Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Astrophysics- Calculate the altitude of a geosynchronous orbit

  1. Sep 16, 2008 #1
    a)Calculate the altitude of a geosynchronous orbit (an orbit that has an orbital period of one sidereal day)(altitude is measured from the surface of the earth/ The "r" in gravitational equations is always measured from the center of mass of an object. one may assume a circular orbit.)

    b) how does the altitude of this geosynchronous satellite compare to the average 354 km altitude of the International Space Station?

    c) Calculate the orbital period of the international Space Station (assume circular Orbit)

    this was my attempt

    a= (mu*(1/(2pi))^2)^(1/3)
    a= (398600(1/(2pi))^2)^(1/3)

    but for b) im not sure if my prof. wants a word explanation or to solve the actual difference so i provided a word explination

    then for c)

    T = ((2\pi)/(mu)a^(3/2))^(1/3)
    but am unsure what mu would be.

    i'm not sure if what i'm doing is correct because we never went over this in class so i tried do this based off internet research. any help would be appreciated
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 16, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    The equation you have is Keplers third law (ignoring the mass of the satelite)
    ( period / 2pi )^2 = radius^3 / GM
    If you plugin G and M=mass of the earth you should get the right answer, be careful of the units.
  4. Sep 16, 2008 #3
    can this equation be used for both part a and c?
  5. Sep 17, 2008 #4


    User Avatar
    Science Advisor
    Homework Helper

    The law describing their behaviour is the same, you simple have to find radius in one case given the period and the period in the other case given the radius.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook