The idea was nice and fitted the theme.
Mechanically, it was strange that the more I got hit, the easier it became, because I only had to focus on one beam. I think there should be an advantage to having multiple canons, maybe multiple could fire independently?
I also didn't find that the repairing added too much to the game, especially with such a long delay. I would probably make it so you game over when you don't have any canons, but they either repair themselves over time, or have a way to build them up.
Nice entry, and good luck :)