1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Putting a satellite into an elliptical orbit

  1. Feb 10, 2010 #1
    1. The problem statement, all variables and given/known data

    It is required to put a satellite into an orbit with apogee of 5R/2, where R is the radius of the planet. The satellite is to be launched from the surface with a speed Vo at 30degrees to the local vertical. If M is the mass of the planet, show that (Vo)^2 = 5GM/4R. Assume zero rotation.

    2. Relevant equations

    3. The attempt at a solution

    I tried to use conservation of energy first i.e., 1/2*m*Vo^2 - GMm/R = 2GmM/3R
    3R/2 - distance between planet's surface and apogee).

    Needless to say, that doesn't yield the right answer, I was wondering perhaps elliptical orbits have some other requirements -- perhaps the inclusion of angular momentum?

    Thanks, I appreciate any nudge towards the right direction.
  2. jcsd
  3. Feb 11, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    I haven't worked on elliptical orbit problems myself, but I see nobody else has responded so I'll go ahead and comment on two issues I see with what you've done:

    1. For potential energy, use the distance from the satellite to the center of the Earth, not the Earth's surface.

    2. At the apogee of the elliptical orbit, v is not zero. So there should be a kinetic energy term in your expression for the total energy at apogee.

    And, as you said, using angular momentum may be useful here.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Putting a satellite into an elliptical orbit