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from __future__ import division from visual import * from visual.graph import * scene.width=1024 scene.height=760

1. CONSTANTS

G = 6.7e-11 mEarth = 6e24 mcraft = 15000 deltat = 60 t = 0 mMoon = 7e22 scale = 800000 c=2.99792e8

1. OBJECTS AND INITIAL VALUES

Earth = sphere(pos=vector(0,0,0), radius=15e6, material = materials.BlueMarble)

1. Add a radius for the spacecraft. It should be BIG, so it can be seen.

craft = sphere(pos=vector(-60160000,-192000,0), radius=2e6, material = materials.marble) Moon = sphere(pos=vector(4e8,0,0), radius=1.75e6, material = materials.marble) vcraft = vector(735,2849,0) pcraft = mcraft*vcraft

trail = curve(color=craft.color) # This creates a trail for the spacecraft

1. scene.autoscale = 1000000 # And this prevents zooming in or out

pscale = Earth.radius / mag(pcraft) fscale = Earth.radius/ ((G*mEarth*mcraft)/mag(craft.pos-Earth.pos)**2) dpscale = 500 * Earth.radius/mag(pcraft)

r_EarthMoon = Moon.pos - Earth.pos #Relative position vector from Earth to Moon r_EarthMoon_mag = mag(r_EarthMoon) F_EarthMoon_mag = (G*mcraft*mEarth)/(r_EarthMoon_mag**2) r_EarthMoon_hat = r_EarthMoon/r_EarthMoon_mag

Force_EarthMoon = (-r_EarthMoon_hat)*F_EarthMoon_mag #Force on Moon due to Earth pMoon = Force_EarthMoon / deltat

1. CALCULATIONS

print("p=", pcraft) while t < (10e10):

   rate(500)   # This slows down the animation (runs faster with bigger number)
   rE =  craft.pos - Earth.pos
   rEmag = mag(rE)
   FEmag = (G*mcraft*mEarth)/(rEmag**2)
   rEhat = rE/rEmag
   FEnet = (-rEhat)*FEmag

   rM =  craft.pos - Moon.pos
   rMmag = mag(rM)
   FMmag = (G*mcraft*mMoon)/(rMmag**2)
   rMhat = rM/rMmag
   FMnet = (-rMhat)*FMmag
   
   Fnet = FMnet+FEnet

   pcraft_i = pcraft + vector(0,0,0)
   pcraft_ii = mag(pcraft_i)    
   pcraft = pcraft + ((Fnet)*deltat)
   pcraft_f = pcraft
   pcraft_ff = mag(pcraft)
   vavg = pcraft/mcraft
   speedcraft = mag(vavg)
   craft.pos = craft.pos + vavg*deltat

   Fnet_tangent = ((pcraft_ff-pcraft_ii)/deltat)*(pcraft/mag(pcraft))*pscale
   Fnet_perp = Fnet - Fnet_tangent

   r_EarthMoon = Moon.pos - Earth.pos #Relative position vector from Earth to Moon
   r_EarthMoon_mag = mag(r_EarthMoon)
   F_EarthMoon_mag = (G*mcraft*mEarth)/(r_EarthMoon_mag**2)
   r_EarthMoon_hat = r_EarthMoon/r_EarthMoon_mag
   
   r_craftMoon = Moon.pos - craft.pos#Relative position vector from spacecraft to Moon
   r_craftMoon_mag = mag(r_craftMoon)
   F_craftMoon_mag = (G*mcraft*mEarth)/(r_craftMoon_mag**2)
   r_craftMoon_hat = r_craftMoon/r_craftMoon_mag    

   Force_EarthMoon = (-r_EarthMoon_hat)*F_EarthMoon_mag #Force on Moon due to Earth
   Force_craftMoon = (-r_craftMoon_hat)*F_craftMoon_mag#Force on Moon due to spacecraft
   Fnet_Moon = Force_EarthMoon + Force_craftMoon #Net force on Moon

   momentum_Moon = pMoon + Fnet_Moon*deltat#Update momentum of Moon
   vavg_Moon = momentum_Moon/mMoon
   Moon.pos = Moon.pos + vavg_Moon * deltat #Update momentum of Moon

   trail.append(pos=craft.pos)  
   t = t+deltat
   pcraft = pcraft_f
   deltap = pcraft - pcraft_i