ok... we need to do several things:
better asteroid fields, and make capships automatically defend themselves against asteroids [they have guns, they can shoot their own way through asteroid fields with primary non-beam weapons [or fighter particle beams]]
celestial objects - like planets, stars, black holes, etc which would have gravity wells and certain physics alterations as you get near them... ie a planet would have a set of distances MaxAtmosphere and StartAtmosphere - the distances at which the Atmosphere becomes it's "thickest" and the distance at which it begins - if you go past MaxAtmosphere the game momentarily pauses and switches from Space-flight mode to Terrain-Skimming mode, or with Stars if you get so close you burn up, or black holes you get pulled in [all celestial objects will have a $gravity coefficient.. earth being g=9.81m/(s*s) would be 1, something that's 19.62m/(s*s) would be 2, etc
Terrain-Skimming mode for skimming planets, some format for expressing permanant terrain features would have to be created.. i leave implementation to the terrain-experts