Thank you very much for your prompt replay. At the moment I am using eclipse as IDE, do you think it is a good way to start?

I think that most of the problem is to understand the way an OO application works: do you think it would be possible to you to prepare a simple simulation for a 3D circular orbit around the earth? That would be a nice way to start, in order to implement new features like elliptic orbits, perturbations due to the earth oblateness, drag, third body and, most of all, understand the technique involved in this example.

Best regards,
Daniele Romagnoli