Voyager Applets:
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The physics of this applet are pretty simple -- orbits in a Keplerian (i.e., point mass) gravitational potential. For this problem, analytic solutions exist for the position and velocity of an orbiting object as a function of time, given its orbital properties. See the "Links" section for references describing orbital calculations. We do make a few simplifying assumptions, most notably:
For Grand Tour, we calculate energy in an admittedly simplistic fashion. Each time the spacecraft needs to change velocity (to leave a planet, or to rendezvous with a planet), the energy used is considered simply to be the difference in the kinetic energy between those two velocities. So there's energy used each time it leaves a planet (where it needs to be boosted into a higher orbit) and each time it arrives at a planet (where it needs to match the planet's orbital speed). |