Scott Kelly wrote in his book that it took him a long time to adjust to life on Earth after he returned from space. While his identical twin was on Earth, Kelly lived and worked on the International Space Station. The long and painful recovery that Kelly described in his book was different from the results of the study.
People who spend long periods in space may never recover. After assessing the bone strength of multiple astronauts before and after they went to space, an international team led by the University of calgary concluded that the astronauts' bones were strong. The astronauts bones had not regenerated completely after a year of recovery. Future missions that include stays in space, on the Moon, and Mars could be affected by these findings.
The leader of the study was a member of the McCaig Institute for Bone and Joint Health and the University of calgary. She was joined by researchers from the Human Performance Laboratory at UofC, the German Centre for Immunotherapy, the University of Bonn, and the University of Texas Medical Branch. The study describing their research was published in Science Reports.
Long-term exposure to microgravity can affect the health and well-being of astronauts. The loss of muscle mass, bone density, eyesight, cardiovascular health, organ function, psychological effects, and genes are included. Every cell in the body is forced to move towards Earth's center in order to reacclimate to Earth's gravity.
The effects are dependent on the length of an astronauts stay in space. Space agencies are eager to determine how long astronauts can stay in space, the toll this will have on their health, and whether or not they can recover once they are home. The director of the McCaig Institute and co-author of the paper explained to Universe Today via email.
“The effects of space flight varied depending on the time astronauts spent in space in our study, which ranged from 4 to 7 months. Those who spent more time in space lost more bone and couldn’t recover it after 12 months back on Earth. The concern is that with anticipated missions to Mars, which could take years, bone loss could be substantial. We don’t know if at some point bone loss will taper and stabilize. The next phase of our study is to participate in NASA’s CIPHER project which monitors several aspects of human health (including bone health) in longer-term missions of up to a year. We hope that we won’t see much worse bone loss after a year compared to ~6 months, but we don’t know…”
The amount of bone loss can be measured with the use of the dual X-ray Absorptiometry. The team examined the bone health of seventeen astronauts using high-resolution peripheral computed tomography. The team was able to measure bone density with a resolution of 61 nanometers.
After 6 and 12 months after the astronauts returned to Earth, the team measured bone turnover and exercise activity. Some of the loss is never completely recovered.
“If you used the metaphor of the Eiffel Tour, the metal rods that comprise the tour are akin to the bone structural elements that we can see at high resolution. During space flight, some of those ‘rods’ become disconnected as bone is resorbed. Back on Earth, some bone is recovered, but the new bone is laid onto the remaining structure. The body cannot magically reconnect those ‘rods’ and this results in a permanently different structure, even if the bone density is partially or even fully recovered. It’s like the Eiffel Tour had nearly the same amount of metal, but fewer rods and therefore not as strong.”
Their analysis showed that astronauts lost bone mineral density. The astronauts had similar differences in their trabeculae and cortical BMD values. The porous microarchitecture that makes up the interior of bones and the dense outer bone layer make up nearly 80% of the skeleton.
The research shows how long stays in the space station have an effect on the human body. The findings have significant implications for the future of spaceflight.
“We need to understand the long-term effects of microgravity on bone health so that during longer missions we can be sure that the astronaut’s bones don’t become too weak. We also need to know whether the astronauts can recover once back on Earth so that they can go about doing their normal activities. The amount of bone loss deficit at 12 months after return to Earth doesn’t mean astronauts will start breaking their bones, but if they lose even more in long-duration flights, it could become a major concern.”
When the two planets are closest to each other, NASA and China hope to send crews to Mars every 26 months. A one-way trip to Mars will take six to nine months using conventional technology. The astronauts will have to spend up to a year and a half in microgravity and several months in Martian gravity before they are able to return to Earth.
Closer to home, NASA, the European Space Agency, China, Russia, and several commercial entities are working on exploration programs that will create a sustained program of lunar exploration. The creation of surface habitats that can accommodate rotating crews will be included. This means that astronauts will spend a lot of time in lunar gravity.
There is little doubt that the future of humanity can be found in the exploration and commercialization of space. We need to be aware of the risks and opportunities before we start. The potential for scientific breakthrough is great, but so are the dangers.
There is further reading on nature.
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