"Note: Make sure you have Java enabled on your browser to see the applet. This applet is provided as a 3D orbit visualization tool. The applet was implemented using only 2-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances. See the "High-Accuracy Ephemeris" link in middle of the page to do this."

I've noticed the same types of problems before. I think this simple program is only good for near term illustration of position and orbit diagramming. They use far more sophisticated software for the sentry calculations.

Regards,
Mark