Small Centrifuge Exercise

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. 10 rpms is considered  impossible 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 from 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 the rotating field. If it is possible that this is true, then experiments could be performed  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.

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I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.

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19 Responses to Small Centrifuge Exercise

  1. Participants in a long term bed rest experiment at the Univ. of Texas Galveston lost no muscle mass if they spent 30 minutes per day in a small centrifuge at 30 rpm producing 2.5 g:

    In this case, they were just laying radially and, I assume, they didn’t try to do anything more active than listen to music. This apparently raises the tolerable RPM level. Don’t know if subsequent experiments have looked at whether the centrifuge treatment had any effect on bone density.

  2. john hare says:

    I liked the mention that the device wasn’t ready for space because it was more than twenty feet long. That is something that could be designed in to a ship next year.

    I can tell I’m out of practice when I spell the title wrong and don’t even notice until checking comments.

  3. Zach T. says:

    I’m not sure artificial gravity for long duration missions is really the long poll in the tent. Using a spent stage and a tether to provide AG is fairly low hanging fruit technically and there is certainly experience navigating rotating spacecraft from a variety of probes.

  4. Paul says:

    Zach T,
    “Using a spent stage and a tether to provide AG is fairly low hanging fruit technically”

    I don’t know, NASA’s had a bad run with tethers. I suspect fear would keep them from including it as a must-have.

    “and there is certainly experience navigating rotating spacecraft from a variety of probes.”

    There’s a big difference between controlling a single rotating solid and two masses at the end of a rotating tether.

    (I sayed it afore, an’ I says it agin: For fifty years of human space flight, there are some pretty basic questions unanswered.

    Between Mercury and Apollo 11, NASA had a pretty good pattern of saying “Right we need to know how to do this and how this works in freefall.” And breaking it up over so-many missions, getting the hang of each requirement of the final Apollo mission plan. Docking, EVA, etc. But for the entirety of the shuttle program, that seems to have vanished. The agency wants to be sent to Mars, but isn’t really studying (in orbit) the little pieces they’ll need to put together.

    They even seem to lack the desire to explore their own existing craft. It took the Columbia accident before they practiced in-orbit repair. (24 years, 114 flights! For ideas that I read about in the ’80s!) They never staged a mock rescue, never flew two shuttles together, never practiced “emergency rationing” of life-support (how long they could keep a shuttle up there, as if waiting for rescue), never practiced an in-orbit resupply. Etc etc. It just seems a waste.)

  5. Ralph Buttigieg says:

    “I don’t know, NASA’s had a bad run with tethers. I suspect fear would keep them from including it as a must-have.”

    Paul, NASA has spent decades and god knows how many billions trying to come up with ways for humans to adapt to micro-gravity with limited success. Living in Space is still a wretched affair. If they were really interested in human space exploration they would have perfected artificial gravity years ago.



  6. Brad says:

    Wasn’t the Gemini 11 experiment with a 100 foot long tether to the Agena spacecraft a success? Sounds like that should be the logical starting point for future AG spaceflight experiments. Perhaps a Dragon Lab tethered to a spent Falcon 9 second stage?

  7. Andrew Platzer says:

    Here’s the paper about the experiment:
    Unfortunately they didn’t try different rotation rates or durations – not a surprise with only 7 test and 8 control subjects. 2.5g at the feet gives 1g at the head so I could imagine a rate of 75% may still be effective.
    A BA-330 is 22′ in diameter.

  8. Pete says:

    A piston type motion is another possibility. Lie a person between two padded surfaces that oscillate back and forward at some significant acceleration. Various scales, accelerations and combinations of angular and linear accelerations are possible.

    Might higher rotations potentially be possible if interspersed with short periods of linear acceleration during which the brain IMU might reset? Yet another set of experiments that might be performed on little furry animals at small scale…

  9. Paul says:

    Different NASA. 🙁

  10. john hare says:

    The link that Clark provided is well worth checking out if anyone is interested in avoiding the possible complications of tethered pairs of ships. This is something that could be developed and installed in a Bigalow module early on with a very high degree of confidence.

    While the tether solution is certainly technically feasible and desirable, fear of the potential problems scare off most of the players at this time. Time to market works against tethers when the whole spacecraft design and mission must be built around them.

  11. John Schilling says:

    The Gemini 11 experiment was a success in that it did achieve its stated objectives, but those objectives were very limited (~0.001 G for three hours with no other maneuvers) and they found it much more difficult than they expected to acheive that much. Subsequent tether research, and I count at least twenty experiments since Gemini 11, follows the same pattern. Sometimes the tether won’t deploy, sometimes it deploys and then breaks, and sometimes it bounces around more than would be acceptable for a long-term mission. Roughly one-third of the time things actually go according to plan, but even the successes do not seem to be reliably repeatable.

    This is not technological “low-hanging fruit”; the idea may be simple but the implementation is surprisingly hard.

  12. Brad says:

    John, as far as I know the primary difficulty during Gemini 11 was during the EVA, but then almost all Gemini missions which involved manual labor during EVA ran into difficulties. That was a reflection on the then novelty of EVA work, not of difficulty with a tether.

    As far as I am aware the Gemini 11 experiment was the only manned mission to experiment with spinning two craft tethered together, and no experiment in space manned or otherwise has tried to use a tether in the context of working towards the goal of artificial gravity for improved crew health. John, you say you have counted twenty tether experiments since Gemini 11, do any of those experiments prove me wrong? If so please tell me which, as I would dearly like to know the details.

    It seems to me that the the potential for using a tether for AG has hardly been scratched. I think it is well worth it to pursue the idea further to get some hard data before giving up on the concept.

  13. Brad says:

    john hare, I don’t know if short term high G centrifuge would be adequate for what’s required. Clark hit the nail on the head, “Don’t know if subsequent experiments have looked at whether the centrifuge treatment had any effect on bone density.”

    Loss of bone density, instead of lost muscle, seems like the greater health threat from long term microgravity. From what little I know complex factors like changes in the human body fluid distribution under microgravity might be involved in bone loss. Could short term high G centrifuge treatments solve that?

    To answer that question I imagine we will have to experiment in space. I’m not aware of any ground based experiments, such as bed rest, which can replicate the bone loss found in microgravity conditions.

  14. john hare says:

    I believe most of us agree that tether based or other means of full time gravity equivilent is the desirable long term solution. My thought is that it is possible that this smaller system concept would be easier to verify or refute than a full scale tether demonstration.

    If investigation shows that this would provide an early relief to the health problems on smaller vessels, it could be well worth developing. It should be (relatively) inexpensive to prove wrong if it won’t work.

    I won’t scream that this is THE answer, or even a correct answer just because I posted the idea and Clarks’ link seemed to back it up. A small mammal experiment should be affordable in the larger scheme of space development.

  15. Paul says:

    Saw some footage recently of Skylab (the one where the astronauts are “jogging” around the rim of the module, a la 2001, via self-induced centripetal acceleration, and was stunned at the internal diameter of the module compared to ISS modules. Would have been an ideal place to have a centrifuge experiment. Particularly because it was launched in one piece (sigh) so could have been more easily built in. I know I sound like a broken record, but seriously… 50 years…

    (Physics question: Say you had a new ISS module (or free-flying lab) that had two internal full-diameter, half-length centrifuges, one each end, counter-rotating. They would counter-balance each other, stopping them from rotating the module along its long-axis. However, would you get short-axis rotation (“tumble”) from precession? Ie, would counter-rotating wheels counter or reinforce each other’s direction of precession? It’s been way (way!) too long since I did this stuff in high-school.)

  16. Brad says:

    If a small high G centrifuge could do the job, that would be fantastic since that is the only solution that might be practical for a surface base on the Moon or Mars.

    In my opinion the long term health factor in microgravity is the biggest unknown for Mars manned mission planning, and should be the first issue addressed. Because if the human body falls apart even under Mars gravity we can forget about high efficiency long-stay conjunction type missions such as Mar Direct.

    As to whether a small scale centrifuge or a tether human experiment would be easier to do in space, that’s debatable. The Dragon experiment I suggested would be cheap and easy, but probably limited to no more than two men and limited to two to four weeks duration. Useful for early indicators but hardly definitive. A Bigelow module with a centrifuge could conduct as long a study as desired, but would probably require an entire deck to support it.

    Why not do both?

  17. Brad says:

    Oops! I said, “…the long term health factor in microgravity is the biggest unknown for Mars manned mission planning…”, when I should have said, “…the long term health factor in LOWER gravity is the biggest unknown for Mars manned mission planning…”

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