Alien Zombie Death

You are a lone Spaceman doing something or other on a mining platform floating around a random planet. They are the Alien Zombies. Intent on the destruction of all Spacemen doing stuff... in space. How long can you hold off the hordes? There are seven planets in the solar system each with one moon, making 14 levels. The planets and moons are initially locked and can be unlocked by collecting medals. Medals are awarded for killing various quantities of aliens, picking up coins and achieving scores.