Asteroid Colony - Refinery (cannot attack it) and Rock Formations are the main object.
About 40 minutes to kill everything with Proteus+Warden. It has huge waves.
Note: Grand Admirals hit HARD at 70km.
Warping to 100 put enemies 100-120km away.
Initial wave
Next wave spawned after killing one of the destroyers
Next wave
Next wave
Next wave
The end.