Icarus is a multiplayer survival game that uses mission-based sessions. These are called prospects which give the player a certain amount of time to complete their mission and return to orbit. While on the surface, the players can explore, gather resources, and build a base. But you may be wondering if your base remains after completing missions.
After you complete a mission, any base or other things you have left behind on the planet are destroyed. This means you cannot return to the planet and pick up where you left off. Each time you return to the planet on another mission, you must start over.
The exception to this is the Outpost mode. In this mode, players can drop in and out as they want, and any structures they build will remain. Players cannot complete missions or gain experience in this mode. They also cannot take anything from Outpost mode into the main game mode.
You are better off building small shelters or using caves as your bases on shorter missions. Building a large base is pointless unless you have a lot of time so think carefully before building.
For more information on Icarus, check out How to complete Kill List Extermination Prospect in Icarus and Where to find gold ore in Icarus on Pro Game Guides.