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Eccentricity of orbit. Apogee and perigee positions and distances

  1. Aug 2, 2008 #1
    1. The problem statement, all variables and given/known data

    A satellite is in an elliptical orbit about the Earth. The center of the earth is a focus of the elliptical orbit. The perigee (C) is the point in the orbit where the satellite is closest to the Earth's center (F). The perigee distance (P) is the distance from the perigee to the earth's center. The apogee (D) is the point furtheest from the earth's center. The apogee distance (A) is the distance from the apogee to the earth's center.

    Show that the eccentricity of the orbit in terms of A and P is e=(A-p)/(A+P).

    3. The attempt at a solution

    Not sure where to begin, i know the distance from the center of the orbit to F is sqrt(a^2 - b^2), where a is the semi-major axis and b is the semi-minor axis.
     
  2. jcsd
  3. Aug 2, 2008 #2

    Kurdt

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    Re: Eccentricity

    How is the distance from a focus of an ellipse to the centre calculated?
     
  4. Aug 2, 2008 #3
    Re: Eccentricity

    I mean the center of the elipse.

    Let c equal the distance between the elipse center and a focus.
    a = the semi major axis
    b = semi minor

    c=sqrt(A^2 - b^2)

    Is that what you meant?
     
  5. Aug 2, 2008 #4

    D H

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    Re: Eccentricity

    The center of the Earth is not at the center of the ellipse. It is at one of the two foci of the ellipse.
     
  6. Aug 3, 2008 #5
    Re: Eccentricity

    Sorry my bad, I did allready understand that, just struggled to put it into words
     
  7. Aug 3, 2008 #6

    D H

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    Re: Eccentricity

    It's a bit hard to help you here because you left out a very important part of the original post:

    2. Relevant equations

    What equations are relevant to solving this problem?
     
  8. Aug 3, 2008 #7

    Kurdt

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    Re: Eccentricity

    If you look up an ellipse in a text book or even on the internet you'll probably find what you need to do this question.
     
  9. Aug 3, 2008 #8
    Re: Eccentricity

    yeh i will just ask my teacher, i can get an answer that isnt wrong, just not sure if its the answer the teacher is looking for.

    Thanks for all your help you guys!
     
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