Thanks! And yeah I've had gates blocked before too, but I've also seen another asteroid come along and then clear the gate! The problem is if you make all the gates bigger it's easier, and I wanted a challenge. That said, as I'm typing this now I realise I could have implemented some sort of check to see if the gate was blocked and then manually clear it. Oh well!
And with regards using the keyboard instead of the mouse, it means you'd be limited to one system failing at a time, otherwise how would you know what you were inputting for? And one broken system at a time? That's not very unstable at all! ;)