What is this quotient space of the torus?

If spending time in microgravity is detrimental to human bone, why didn't the ISS get designed as a torus a la 2001 A Space Odyssey which then allows for the creation of artificial gravity?

• Several science fiction movies show "doughnut" shaped space stations rotating about the axis of the "hole" thus providing artificial gravity via centrifugal force.

• Answer:

  The main answers are suitability to mission, cost and safety.  As viewed in the film, the 2001 torus was designed as a transportation hub much like a terrestrial airport.  It's main function seemed to be to aggregate the housing and travel needs of voyagers throughout near earth and cis-lunar space.   Presumably, comfort of the travelers and the effectiveness of operations personnel were the predominant objectives of such a facility.  As a consequence, gravity (or in this case its centripetal equivalent) would be an important element in achieving those ends. In contrast, the International Space Station (the "ISS") was designed as a laboratory for examining the space environment and the effects of micro-gravity in particular.  These objectives would be defeated or seriously undermined with a design that rotated.  Any observational instruments or experiments would have to be motion-isolated (a proposition that would likely never provide as ideal an experimental environment as a zero gravity facility) from the habitation structure or placed in a completely separate, free flying, configuration.  Either way, this would require costly, additional construction.  Moreover, the stresses posed by the rotation would mandate further design consideration (and possibly experimentation) and mass to compensate for the increased stresses on the structure.  Also, there are reliability issues with any stability mechanism.  The ISS design did include a human rated centrifuge with a variable rate rotation capability.  The intent was to conduct experiments on the space station crew to determine the ideal level of simulated gravitational exposure to defeat micro-gravity related atrophy.  Unfortunately, the centrifuge was diminished and ultimately eliminated from the US station budget during the various redesigns in the 1990s.  As an alternative, however, an effort was made to include the more limited, Japanese Centrifuge Accommodations Module (the "CAM") on the ISS (the cost was borne by the Japanese government in exchange for launching the Kibo science module to the ISS via the space shuttle).  Unfortunately, the CAM was canceled in 2005.