Universe Today
"The amount of material for an effective shielding may then be well beyond what is practicable for most aerospace applications. The aluminum walls of the ISS, for example, are about 7 mm thick and are effective in LEO, but it is unlikely that such shields would be enough in interplanetary space, where they might even increase the dose absorbed unless substantially thickened."
"A NASA study found that a large space station or habitat required a shielding of 4 t/m2 of martian regolith (considering that its density is between 1,000 kg/m3 at the surface to 2,000 kg/m3 at a depth of a few cm, this corresponds to a thickness of 2 m, or less if the material is compacted [by being] sintered by lasers), to achieve an effective dose rate of 2.5 mSv/y...
"An underground shelter can be used also as sleeping quarters and for all those activities in which there is no need for looking outside (such as looking to videos or enjoying other entertainments), but living always in underground structures may put at risk the psychological health of the colonists (claustrophobia), decreasing also their ability to assess distances when outside the outpost (difficulties in performing EVA tasks) and may be particularly bad in case one of the activities of the outpost is space tourism. Another problem is the construction of greenhouses, which should allow the light from the Sun to enter for powering the plants’ biological mechanisms."
"At the boundary of the "traveling sphere" there will be the propulsion systems necessary for both the voyage and the contemporary rotation of the space vessel, in order to generate artificial gravity during the roundtrip. These spacecraft have been developed to better integrate the load-bearing elements of the ship with the structure of the modules. The bearing structure of the sphere, which constitutes the body of the vessel, is formed by a hexagonal and pentagonal diagrid and therefore it is easier to connect and aggregate the modules, which have similar shapes."
