The documentation has this to say about Space Modules:
Space Modules are the most expensive parts of spaceships. There are three different types of Space Module:
- Habitation Module: provides living space for 10,000 people.
- Life Support Module: provides food and water for the population of one Habitation Module.
- Solar Panels: provides the energy needed for any two of the other Modules.
You can build up to 4 Space Modules of each kind.
But what about the Habitation Module and Life Support Module?
Which is which? Is the one with four circles a Habitation Module or a Life Support Module?