Eventually, orbital stations and deep-space manned craft will have to incorporate some kind of rotating habitat within a fixed shell, akin to designs appearing in recent sci-fi flics. The superstructure of a spaceship would not rotate, but would contain a rotating element accessible from the zero-G axis.<p>An orbital station would likely be similar, with a rotating section and a stationary section, for ease of docking and to reduce the dangers of space walks (we don&#x27;t want astronauts flying out the airlock at 1 g acceleration).  I believe this was the flaw in the orbital station in <i>2001: A Space Odyssey</i>.<p>The criticism of centripetal force as a substitute for planetary gravity is that it has directional vectors of force that would make you dizzy every time you turn your head.  Presumably, the larger the structure, the more subtle these forces become.  Perhaps humans can get used to these lateral forces over time, if indeed it is an issue at all.  Having the simulated gravity would be very useful, especially in medical situations but also simply for the purposes of maintaining bone density and muscular health, both of which suffer enormously in zero-G conditions over long stretches.