Just as we reach space, aliens find our planet and decide to take it over. There is now an all out invasion focused on wiping us off the planet. Thankfully our scientists have discovered a way to build high-tech turrets in space to let us destroy these aliens before they even get into our atmosphere. Hit the B button to choose a turret to build and place it in the way of the aliens. As you destroy the ships you get money from their salvage which can then be used to upgrade then turrets and build more. Hit the spacebar to send the next wave down and make sure your defenses are suitable beefed up enough to destroy all the aliens and save the earth.