Nice concept and idea, pretty good execution just a few bugs I found, the money didn't go down when you purchased selected an upgrade, and the angle of the ship is slightly off for me in to its angle from the earth,
Some suggestions, You could try to make a slightly hi-res earth, I like the pixel style and animation but the resolution felt a bit lacking compared to the asteroids, but the asteroids themselves and their animations were fantastic! Try to randomize the pitch of the sound effects a bit as well so they don't sound so repetitive but over all a pretty short but fun game!