from visual import *
from __future__ import division

G = 6.7e-11
deltat = 100
numberOfSteps = 500
t = 0

Earth = sphere(pos = vector(0,0,0), radius = 6.4e6, color = color.blue)
craft = sphere(pos = vector(-13e7,6.5e7,0), radius = 3e6,color = color.green)

craft.m = 15e3
craft.p = craft.m*vector(3e3,0,0)
Earth.m = 6e24

trail = curve(color = craft.color)

while t < numberOfSteps*deltat:
    rate(100)
    r =    # you need a vector that points from the Earth to the spacecraft
    rmag = mag(r)
    Fmag =   #calculate the magnitude of gravitational force on the craft due to the Earth
    rhat =  #what is the direction of the vector that points from the Earth toward the craft?
    Fnet = -Fmag*rhat

    craft.p =  #update the craft's momentum
    craft.pos =#update the craft's position

    trail.append(pos = craft.pos)

    t = t+deltat