Note that Star Citadel has two variants: a modern version, from which these screenshots are taken, and a classic version, which is designed to play as much like the original Star Castle as possible.
Click on the images to see larger versions.
Well this is really the conclusion of our final attack run from the second gallery. You can see that I've done solid damage to the shields, even managing to punch all the way through, because the cannon is in the process of firing back (it'll take advantage of the smallest gap - here only one segment of the inner ring has been destroyed).
And I've managed to come back in for another attack run, but some wild firing means I haven't done much other than destory a couple of extra shield segments. The mines are now on the prowl as well. Unlike the original Star Castle, these leave a short trail behind themselves, which makes them slightly easier to keep track of.
However, this has now become a very risky situation as I've inadvertently flown inside the radius of the shields. It looks like I might have got a good shot off but, if that goes wide, it's pretty likely the cannon will be able to swing round and blow me away whilst I'm trapped close to it as that yellow shield segment passes me.