The De-Spun Platform at the very center of the station is stationary with respect to the Sun. This allows the X-axis rotation of the Solar Arrays to track the Sun's relative altitude and remain perpendicular to its rays as the station circles the Earth.
The two Hubs that sandwich the De-Spun Platform in the +Z and -Z directions form the base for the ten Suite Towers and the bearing upon which the inflatable Hydroponics and Sports modules rotate. The hubs counter-rotate in relation to each other in order to provide an ever-changing direction in which to view Earth and the Universe, to properly manage heat buildup and to provide additional stability. The rotation rate is slow enough so as to not induce motion sickness; more on the order of a minute hand than a gyroscope. The five "small" cylindrical sections that form the base of each Suite Tower that extend outward in both directions from these are the diameter of Shuttle External Tanks.
The De-Spun term is relative. In actuality, all of the station's sections are rotating, depending upon your frame of reference.Next: Solar Arrays
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