> small fast-spinning not equivalent to a big slow-spinning spaceship The smaller the radius of the spin the larger the differential in gravity and motion betw

> small fast-spinning not equivalent to a big slow-spinning spaceship The smaller the radius of the spin the larger the differential in gravity and motion between your head and feet. This wreaks all kinds of havoc on the vestibular system which leads to short-term issues (think motion sickness like on a boat) which some people don't have issues with issues, some grow accustomed to, or some treat with drugs (generally some combination of the three) and much longer-term issues that we really don't fully understand but can begin to affect cognition and physical well-being beyond the obvious motion-sickness-like events. The Zubrin book mentioned goes into a lot of this and suggests a novel solution of providing a tiny amount of gravity, basically enough that liquids pour, at the end of a very long tether such that there is minimal difference in gravity between your head and feet and minimal speed so you don't sense motion. This can, theoretically, allow for much easier and more productive exercise as well. I highly recommend reading _The Case for Mars_; it is an excellent technical volume that explains in a lot of detail exactly why our current space program faltered after Apollo and how to get us focused again. The chemistry bits were a bit too complex for me, but are very easy to skip.