Question of the Week

What is the minimum gravity needed to keep astronauts healthy?

Sat, 22nd Oct 2011

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Jim Morris asked:



Are there any theories regarding the minimum gravitational force required to keep astronauts healthy during a long space voyage such as a trip to Mars? Would it take a full 1 "g" or could we get away with less perhaps in a rotating crew module in a spacecraft?


Jim Morris


Tampa, Florida



We posed this question to Dr. Kevin Fong, Co-Director of the Centre of Aviation Space and Extreme Environment Medicine...

Kevin -   That's an excellent question and the answer is probably.  The problemAstronaut Bruce McCandless II, mission specialist, participates in a extra-vehicular activity (EVA), a few meters away from the cabin of the shuttle Challenger.  With an umbrella. with long duration space flight is that microgravity has a range of very negative consequences for the human body over extended durations and we’re talking about going to Mars, missions that may be up to a thousand days in microgravity or only partial gravity.  The big question is, how do you protect astronauts during that time and you've got two options – either you go quickly and reduce the exposure to microgravity or you put up with a long duration stay in space and you introduce a counter measure, and that counter measure should be artificial gravity. 

They've experimented with what might be the best prescription for gravity.  You can think of gravity like a drug.  certainly on Earth, we are not constantly exposed to an unchanging 1 G environment when you run up and down a flight of stairs, you shock load your joints, and you get more than one G loading at load bearing areas during exercise or impact.  When you're asleep and you're lying horizontally on your beds along the vertical axis, your body is essentially perpendicular to the gravitational field and so is gravitationally unloaded. And indeed, that's how we simulate microgravity here on Earth, we put people in bed and tilt them 6 degrees head down.  So what is the dose of gravity that would work? I was involved in a pilot study that suggested that if you lay someone down on a short arm centrifuge, and you centrifuge them at a rate of about 40 revolutions per minute on a device that has a radius of about 3 metres that that provides sufficient loading if you do it only twice a day two one-hour doses to protect a lot of the systems of the body, but not all of them.

Diana -   So, centrifuging astronauts in a wheel similar to the ones you find at the fair ground may be one way of counteracting microgravity and its effects.  On the forum, Clifford K said that, “Given gravity very slightly across the Earth, it should be expected that humans can tolerate some differences.  But more research is needed to find out if an environment with less than 1G will still be sufficient to maintain good health over time.”  Next week, why not grow a moustache to answer this question.



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minimally, the turd needs to fall upon excretion CZARCAR, Mon, 17th Oct 2011

Certainly Osteoporosis and loss of muscle tone are serious issues from a zero-G environment.  There was also a question earlier about whether Zero-G was related to sterility, or perhaps it was related to cosmic rays, or other issues in space.

I don't think humans have ever been exposed long-term to a partial-G environment, although perhaps the experiments have been conducted with other mammals in space.

I would think that muscle tone loss and osteoporosis would be proportional to the gravity, so 50% of the "normal" gravity would give half the typical bone loss.

So, one might get better results with, say 150% Earth Gravity.

CliffordK, Tue, 18th Oct 2011

dont 4get the heart has to pump CZARCAR, Tue, 18th Oct 2011

Any deviation from 1 g would cause health effects. Like CliffordK said, it would be proportional to the change of gravity. Although I doubt its 1:1. I would say increased gravity would also have a negative effect. We simply aren't evolved for such an environment. Think about the constant wear on our bones and the heart needing to pump blood up from our lower extremities. I imagine decreased gravity means decreased blood pressure, and if this continues the body may become accustomed to such a setting that returning to earth and instantly being subjected to such a force may be fatal. The Penguin, Tue, 18th Oct 2011

Gravity naturally varies from G (9.80 m/s2) around earth by about ± 0.3%.

So, naturally one would expect some variability to be tolerable, especially when coupled by resistance exercise. 

I hadn't thought about the cardiac effects.

In a sense, much of the muscle tone loss and bone loss that would occur in space can be seen with paraplegic patients.  In fact, one can see some of the muscle tone loss with an ordinary plaster cast on a limb.

Quadriplegic patients are a more extreme case, and also have associated cardiovascular disease. 

Perhaps there would be some crossover in muscle stimulus treatments, although the causes are different between what occurs with spinal injuries on Earth and what occurs with normal individuals in Space.  But, this would indicate that it would be unlikely that nocturnal gravity treatment would be sufficient to maintain health. CliffordK, Tue, 18th Oct 2011

I've actually spoken to Russian astronaut Valeri Polyakov who has the longest record of being in space, 438 days in the Mir spacecraft. He said it took him 10 days before he felt normal  again after returning to earth due to muscle and bone weakness. FuzzyUK, Thu, 27th Oct 2011

Probably, like the "great mambo chicken"!!

Drumsticks to die for! wolfekeeper, Fri, 28th Oct 2011

I'm surprised of the rapidity of the response.
I assume there are physiological studies too.
Bench Press, Squats, Bicycling, etc.
As well as bone density studies.

There was a story about the Burmese Phyton on NPR the other day that discussed rapid conditioning that it undergoes after a really big meal, attributed to certain fatty acids in the blood.  Perhaps it is an area that NASA should follow up. CliffordK, Sat, 29th Oct 2011

I have lifted weights on and off for the last 30+ years.  One thing I know about is gravity. :)  With that being said, I would have to conclude in a non-gravity environment resistance workouts (no gravity required) Machines supply the resistance.  Only way to maintain bone and muscle density the way I got it figured.  Most likely will be a full workout each day considering a non g environment more so than days while in a g. environment.  Only drawback is the oxygen usage during workouts as this will definitely increase during the workouts.        swadewade8, Sat, 12th Nov 2011

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