One of the sticking point of long duration missions to other planets is the bone and muscle loss during extended periods in free fall. Using very small centrifuges to simulate gravity has the problem of causing motion sickness with 3 rpms being the accepted limit for selected humans.Â 10 rpms isÂ considered Â impossibleÂ for anyone to adjust to even with extensive mitigation.
The problem with low rpm artificial gravity is that it requires a very long arm to work effectively. Arms of hundreds to thousands of feet require very different space craft configurations than anything that has ever flown. Depending on which organization tries to develop such a craft, the first vehicle could cost fromÂ under one to hundreds of billions.
If some method of using very high rpms can be used, then a much smaller radius can be used for the centrifugal gravity simulation to keep the astronauts healthy during long journeys. There may be a way of keeping the astronauts from getting sick for short stays in a high rpm field. Short stays of half an hour or so at a time could be used for the exercise periods only, which may be sufficient to keep them health if a 1.00 gee or greater field is used.
The cause of the motion sickness seems to be mostly an inner ear problem when any head movement at all is used in a high rpm field. It seems possible that considerably higher rpms could be tolerated for fairly short periods of time if the head were restrained to one particular orientation in theÂ rotating field. If it is possible that this is true, then experiments could be performed Â on the ground for a fairly small investment.
I suggest that some existing centrifugal device, such as a carnival ride or NASA training system could answer this question within a few months, if of course, it hasn’t already been answered in the negative decades ago.
With the head restrained in a properly vibration damped seat, it seems possible that 10-20 rpms could be tolerated for a few minutes at a time. Different orientations could be tried to determine the best positions for highest tolerance. If higher rpms can be tolerated this way, then a variety of exercise machines can be installed in the centrifuge to determine the effects of head restraint while working with cardio and weight devices. While the guinea pigs for these experiments would be dealing with substantially higher than normal gee fields, much information on rpm tolerance should transfer directly to spacecraft operations.
It seems possible that using the centrifugal field at 1.25 or more gee could cut the required exercise periods to 30 minutes or so per day. I would be amazed if this thought hasn’t been checked out and answered decades ago.