Spaceflight: The human body to the limit

Microgravity has a negative impact on almost every aspect of the human body making the outlook for colonising Mars seem less than promising.

Written by: Heather White

Art by: Cheng-Yu (Kou)

Exploration has always  been a part of human nature, from the discovery of the ‘New World’ by Christopher Columbus to the conquering of Mount Everest by Edmund Hillary and his Sherpa, Tenzing Norgay. Within the last 60 years alone human exploration has led to extra-terrestrial endeavours, including the first man in space (Yuri Gagarin), the first man on the Moon (Neil Armstrong) and the construction of the International Space Station. A trip to the International Space Station is certainly not for the faint hearted. Mission success can be jeopardised from as soon as T=0, with launch pad explosions risking crew lives and extreme G-forces upon the body affecting the mechanical functioning of the lungs.  

For astronauts, the launch is only the beginning of the physiological challenges that will stretch their bodies to the limit. Microgravity causes an almost immediate sense of disorientation, nausea and vomiting, due to the lack of a gravitational input to the inner ear. As a consequence, astronaut performance, equipment operation and emergency response could be seriously hindered, which can have a catastrophic impact on mission success. On Earth, blood pools in our legs due to the force of gravity; a physiological pump is then responsible for returning blood to the head so as to avoid oxygen starvation to the brain and unconsciousness. When gravity is removed, fluid becomes evenly distributed across the body, resulting in an effect that is commonly described by astronauts to  manifest itself as a puffy face and chicken legs. The changes have been reported to be so substantial that astronauts have become almost unrecognisable to family members during video calls. Thankfully, within a matter of days space motion sickness is corrected, and fluid distribution returns to normal soon after landing.

However, the worst problems are yet to come. Muscle mass decreases by as much as 20% across a six-month mission. It is seen alongside a decrease in strength that has been reported to be as large as 30% in one month. The long-term problems do not end there, as the lack of a gravitational stimulus has been associated with severe bone loss that is often compared to osteoporosis occurring in ageing. Bone deterioration in spaceflight is so great that bone loss from one month in space is equivalent to a whole year of ageing on Earth. If one were to continue to live a peaceful existence in microgravity these adaptations would have no serious consequences. The problem exists when returning to Earth. Astronauts have to undergo intensive rehabilitation in order to return to as close to their pre-flight functioning level as possible. Note the word ‘close’: for bone loss, recovery is thought to take at least as long as the flight duration, leaving astronauts highly susceptible to fractures. At a recent conference, Major Tim Peake informed the audience that a year and a half on from his Principia mission his bone microarchitecture was still recovering from the immense environmental stress his body was placed under in space.

Despite having 20/20 vision on selection to become an astronaut, after six months on board the International Space Station, Scott Kelly had to wear reading glasses when returning to Earth. This is not an isolated account of poor vision it is in fact one of many persistent astronaut reports. It is only recently though that  space agencies have identified this problem as a serious concern and have begun targeting research to identify its causes. Whilst the condition is not fully understood, it is thought that changes in brain pressure lead to flattening of the eye and inflammation of its nerve, ultimately causing poorer vision. The condition is commonly referred to as visual impairment intracranial pressure (VIIP). Space agencies are immensely worried about the impact of VIIP; it is thought that some of the structural changes may be irreversible upon return to Earth, with concern that astronauts may experience a loss of vision entirely. Such changes would be unmistakably disastrous for long-term missions to Mars and could be seriously debilitating to the future of human spaceflight.  

Astronauts are exposed to astronomical risks simply being on board the International Space Station, in low Earth orbit. The ultimate ambitious goal for the field of human spaceflight, however, is the colonisation of Mars. Clearly this endeavour will come with many risks and will likely push human performance to a limit that has never been tested before.  

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