After receiving some feedback, the button press sound effect has been changed from a hard click to a softer, lower-frequency "bomp."  Hopefully, this will provide a less jarring aural experience for everyone.

The position of the two options from the Main Menu, "Lunar Orbit" and "Horizon Diagram," have been switched.  It seems to make more sense to have the first simulator that one would use on the left, and the second on the right.

As promised long ago, I've uploaded a PDF of the laboratory exercise for which this simulator was designed.