Mars has no significant geomagnetic field to deflect harmful solar flares or cosmic rays. For NASA to have any sustained human presence there, it will need to protect inhabitants from deadly radiation exposure. The most sought after real estate is likely to be subterranean caves, which provide a natural buffer against the harsh conditions. But if Mars’s explorers land in spots far from such rocky hollows, their protection will need to come from habitats with meter-thick walls and ceilings that reduce radiation exposure to tolerable levels. (See the Quick Study by Larry Townsend, Physics Today, March 2020, page 66.)
Obtaining bulk material for that purpose is a challenge. With no infrastructure or economy on the red planet, it won’t be as simple as popping down to a local builders’ supply store for a few bags of cement or pile of bricks. Everything used on Mars will have to...