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Thread: Living on Mars?

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    Quote Originally Posted by hamishspence View Post
    Clarke understood more about space technology than the average journalist would about relativity, I think.
    Nevertheless, he is not an authority on subject. Not without presenting an actual research.

    Quote Originally Posted by hamishspence View Post
    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.
    Limit is practical. 100 meter wide elevator tower would make sense only for an extremely advanced (mature) development of space elevators. The one we are not going to reach until we literally build hundreds - if not thousands - of space elevators all around globe, and the proceed to improve them again and again.

    I.e. that is not something that is being discussed or suggested when we talk about actual space elevators.



    Quote Originally Posted by Bohandas View Post
    I think a million people per year is a bit more than rudimentary. Let's start with Plymouth levels and work up.
    I'm sorry, but having a hundred people on Mars is called "scientific expedition", not "colonization".

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    Quote Originally Posted by hamishspence View Post
    Can we agree that, if Mars is to be the subject of widespread colonisation, space elevators (on Earth and Mars) will help facilitate it?
    Then there is a problem (which I mentioned) that there simply is no reason to colonize Mars. Future is space stations, not planet-based colonies.

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    I could see colonising The Moon as a better "stepping stone in the process of advancing space technology" than colonising Mars. Mars might be more of a digression.
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    Quote Originally Posted by Lazymancer View Post



    I'm sorry, but having a hundred people on Mars is called "scientific expedition", not "colonization".
    There's a pretty large gap between 100 person "scientific station" and a million per year "Evacuate the earth minimum shipping amount."

    The SpaceX plan is to make it economically viable for 1 million pioneers to spend their own money to live on mars. They estimate that a million person colony has enough redundancy and population base to operate an industry that can make them ACTUALLY independant from earth.

    They arnt going to make that viable with elevator cable "launches" every other week (because it takes half that time for the climber to go each way) and needing to repair LEO velocity paintchip damage. They need DAILY launches from hundreds of pads around the world to bring down the costs to airliner-like... so that's what they want to build.
    Last edited by Rakaydos; 2017-12-09 at 11:19 AM.

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    I've said it before, living on Venus is a better idea than living on Mars (probably in another thread). Sure the temperature needs to come down, but a sunshade made out of thousands of autonomous solar sails around the https://en.wikipedia.org/wiki/Lagrangian_point Venus/Sol L1 point should do that fine, and keep the temperature down afterward if needed.

    Space elevators on Earth are a great idea, hopefully we will build one and eventually more in the future, but for now we're stuck with rockets, because they work using the materials and techniques we have now.

    On the whole, I agree that space not planets ought to be our species' future main home, but almost all of those now living on Earth will never leave it, most of the future non-Earth population will be born off the Earth, sure there are problems to be overcome, but I have no doubt that they can be overcome.
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    Quote Originally Posted by halfeye View Post
    I've said it before, living on Venus is a better idea than living on Mars (probably in another thread). Sure the temperature needs to come down, but a sunshade made out of thousands of autonomous solar sails around the https://en.wikipedia.org/wiki/Lagrangian_point Venus/Sol L1 point should do that fine, and keep the temperature down afterward if needed.
    And possibly be used as a solar power generator as well?
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    Quote Originally Posted by hamishspence View Post
    And possibly be used as a solar power generator as well?
    I suspect not with current technology, they would be a bit far off. The Earth/Sol L1 is at about 1.5 million kilometres from Earth, so I'd guess the Venus/Sol L1 would be something like 0.75 to 1.0 million kilometres from Venus.
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    It doesn't have to generate power for the residents of the proposed Venus colony - instead it can generate power for space stations under the "sunshade".
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    A million people isn't a colony, it's a mass exodus
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    Quote Originally Posted by Rakaydos View Post
    There's a pretty large gap between 100 person "scientific station" and a million per year "Evacuate the earth minimum shipping amount."

    The SpaceX plan is to make it economically viable for 1 million pioneers to spend their own money to live on mars. They estimate that a million person colony has enough redundancy and population base to operate an industry that can make them ACTUALLY independant from earth.

    They arnt going to make that viable with elevator cable "launches" every other week (because it takes half that time for the climber to go each way) and needing to repair LEO velocity paintchip damage. They need DAILY launches from hundreds of pads around the world to bring down the costs to airliner-like... so that's what they want to build.
    And as mentioned before, this is meaningless until we can make artificial selfsufficient food sources on Earth. Putting the donkey before the race car here.
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    Quote Originally Posted by Rakaydos View Post
    They arnt going to make that viable with elevator cable "launches" every other week (because it takes half that time for the climber to go each way)
    That's not how a space elevator would be used. The design allows for multiple climbers on the tether at any given time. Yes, each one takes days to arrive, but once the first one arrives, the next one is just a couple of hours behind it. Also, the pods will be disposable: either flung into deep space, or put in a shell and dropped back to Earth. But they won't be taking up tether time to go back down.

    GW
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    Quote Originally Posted by Grey_Wolf_c View Post
    That's not how a space elevator would be used. The design allows for multiple climbers on the tether at any given time. Yes, each one takes days to arrive, but once the first one arrives, the next one is just a couple of hours behind it. Also, the pods will be disposable: either flung into deep space, or put in a shell and dropped back to Earth. But they won't be taking up tether time to go back down.

    GW
    Doesnt matter. One climber or many, the cable can only support a certian mass of climbers at a time.

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    Quote Originally Posted by Tvtyrant View Post
    And as mentioned before, this is meaningless until we can make artificial selfsufficient food sources on Earth. Putting the donkey before the race car here.
    Google "vertical farm."

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    Quote Originally Posted by Rakaydos View Post
    Google "vertical farm."
    If they actually worked third world countries wouldn't be destroying their trade balance by purchasing grain shipments from the US, they would be building vertical farms.

    You need a system that can actually work without massive and continuous external inputs from a wealthier place, otherwise Mars becomes forever dependent on material shipments from Earth. This is not a good situation to be in when you have no balancing exports.
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    Quote Originally Posted by Tvtyrant View Post
    If they actually worked third world countries wouldn't be destroying their trade balance by purchasing grain shipments from the US, they would be building vertical farms.
    By that logic regular farms don't work either or else the third world would grow their own food in regular farms.
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    Quote Originally Posted by Bohandas View Post
    By that logic regular farms don't work either or else the third world would grow their own food in regular farms.
    They only work in specific regions. Civilization is an export, hence why those regions have seen mass migration to cities as food imports replace tiny self sustaining farms.

    Comparing the two, if vertical farms work like third world farms no one in their right mind is going to go to Mars.
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    Quote Originally Posted by Rakaydos View Post
    Doesnt matter. One climber or many, the cable can only support a certian mass of climbers at a time.
    It does matter, especially when I hear nonsense like "it takes two weeks between launches" as a "problem" for space elevators. By all means tell me what numbers you have in mind, because I'm tired of having the burden of evidence dumped on me every time someone comes boldly announcing that space elevators are useless but can't be bothered to actually do even basic calculations themselves.

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    Quote Originally Posted by Grey_Wolf_c View Post
    It does matter, especially when I hear nonsense like "it takes two weeks between launches" as a "problem" for space elevators. By all means tell me what numbers you have in mind, because I'm tired of having the burden of evidence dumped on me every time someone comes boldly announcing that space elevators are useless but can't be bothered to actually do even basic calculations themselves.

    GW
    My understanding is that when people say things about how big of a climber a space elevator can support, they typically are talking about the case where they have the tether pretty much full and are just putting one on the bottom as fast as they take one off the top. If you have a bunch of climbers spaced evenly over the tether, they mostly add to the tension rather than to the orbital mechanics.
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    Quote Originally Posted by Grey_Wolf_c View Post
    Also, the pods will be disposable: either flung into deep space, or put in a shell and dropped back to Earth. But they won't be taking up tether time to go back down.

    GW
    This seems wasteful. Mass in orbit is valuable. The pods should be recycled in place, either used in architecture, broken up for parts, scrapped for raw material or decomposed and used as extra reaction mass.

    Near the top of the tether it might be worthwhile to use the previous batch of crawlers as counterweights to assist the climb of a new group of ascending crawlers.
    Last edited by Bucky; 2017-12-10 at 03:38 PM.
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    Quote Originally Posted by Grey_Wolf_c View Post
    It does matter, especially when I hear nonsense like "it takes two weeks between launches" as a "problem" for space elevators. By all means tell me what numbers you have in mind, because I'm tired of having the burden of evidence dumped on me every time someone comes boldly announcing that space elevators are useless but can't be bothered to actually do even basic calculations themselves.

    GW
    I'm not saying the elevator is somehow worse than "1 launch every other year" disposable SLS. I understand the elevator is scalable- if you need more capacity, you spend some capacity bringing up more filaments to make the tether stronger.

    But there's no fundamental reason a rocket cannot me made with enough margin that it refuels and reflies after a single day. (Elon apparently wanted a 12 hour turnaround- the engineers convinced him that 24 hours was reasonably possible.) For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?

    Space elevators are popular because rocket technoligy has been stuck in the 70s for almost half a century. Looking at the lack of progress national spaceflight programs made, it's easy to believe that the saturn 5 was the best rocket that CAN exist.

    But that's wrong. Microchips, CAD programs, new material technologies and new manufacturing techniques mean rockets can be... and with both Blue Origin and SpaceX, along with smaller companies like Electron and Reaction Engines Limited, are becoming... so much better options. The Space elevator isn't even possible yet, and it's already becoming obsolete.

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    Quote Originally Posted by Rakaydos View Post
    I'm not saying the elevator is somehow worse than "1 launch every other year" disposable SLS. I understand the elevator is scalable- if you need more capacity, you spend some capacity bringing up more filaments to make the tether stronger.

    But there's no fundamental reason a rocket cannot me made with enough margin that it refuels and reflies after a single day. (Elon apparently wanted a 12 hour turnaround- the engineers convinced him that 24 hours was reasonably possible.) For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?
    Including non-reusable fuel? Not many.

    Space elevators are popular because rocket technoligy has been stuck in the 70s for almost half a century. Looking at the lack of progress national spaceflight programs made, it's easy to believe that the saturn 5 was the best rocket that CAN exist.
    Saturn 5 was the '60s, it doubtless changed a little over time, but it first went to the moon in '69.

    But that's wrong. Microchips, CAD programs, new material technologies and new manufacturing techniques mean rockets can be... and with both Blue Origin and SpaceX, along with smaller companies like Electron and Reaction Engines Limited, are becoming... so much better options. The Space elevator isn't even possible yet, and it's already becoming obsolete.
    Rockets burn fuel, it's a large part of their cost, the fuel costs in going up a space elevator ought to be a lot less, economics is the main advantage the space elevator has.
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    Quote Originally Posted by Bucky View Post
    This seems wasteful. Mass in orbit is valuable. The pods should be recycled in place, either used in architecture, broken up for parts, scrapped for raw material or decomposed and used as extra reaction mass.
    The NASA design calls for using the first few thousands to build up the counterweight at the far end of the elevator.

    Quote Originally Posted by Bucky View Post
    Near the top of the tether it might be worthwhile to use the previous batch of crawlers as counterweights to assist the climb of a new group of ascending crawlers.
    Unless you can show me how that'd even be done, I don't think that is a thing that could happen with the tether-crawler design.

    Quote Originally Posted by Rakaydos View Post
    For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?
    Again, stop shifting the burden of evidence onto me. This is your argument, YOU present the numbers that make your case. Figure out what ballpark numbers Elon is promising, and compare them to the numbers expected for a space elevator. Simply saying "I'm sure that X-Space will be cheaper" is not an actual argument.

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    Quote Originally Posted by halfeye View Post
    Including non-reusable fuel? Not many.

    Rockets burn fuel, it's a large part of their cost, the fuel costs in going up a space elevator ought to be a lot less, economics is the main advantage the space elevator has.
    "Propellant

    Musk has famously stated at the National Press Club that the cost of propellant is only 0.3% the cost of the [falcon 9] rocket, which yields about $200,000 for a $60m launch."
    https://space.stackexchange.com/ques...alcon-9-launch

    The 2017 BFR is fueled with about 4000 tons of Natural Gas (Methane) and Medical grade oxygen. Best estimate put the fuel costs at $500,000 dollars for 150 tons to orbit. (Methane is cheaper per ton than the Falcon 9's Kerosene) The rocket itself is more expensive, but is intended to be flown 1000 times per airframe, amortising the costs significantly.

    @greywolf: https://www.sciencedaily.com/release...0412105109.htm
    Not up to space elevator standards, but I'm not including BFR refurbishment or amortization costs either, so I'll call it a wash.
    At $15 per gram of carbon nanotubes, and a minimum strand mass of 750 tons (earlier in this thread) is 750 million grams, or over 11 billion dollars for a single strand.

    With the same money, you could refuel the BFR over 20,000 times, presumably putting 150 tons into orbit each time.

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    It should be noted that the fuel is non-renewable as well
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    Quote Originally Posted by Bohandas View Post
    It should be noted that the fuel is non-renewable as well
    Fuel is cheap. Precision engineered spacecraft (or escape-length atom-precise nanotubes) are expensive.

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    Quote Originally Posted by Rakaydos View Post
    Fuel is cheap. Precision engineered spacecraft (or escape-length atom-precise nanotubes) are expensive.
    Fuel is also a pollutant when burned - and while that's pretty negligible at current rates (e.g. haloform production associated with the space shuttle which is at .25% of the world total) it can't be reasonably assumed that that stays true given a significant uptick in launches. Hydrogen-oxygen systems are generally better about this, but they aren't completely pure fuels as used and still cause problems.

    Meanwhile if a space elevator is successfully produced the energy requirements drop precipitously.

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    Quote Originally Posted by Rakaydos View Post
    Not up to space elevator standards, but I'm not including BFR refurbishment or amortization costs either, so I'll call it a wash.
    At $15 per gram of carbon nanotubes, and a minimum strand mass of 750 tons (earlier in this thread) is 750 million grams, or over 11 billion dollars for a single strand.

    With the same money, you could refuel the BFR over 20,000 times, presumably putting 150 tons into orbit each time.
    And what do you do then? Just stop supplying your space colonies and space stations, which we're assuming you're going to have by this point (given the purpose of the thread)? Whereas if you built the space elevator, and hopefully did a decent job of it, you can keep using it to send stuff up.

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    Quote Originally Posted by factotum View Post
    And what do you do then? Just stop supplying your space colonies and space stations, which we're assuming you're going to have by this point (given the purpose of the thread)? Whereas if you built the space elevator, and hopefully did a decent job of it, you can keep using it to send stuff up.
    I cant see to find maintinance costs for multi-KM atomic-precice structures that undergo regular mechanical stress. Can you please suggest some values?

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    Quote Originally Posted by Knaight View Post
    Fuel is also a pollutant when burned - and while that's pretty negligible at current rates (e.g. haloform production associated with the space shuttle which is at .25% of the world total) it can't be reasonably assumed that that stays true given a significant uptick in launches. Hydrogen-oxygen systems are generally better about this, but they aren't completely pure fuels as used and still cause problems.

    Meanwhile if a space elevator is successfully produced the energy requirements drop precipitously.
    If that becomes a problem, they CAN reuse fuel, though not as cheaply. The Sabatier Reaction turns CO2 and H2O into CH4 and O2, and they are already building this tech for the mars end of the journy. Build it on the earth end as well, and counting the fuel lost in space forever, it's actually a net exporter of CO2.

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    Quote Originally Posted by Rakaydos View Post
    If that becomes a problem, they CAN reuse fuel, though not as cheaply. The Sabatier Reaction turns CO2 and H2O into CH4 and O2, and they are already building this tech for the mars end of the journy. Build it on the earth end as well, and counting the fuel lost in space forever, it's actually a net exporter of CO2.
    Methane-oxygen rockets are almost certainly not good enough for fuel purposes, and CO2 is far from the only pollutant of concern.

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