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I feel like the difficulty of obtaining rocket fuel on a given rocky planet is equivalent to within the limits of napkin math. I've never heard a particularly c

I feel like the difficulty of obtaining rocket fuel on a given rocky planet is equivalent to within the limits of napkin math. I've never heard a particularly convincing argument for using the Moon as a springboard to the wider universe as opposed to Mars or Venus. Perhaps someone could offer some correction.

abecedarius 9y ago
Rotating tethers ought to be practical around the moon even with current materials: https://en.m.wikipedia.org/wiki/Momentum_exchange_tether#Cislunar_transportation_system https://en.m.wikipedia.org/wiki/Momentum_exchange_tether#Cis...
sparky_z 9y ago
Not a rocket scientist, nor do I have any hard numbers, but off the top of my head the Moon has a much smaller gravity well than Mars or Venus. On Mars, you would waste much more fuel just getting back into orbit. And Venus is just comically toxic. We weren't even able to build a single probe that lasted more than a couple hours on the surface of Venus before corroding, much less a permanent settlement. Also, the moon is only a few days of travel away, instead of months-to-years (so someone on a permanent base could be medically evacuated if they have a tricky tumor, say.)
- taneq 9y ago
  The Moon's gravity well is smaller but, with no atmosphere, it's both much easier to escape, and much harder to land softly on. If anything, I'd guess our best bet is a propellant factory on the Moon, using a magnetic launcher to shoot the fuel into lunar orbit to supply an orbiting fuel station.
  - stoolpigeon 9y ago
    Giving the moon magnetic catapults is giving the moon weapons for their eventual war for freedom from earth.
    - taneq 9y ago
      TANSTAAFL!
      - Pica_soO 9y ago
        Silence, Comrad - you will blow our cell! Or are you working for Warden - Catapulthead-svinoi!
  - jagger27 9y ago
    Magnetic launchers can be used in reverse as catchers too as a sort of atmosphere replacement.
    - NegativeLatency 9y ago
      How so? Would you have to "land" by going back down the barrel of the launch device?
    - taneq 9y ago
      That'd be quite a trick if you could pull it off - the precision required seems formidable, though.
      - ricardobeat 9y ago
        Like trying to land a rocket upright back on its launchpad. Lunacy.
        taneq 9y ago
        The rocket gets to 'fly' in, taking advantage of the atmosphere for control and braking. Not that it's not a bonkers achievement but the speeds are much higher and the tolerances much lower to slot an orbiting payload back into a linear rail.
        e12e 9y ago
        Magnetic Lander might be a decent smartphone game...
      - dogma1138 9y ago
        How is that that much different than landing on an aircraft carrier?
        kwhitefoot 9y ago
        Should be easier if we can assume that the vehicle is powered because the landing stage is not moving.
  - hordeallergy 9y ago
    How about a space elevator?
    - sfifs 9y ago
      Actually can be built with existing materials I remember reading
    - Iv 9y ago
      Unfortunately the moon turns very slowly. It is tidally locked to Earth. The cable of a moon space elevator would have to be the length of the moon-earth distance.
  - sethrin 9y ago
    You should look up proposals for Venusian cloud cities. In many senses Venus is more hospitable than Mars.
    - nine_k 9y ago
      On Mars, or on Moon, you have a lot of local materials to build from. A Venusean floating city needs to be brought in completely from the outside.
      - sethrin 9y ago
        I can see how you might think that, I suppose, but you do actually have an entire planet full of useful resources at hand, even if they're not ones that you might immediately think of. There are many things that you can reasonably extract or synthesize from the Venusian atmosphere, particularly plastics. This StackExchange answer has more details: https://space.stackexchange.com/questions/9158/what-useful-materials-can-be-extracted-from-venusian-atmosphere https://space.stackexchange.com/questions/9158/what-useful-m...
ChuckMcM 9y ago
The lower gravity and lack of oxygen make launching things with maglev sleds into orbit feasible. There have been a number of studies of a launch rail with a reusable 'bucket' carrier that would be built along an incline for a suitable orbit. The bucket would be accelerated electromagnetically along the rail, imparting sufficient energy to put the contents of the bucket into orbit which would be circularized at apogee with a small rocket burn. The rail would be powered by an array of solar panels and batteries, or possibly a flywheel similarly to the way the EMALS[1] system was designed. Landing is the challenge on the moon as there isn't anything to push against or dump energy into. I don't know if anyone has considered a space elevator, I expect keeping it in position would be a challenge given the orbital dynamics involved. [1] https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launch_System https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launc...
- greglindahl 9y ago
  Not only have people considered a lunar space elevator, but, you can actually build it with today's materials science: https://en.wikipedia.org/wiki/Lunar_space_elevator https://en.wikipedia.org/wiki/Lunar_space_elevator
- Pica_soO 9y ago
  You could create a semi atmosphere- by Electrically Blowing Up Sand? Sort of like simulating Atmosphere with a shotgun blast?
  - ChuckMcM 9y ago
    If you are asking whether or not you should somehow accelerate lunar regolith upward and use it to decelerate an incoming lander, then yes you probably could. Although it would no doubt cause damage to the landing craft much as an atmosphere braked entry 'burns up' the heat shield of a landing craft. Further the dust contains a lot of aluminum silica and that is essentially sand paper so you would get a lot of abrasion.
baybal2 9y ago
For as long as ice is present on the moon, using it is a matter of melting it, filtering, and electrolyzing. Moon is also a sure source of aluminium. Components can be shipped flatpacked to the moon, where they will be placed on locally produced aluminium "skeleton"
- e12e 9y ago
  I wonder if it would be feasible to build a solar furnace capable of melting aluminium with focused sunlight - the light side must have pretty steady and strong incoming solar radiation, with no atmosphere?
wfunction 9y ago
> I've never heard a particularly convincing argument for using the Moon as a springboard to the wider universe as opposed to Venus The mere fact that Venus has a thick CO2 atmosphere surrounding a surface with a temperature 872°F should be more than convincing, let alone the 90 atmosphere pressure and sulfuric acid clouds and all the other icing on the cake.
- sethrin 9y ago
  You should read more about proposals for Venusian colonies before assuming that your knowledge of the subject is sufficient for discussion. No one is proposing to live on the surface, and the sulfuric acid is not a particularly large problem.
  - wfunction 9y ago
    When was the last time you saw a hovering colony on Earth that now you think we could make one on Venus?
    - sethrin 9y ago
      Please review the existing literature on this subject. Particularly, take note that an Earth-normal atmosphere constitutes a lifting gas on Venus. This is not the game where you utter every trivial objection that springs to mind on the basis that no one has bothered to give the subject more than five minutes' thought. Your statement about surface temp/pressure is a clear indicator that you have not bothered to research this issue in the slightest degree, and this comment is an ineffectual attempt at saving face. The people publishing papers on this topic seem to think it's reasonable. Your sarcasm and ignorance on this matter are extremely offensive.
      - wfunction 9y ago
        Dude, put down your guns and chill out a bit? When you said "obtaining rocket fuel on a given rocky planet" and "springboard to the wider universe" I naturally assumed you meant launching a rocket from Venus's surface, not making a colony in the upper atmosphere. That seemed quite reasonable to me, but obviously not to you. So you replied with a snarky comment telling me to read the literature of Venusian colonies (which wasn't even the topic), and after you changed the subject, I asked what makes YOU think we could actually build one when we haven't even had anything like it on Earth. (I emphasize YOU because you had asked us to convince YOU, not some random researcher in NASA.) My comment there wasn't sarcastic; it was a completely serious comment that did consider the fact that people have been researching the idea seriously. I stand by it: just because people are proposing the idea of a base over Venus seriously that doesn't mean much about its feasibility compared to a base on the moon, and just because one person is convinced something is possible, that doesn't mean another person will be. (As a more Earthly example of this, I might respect Elon Musk, and I know he knows what he's talking about more than I ever will, but that still doesn't mean I'm convinced the Hyperloop is as feasible as he seemed to think. I still respect the idea and will take it seriously if he does, but that doesn't mean I'm convinced by it in any way. Same here.) Now, instead of firing all your cannons at me and flaming me, I suggest you calm down and take a walk before replying, so we can be a little more civil here. If you're already an expert on the topic, maybe explain a little more of what you already know and why you do/don't find it convincing when you're asking your question, so the rest of us plebeians have a foundation to build on that you won't find "offensive".

abecedarius 9y ago

Rotating tethers ought to be practical around the moon even with current materials: https://en.m.wikipedia.org/wiki/Momentum_exchange_tether#Cislunar_transportation_system https://en.m.wikipedia.org/wiki/Momentum_exchange_tether#Cis...

sparky_z 9y ago

Not a rocket scientist, nor do I have any hard numbers, but off the top of my head the Moon has a much smaller gravity well than Mars or Venus. On Mars, you would waste much more fuel just getting back into orbit. And Venus is just comically toxic. We weren't even able to build a single probe that lasted more than a couple hours on the surface of Venus before corroding, much less a permanent settlement. Also, the moon is only a few days of travel away, instead of months-to-years (so someone on a permanent base could be medically evacuated if they have a tricky tumor, say.)

taneq 9y ago
The Moon's gravity well is smaller but, with no atmosphere, it's both much easier to escape, and much harder to land softly on. If anything, I'd guess our best bet is a propellant factory on the Moon, using a magnetic launcher to shoot the fuel into lunar orbit to supply an orbiting fuel station.
- stoolpigeon 9y ago
  Giving the moon magnetic catapults is giving the moon weapons for their eventual war for freedom from earth.
  - taneq 9y ago
    TANSTAAFL!
    - Pica_soO 9y ago
      Silence, Comrad - you will blow our cell! Or are you working for Warden - Catapulthead-svinoi!
- jagger27 9y ago
  Magnetic launchers can be used in reverse as catchers too as a sort of atmosphere replacement.
  - NegativeLatency 9y ago
    How so? Would you have to "land" by going back down the barrel of the launch device?
  - taneq 9y ago
    That'd be quite a trick if you could pull it off - the precision required seems formidable, though.
    - ricardobeat 9y ago
      Like trying to land a rocket upright back on its launchpad. Lunacy.
      - taneq 9y ago
        The rocket gets to 'fly' in, taking advantage of the atmosphere for control and braking. Not that it's not a bonkers achievement but the speeds are much higher and the tolerances much lower to slot an orbiting payload back into a linear rail.
      - e12e 9y ago
        Magnetic Lander might be a decent smartphone game...
    - dogma1138 9y ago
      How is that that much different than landing on an aircraft carrier?
      - kwhitefoot 9y ago
        Should be easier if we can assume that the vehicle is powered because the landing stage is not moving.
- hordeallergy 9y ago
  How about a space elevator?
  - sfifs 9y ago
    Actually can be built with existing materials I remember reading
  - Iv 9y ago
    Unfortunately the moon turns very slowly. It is tidally locked to Earth. The cable of a moon space elevator would have to be the length of the moon-earth distance.
- sethrin 9y ago
  You should look up proposals for Venusian cloud cities. In many senses Venus is more hospitable than Mars.
  - nine_k 9y ago
    On Mars, or on Moon, you have a lot of local materials to build from. A Venusean floating city needs to be brought in completely from the outside.
    - sethrin 9y ago
      I can see how you might think that, I suppose, but you do actually have an entire planet full of useful resources at hand, even if they're not ones that you might immediately think of. There are many things that you can reasonably extract or synthesize from the Venusian atmosphere, particularly plastics. This StackExchange answer has more details: https://space.stackexchange.com/questions/9158/what-useful-materials-can-be-extracted-from-venusian-atmosphere https://space.stackexchange.com/questions/9158/what-useful-m...

ChuckMcM 9y ago

The lower gravity and lack of oxygen make launching things with maglev sleds into orbit feasible. There have been a number of studies of a launch rail with a reusable 'bucket' carrier that would be built along an incline for a suitable orbit. The bucket would be accelerated electromagnetically along the rail, imparting sufficient energy to put the contents of the bucket into orbit which would be circularized at apogee with a small rocket burn. The rail would be powered by an array of solar panels and batteries, or possibly a flywheel similarly to the way the EMALS[1] system was designed. Landing is the challenge on the moon as there isn't anything to push against or dump energy into. I don't know if anyone has considered a space elevator, I expect keeping it in position would be a challenge given the orbital dynamics involved. [1] https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launch_System https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launc...

greglindahl 9y ago
Not only have people considered a lunar space elevator, but, you can actually build it with today's materials science: https://en.wikipedia.org/wiki/Lunar_space_elevator https://en.wikipedia.org/wiki/Lunar_space_elevator
Pica_soO 9y ago
You could create a semi atmosphere- by Electrically Blowing Up Sand? Sort of like simulating Atmosphere with a shotgun blast?
- ChuckMcM 9y ago
  If you are asking whether or not you should somehow accelerate lunar regolith upward and use it to decelerate an incoming lander, then yes you probably could. Although it would no doubt cause damage to the landing craft much as an atmosphere braked entry 'burns up' the heat shield of a landing craft. Further the dust contains a lot of aluminum silica and that is essentially sand paper so you would get a lot of abrasion.

baybal2 9y ago

For as long as ice is present on the moon, using it is a matter of melting it, filtering, and electrolyzing. Moon is also a sure source of aluminium. Components can be shipped flatpacked to the moon, where they will be placed on locally produced aluminium "skeleton"

e12e 9y ago
I wonder if it would be feasible to build a solar furnace capable of melting aluminium with focused sunlight - the light side must have pretty steady and strong incoming solar radiation, with no atmosphere?

wfunction 9y ago

> I've never heard a particularly convincing argument for using the Moon as a springboard to the wider universe as opposed to Venus The mere fact that Venus has a thick CO2 atmosphere surrounding a surface with a temperature 872°F should be more than convincing, let alone the 90 atmosphere pressure and sulfuric acid clouds and all the other icing on the cake.

sethrin 9y ago
You should read more about proposals for Venusian colonies before assuming that your knowledge of the subject is sufficient for discussion. No one is proposing to live on the surface, and the sulfuric acid is not a particularly large problem.
- wfunction 9y ago
  When was the last time you saw a hovering colony on Earth that now you think we could make one on Venus?
  - sethrin 9y ago
    Please review the existing literature on this subject. Particularly, take note that an Earth-normal atmosphere constitutes a lifting gas on Venus. This is not the game where you utter every trivial objection that springs to mind on the basis that no one has bothered to give the subject more than five minutes' thought. Your statement about surface temp/pressure is a clear indicator that you have not bothered to research this issue in the slightest degree, and this comment is an ineffectual attempt at saving face. The people publishing papers on this topic seem to think it's reasonable. Your sarcasm and ignorance on this matter are extremely offensive.
    - wfunction 9y ago
      Dude, put down your guns and chill out a bit? When you said "obtaining rocket fuel on a given rocky planet" and "springboard to the wider universe" I naturally assumed you meant launching a rocket from Venus's surface, not making a colony in the upper atmosphere. That seemed quite reasonable to me, but obviously not to you. So you replied with a snarky comment telling me to read the literature of Venusian colonies (which wasn't even the topic), and after you changed the subject, I asked what makes YOU think we could actually build one when we haven't even had anything like it on Earth. (I emphasize YOU because you had asked us to convince YOU, not some random researcher in NASA.) My comment there wasn't sarcastic; it was a completely serious comment that did consider the fact that people have been researching the idea seriously. I stand by it: just because people are proposing the idea of a base over Venus seriously that doesn't mean much about its feasibility compared to a base on the moon, and just because one person is convinced something is possible, that doesn't mean another person will be. (As a more Earthly example of this, I might respect Elon Musk, and I know he knows what he's talking about more than I ever will, but that still doesn't mean I'm convinced the Hyperloop is as feasible as he seemed to think. I still respect the idea and will take it seriously if he does, but that doesn't mean I'm convinced by it in any way. Same here.) Now, instead of firing all your cannons at me and flaming me, I suggest you calm down and take a walk before replying, so we can be a little more civil here. If you're already an expert on the topic, maybe explain a little more of what you already know and why you do/don't find it convincing when you're asking your question, so the rest of us plebeians have a foundation to build on that you won't find "offensive".