One of the biggest challenges towards colonizing the solar system (and beyond) is gravity–or rather the lack thereof. Gravity plays an important role in the health of the human body, and the lack of it for long periods of time can be dangerous for future space colonists.
Although it is currently unknown at what percentage of Earth gravity is necessary for human survival, we may have to build enormous space stations that can simulate gravity via centripetal force.
(AstroProf’s Page) In science fiction, this is an easy problem to solve – you use artificial gravity generators. Actually, I rather think that this is an invention of producers who wanted to keep special effects budgets down rather than any attempt to overcome physiological problems! […]
For large space colonies, with a very big radius, the colony could be rotated at a comfortably gently rate, people living in the ring at the outer edge of the colony would feel just like they were on Earth (if f = 1). So, this is how we’d more likely generate artificial gravity, rather than with the graviton generators used in science fiction.
Since most of the solar worlds lack the necessary gravity to enable human colonies upon their soils, we may be stuck living in orbital stations except for brief visits to the surface.
Although this may produce an acute form of cabin fever (if the stations are small that is) it is better to ere on the side of caution in this regard than to suffer the side effects of micro-gravity.
Update: Adjusted image for size and credit. Also added extra category for post.