I am currently working on the fourth level. Here is a draft of the in-game level description:
You will need to sneak into the area of the colony that has been taken over by the aliens, plant explosives, and escape. In order to get into the alien territory without being detected you have to take a very dangerous route though the ore refinery. The refinery has an ore crushing system which consists of closing walls and large moving parts. It is not an area that one would expect to be able to travel through and this is why we expect your entry will not be detected.