First I would like to say that it's great to find a program like that and on top of it it's open-source!!! - Thanks!!!
I would like to see the Shoemaker-Levy's course in Celestia. I understand that it's problematic to desribe it's movement with mathematical formulas because it's stopped existing in 1994 (one could do it dividing its move into periods). Sorry if it's a lame question but I don't know how astronomy (and celestia) describes moves of objects. Google search returned a lot of noise
Best regards,
Marek
spec (at) webtech (dot) pl