2nd generation lunar habitats can be further divided into four main structural types:

- Inflatable structures
- Cable structures
- Rigid Structures
- Underground construction

All structures have to satisfy many different design criteria, among them transportation, ease of construction and maintenance. The one optimum solution is non-existent. So every concept's strengths an weaknesses have to be judged carefully.
For example, one of HE-SQUARED's designs for a lunar habitat is a half-cylindrical rigid shell approach.