You are the last soldier of an expedition to Mars. Another intelligent life-form raided your ship for supplies. You and 3 others managed to escape in an escape pod, but you were too far from Earth, forcing you to land on the moon instead. Your companions have perished, due to lack of water and and food. You must make your way across the moon with limited rations to the moon base, all while fighting off the aliens, who are seemingly determined to wipe out the entire human race. Your only weapon is a phaser pistol, which is solar powered. Your advanced space suit, the O2 SS Mark II, creates oxygen out of an endless fuel source that scientists created, so lack of oxygen isn't a worry.