Among the many challenges facing would-be space explorers, from the enormous cost of fuel, the long time periods involved, and the complexity of life-support systems, the physical health of astronauts is perhaps the most overlooked factor. But numerous studies conducted over the years have shown that travel in space – even if in a near-Earth orbit, can quickly degrade human health. When planning complex missions – such as a trip to Mars, which could take years to complete – the health of astronauts suddenly becomes a paramount concern.
A recent study spearheaded by Dr. Gilles Clément and published in the Journal Advances in Space Research followed the medical condition of six European astronauts who flew missions on the Mir space station in the 1990s. All of the subjects in the study experienced health effects from their flights, which included reduced muscle, bone and body mass, as well as lower hemoglobin counts. Time in space ranged in length from only two weeks to several months.
According to the research, astronauts can expect their body weight to decreases by about 5% during spaceflight, independently of mission duration. This is because astronauts are actually under considerable stress even as their muscles remain underused in zero-g environments, and they might be on reduced calorie and liquid intake during missions. But the astronauts in the study recovered their body mass relatively quickly once they were back on earth.
Space travel also causes pronounced skeletal muscle wasting in humans, which has been observed after only nine days in orbit. In the European study, five of the subjects who spent more than two weeks in orbit demonstrated a reduction in the circumference of the thigh and calf by 3.2% and 4.1%, respectively. According to the researchers, there was no significant difference between short-duration and long-duration flights.
More frightening is the direct influence of space flight on bone mass, which decays steadily even when astronauts are given countermeasures like resistance training exercises while in flight. The rate of bone loss for the Mir astronauts ranged from 1.35% to 2.0% per month in the pelvis, and 1.1% per month at the lumbar spine level.
On board the MIR, radiation was a concern as well, but doses were not as severe as they would be for flights into deeper space. For the astronauts in the study, individual radiation doses corrected by ambient dose ranged from 28.1–93.7 mrem/day. While those numbers are within the established guidelines currently used by NASA, they still equate to the equivalent of getting 3-6 medical X-rays per day. An astronaut orbiting the earth in the MIR space station would receive about 50 times the regular earthly radiation dose over the course of a year.
It is clear from this report that long-distance space travel is not simply a matter of getting enough thrust; mission planners will have to make sure that the precious human payload has plenty of nutritious food and exercise, and that they are well-protected from the damaging effects of cosmic radiation. Not a small task when it comes to exploring the outer reaches of our solar system, which is already a monumental endeavor.