Habitability
These stations have various issues that limit their long-term habitability, such as very low recycling rates, relatively high radiation levels and a lack of gravity. Some of these problems cause discomfort and long-term health effects. In the case of solar flares, all current habitats are protected by the Earth's magnetic field, and are below the Van Allen belts.
Future space habitats may attempt to address these issues, and could be intended for long-term occupation. Some designs might even accommodate large numbers of people, essentially "cities in space" where people would make their homes. No such design has yet been constructed, since even for a small station, the current (2010) launch costs are not economically or politically viable.
Possible ways to deal with these costs would be to build a large number of rockets (economies of scale), employ reusable rockets, In Situ Resource Utilisation, or non-rocket spacelaunch methods such as space elevators. For example, in 1975, proposing to seek long-term habitability through artificial gravity and enough mass in space to allow high radiation shielding, the most ambitious historical NASA study, a conceptual 10000-person spacestation, envisioned a future mass driver base launching 600 times its own mass in lunar material cumulatively over years.
Read more about this topic: Space Station