100* would be kinda small... Maybe the player will notice the repetition (every cube has the same arrangement - if you make it too small, it might become a visible pattern)
*(Btw, I have no idea if the unit for cube_size is the same measurement the game uses for solar objects... I don't think so because 100 is really small.)
Therefor, you might want to add a few asteroids archetypes to the cube. I'm not 100% sure but I've always taken the 1st three values as X,Y,Z coordinates within the cube, and the 2nd three as X,Y,Z rotational values. E.g.:
<pre><font size=1 face=Courier>{Cube}
asteroid = minedout_asteroid10, -0.100000, 0.200000, -0.200000, 22.5, 0, -22.5
asteroid = ice_crystal_asteroid80, 0.700000, 0.300000, -0.300000, -22.5, 0, 22.5
asteroid = ice_crystal_asteroid120, 0.200000, 0.400000, 0.200000, 22.5, 0, -22.5
asteroid = planet_frag_asteroid60, 0.350000, 0.800000, 0.300000, -22.5, 0, 22.5
asteroid = nonmineable_asteroid60, 0.500000, -0.700000, -0.200000, 22.5, 0, -22.5
asteroid = planet_frag_asteroid30, -0.500000, -0.300000, 0.800000, -22.5, 0, 22.5
asteroid = planet_frag_asteroid90, -0.300000, -0.100000, -0.600000, 22.5, 0, -22.5
asteroid = ice_asteroid60, -0.700000, 0.400000, -0.400000, -22.5, 0, 22.5
asteroid = minedout_asteroid10, 0.800000, -0.500000, 0.800000, 22.5, 0, -22.5 </font></pre>
and make sure the TexturePanels are included:
<pre><font size=1 face=Courier>{TexturePanels}
file = solar\asteroids\rock_shapes.ini
file = solar\asteroids\ice_shapes.ini </font></pre>
And if I remember correctly, there are a few quite large asteroids (.3db files, or .cmp's, whatever they are) included in the game that are not yet defined. You can define them and use them in your cube. This way you can create a cavern-like structure (drawback: the asteroids are only rendered at relatively short distance, which might look weird. You can change that too, but that might give your pc's processor much more work)