After showing the Planetary Orbit Simulator at the AAPT workshop in Edmonton we realized that the orbit scaling method could be made more intuitive. Here is the new version with improved scaling:

Updated Planetary Orbit Simulator

Notice that instead of staying at a fixed size on the screen the orbit temporarily expands or contracts as the semimajor axis length changes. Check out the old version for comparison.

Other changes to note: there's now a scale bar in the Visualization panel, grid lines are now optional, and there are more options in the Newtonian Features panel.