Astronaut Bone Loss
Published on Mar 12, 2007 at 12:33 pm.
7 Comments.
Filed under space exploration.
Until the Skylab project of the early 1970’s, most American space missions had lasted fairly short periods of time. Skylab missions, though lasted about a month each. Until that time, the longest missions had one of the Gemini flights (Gemini VII spent a little under 2 weeks in orbit) and some of the trips to the Moon (Apollo 17 lasted 12.5 days). These previous long duration missions showed that astronauts lost some bone mass in space. However, one speculation for this was that most of their time was spent sititng and floating in tiny capsules, and not getting much exercise. For all practical purposes, they were couch potatos.
The Skylab missions sought to mitigate this trend in bone loss by providing astronauts with exercises. The Skylab interior was mostly like a bit cylinder, and in part of that cylinder, astronauts could run along the walls of the space station, with the force of the walls providing a centripetal force on their body, which acted as a weak sort of artificial gravity. On a much larger scale, one suggestion for providing artificial gravity in space stations or on a long duration spaceflight is to rotate the vehicle itself. Unfortunately, that is an expensive proposition and poses numerous engineering issues (particularly in maintaining antenna alignment with Earth as well as docking of spacecraft) as well as safety concerns for astronauts in extravehicular activities (if they lose their grip, they hurl off into space).
Unfortunately, even with the exercise regimine aboard Skylab, astronauts still lost bone mass. The Soviet Union found this bone loss to be extremely severe, even crippling, for cosmonauts on very long missions to the Mir space station. The general feeling among scientists studying this phenominon continued to be that lack of exercise was the prime reason for the bone loss. Even vigorous exercise once a day was did not offset the less vigorous activities the rest of the day. But, it may be a deeper problem than that.
For some years now, astronauts have had a variety of exercise machines with them on long duration missions (the longer space shuttle missions as well as missions to Mir and the International Space Station). These machines have included treadmills with elastic straps holding the astronauts down, providing the tension and forces along their muscles and bones that are lacking in a near weightless environment. Other machines have involved leg presses, stationary bikes, etc. All have sought to have some resistance to motion to force muscles and bones to have some stresses. These exercises have slowed the bone loss a bit, but did not stop it. Astronauts continue to lose bone mass. A few years ago, NASA researchers thought that they might have a solution in that small vibrations seemed to slow bone loss, but even that seems to be only somewhat effective. Stronger straps on treadmills and exercise bikes help, but not enough. No matter what they try, astronauts lose bone mass in space. This bone loss is rather extreme, too. Studies have shown up to 1.5% loss per month in orbit. That is over 10 times the rate that elderly women suffer bone loss when dealing with osteoporosis! Each month in orbit, astronauts lose as much as these women do in a year’s time! And, recent reports indicate that the bone mass is not made up right away, and it may take years to recover, if they ever recover fully. And, if that isn’t bad enough, the calcium in the bones doesn’t just cease to exist, it goes into the bloodstream, where it can significantly increase the risk for kidney stones.
This is of concern for long duration space missions. We don’t yet know how much or how vigorous exercise might alleviate the problem. We don’t know how much artificial gravity is needed, nor for how long (continually, or only for a few hours per day?). For space station missions, the answer is simple: keep the missions short. But, for a planned Mars mission, that is not a viable option as yet. A round trip Mars mission will take nearly three years. So far no one has ever been in space for that length of time, and those in space for more than a few months have serious issues with bone mass loss. One solution would be to maintain high thrust, such as near 1g, for the whole trip to Mars (part of the time accelerating, and part of the time decelerating), but that involves far more energy and thrust than conventional rockets would allow. There has been some talk of reviving the old Orion idea (the original Orion, not the new program by the same name). But, that would still be many years into the future, if it were to ever happen. So, until then, we keep working with other strategies to combat bone loss. The problem is that we don’t know what causes it. There are now some who are questioning if it is really inactivity that causes it, or something else associated with weightlessness.
And, this is as good a reason as any to have a permanent orbital space station. If we really do plan to go to Mars, we need to work out these issues well in advance. This may also be a problem with a permanent moonbase, too. As I said, no one knows just what the reason for the bone loss is, and likewise no one knows the solution. The next step would be to build a rotating space station and test the idea for artificial gravity. Would that really solve the problem? Most people think that it will, but we don’t know for sure. And, of course, we don’t know how much gravity is needed. The Moon only has 1/6 of Earth’s gravity. Is that enough to fight this bone loss on astronauts on the lunar surface? We don’t know. If it isn’t, could the astronauts wear heavy weights so that their muscles and bones have to work as hard as they do on Earth? Would that work? We don’t know. There are still a lot of questions, and a lot of work needs to be done.
If we can’t find a solution, the a Mars trip might be out of the question. The astronauts would have such brittle bones that then would risk serious injury on the Martian surface, and even more so when they return to Earth.
-Astroprof
(Images courtesy of NASA)
Darnell Clayton on March 12, 2007 at 8:42 pm: 1
Excellent (yet ultra sad) post. I wonder whether the pay off (species wise) will be worth the risk?
Ones own health for colonizing the final frontier? That’s quite a gamble.
I. Tenor on March 13, 2007 at 11:32 am: 2
Isn’t the bone loss likely just the body’s way of adapting to a lower gravity environment? It seems unduly miserly of nature to immediately jettison bone in response to lower requirements from the gravitational environment, but the level of bone density/strength needed to move our bodies around on a higher gravity planet isn’t needed in a lower gravity environment. This would presumably also lessen energy needs for those bodies…lower food intake necessary, etc. (Likely this is a more complicated problem, since the body is a complex interactive environment.) Seems as though the main problem is the return from a lower to higher gravity environment. If the moon or Mars base were permanent, i.e. inhabitants there never returned to earth, the bone loss might not be the problem it is when transitioning back and forth between low and high gravity. So, exile from earth would be the sacrifice made.
A Ler…-- Rastos de Luz on March 13, 2007 at 5:58 pm: 3
[…] “Astronaut Bone Loss“, no Astroprof’s Page. Um artigo muito bom sobre as consequências das missões para os astronautas, principalmente as mais longas; […]
Astroprof on March 13, 2007 at 10:51 pm: 4
The assumption had always been that the lack of exercise and stress in low gravity meant that the body didn’t need so much bone mass, but exercise was supposed to fix that. It doesn’t, so there may be more to it than that. The fear is that the bones are brittle enough that even a sharp bump in space could break them. We really need to find a solution to this.
I. Tenor on March 19, 2007 at 9:33 am: 5
This topic particularly interests me because I have severe osteoporosis. I break bones regularly, and have been for years now. The break always seem to be associated with extra weight, not sharp impacts. I’ve broken ribs lifting heavy boxes, and broke some bones in the ball of my foot just by putting that foot down, ‘ball first’, on a very hard surface while carrying a heavy box.
It still seems to me that, as long as everything in the new environment is kept equal, i.e. no higher gravity is suddenly applied (as in artificial gravity) the bones should be ok. Lower gravity means less weight involved in any bumps or impacts; not the same as subjecting brittle bones to more severe impacts (with more weight behind those impacts) under higher gravity.
Noneofurbusuness on January 11, 2008 at 9:51 am: 6
I dont understand!:P
Emily W. on October 28, 2009 at 9:27 pm: 7
Gravity is so NOT the only thing at work here. How do I know this? I was recently diagnosed with osteoporosis and like a good little nerd began researching. One of the most fascinating things that I saw was a US map with the distribution of hip fractures. It wasn’t random folks. Gravity is pretty uniform all over the United States; but osteoporosis isn’t random. That means something else is going on.