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Typical energy ratios to get into orbit? (height, friction, velocity)

  1. Oct 29, 2013 #1
    I realize the answer depends how where in the atmosphere speed is increased more, and whether a higher orbit or lower orbit is desired, and the shape size and weight of the craft. But I'm just curious about typical ratios.

    About what fraction of the fuel goes to lifting the weight of the craft? The weight of the fuel? (giving them potential energy)
    What fraction goes to giving the craft the kinetic energy (final speed)?
    What fraction goes to just overcoming friction through the atmosphere?

    Thanks. lots of math with the atmosphere thinning and the reynolds numbers changing and fuel mass and speed changing.
     
  2. jcsd
  3. Oct 29, 2013 #2

    mfb

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    Most of the energy goes into the velocity and heat of the fuel, most of the interesting energy goes into the kinetic energy of the rocket (for low earth orbits), and some smaller fraction (I think it was something like 10% compared to the kinetic energy) into potential energy.
    For higher orbits or even escape routes, the initial part is the same. Gravity exchanges kinetic energy for potential energy afterwards.

    For a given rocket, it is easy to calculate the final potential and kinetic energy of the rocket. Atmospheric drag is hard to evaluate, but it is a small contribution.
     
  4. Oct 29, 2013 #3
    That all makes perfect sense. I kind of should have known drag would be a small portion, since it only goes 400 miles up, and most of that is through very thin air. Only about 3-5 miles of the air is remotely thick. However, high velocity through thin air could still mean high drag.

    So kinetic energy is the hurdle...

    I guess the reason we don't have large telescopes hanging from balloons instead of in orbit is the telescopes are too heavy and would need a very big balloon. The balloon blocking the view could be solved by suspending the telescope well below the balloon so it is angularly small at that distance.
     
  5. Oct 29, 2013 #4

    mfb

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    Right.

    Balloons are also unstable.
    For small telescopes, the atmosphere is not so problematic, and large telescopes are really heavy.
     
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