Defend the Earth

You are a veteran space force pilot. A unknown extraterrestrial civilization has just started invading Earth, and now the fate of mankind rests in your hands! Will they be stopped or succeed in their invasion? Features: Campaign with 5 levels4 difficulties (Easy, Normal, Hard and Nightmare)Destroy alien ships and asteroids to earn money6 purchasable spaceships4 purchasable upgrades Controls: WASD/Arrow Keys to moveLeft Mouse Button/E to shoot