It always annoys me when some article or TV report says “space travel causes [some ailment]” when what they really mean is that prolonged weightlessness causes that ailment. We are, after all, traveling in space right now. We just happen to be traveling on a modest sized object that grips us to its surface with a level of gravity to which we have become accustom.
The Moon and Mars also have gravity and we don’t know yet if the levels of gravity on those bodies are sufficient to maintain good health for long stays.
In free space, we can rotate our habitat so as to create apparent gravity via the centrifugal effect. This is referred to as artificial gravity or spin gravity. So far, no space station has been constructed to do this. This is basically for two reasons: (1) The main goal of the stations was to use microgravity for a range of basic and applied research areas; (2) It was simpler and cheaper to build non-rotating stations.
Here’s an article that discusses this missing piece in our in-space infrastructure: Why Don’t We Have Artificial Gravity? – Popular Mechanics.
Eventually though, practical spacefaring will require the implementation of spin gravity and the sooner we start to develop ways to do it, the better.
Joe Carroll gave an informative online course on the Space Show in which he reviewed a wide range of issues involved in spin gravity: Lesson Three Presentation Material, 5-3-11 – The Space Show Classroom Blog
He is an expert on tethers and the first implementation of spin gravity will most likely involve connecting a habitat to a counter-weight via a long tether. The rotation rate of this “dumbbell” arrangement can be much lower for a given level of spin gravity compared to rotating a modest sized structure. It will be awhile before we can build a large wheel shaped station like that seen in 2001: A Space Odyssey.
You can use the online tool SpinCalc to vary values of spin gravity for different spin rates, radii and tangential velocities.
The Space Studies Institute is proposing the development of the orbital G-Lab to study the effects of long term exposure to fractional levels of earth’s gravity on lab animals:
Update: A good review of many aspects of spin gravity: Gravity in the Elysium Space Station – Wired Science/Wired.com.