Habitats

Pressure wants a light, sealed, curved shell. Radiation wants metres of dense material. A pressurised structure that also carries three metres of regolith on its roof is carrying roughly five tonnes per square metre — which is why almost every credible design decouples the two: an inflatable or rigid pressure vessel inside, and an independent shielding layer of regolith piled, bagged or printed over the top.

That is where 3D printing enters. Regolith can be sintered or bound into structural blocks and shells using local material and machine time instead of launch mass — the approach behind NASA's 3D-Printed Habitat Challenge and most agency concepts. The habitat arrives as a compact pressure vessel; the shielding is manufactured on site over months.

The strongest option is not built at all. Mars has lava tubes, and Martian gravity allows them to be far larger than terrestrial ones — candidate tubes over a hundred metres wide have been identified from orbit. A habitat inside one sits beneath tens of metres of solid rock: better radiation protection than anything constructible, plus a stable thermal environment and complete shelter from dust storms and micrometeorites.

Whatever the shell, the interior is the same problem. Airlocks become dust-control boundaries, suitports keep contaminated suits outside the pressurised volume entirely, and the greenhouse area needed to feed the crew is several times the living area. A Mars habitat is mostly agriculture and machinery with people living in the gaps.