I've heard this was originally conceived as two movies. The first was about a mining ship in deep space whose crew was woken from cryo to check out a distress signal of unknown origin (if you're asking 'then what?' then you've gotten the point). The other was about a gremlin who gets into a WWII fighter plane and kills a buncha people. Put two and two together, throw in some HR Giger and tabby cat, and of course the ever gratuitous nuclear explosion, and somewhere along the line you get what would later become the model for every Hollywood attempt at an intelligent sci-fi/horror movie.