I've been working on an add-on to Celestia with the planets and some stuff like Enif Station and 3rd Fleet Headquarters.
I am ignoring stuff like the difference between Freespace Capella and Real Capella.
I've created a
thread on the shatters.net forums showing it.
You can download the add-on from
http://klightspeed.killerwolves.net/freespace2.tar.gz.
Due to not knowing whether I am permitted to distribute the textures and models with the add-on, the add-on must be built from the textures and models from Freespace2.
Note that to use the add-on, you will need to extract the textures from Freespace2 and possibly the media VPs to freespace2/textures/medres and the models to freespace2/models. With the textures and models in place, and with the above tarball extracted, you will need to "make textures" and "make models" from the freespace2 directory.
Here's the GTD Orion wreck portrayed in the opening cutscene of Freespace2:

Celestia URL:
cel://syncorbit/Deneb:a:h:GTD%20Orion%20Wreck/2367-01-01T16:27:47.61259?x=WgYB9nYVIURNqLRX&y=B2NGGzEnfR+aLIqm&z=1NQx6bIV48bBJUko&ow=0.178307&ox=0.616308&oy=0.751540&oz=-0.153487&select=Deneb:a:h:GTD%20Orion%20Wreck&fov=45&ts=1<d=0&rf=841623&lm=2048