When
the first humans travelled into space in the early sixties, these men
and women were carefully selected on their resistance to extreme
physical and mental strain. So, only very few people which had the
manual skills, physical constitution, stress tolerance and health needed
for the job were chosen to become astronauts or cosmonauts. Even today
NASA astronauts have to pass strict medical exams. The introduction of
space tourism will change everything. All of the skills mentioned above
will not be required anymore, at least not from the space tourists. Any
human will be able to go to space providing he is physically and
mentally healthy enough to go and come back with a minimum risk to be
hurt. The question is - what does 'physically and mentally healthy
enough' actually mean?
For the time being there is no answer to this question. Doctors are unsure about how to set medical standards and some argue that standards should not be set at all, as they would disturb the development of the space tourism market.
Health requirements:
In terms of age there will probably be no general upper limit, that is to say every person that has sufficient physical fitness will be able to go to space, regardless of his/her age. The limit at the lower end of the age scale will probably be oriented at the ability of persons to follow strict safety rules and to use a certain kind of technology in case of an emergency, for example.
Physical requirements for human space flight dropped with the advent of the space shuttle and with knowdlege about the reduction of g-loads. Nowadays spaceships can be limited to less than 3g's maximum acceleration. (Fyi: G-force is a measurement of acceleration felt as weight. On Earth 1g is equal to the force of gravity at the Earth's surface, which is 9.8 meters per second per second.) Excessive g-loads can cause serious damage to one's health depending on its duration. Psychological and educational requirements remain on a high level, not to say that they actually increase. This is connected mainly to longer stay times in the orbit and because of the necessity of performing complex tasks on board.
For the time being there is no answer to this question. Doctors are unsure about how to set medical standards and some argue that standards should not be set at all, as they would disturb the development of the space tourism market.
Health requirements:
In terms of age there will probably be no general upper limit, that is to say every person that has sufficient physical fitness will be able to go to space, regardless of his/her age. The limit at the lower end of the age scale will probably be oriented at the ability of persons to follow strict safety rules and to use a certain kind of technology in case of an emergency, for example.
Physical requirements for human space flight dropped with the advent of the space shuttle and with knowdlege about the reduction of g-loads. Nowadays spaceships can be limited to less than 3g's maximum acceleration. (Fyi: G-force is a measurement of acceleration felt as weight. On Earth 1g is equal to the force of gravity at the Earth's surface, which is 9.8 meters per second per second.) Excessive g-loads can cause serious damage to one's health depending on its duration. Psychological and educational requirements remain on a high level, not to say that they actually increase. This is connected mainly to longer stay times in the orbit and because of the necessity of performing complex tasks on board.
Although some argue that potential health risks associated with space tourism are not more severe as for comparable tourist activities like diving, potential health risks should not be underestimated.
Health risks:
Inherent health risks in space are associated with vacuum, micro-gravity and high energy radiation:
Spacecrafts, space hotels and space suits will be designed for operation in vacuum. If the structure of any of these happens to be damaged, space tourists will be in acute danger. Damage may come from micro meteorites and space debris. If people are exposed to space without protective clothing and beyond the Earth's atmosphere in a vacuum they can suffer from ebullism (formation of bubbles in body fluids), hypoxia (rapid de-oxygenation of the blood), hypocapnia (reduction of blood carbon dioxide levels) or decompression sickness (gases coming out of solution into bubbles inside the body).
Exposure to high energy radiation is also a major health risk for space tourists. There are different kinds of radiation in orbit, namely Solar Cosmic Radiation (SCR), Solar Flares and Galactic Cosmic Radiation (GCR), all of which have different biological effects. Whereas space hotels will probably provide protection against normal radiation, protection against radiation events like solar flares may not be guaranteed. Consequently, space tourists might have to be evacuated to Earth. Radiation loads of up to 0.5 Sievert can be tolerated by humans. Any radiation above 0.5 Sievert can cause serious damage to one's health starting with nausea and severe symptoms of radiation sickness, such as loss of appetite, diarrhoea and minor bleedings, and eventually leading to strong symptoms of radiation sickness, such as fever, bleedings, emaciation and even death.
Micro-gravity imposed risks vary depending on the stay times in orbit. That is to say, space tourists who only stay in space for a very limited period of time are exposed to other risks than, for example, the space hotel personnel which spends longer periods of time in orbit. Generally, tow categories of g-force-imposed problems must be considered - medical and comfort aspects.
Medical aspects include short duration effects, such as the space sickness syndrome (which is similar to seasickness or general travel sickness on Earth) which usually begins shortly after reaching micro gravity. The symptoms include dizziness, increased perspiration and nausea. Luckily they normally disappear after a few hours or a few days and can be treated medically. Long duration effects include loss of bone and muscle mass which is caused by the adaptation of the body to the lack of gravity and the lack of use of bone and muscle mass. These effects are usually accompanied by a decrease of physical and mental performance in orbit, as well as by cardiac arrhythmia. It has been shown that humans loose about 10% (!!!) of bone mass within a year in space under the influence of g-forces. The loss can only partly be avoided by regular training. After staying in space for more than half a year, the loss is not fully reversible. Thus, the space hotel personnel must not stay in orbit longer than six months. Avoiding long duration effects would only be possible by providing artificial gravity.
This leads us to comfort aspects. Providing artificial gravity in, for instance, a space hotel is essential for passenger comfort, notably in order to enable efficient hygiene. Artifical gravity, however, is only possible in a rotating space station. This rises the question of how the centrifugal acceleration may influence passenger comfort which may, for example, disturb the passenger's sense of orientation and balance.
It has also been shown that astronaut's hearts become spherical in space. This basically means that hearts change their shape during long periods of microgravity. You probably wonder how this is possible. Well, in space the heart does not work as efficiently as on Earth. This is what can cause a loss of muscle mass and consequently change the heart's shape. Luckily the rounder shape is only temporary and the heart returns to its original, normal, elongated shape shortly after the return to Earth. However, the change of shape may lead to cardiac problems later. Yet, the doctors are uncertain about the long-term health effects of this kind of change. They do agree, however, that regular exercise can keep the heart healthy and is crucial to guarantee safety on long missions in space.
Other health issues to worry about in zero gravity include anemia, blurry vision and kidney stones. The only good news is that it has been found that thyroid cancer cells become less aggressive in space.
Inherent health risks in space are associated with vacuum, micro-gravity and high energy radiation:
Spacecrafts, space hotels and space suits will be designed for operation in vacuum. If the structure of any of these happens to be damaged, space tourists will be in acute danger. Damage may come from micro meteorites and space debris. If people are exposed to space without protective clothing and beyond the Earth's atmosphere in a vacuum they can suffer from ebullism (formation of bubbles in body fluids), hypoxia (rapid de-oxygenation of the blood), hypocapnia (reduction of blood carbon dioxide levels) or decompression sickness (gases coming out of solution into bubbles inside the body).
Exposure to high energy radiation is also a major health risk for space tourists. There are different kinds of radiation in orbit, namely Solar Cosmic Radiation (SCR), Solar Flares and Galactic Cosmic Radiation (GCR), all of which have different biological effects. Whereas space hotels will probably provide protection against normal radiation, protection against radiation events like solar flares may not be guaranteed. Consequently, space tourists might have to be evacuated to Earth. Radiation loads of up to 0.5 Sievert can be tolerated by humans. Any radiation above 0.5 Sievert can cause serious damage to one's health starting with nausea and severe symptoms of radiation sickness, such as loss of appetite, diarrhoea and minor bleedings, and eventually leading to strong symptoms of radiation sickness, such as fever, bleedings, emaciation and even death.
Micro-gravity imposed risks vary depending on the stay times in orbit. That is to say, space tourists who only stay in space for a very limited period of time are exposed to other risks than, for example, the space hotel personnel which spends longer periods of time in orbit. Generally, tow categories of g-force-imposed problems must be considered - medical and comfort aspects.
Medical aspects include short duration effects, such as the space sickness syndrome (which is similar to seasickness or general travel sickness on Earth) which usually begins shortly after reaching micro gravity. The symptoms include dizziness, increased perspiration and nausea. Luckily they normally disappear after a few hours or a few days and can be treated medically. Long duration effects include loss of bone and muscle mass which is caused by the adaptation of the body to the lack of gravity and the lack of use of bone and muscle mass. These effects are usually accompanied by a decrease of physical and mental performance in orbit, as well as by cardiac arrhythmia. It has been shown that humans loose about 10% (!!!) of bone mass within a year in space under the influence of g-forces. The loss can only partly be avoided by regular training. After staying in space for more than half a year, the loss is not fully reversible. Thus, the space hotel personnel must not stay in orbit longer than six months. Avoiding long duration effects would only be possible by providing artificial gravity.
This leads us to comfort aspects. Providing artificial gravity in, for instance, a space hotel is essential for passenger comfort, notably in order to enable efficient hygiene. Artifical gravity, however, is only possible in a rotating space station. This rises the question of how the centrifugal acceleration may influence passenger comfort which may, for example, disturb the passenger's sense of orientation and balance.
It has also been shown that astronaut's hearts become spherical in space. This basically means that hearts change their shape during long periods of microgravity. You probably wonder how this is possible. Well, in space the heart does not work as efficiently as on Earth. This is what can cause a loss of muscle mass and consequently change the heart's shape. Luckily the rounder shape is only temporary and the heart returns to its original, normal, elongated shape shortly after the return to Earth. However, the change of shape may lead to cardiac problems later. Yet, the doctors are uncertain about the long-term health effects of this kind of change. They do agree, however, that regular exercise can keep the heart healthy and is crucial to guarantee safety on long missions in space.
Other health issues to worry about in zero gravity include anemia, blurry vision and kidney stones. The only good news is that it has been found that thyroid cancer cells become less aggressive in space.
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