Buried settlements and mutual support around Mars

Radiation makes digging into the Moon or Mars a core design requirement. The Earth-facing Moon is close enough to support early testing and emergency intervention before the same methods move outward. Once Mars has both a surface settlement and a moon base, each can provide an evacuation destination and support point for the other within days. Underground spaces also make temperature, pressure, oxygen, and moisture easier to control than exposed surface habitats, while stored water can perform useful work as radiation shielding instead of remaining dead mass. The result resembles naval damage-control thinking: survivability comes from protection, compartmented systems, and a nearby fallback when failures occur.