This is DEFINITELY one thing that will be changed, but here is a suggestions:

(1) make the asteroid bigger and maybe move faster to account for it destroying the SD tower so easily
(2) show the SD get a quick laser shot or two to show that the commander just wasn't watching this big, huge asteroid coming straight for his bridge and just twiddling his thumbs.
(3) just don't add a different (and better) explosion; show the asteroid plowing into the conning tower, with the tower collapsing inwards and blowing apart, with the asteroid turning into chunks or the force of the explosion launches it in an upward 30 degree arc (for reference, watch NIGHTMARE ON ELM STREET 4 when Freddy's claw comes out of the ground and the truck hits it full force and wraps around the glove for an idea of what to do with the conning tower when hit)