Is it possible to make working orbit physics like in orbiter or kerbal space program?
Yes, there are some functions in GD that allows to put an object at a specific distance of another object or position in a specific angle.
So, the tools to visually implement orbital realistic physics are there but you have to do the math:
I’ll see if I have Gravicannon laying around anymore.
//edit: It’s here: dl.dropboxusercontent.com/u/210143/gcannon.rar but you’ll need to fix it. Somehow it got broken (probably because it was made with GD 2.xx), culprit seems to be function events.