Once done, I think, if successful, NASA will plan bigger ones.

In other words if we want more mass possible per climber, we need bigger space elevators. And I'm pretty sure that mass per climber is directly proportional to cross-section area. Nevertheless, a standard shipping container is 2.3 tons empty, so unless we were trying to move raw materials to earth in bulk we can probably do everything we want with 20 ton climbers. If we want to get crazy, we will make 1500 ton ribbons instead.

[Lazymancer]

A. C. Clarke knows more about what would be needed than most sci-fi writers, at least - being virtually "the father of the space elevator".

He is not. The concept dates back at the very least to 19th century (Tsiolkovsky). Modern design was developed in 1950s - by scientists, not Clarke.

However, I really doubt that a space elevator can be as light as 750 tonnes.

That's the initial one. Fully functional will be heavier - but nowhere near the "100 meters in diameter" nonsense.

EDIT: need more sleep. Read as "750 kg"

[hamishspence]

He is not. The concept dates back at the very least to 19th century (Tsiolkovsky). Modern design was developed in 1950s - by scientists, not Clarke.

Hence "virtually" - he was the guy who did a lot of the work of bringing the concept into the public eye - and he's the one that gets mentioned in the above FAQ.

Q: Several science fiction authors have written on this subject. Was Arthur C. Clarke the first? Who has come closest to current theory?
Mitch Burte, Andover, Massachusetts

Edwards: I believe Clarke was the first in a novel, and his most recent novel with Stephen Baxter uses the newest data. They did a very good and accurate job.

Something similar applied with communications satellites, before Sputnik:

http://lakdiva.org/clarke/1945ww/

I'm pretty sure that mass per climber is directly proportional to cross-section area. Nevertheless, a standard shipping container is 2.3 tons empty, so unless we were trying to move raw materials to earth in bulk we can probably do everything we want with 20 ton climbers.

I see moving materials to space in bulk, as one of the main benefits of space elevators (though these might be less "raw" and more "components for stations or spaceships".

That said, shipping stuff down at the same time as stuff is being shipped up, does provide energy that can be used for lifting things up, if it's set up right.

[Rockphed]

I see moving materials to space in bulk, as one of the main benefits of space elevators (though these might be less "raw" and more "components for stations or spaceships".

That said, shipping stuff down at the same time as stuff is being shipped up, does provide energy that can be used for lifting things up, if it's set up right.

I used the size of a cargo container because a lot of our current transportation infrastructure is built around moving things in cargo containers. Pretty much the only things not moved in cargo containers are bulk raw materials (e.g. coal, ore, grain, oil, etc.). And if we want to get those down from space we can either stuff them into descenders with regenerative braking, or just strap some heat shielding and drop them in a body of water. So long as the container is light enough for a climber to carry up, volume doesn't matter a lot, so they could theoretically float.

[hamishspence]

If a cable was built with 1000 ton load climbers, the climber might end up, most of the time, carrying 50 loaded regular containers weighing 20 tons, rather than any single 1000 ton item.

[Rakaydos]

I'm not sure why this thread has gone into SpaceElevator digressions.

Shouldn't we be talking about "150 tons to LEO, refuel, 150 tons to mars" SpaceX BFR?

[hamishspence]

I'm not sure why this thread has gone into SpaceElevator digressions.

Fairly early on, there was the "shipping people to Mars in large numbers will only be viable if we have space elevators" argument:

IIRC, the number was around 100 million people (each with cargo of up to ~1 ton) per year. Doable only if we'll build and master space elevators.

and later, there were questions on whether a crashing space elevator (on Earth, or on Mars) would be dangerous, or not.

[Bohandas]

This is no different from saying "Isaac Asimov had FTL drives. Therefore, eventually, they would need to exist, to support a thriving space industry."

Clarke, Asimov et al are not constrained by physical realities. Clarke was able to assume a material capable of holding up its own weight even when it weighted megatons. But since we don't know of any such material, saying "if the Space Elevator was made of unobtainium and then fell over it would destroy Earth, therefore all Space Elevators are dangerous" is a non-sequitor.

Agreed. I mean, seriously, Clarke's most famous work is a movie about killer robots, magic aliens, and magic alien robots. Take him with a grain of salt.

[Rakaydos]

Fairly early on, there was the "shipping people to Mars in large numbers will only be viable if we have space elevators" argument:



and later, there were questions on whether a crashing space elevator (on Earth, or on Mars) would be dangerous, or not.

But that argument is specius, if the BFR enters operation, and especially if it is later supplemented with something resembling the 2016 ITS rocket.

[Lvl 2 Expert]

They have a rocket that can lift 750 tonnes to orbit?

20 tonnes.

https://en.wikipedia.org/wiki/Space_elevator

One plan for construction uses conventional rockets to place a "minimum size" initial seed cable of only 19,800 kg.[2] This first very small ribbon would be adequate to support the first 619 kg climber. The first 207 climbers would carry up and attach more cable to the original, increasing its cross section area and widening the initial ribbon to about 160 mm wide at its widest point. The result would be a 750-ton cable with a lift capacity of 20 tons per climber.

Still a lot, roughly a truckload, but at least weight wise in reach of our rockets (no idea how the actual cable stretching thing would happen).

[Lazymancer]

Hence "virtually" - he was the guy who did a lot of the work of bringing the concept into the public eye

I'm sorry, but a journalist who gives a tl;dr on Theory of Relativity for general public does not become the go-to expert on the topic.

Why should - much less rigorous - science fiction grant such authority?

Something similar applied with communications satellites, before Sputnik:

So, Sputnik was launched because of Clarke? Those damn commies, stealing American inventions...

---

I'm not sure why this thread has gone into SpaceElevator digressions.

Because any serious expansion into space requires ability to put a lot of stuff into said space. Rockets simply aren't cutting it.

But that argument is specius, if the BFR enters operation, and especially if it is later supplemented with something resembling the 2016 ITS rocket.

What is specious? Let's say we need to put 1 ton of cargo into space per person (I'm being generous).

A very rudimental colonization requires ability to put millions of people into outer space: that means millions of tons.

BFR - if it works - can haul 150 ton at once. I.e. deliver 150 people per launch. To have at least one million of people going into space per year (a very rudimental colonization) we need almost 7,000 BFR launches per year. I don't see this happening.

[hamishspence]

So, Sputnik was launched because of Clarke? Those damn commies, stealing American inventions...

Sputnik wasn't a communications satellite in geostationary orbit - all it did was bleep, in low orbit.

Clarke isn't the only person labelled "the father of satellite communications" but he's one of them.

[Lazymancer]

Sputnik wasn't a communications satellite in geostationary orbit - all it did was bleep, in low orbit.

Clarke isn't the only person labelled "the father of satellite communications" but he's one of them.

Okay. What was the point of the whole "Clarke wrote about satellite communications"?

[hamishspence]

I'm sorry, but a journalist who gives a tl;dr on Theory of Relativity for general public does not become the go-to expert on the topic.

Why should - much less rigorous - science fiction grant such authority?

Clarke understood more about space technology than the average journalist would about relativity, I think. His speciality was hard sci-fi, and he wasn't just a sci-fi writer - he was an inventor, a futurist, and so on:

https://en.wikipedia.org/wiki/Arthur_C._Clarke

As such, he's more of an authority than a soft-sci-fi writer without this kind of background, would be.

Plus, the people actually working on space elevators, emphasise his accuracy, and repeat the same thing he said about how, theoretically, there is no upper limit on the size of a space elevator- or at least, that it is difficult to state.

Q: How big can the elevator get? What I mean is, what is the maximum amount of cargo that a theoretical elevator could take up into orbit at once?
Anonymous

Edwards: An upper limit is difficult to state, but we have already considered possible systems that could carry up to 1,000 tons.

[Bohandas]

BFR - if it works - can haul 150 ton at once. I.e. deliver 150 people per launch. To have at least one million of people going into space per year (a very rudimental colonization) we need almost 7,000 BFR launches per year. I don't see this happening.

I think a million people per year is a bit more than rudimentary. Let's start with Plymouth levels and work up.

[hamishspence]

Can we agree that, if Mars is to be the subject of widespread colonisation, space elevators (on Earth and Mars) will help facilitate it?