Nice work, especially as a solo dev! I liked the mechanic of getting knocked away from the thing you were supposed to protect -- I felt like you didn't even need lives at that point: just have the aliens knock you away and then demolish the Earth. That said, I'm glad you didn't do that, because the knockback effect, coupled with the lower thrust on the player ship, made navigating back to Earth brutally hard. :P
A fun game that evokes arcade classics. Wish you had had more time as I think you are on to something fun!