I really liked the mechanic and the game is fun. Very well done!
2 small things I'd like to point out:
first I did`t realise there are numbers on earth for the turrets so maybe have them stand out a little more and also something more eyecatching for which turret is active - I don`t know what might fit best - make the whole turrets a bit darker when they are off or make the little light change from a bright red to a bright green so that it pops more - or just do that with the numbers - or have like a little force field around the active turret...just some ideas