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Moon slingshot powered atmosphere scoop?

  1. Apr 3, 2007 #1
    Here is the scheme:
    A craft from earth slingshots around the moon back towards the earth, gaining some speed (and slowing the moons orbit slightly). a few days later it expends this energy skimming the earths atmosphere, scooping some atmosphere into its tanks. It heads back towards the moon with the same speed it had initially, but more mass.

    (interestingly, its efficiency increases rather than decreases each time it gathers more mass, because more mass lets it grab more momentum from the moon with each slingshot allowing it to skim more earth atmosphere)

    Can anyone comment on the validity of this idea?
    • Can slingshotting like this work? I initially thought it would add exactly the moon's orbital velocity of about 1km/s but Im no longer sure its that simple.
    • Can aerobreaking maneuvers be designed that create the correct reduction in velocity AND the correct trajectory back towards the moon, especially given that the mass will probably be different each time?
    • If it holds up theoretically, what about practically? eg how strenuous would the aerobraking be? What would the atmospheric pressure in the scoop be?.. (we would need to choose a width of the scoop to answer that of course, but I dont think details of the earth's atmosphere are required. Instead we are asking how many newtons to lose how much velocity in a semicircular low earth orbit.. I think)
    • If it holds up theoretically, has it already been investigated? any reference?

    Im not expecting someone to solve all my problems for me (that is well beyond the scope of this thread ;) ) but any pointers would be appreciated.
    Last edited: Apr 3, 2007
  2. jcsd
  3. Apr 6, 2007 #2
    No one can help? Forget all that scoop stuff.
    Im confident the moon can be used to add energy to the craft. What I am unsure of is if the new orbit can be designed have the exact same minimum distance from the earth as the initial orbit.
  4. Apr 6, 2007 #3


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    Staff: Mentor

    I guess I'm not sure what the point of this is.
  5. Apr 6, 2007 #4
    Well it's twofold really. Firstly it is one more wacky scheme for getting mass into orbit at a lower $/kg. It can only gather atmosphere, mostly nitrogen and oxygen. But oxygen is most of the mass of rocket propellent, and nitrogen is (Im guessing) important for growing things in space or within a moon colony.

    Secondly, its for the joy of exploring problems with a bit of maths. If it needs a lot of maths I probably cant handle it, though maybe I could write a simulator. However I was wondering if there was a simpler principle that someone with more experience might immediately spot that would make this unnecessary, eg a simple argument that adding velocity in this way would necessarily increase the nearest approach to the earth.
  6. Apr 6, 2007 #5


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    Staff: Mentor

    It seems like you could come up with some trajectories that would work, at least for a few passes until the maneuvering fuel ran out on the spacecraft. You wouldn't be able to transfer much air mass per orbital pass, I wouldn't think though. Plus, it wouldn't be too popular with most of the folks here on the Earth -- transferring a portion of our atmosphere to the moon....
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