Re: Shuttle landing path

From: George Roberts (
Date: Thu Jul 21 2011 - 22:00:28 UTC

  • Next message: Paul Grace: "RE: Shuttle landing path"

    Wow, rick, nice find!  To summarize the above thread there are 2 more 
    reasons why ascending is better.
    1) Noctilucent clouds are more prominent further north and nasa was 
    concerned about the ice particles possibly causing damage at mach 25 
    although it sounds like further research has deemed it safe for the shuttle 
    but nasa probably didn't feel a strong need to change their policy.
    2) More fuel is needed for descending path or alternatively higher insertion 
    angle accuracy is needed.
    #2 is more complicated.  When the shuttle first "hits" the atmosphere, 
    because of the rotation of the earth, the farther north you hit the 
    atmostphere the higher the speed differential because the earth moves more 
    slowly at higher altitudes (more slowly away from the shuttle).  This is 
    supposedly 291 meters per second difference on ascending versus descending 
    from the ISS although that number sounds suspect to me.
    If the shuttle "hits" the atmosphere at a higher velocity, then the angle 
    you hit the air at has to be even more precise so you don't accidentally 
    skip right out of the atmosphere again and have to start over but with 
    possibly no propellant left or alternatively hit "too hard".  This angle has 
    a 0.1 degree tolerance.  So they prefer to use more propellent to slow the 
    shuttle down more on descending passes to keep this tolerance the same.  I 
    suspect this also has to do with the ancient software used to land the 
    Obviously the shuttle doesn't hit the air instantly - it is a gradual 
    thing - but this explanation, although simplified, still holds on a gradual 
    entering of the atmosphere.
    Although I doubt they save and sell the extra propellent - I suspect it is 
    all vented away.  So I don't see how this matters much.
    - George Roberts
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