By Girvan McKay
Those of us who attended COSMOS 2001 may remember that the Russian Cosmonaut Colonel Alexander Volkov told us that when he returned to Earth after months in space, he wasn't in great physical condition. If I remember rightly, he said that his blood count was down to half what it should be. Some years before that we had seen pictures on the television of US astronauts being carried from their space capsules because their legs had lost muscle after living in weightless conditions.
When the day comes that there are manned expeditions to other planets such as Mars, and perhaps attempts to live for a while, or even to colonise these planets, it's clear that there are some huge obstacles to overcome and great hazards to face. Our bodies have developed under Earth conditions and are adapted to life here, not on other much more hostile worlds. I've taken down some notes on the problems of survival in space, and here are some of them:
We have no problem in living under the conditions found on Earth because our bodies are perfectly adapted to its gravity and our lungs are able to extract from the air the oxygen that we need to breathe. The Van Allan Belt that surrounds our globe shields us from deadly radiation. The Sun is just the right distance from us to provide warmth without roasting us. The Earth's atmosphere helps to give us some protection from falling meteorites, although not entirely.
However, when we leave the Earth and attempt to travel out into space we leave the environment that we are use to and the only one in which we are able to live naturally.
Effect of G-Forces on the Human Body
When a spacecraft leaves the ground astronauts are subjected for the first few minutes to severe g-forces. (The abbreviation "g" stands for gravity and 1 g is the normal force that keeps us on the Earth. We commonly refer to this as our weight but it varies if we are subjected to outside forces.) To a very slight degree you can feel something of the g-force, for example, from the pressure on our feet of the floor of an accelerating lift. If you were to stand on a weighing machine inside a lift, you'd find that your "weight" so-called had increased by a few pounds. Gravity pulls you down in the direction of the centre of the Earth and makes your body resist upward movement. This resistance makes you slightly heavier so that you then weigh slightly more than 1 g. What an astronaut has to endure immediately after the launch of a spacecraft is enormously greater than this. It pushes him down in his seat and temporarily distorts his face.
On the first space flights, g-forces built up to as high as 10 g during the first minutes of launching, and they increased again as the spacecraft slowed down. This could cause severe damage to the body, but the effect can be withstood if the astronaut is lying down and facing in the same direction as the movement of the spacecraft. Even so they have to receive special training to be able to withstand it.
On the latest US space shuttle the g-forces are reduced to no more than 3 g which can be borne by even people who haven't received special training. Of course, powerful g-forces can also damage equipment but this is no longer a problem on the shuttle.
Effects of Weightlessness on the Body
Once a spacecraft has reached escape or orbital velocity astronauts are no longer subjected to g-forces - not even the 1-g force of Earth. Everyone on board the spacecraft or space station then experiences weightlessness or zero gravity. They virtually weigh nothing at all and float in space like a feather or a fish. This, of course, presents quite different problems. One way of dealing with these is to string lines across the spacecraft cabin, and crewmembers are able to pull themselves along hand over hand along these lines. Also the soles of the crews' footgear and the floor are covered with a material like Velcro which helps the astronauts to walk although weightless. They have to learn how to live under weightless conditions: how to eat, drink, handle tools, sleep on a floating position in special sleeping bags attached to the walls, use special showers and toilets, and so on.
It is very important under weightless conditions to exercise as far as is possible in the very cramped quarters; otherwise it is possible that bones, muscles, the heart and blood vessels could suffer damage. Even on earth, limbs and bodily systems that are not used for even a few weeks (as in hospital) can cease to function properly.
It is important not to allow objects to float in the spacecraft during weightlessness. Large objects can cause injury and damage while small particles can be ingested or breathed in.
This is another problem for astronauts. It is akin to seasickness, but probably can be much worse as it is caused not by the motion of the sea or of a land vehicle but by lack of gravity. After a few days the body can adapt but in the meantime the astronaut may be unable to function normally. Some drugs, like those used against seasickness, may alleviate space sickness.
Because space is almost a total vacuum, there is no air and no pressure to admit air to the lungs if it existed. Therefore astronauts can only survive in a pressurised cabin or a clumsy pressurised spacesuit. . The ventilating system in the spacesuit removes carbon dioxide and sweat. The backpack accompanying the spacesuit contains transmitters which enable the wearer to communicate with other crew members and relay information about the physical condition of the wearer, the oxygen supply, temperature and pressure within the suit as we, as well as the amount of power left in the backpack's battery. If the astronauts have to go outside the spacecraft, the pressurised suit also has to protect them from the intolerable cold and the vacuum of space which would cause their blood to boil. The ventilating system in the spacesuit removes carbon dioxide and sweat. Conditions would be just as hostile on the surface of a planet such as Mars. Heavy space suits are uncomfortable and no one would wish to wear one for long. When on board the spacecraft the astronauts wear light space suits which can be pressurised in an emergency.
Inside the spacecraft, besides the pressurising environment, there is an air conditioning system, which also purifies the air, removes moisture and carbon dioxide.
The craft protects the astronauts from the extreme cold of space, the heat of the sun and the heat of re-entry into Earth's atmosphere. However on long space voyages, such hazards as meteorites, cosmic radiation and system breakdowns could not be discounted.
The astronauts can communicate from the spacecraft with ground controllers on Earth, but the time delay between message sent and message received increases with distance from the Earth.
Food, Water, and Wastes
Ordinary food is too heavy and bulky to take on board. Perishable goods cannot be carried. So food used in space is dehydrated and freeze-dried, reducing them to as little as a tenth of their original weight. Water must be added to the freeze-dried items. The food can be squeezed out of the bag or sometimes eaten with a spoon. At COSMOS 2001, Dr. Martynov and Colonel Volkov showed us some of the foods and drinks that were consumed by the Russian crews on Mir. These were of the kind described. In addition, they showed a film in which we saw how they experimented with various vegetables grown in space from seeds, and with the raising of chickens from small chicks.
On longer voyages fresh water for washing, drinking and preparing food is produced by devices called fuel cells. These also generate electricity for the spacecraft. Oxygen and hydrogen are piped into the fuel cells where they combine, forming water. During this reaction electricity is also produced.
It is very necessary to have some means of dealing with bodily waste. Liquid waste is processed in a purifying system that separated the water from the other materials and purifies the water so that it can be used again. This isn't a very pleasant thought but it's more or less what is done in water treatment plants on Earth we reprocess our own sewage. Anyone who has been in a room when a baby is being changed will be familiar with the pungent smell of ammonia. This is a component of animal waste and, in fact, encyclopaedias tell us that ammonia used to be extracted from camel dung. As Seán McKenna was telling us in a recent lecture, ammonia is highly toxic and must be dealt with. He showed us pictures of an "artificial nose" designed to detect ammonia. Solid waste materials are stored in plastic bags that are discarded after returning to Earth - another unpleasant thought!
Surviving on Long Space Flights
It is calculated that a journey to Mars will take about two and a half years. Astronauts will probably carry processed food and use chemical purifying systems for air and water, but it is hoped that it will be possible to provide most of the food by so-called "space farms". This, on a very small scale, was what the Mir crew was attempting. Growing plants give out oxygen and take in carbon dioxide, thus helping to maintain a breathable atmosphere. They can also be used to purify water. A space station 12 metres (40 feet) long and 4 metres wide could accommodate a space farm large enough to support a crew of four.
In the event of it being possible to establish living quarters on another planet, such techniques would have to be developed and extended to a far greater degree.
Possible application of stem cells in aiding survival in space
Even with these techniques, it is going to be far from easy to maintain the health and wellbeing of humans in space. A recent suggestion is that stem cells could play a useful part in this respect. Stem cells are master cells that produce to a multitude of tissue types found in the human body. They consist of are two broad varieties: embryonic stem cells and adult stem cells. The embryonic cells, which are taken from early-stage human embryos, can form any kind of tissue, whereas adult stem cells, which come in several varieties, are more restricted in their potential.
Both types of cell, but especially the embryonic variety hold promise for treating paralysis. The idea is to coax stem cells to grow into neurons that can then be transplanted into the spinal cord, bridging the severed section. There have been some reasonably successful trial experiments on rats, but no human trials have been tried yet. Christopher Reeve who played Superman and who died recently was very much a supporter of embryonic stem cell research as he hoped it could heal people paralysed by spine injury like himself embryos in this way.
It was recently reported that embryonic stem cells may not actually have to grow replacement body parts in order to be useful. They also secrete healing molecules which can, for example, reverse birth defects in mice. It is suggested that perhaps stem cells could help to safeguard space travellers from lethal cosmic radiation and to repair damage to the body which had already taken place.
However, this is a very controversial issue. Many people, including religious leaders, are very much opposed to the use of human embryos in this way.
Stem cells have the remarkable ability to develop into many different cell types in the body. They can serve as a kind of repair system for the body because theoretically there is no limit to their potentiality to divide in such a way as to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential either to remain a stem cell or to become another type of cell with a more specialised function, such as a muscle cell, a red blood cell, or a brain cell.
Other possible problems of Space Exploration
Besides the physical factors already discussed there could be many other psychological hazards for humans in space. At the best of times it isn't easy for small groups of people to live cooped together in a small space for prolonged periods. Sometimes under such conditions a person's habits or personality can drive another to thoughts of murder. Also, we can only imagine how a space traveller might feel seeing the Earth growing smaller and smaller until it is only a small point in the sky. Almost anyone who has emigrated or even gone away to live in a different town from his or her family knows what it is to feel homesick. To be "Earthsick" must be even worse. Also, there is no certainty that anyone going out into space will ever be able to return, particularly if the journey is to a planet as hostile as Mars. The kind of person accepted for such a journey will not only have to be fit and well-trained but also to have to have a very even, balanced personality and to be able to regard the great experience of space travel as being worth the odds against possible return to Earth. We may be able to send humans out but we may be unable to bring them back alive. That's another of the challenges of space travel.
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