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!

Energy required to move an object in orbit?

  1. Jan 4, 2010 #1
    The International Space Station, with a mass of 370,000 kg, is orbiting the Earth at a height 335 km and needs to be boosted to an orbit of 352 km. Calculate the energy needed to boost the ISS to its new height.

    m = 370,000 kg
    M = 5.98 x 10^24 kg
    G = 6.67 x 10^-11 Nm^2/kg^2
    Initial distance from earths center = (6.38 x 10^6m) + 335000m
    Final distance form eath's center = (6.38 x 10^6m) + 352000m

    Using Ep = GMm/r

    I calculated
    Epi = (6.67x10^-11)(5.98x10^24)(370000)/((6.38x10^6)+(335000)) = 2.316682247E13


    Epf = (6.67x10^-11)(5.98x10^24)(370000)/((6.38x10^6)+(352000)) =2.316676064E13

    I found the difference of the two, and took it as my answer, 6.2x10^7 J

    I feel I'm doing something wrong, Thanks in advance for any help!
  2. jcsd
  3. Jan 4, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Have you considered the difference in speed (and so Kinetic energy) for the two orbits?
  4. Jan 6, 2010 #3
    Hmmm, so I would have to find the total energy,

    Et = Ep + Ek = G Mm/r + .5mv^2

    ok I think I got it now.
  5. Jan 6, 2010 #4


    User Avatar
    Science Advisor
    Homework Helper

    Remember that V is also a function of r and M (there is a fixed speed for each orbital height)
  6. Jan 6, 2010 #5
    yes, v = sqrt(MG/r)

    so figuring out the difference in total energy, would that give me the amount of energy needed to boost the space station to its new height?
    what I mean is, does difference in total energy = amount of energy required to boost to new height?
  7. Jan 6, 2010 #6


    User Avatar
    Science Advisor
    Homework Helper

    Yes actualy thats the minimum energy, assuming you want it to orbit in the same direction
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook