>>115625652= A cylinder free floating in space with the endcapps stationary for docking? This means that any debris can get into the rotation mechanisms. Anything from a small screw that got away from a workman who was fixing solar panels to meteoric micro-fragments can get into the gears , the colony tears itself apart and , again , your colony is dead. (Remember that the 'meteors are rare' argument does not actually hold due to the fact that the planet or moon that you are orbiting is actively ATTRACTING thousands of tons of material every single day and even the Lagrange points are vulnerable).
The clear and fairly obvious answer to these problems seems to be to enclose the cylinder in a sheath. A vacuum would be maintained in the sheath to avoid friction related issues and the space that would have been wasted on the windows now becomes available for other uses. External solar accumulators power solar lamps in the center of the cylinder indirectly , thus reducing radiation concerns. (Although not eliminating them, this IS space after all and radiation is seldom your friend.)
