Around 60 to 70% astronauts experience space motion sickness, which subsides within 2 to 3 days as they get used to the environment in space.
We all know that our bodies are specifically designed to live on Earth. We are so well adapted to the Earth's environment that even the slightest change in this environment can wreak havoc on the body and disrupt the smooth functioning of its various organs.
This disruption magnifies even more when astronauts move into outer space, where the environmental conditions are totally different from the Earth's environment. The moment an astronaut exits the Earth's atmosphere, his body starts experiencing several changes due to the change in environment. The most important change, we all know, is microgravity.
When on the Earth, the human body, as a whole, responds to the Earth's normal conditions, and adjusts accordingly. On the other hand, when an astronaut enters space, his body starts responding to the normal conditions over there. While doing so, it starts experiencing certain mild to severe effects on their bodies, which have been discussed here.
Effects of Weightlessness on Humans
This further causes the lengthening of the spine, and the astronaut grows taller by about 2 inches. Since the muscles and ligaments in the back are completely relaxed, the astronaut may experience mild to severe backache. However, the increase in the height is temporary, and once the astronaut returns to Earth, he shrinks to his original height.
Cardiovascular Alterations and Fluid Shift
On Earth, the human heart works against the force of gravity, and pulls the blood away from the lower body parts for its distribution to the organs. However, in space or zero gravity, the heart doesn't have to work very hard for circulating the blood to the upper parts of the body, which gradually leads to the reduction in its size and deconditioning.
Astronauts who are on long-duration space missions with preexisting, but undetected, cardiovascular problems, are at a higher risk of developing complications in their condition.
Since the astronauts dwell in an environment that does not have a gravitational pull, and there is major change in cardiovascular functioning, fluid shift occurs in their bodies. In this situation, the blood that usually gets pulled towards the lower parts of the body, now shifts and gets redistributed upwards, towards the torso and the head.
Due to this, astronauts often experience a puffy face and a feeling of congestion in their head. Also, a kind of disproportion can be experienced, wherein the legs are smaller than the head and the upper torso.
The Earth's atmosphere and magnetic field prevent space radiations from penetrating its surface, and harming the living organisms. However, this protective shield is absent in space, and hence, astronauts are directly exposed to greater amounts of space radiation.
The acute health problems caused by radiation include nausea, vomiting, fatigue, skin injury, alterations in white blood cell count, and the immune system. These health problems may subside once the astronauts return to Earth.
The long-term effects of radiation that an astronaut may experience, include problems with vision, gastrointestinal system, lungs, and the central nervous system.
Radiation may also affect the endothelial cells (the thin lining of blood vessels), which may lead to coronary heart disease. Furthermore, radiation exposure for extended periods may lead to impairment of an astronaut's performance, resulting into mission failure.
As mentioned earlier, most astronauts experience space motion sickness in the form of nausea, vomiting, headache, and uneasiness a few hours after entering space. Usually, motion sickness is caused by alterations in blood circulation, and the symptoms can subside within 2 to 3 days after launching.
Therefore, if an astronaut has to move from one point to another, he just has to give a slight push against the walls of the spacecraft. This obstructs the functioning of muscles, thereby, making them weaker.
Similarly, even the bones aren't used so much in space, which may lead to deterioration and ultimately, cause osteoporosis. The bones in the lower body perform the task of weight-bearing on Earth. When a person enters into space, the bones in the lower body no longer have to bear the weight of the upper body, and hence, start becoming brittle and weak.
With extended periods of space travel, this condition progresses to a complex level, wherein, there is increased bone breakdown with calcium and phosphorus release.
The released calcium and phosphorus is reabsorbed by the body, making the bones all the more brittle. Further, the release of calcium can increase the risk of kidney stone formation and bone fractures.
The effects of space travel have a great impact on an astronaut's performance. Therefore, the National Space Biomedical Institute's (NSBRI) science and technology program is researching ways to minimize the changes occurring in the human body in space, and enhance the performance level while enabling the astronauts to survive long-duration missions.