This is a paid asset, but now you can download SciFi Space Base Free.
Detail this asset from Unity Store: Original Link
SciFi Space Base v1.0.1
This pack includes over 300 modular & customizable prefabs for building your own space base. It’s designed to work in space and also as colonial base in outer planets. It includes several rooms and corridors wich can be divided with doors. You can create your own rooms with modular assets. Also materials can be customized for each part of the asset. You can use the included or your own custom ones. It doesn’t require many lights since everything is illuminated from GI with textures. It is suitable for exteriors, interiors and also Top/Down games.
Finally decorate the level with the props library included or mixed with other assets and you’ll have your space scene ready!
Asset includes additionally some extra freebies from Essential terrain & Alien terrain and other extra material.
Check out [ASSET INFO] link above for extended info.