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Thread: Landing cargo on moon

  1. #1
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    Landing cargo on moon

    In a large scale moon colonisation scenario where water would be precious commodity not to be wasted making fuel.

    Would it be worth a moon base building a landing pad on top of a tall tower, to reach lower gravity?
    The moon rotates too slowly to ever build up to geosync orbit.
    What else could be done to reduce fuel costs?
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

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    To save a great deal of fuel and cost, a bulk commodity such as water ice could be lithobraked directly into the moon without soft landing and then mined from the resulting crater.

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    A raised platform would do little. Gravity is very persistent over long distances.

    Give Luna an atmosphere, apply aerobraking.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    A really long runway.

    Somewhat serious. It might be feasible to brake a spacecraft against a long, flat aluminum surface using a combination of electromagnetic braking and a gas cushion. You don't want to hit a bump, though.

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    I was thinking in terms of a tower 10 km high, top part of a buried magnetic launcher. No real drop in gravity but would it be worth putting a landing pad on top?
    Would only save the potential energy compared to launching up to 10 km.
    I was thinking, the landing pads need to be on towers to stop lunar dust being blown up with dangerous speeds. The question was how tall?

    Aluminium runway sounds fun, orbital speed at zero altitude is a bit fast! I was thinking the magnetic lifting force would be of the same order as the breaking force so you would need thruster to hold lander down?
    Aluminium plate runway with the plates suspended or floating on something so they could absorb energy by moving downwards?
    Some kind of amazing hook that could catch a dragline would be great. Suggestions?

    As for creating an atmosphere, I was considering aerobraking into a tube filled with Perfluoropentane or something of similar density.
    What would be the easiest dense gas to make on the moon?
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

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    Use a space elevator. One could be strung from anywhere on the lunar surface to the L1 and/or L2 points of the Earth/Moon system, using materials that we already have, like Kevlar.

    Grant Hutchison
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    Quote Originally Posted by grant hutchison View Post
    Use a space elevator. One could be strung from anywhere on the lunar surface to the L1 and/or L2 points of the Earth/Moon system, using materials that we already have, like Kevlar.

    Grant Hutchison
    Would you need to balance the mass of material going up to that going down or use thrust to correct position?
    Even only rotating once a month conservation of angular momentum gets to be an issue over large distances.
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

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    Quote Originally Posted by PetTastic View Post
    Would you need to balance the mass of material going up to that going down or use thrust to correct position?
    Even only rotating once a month conservation of angular momentum gets to be an issue over large distances.
    The moon is your angular momentum bank. If the net mass transfer is downwards, then the elevator will gain angular momentum and sway in the direction of rotation. That creates additional tension in the cable which will slightly increase the moon's rotation speed, which will then be tidally damped by interaction with the Earth's gravity. So you end up with a slightly tilted elevator, a lunar tidal bulge that's slightly skewed, and a gentle warming of the moon. All of which would be too small to detect, I'd guess, for any reasonable level of cargo delivery to the surface.

    Grant Hutchison
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  9. #9
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    Quote Originally Posted by PetTastic View Post
    Would it be worth a moon base building a landing pad on top of a tall tower, to reach lower gravity?
    The moon rotates too slowly to ever build up to geosync orbit.
    What else could be done to reduce fuel costs?
    A problem to consider is that to land on the moon, gravity is not the only problem, because you’re not simply dropping the stuff from a high place. I think that bleeding off the speed you built up to get to the moon is perhaps a bigger problem, and a tower won’t help there.



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    Quote Originally Posted by grant hutchison View Post
    The moon is your angular momentum bank. If the net mass transfer is downwards, then the elevator will gain angular momentum and sway in the direction of rotation. That creates additional tension in the cable which will slightly increase the moon's rotation speed, which will then be tidally damped by interaction with the Earth's gravity. So you end up with a slightly tilted elevator, a lunar tidal bulge that's slightly skewed, and a gentle warming of the moon. All of which would be too small to detect, I'd guess, for any reasonable level of cargo delivery to the surface.

    Grant Hutchison
    Its not the moon end of the cable that is the problem.
    The L1 & L2 points are nearer and closer to the Earth being the centre of rotation of the system, so moving along the cable is changing the distance from the centre of rotation.
    Deflecting a long cable creates a huge mechanical advantage over the tension in the cable.
    Deflect the middle of a 100,000km cable sideways by 1 km only shortens the distance between end point by 0.00001999999km (Google calc, Pythagoras) (50000 - (50000^2 -1^2)^0.5)*2
    Any sideways force needs 50000x tension in cable to correct.
    The station on the other end of the cable would need to be well beyond the Lagrange points or how far would the cable be allowed to deflect?
    The more deflection allowed the larger the lateral forces get.
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

  11. #11
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    Yes, you'll have Coriolis forces deflecting the cable, and they'll increase the faster the cargo moves. But the tension in the cable is huge, and Coriolis fairly feeble in a system that rotates once a sidereal month. For transit speeds of 50m/s, the lateral acceleration is about 30 microgravities.
    The upper end of the cable would be fixed to a counterweight beyond the Lagrange point, which generates the tension to support the cable against its own weight, and which is also sitting in a saddle in the effective potential surface which exerts a restoring force against any deflection.

    Grant Hutchison
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  12. #12
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    Quote Originally Posted by PetTastic View Post
    In a large scale moon colonisation scenario where water would be precious commodity not to be wasted making fuel.

    Would it be worth a moon base building a landing pad on top of a tall tower, to reach lower gravity?
    The moon rotates too slowly to ever build up to geosync orbit.
    What else could be done to reduce fuel costs?
    Why do you think water is required to make fuel?
    And why do you think waer has to be hauled to the moon? There is probaly plenty there already.
    Last edited by John Mendenhall; 2018-Apr-18 at 04:19 PM.

  13. #13
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    Quote Originally Posted by John Mendenhall View Post
    Why do you think water is required to make fuel?
    I'm guessing thinking of either old-fashioned LH2/LOX or ALICE.
    But using aluminium+oxygen propellant (both mined from lunar soil) would be a way of avoiding taking lunar water out of the recycling loop.

    Grant Hutchison
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  14. #14
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    Quote Originally Posted by Jens View Post
    A problem to consider is that to land on the moon, gravity is not the only problem, because you’re not simply dropping the stuff from a high place. I think that bleeding off the speed you built up to get to the moon is perhaps a bigger problem, and a tower won’t help there.
    Just to add to what I wrote, and perhaps somebody will correct me, but for example, when Apollo approached the moon it was going 5,000 miles per hour, and that speed had to be reduced to 0. I think that losing that velocity is the key issue and not necessarily the gravity of the moon. Stopping on an asteroid with virtually no gravity would be easier I think but not easy. So having a platform won't really help very much. Having a system to "catch" cargo would be more important, like a net or something. On earth it's beneficial to launch things from high places, but I think primarily because the atmosphere would be thinner. For example, on earth, getting to the height of the ISS is not that hard if you just go up and come down, but catching up with it at 17,000 miles per hour is harder.
    As above, so below

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    Quote Originally Posted by Jens View Post
    Just to add to what I wrote, and perhaps somebody will correct me, but for example, when Apollo approached the moon it was going 5,000 miles per hour, and that speed had to be reduced to 0. I think that losing that velocity is the key issue and not necessarily the gravity of the moon. Stopping on an asteroid with virtually no gravity would be easier I think but not easy. So having a platform won't really help very much. Having a system to "catch" cargo would be more important, like a net or something. On earth it's beneficial to launch things from high places, but I think primarily because the atmosphere would be thinner. For example, on earth, getting to the height of the ISS is not that hard if you just go up and come down, but catching up with it at 17,000 miles per hour is harder.
    Each are both. The delta-v you quote is about the velocity required to get from the lunar surface to L1, and that's what it is because of the gravity of the moon. We can imagine the S-IVB stage providing just enough thrust to push Apollo across the L1 saddle at close to zero velocity, and then the conversion of potential to kinetic energy on the other side is responsible for the increase in velocity that has to be counteracted during the descent to the lunar surface.
    So if you could transfer cargo so that it arrives at L1 at zero velocity (relative to the Earth-Moon system), then you could pop it on board a space elevator at that point, and use the moon (and your magnetic brake-pads) as your energy sink while you descended slowly towards the lunar surface.

    Grant Hutchison
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    Note:
    During life, we all develop attitudes and strategies to make our interactions with others more pleasant and useful. If I mention mine here, those comments can apply only to myself, my experiences and my situation. Such remarks cannot and should not be construed as dismissing, denigrating, devaluing or criticizing any different attitudes and strategies that other people have evolved as a result of their different situation and different experiences.

  16. #16
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    Quote Originally Posted by grant hutchison View Post
    I'm guessing thinking of either old-fashioned LH2/LOX or ALICE.
    But using aluminium+oxygen propellant (both mined from lunar soil) would be a way of avoiding taking lunar water out of the recycling loop.

    Grant Hutchison
    I'm thinking in terms of an urgent large scale colonisation out of necessity, hence the landing-pads on towers to stop dust being blasted around at dangerous velocities by rocket motors.

    In a vacuum, ALICE or other aluminium burning tech are out of the question. Blasting spacesuits and habs with aluminium-oxide splatter would be more of a weapon of mass destruction (well not nice anyway).
    ------
    Ion thruster also would be unfriendly to point down at a moon base but could be used to reduce lateral velocity maybe.

    Getting water from asteroids beyond Mars is a bit of a longer term plan.
    See: 'The God Kit' -- 'The Brigadier And The Pit' -- Carl N Graham -- Sci-fi blog: The Alien Reporter

  17. #17
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    let's get there first

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