It turns out that there are a few bugs yet to be worked out, and not just the radiation issue. It has come to the attention of some in the aerospace community that long periods of little to no gravity can result in loss of vision - a phenomenon now referred to as visual impairment intracranial pressure syndrome (VIIP). It seems to be caused cerebrospinal fluid buildup in the eye sockets due to the relative absence of gravitational forces.
Considering that there's sort of a goal to send astronauts to Mars in fourteen years or so, there's an emerging school of thought in which it's postulated that it might be useful for them to be able to see upon arrival. Perhaps Kubrick was on the right track with his "Space Odyssey" films in which artificial gravity is induced through centrifugal force during long periods in space.
Not that it would matter one way or another to HAL.