Never played this game but from the many screenshots I've seen and discussions I've read sounds like your describing something like Planetside.  (Is that right?  Not sure if that's the name - eh just throwing that out there) 

Planet Side really doesn't have space fighting.   Its got fighters and bombers and Transports that assist ground invasions of bases.

In alot of ways its like First Strike.  It to has a system similar (if not identical) to Whithering Fire.  Everyone can damage tanks/turrets/mechs but only Anti Heavy Armor weapons really get the damage on, and those don't do much damage to infantry (since its hard to hit someone directly with it)

Know what... when I think of the rest of Planetside... FS is ALOT like it, just with a different theam :-P

This may sound stupid and is probably stupid, i have no idea of coding/mapping (im going to start mapping soon) but what if the space battle is underground? Ok this is a stupid idea, but ima proceed anyway:

So lets say hoth, the map level of hoth would be so high there would be so much space under it for a little space map, so the idea would be if you fly high enough in the sky, you would get warped or something under the actuel map, wich would be a space map, there the transporters or whatever need to get out of hoth space. This is most likely impossible.

My other idea would be reduce escape from hoth drasticly, and make hoth image in space smaller, so when u approach, some kind of trigger could make the engine believe you are no longer in space and you can eject while seeing a small map when u fly closer to the planet, there u could land and do ground battles. It would be as a little pizza map in space itself, but the engine would believe you are no longer in space. If this would work, there would still be the problem that on the ground you would feel like your on a un-protected open ship with stars all around you.

'Kick pie? what was that matt?' 'You know kick pie! Everyone says. Join the party dude!'
-This was a dramatic reanactment, feelings of Nausea and or Parinoia will pass...

The idea is very cool and believe me if it could be done easily, im sure we would have discussed it.

the only engine i know of with a plane that warps you to another location, is the UT2004 engine, shame nothing like that exists in BF engine... great idea but shame..

i didn't really mean warping i ment something that would give you the illusion of passing through a planet's atmosphere into space. Like a layer that when you enter with your ship is extremely cloudy an visibility is like, 0. This would be teh 'upper atmosphere' which is really just a thin layer in the sky. When your passing through the layer maybe it could make your ship move much slower to give the illusion of a longer jorney thorugh a greater distance, an with no landmarks to check himself agianst the player would be fooled. Of course i know absolutely zilch about programming, an i'd bet having that bi layer up there would probally be super laggy as you've said. Best leave it to the proffesionals i guess