I really don't know if what i'm to say is possible or not, so i will ask you...
I have loved Celestia from years... it is a sexy piece of software. The only thing make me a little annoyed is that Celestia is "fixed".
I've just discovered Orbiter. Is a freeware (not free-source) space flight simulator. (you can find it at http://www.orbitersim.com).
In Orbiter ALL objects (planets, moons, ships, etc...) orbits are calculated. So if you fly in the Space Shuttle, and you do a thruster burn, you change your vectors, and your orbit change.
I know that doing this for Celestia is nearly impossible (Orbiter "world" is confined in a single solar sistem at time). I'm just asking if inserting a "calculated orbit" object in a "fixed orbit" system is really so hard.
Anyway, Celestia is still the best App in my HD.
Sorry for my english, i'm Italian.