Page 4 of 9 FirstFirst 123456789 LastLast
Results 91 to 120 of 266

Thread: Living on Mars?

  1. - Top - End - #91
    Troll in the Playground
     
    Bohandas's Avatar

    Join Date
    Feb 2016

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    Ben Bova's Solar System series (Mercury novel) depicted "falling space elevator" as extremely devastating - because, while it's low density, it's huge. The term "skytower" is used for it.

    Some elevators might burn up:

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

    but this one was on the order of 100 or more metres in diameter. And that might have been at its thinnest point.

    The end coming down from nearly 25000 km up, would also have more time to accelerate to dangerous speeds, with air resistance not being able to mitigate those speeds enough. (The end above the geostationary platform, when the whole thing is severed, would go spinning off into space.)

    Relevant bits from the novel:

    Although buckyball fibers are lighter in weight than any material that is even half their tensile strength, a structure of more than thirty-five thousand kilometers' length weighs millions of metric tons.
    The skytower wavered as it tore loose from the geostationary platform, disconnected from the centrifugal force that had pulled it taut. One end suddenly free of its mooring, its other end still tethered to the ground, the lower half of the tower staggered like a prizefighter suddenly struck by a knockout blow, then began its long, slow-motion catastrophic collapse.

    ...
    The lower half of the skytower slowly, slowly tumbled like a majestic tree suddenly turned to putty. Its base, attached to the rotating Earth, was moving more than a thousand kilometers per hour from west to east. Its enormous length, unsupported now, collapsed westward in a long, long, long plunge to Earth.
    ...
    Slowly at first, but then with ever-increasing speed, the skytower's lower half collapsed to the Earth. Its immense bulk smashed into Ciudad de Cielo, the tethers at its base snapping like strings, the shock wave from its impact blowing down those buildings it did not hit directly. The thunder of its fall shattered the air like the blast of every volcano on Earth exploding at once. Seconds later the falling tower smashed down on the northern suburbs of Quito like a gigantic tree crushing an ant hill. The city's modern high-rise glass and steel towers, built to withstand earthquakes, wavered and shuddered. Their safety-glass facades blew out in showers of pellets. Ordinary windows shattered into razor-sharp shards that slashed to bloody ribbons the people who crowded the streets, screaming in terror. Older buildings were torn from their foundations as if a nuclear explosion had ripped through the city. The old cathedral's thick masonry walls cracked and its stained glass windows shattered, each and every one of them. Water pipes ruptured and gas mains broke. Fire and flood took up their deadly work where the sheer explosive impact of the collapse left off.
    And still the tower fell.
    Down the slope that led to the sea, villages and roads and farms and open fields and trees were smashed flat, pulverized, while the shock wave from the impact blew down woodlands and buildings for a hundred kilometers and more in either direction, as if a giant meteor had struck out of the sky. A fishing village fell under the shadow of sudden doom, its inhabitants looking up to see this immense arm of God swinging down on them like the mighty bludgeon of the angel of death.
    And still the tower fell.
    Its length splashed into the Pacific Ocean with a roar that broke eardrums and ruptured the innards of men, beasts, birds, and fish. Across the coastal shelf it plunged and out beyond into the abyssal depths. Whales migrating hundreds of kilometers out to sea were pulped to jelly by the shock wave that raced through the water. The tsunami it raised washed away shoreline settlements up and down the coast and rushed across the Pacific, flooding the Galapagos Islands, already half-drowned by the greenhouse warming. The Pacific coast of Central America was devastated. Hawaii and Japan were struck before their warning systems could get people to move inland. Samoa and Tahiti were hit by a wall of water nearly fifteen meters high that tore away villages and whole cities. People in Los Angeles and Sydney heard the mighty thunderclap and wondered if it was a sonic boom.
    And still the tower fell, splashing all the way across the Pacific, groaning as part of its globe-girdling length sank slowly into the dark abyssal depths. When it hit the spiny tree-covered mountain backbone of Borneo it snapped in two, one part sliding down the rugged slopes, tearing away forests and villages and plantations as it slithered snake-like across the island.
    The other part plunged across Sumatra and into the Indian Ocean, narrowly missing the long green finger of Malaysia but sending a tsunami washing across the drowned ruins of Singapore. Along the breadth of equatorial Africa it fell, smashing across Kenya, ploughed into the northern reaches of Lake Victoria, drowning the city of Kampala with a tidal wave, and continued westward, crushing cities and forests alike, igniting mammoth forest fires, driving vast herds of animals into panicked, screaming stampedes. Its upper end, still smoking from the titanic electrical discharge that had severed it, plunged hissing into the Atlantic, sinking deep down into the jagged rift where hot magma from the Earth's core embraced the man-made structure that had, mere minutes earlier, stood among the stars.
    Across the world the once-proud skytower lay amidst a swath of death and desolation and smoking ruin, crushing the life from people, animals, plants, crushing human ambition, human dreams, crushing hope itself.
    http://lesswrong.com/lw/k9/the_logic...lization_from/

  2. - Top - End - #92
    Titan in the Playground
     
    Grey_Wolf_c's Avatar

    Join Date
    Aug 2007

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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".
    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.

    GW
    My Motto:
    Forum Motto:
    There is a world of imagination
    Deep in the corners of your mind
    Where reality is an intruder
    And myth and legend thrive
    Quote Originally Posted by The Giant & Yendor View Post
    GIANT IN THE PLAYGROUND: On a saner forum,
    there wouldn't have been such speculation.
    Interested in MitD? Join us in MitD's thread.
    Scientia est similis fluminis te capere non possunt in perpetuum
    (Knowledge, like a river, cannot be constrained forever)

  3. - Top - End - #93
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    While it's possible that the fictionalized versions are impossibly big - I was under the impression that, eventually, they would need to be big, to support a thriving space industry.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  4. - Top - End - #94
    Titan in the Playground
     
    Grey_Wolf_c's Avatar

    Join Date
    Aug 2007

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    While it's possible that the fictionalized versions are impossibly big - I was under the impression that, eventually, they would need to be big, to support a thriving space industry.
    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.

    Grey Wolf
    My Motto:
    Forum Motto:
    There is a world of imagination
    Deep in the corners of your mind
    Where reality is an intruder
    And myth and legend thrive
    Quote Originally Posted by The Giant & Yendor View Post
    GIANT IN THE PLAYGROUND: On a saner forum,
    there wouldn't have been such speculation.
    Interested in MitD? Join us in MitD's thread.
    Scientia est similis fluminis te capere non possunt in perpetuum
    (Knowledge, like a river, cannot be constrained forever)

  5. - Top - End - #95
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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".
    Last edited by hamishspence; 2017-12-08 at 10:38 AM.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  6. - Top - End - #96
    Titan in the Playground
     
    Grey_Wolf_c's Avatar

    Join Date
    Aug 2007

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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
    Last edited by Grey_Wolf_c; 2017-12-08 at 10:40 AM.
    My Motto:
    Forum Motto:
    There is a world of imagination
    Deep in the corners of your mind
    Where reality is an intruder
    And myth and legend thrive
    Quote Originally Posted by The Giant & Yendor View Post
    GIANT IN THE PLAYGROUND: On a saner forum,
    there wouldn't have been such speculation.
    Interested in MitD? Join us in MitD's thread.
    Scientia est similis fluminis te capere non possunt in perpetuum
    (Knowledge, like a river, cannot be constrained forever)

  7. - Top - End - #97
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  8. - Top - End - #98
    Titan in the Playground
     
    Grey_Wolf_c's Avatar

    Join Date
    Aug 2007

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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
    My Motto:
    Forum Motto:
    There is a world of imagination
    Deep in the corners of your mind
    Where reality is an intruder
    And myth and legend thrive
    Quote Originally Posted by The Giant & Yendor View Post
    GIANT IN THE PLAYGROUND: On a saner forum,
    there wouldn't have been such speculation.
    Interested in MitD? Join us in MitD's thread.
    Scientia est similis fluminis te capere non possunt in perpetuum
    (Knowledge, like a river, cannot be constrained forever)

  9. - Top - End - #99
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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".
    Last edited by hamishspence; 2017-12-08 at 10:56 AM.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  10. - Top - End - #100
    Troll in the Playground
     
    Bohandas's Avatar

    Join Date
    Feb 2016

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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

  11. - Top - End - #101
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    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
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  12. - Top - End - #102
    Titan in the Playground
     
    Grey_Wolf_c's Avatar

    Join Date
    Aug 2007

    Default Re: Living on Mars?

    Quote Originally Posted by Bohandas View Post
    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
    My Motto:
    Forum Motto:
    There is a world of imagination
    Deep in the corners of your mind
    Where reality is an intruder
    And myth and legend thrive
    Quote Originally Posted by The Giant & Yendor View Post
    GIANT IN THE PLAYGROUND: On a saner forum,
    there wouldn't have been such speculation.
    Interested in MitD? Join us in MitD's thread.
    Scientia est similis fluminis te capere non possunt in perpetuum
    (Knowledge, like a river, cannot be constrained forever)

  13. - Top - End - #103
    Ogre in the Playground
     
    Lord Torath's Avatar

    Join Date
    Aug 2011
    Location
    Sharangar's Revenge
    Gender
    Male

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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.
    Thri-Kreen Ranger/Psionicist by me, based off of Rich's A Monster for Every Season

  14. - Top - End - #104
    Orc in the Playground
     
    NecromancerGuy

    Join Date
    Aug 2017

    Default Re: Living on Mars?

    Quote Originally Posted by Mechalich View Post
    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.

    Quote Originally Posted by Grey_Wolf_c View Post
    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.

    Quote Originally Posted by hamishspence View Post
    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.

    Quote Originally Posted by Grey_Wolf_c View Post
    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.

  15. - Top - End - #105
    Ogre in the Playground
     
    Griffon

    Join Date
    Jun 2013
    Location
    Bristol, UK

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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.
    Last edited by halfeye; 2017-12-08 at 01:06 PM.
    The end of what Son? The story? There is no end. There's just the point where the storytellers stop talking.

  16. - Top - End - #106
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by halfeye View Post
    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.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  17. - Top - End - #107
    Ogre in the Playground
     
    Griffon

    Join Date
    Jun 2013
    Location
    Bristol, UK

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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?
    The end of what Son? The story? There is no end. There's just the point where the storytellers stop talking.

  18. - Top - End - #108
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by halfeye View Post
    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.
    Last edited by hamishspence; 2017-12-08 at 01:27 PM.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  19. - Top - End - #109
    Ettin in the Playground
     
    Rockphed's Avatar

    Join Date
    Nov 2006
    Location
    Near Giant Graffiti.
    Gender
    Male

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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.
    Quote Originally Posted by Wardog View Post
    Rockphed said it well.
    Quote Originally Posted by Yuki Akuma View Post
    We should change the collective noun for crocodiles to "an abundance of crocodiles".
    Dragontar by Serpentine.

    Now offering unsolicited advice.

  20. - Top - End - #110
    Barbarian in the Playground
    Join Date
    Mar 2017

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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.

    Quote Originally Posted by halfeye View Post
    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"
    Last edited by Lazymancer; 2017-12-08 at 03:15 PM.

  21. - Top - End - #111
    Barbarian in the Playground
     
    WhatThePhysics's Avatar

    Join Date
    May 2012
    Location
    Hell

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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.
    When I was calculating, I used the average air pressure on the Martian surface, to account for the highest possible air resistance. I also used a drag coefficient of 1 for the cable, as I don't think that feathers and cables have the same air resistance due to their different shapes. If you can produce a lower terminal velocity, I'd appreciate it.

    Quote Originally Posted by Grey_Wolf_c View Post
    As to your pet idea, given that MEXTs are just space elevators but with massive hooks that you need to attach to, I don't see how they are no less subject to sabotage, and therefore would cause the same or more damage (since they'd have to have much higher density materials) if attacked. And given NASA's record of trying to capture fast moving objects with hooks, I find the actual practical problem of MEXT to be significantly higher than that of a Space Elevator. Not that I can really compare, since I'm having trouble even finding realistic assessments of the likely issues of MEXTs.

    Grey Wolf
    Compare the odds of sabotage between an enormous and stationary structure, versus a distributed set of small and mobile structures. Consider the possible variation in the sizes, max rpms, and docking methods of any given MEXT. Can you explain why you think they'd need higher density materials, and how much more density it'd need to cause the same or more damage?

  22. - Top - End - #112
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by Lazymancer View Post
    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/

    Quote Originally Posted by Rockphed View Post
    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.
    Last edited by hamishspence; 2017-12-08 at 06:25 PM.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  23. - Top - End - #113
    Ettin in the Playground
     
    Rockphed's Avatar

    Join Date
    Nov 2006
    Location
    Near Giant Graffiti.
    Gender
    Male

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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.
    Quote Originally Posted by Wardog View Post
    Rockphed said it well.
    Quote Originally Posted by Yuki Akuma View Post
    We should change the collective noun for crocodiles to "an abundance of crocodiles".
    Dragontar by Serpentine.

    Now offering unsolicited advice.

  24. - Top - End - #114
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    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.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  25. - Top - End - #115
    Troll in the Playground
     
    Rakaydos's Avatar

    Join Date
    Jun 2011

    Default Re: Living on Mars?

    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?

  26. - Top - End - #116
    Colossus in the Playground
     
    hamishspence's Avatar

    Join Date
    Feb 2007

    Default Re: Living on Mars?

    Quote Originally Posted by Rakaydos View Post
    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:

    Quote Originally Posted by Lazymancer View Post

    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.
    Marut-2 Avatar by Serpentine
    New Marut Avatar by Linkele

  27. - Top - End - #117
    Troll in the Playground
     
    Bohandas's Avatar

    Join Date
    Feb 2016

    Default Re: Living on Mars?

    Quote Originally Posted by Grey_Wolf_c View Post
    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.

  28. - Top - End - #118
    Troll in the Playground
     
    Rakaydos's Avatar

    Join Date
    Jun 2011

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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.

  29. - Top - End - #119
    Ogre in the Playground
     
    Lvl 2 Expert's Avatar

    Join Date
    Oct 2014
    Location
    Tulips Cheese & Rock&Roll
    Gender
    Male

    Default Re: Living on Mars?

    Quote Originally Posted by halfeye View Post
    They have a rocket that can lift 750 tonnes to orbit?
    20 tonnes.
    Quote Originally Posted by hamishspence View Post
    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).
    The ultimate OOTS cookie cutter nameless soldier is the hobgoblin.

  30. - Top - End - #120
    Barbarian in the Playground
    Join Date
    Mar 2017

    Default Re: Living on Mars?

    Quote Originally Posted by hamishspence View Post
    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?

    Quote Originally Posted by hamishspence View Post
    Something similar applied with communications satellites, before Sputnik:
    So, Sputnik was launched because of Clarke? Those damn commies, stealing American inventions...




    Quote Originally Posted by Rakaydos View Post
    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.

    Quote Originally Posted by Rakaydos View Post
    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.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •