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Hot gas expansion rate into outer space

  1. May 25, 2013 #1
    Good Morning Sirs,
    it seems to be surprisingly hard to get the numbers of a mystery:

    How fast expand hot rocket exhaust gases into empty space?
    Of course aside from its exit velocity!
    Does the expansion interfere with the impulse direction?
    I.e. is the impulse omnidirectional effective within the engine nozzle exit angle of assumed 90deg.
    (or even beyond that)?
    Can't hardly wait!
  2. jcsd
  3. May 25, 2013 #2


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    Not sure I really understand you question fully, but the expansion rate of the gasses once they have left the exhaust nozzle is irrelevant to the thrust that they provide for the rocket so it might be an interesting fact to know for some reason but it is does not matter for any practical purpose.
  4. May 26, 2013 #3
    It IS irrelevant - unless you anticipate certain things underneath your engine nozzle.
    Now it's going to disable a certain moon landing skepticism around some friends of mine.
    The argument here: The gases hit the moon ground (at 10ft hight) in less then 2ms
    (at 15,000ft/s)- allegedly quick enough to outgun the immediate expansion of the stream
    (with a force of at least 1,500kp). It would have inevitably left a distinctive impact
    on the flour light dust underneath the firing descend engine cone - easily to see on the scores of images.
    IMHO the expansion rate actually EXCEEDS the stream velocity and distributes the gas-pressure
    evenly everywhere - with a resulting low exposure of the dust surface below.
    I'd be grateful for a proof.
  5. May 26, 2013 #4


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    First you ask about something happening in outer space, now you are talking about the surface of the moon.

    What is it you really want to know?
  6. May 26, 2013 #5

    Vanadium 50

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    Note that moon landing hoax theories are a banned topic on PF. If this goes in that direction, this thread will quickly close or disappear.
  7. May 28, 2013 #6
    Dear Sirs,
    as hopeless American by heart and mind I'm utterly surprised to find here - out of all places -
    a institutional THOUGHT CONTROL.
    The dedicative discussion about some ridiculous "sci"-fi" movies
    surely is more easy to do compared with the real and most strange phenomena
    men kind encountered in the outer space - which includes to me
    the earth moon because of its nature.
    Admittedly its more funny to be with BASICALLY open minded people.
    Therefore: By by and God bless you!
    Jay Hill
    PS Why do I have to think on Bob Dylan?
    I hear him sing: The Disease Of Conceit...
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