Earth Attackers

Earth Attackers (I need a better title) is a game inspired by space invaders and Tyrian 2000. Very early in development but it will have a store in between levels that will allow you to upgrade your abilities, which will be important as the game will get harder and harder.
PLOT:

A massive alien ship has appeared on the edge of the solar system and has released smaller drones that have started to liquefy the earth. Can you save the world from total demolition?