Here's another idea, although it might not be feasible: For the combat-UI asteroids, we could render an animation of an asteroid spinning for, say, four different asteroids. Those animations can then be loaded into the game and placed in a randomized ring around the sun. Yes, this does mean the asteroid's relative "position" will not change with the position of the camera, but in my head, a 2D animation of a 3D object, arranged in 3D space, actually seems pretty cool, and shouldn't take up much resources. It's just an animation, so Ogre won't have to calculate the meshes or whatever.
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