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Homework Help: Hohmann transfer orbit to Jupiter

  1. Sep 12, 2012 #1
    1. The problem statement, all variables and given/known data
    You may assume circular planetary orbits.
    a. Calculate the velocity (relative to Earth) at Earth's orbit of the Hohmann transfer orbit that is tangent to both Earth's orbit and Jupiter's orbit.

    b. calculate the minimum velocity necessary to launch a spacecraft from the surface of Earth to Jupiter, ignoring Earth's rotation

    c. calculate the minimum velocity necessary to launch a spacecraft from the surface of Earth to Jupiter, including Earth's rotation but ignoring its obliquity

    d. calculate the time required for a spacecraft moving along a Hohmann transfer orbit to travel from Earth to Jupiter

    e. repeat part (b) for Hohmann transfer orbits to Mercury and Venus.

    2. Relevant equations

    vis viva:
    GM(2/r - 1/a)

    KE = 1/2mv^2
    PE = -GmM/r

    kepler's 3rd law:
    P^2 = a^3

    3. The attempt at a solution

    a. r = 1 AU = 1.5e11 m
    2a = 1 AU + 5.2 AU = 9.2e11 m .... a = 4.64e11 m

    plug values into vis viva equation, v_h@Earth = 38651.6 m/s

    b. ??? energy balance ???

    c. ??? like (b) with added twist ???

    d. a = 3.1 AU, P^2=a^3 ... P = 5.458 yrs, want 1/2 P which is 2.73 years

    e. ??? same as (b) ???

    I think (a) and (d) are correct, but not sure how to set up for parts (b) and (c) (and thus (d))... please help!!!!!
  2. jcsd
  3. Sep 12, 2012 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Rather than simply guessing "??? energy balance ???" you need to actually try to do the problem and show your work. You have an idea of what you could try, so try it.
  4. Sep 12, 2012 #3
    so i'm not sure how to set up an energy balance for a velocity change, hence me posting the thread...

    total energy should be conserved, so the sums of the kinetic and potential energies should be zero - right?

    but again, i don't know how to set that up for the velocity change.

    i know the hohmann orbit velocity from the vis viva, i don't know how to calculate the launch velocity without rotation (or with rotation). i doubt it is subtracting the earth's orbital velocity from the hohmann orbital velocity, but that's all i've got
  5. Sep 13, 2012 #4


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    Staff: Mentor

    Hohmann orbit velocity is reckoned in the Sun's frame of reference, independent of the Earth's motion. So any motions of the Earth that help or hinder initial velocity change can be taken into account by judicious timing and aiming, and adding the appropriate offsets :smile:

    The other factor is Earth's gravity for a spacecraft leaving the surface or near vicinity of the planet. I suggest pondering on "escape velocity" and consider the asymptotic speed for objects launched (ballistically) at speeds greater than escape speed.
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