Life Support

            There are many health concerns whenever humans endeavor to do something.  This is no exception and actually adds to the number of things that must be taken into consideration for the mission.  Most of the things people are involved in only have to consider the intensity and the danger that the activity incurs.  A manned space flight and planet habitation involves all of the concerns of human physiology.  Issues of concern are oxygen consumption, pressurization, radiation exposure, climate, nutrition, sanitation, bone density loss, and psychological problems.

            The oxygen supply is the most prominent difficulty of the mission.  Oxygen is the most versatile and necessary of the cargo to be transported.  It is used to sustain human physiological needs and for fuel, enabling maneuvering and thrust.  A deficiency in either sector of its use would severely endanger the crew.  If there is not enough fuel it will either lengthen the journey or create an inability of controlling decent.  Depending on when the supply runs out it could be a combination of both things.  If there is a deficiency in the supply to the crew many possibilities arise.  These are mainly from hypoxia or a similar situation of anoxia.  Hypoxia is the lack of oxygen, and anoxia is the total deprivation of oxygen.  Both should be avoided since it is detrimental to the health of the crew.  Hypoxia often results from the body only getting around 1/3 of the oxygen that it receives at sea level.  It leads to altitude sickness; it is termed this because of where it was first encountered.  The body then tries to overcompensate by breathing more, which upsets the blood’s pH balance.  This is caused by too much carbon dioxide being expelled because of the vigorous breathing. (http:/www.nationalgeographic.com/everest/human_toll_content.html)  This is caused by the blood tension necessary to allow hemoglobin oxygenation; it is insignificant to the regulation of the body.  The body tissues generally are on the order of 40 torr, which allows two oxygen molecules to a cell.  If the blood were exposed to an oxygen pressure of 100 torr, as present in ambient air, the hemoglobin would be nearly saturated. (Pathway for Oxygen, Ewald Weibel)  The levels vary widely, and the blood level is theoretical since ambient conditions at sea level can vary.  The muscles receive less, because they generally are provided for after the main body concerns are taken care of.

            These conditions of hypoxia can depend on temperature, personal body efficiency or regulation, the partial pressure of oxygen, and what the person is engaged in.  The temperature affects the pressure caused by the gas, which can affect the amount of gas available for consumption.  Higher pressures at higher a temperature means that there is less available than at the same pressure at lower temperatures.  The body itself causes differences on how much a person requires, because each person is different and has to meet different requirements.  A larger person would need more oxygen than a smaller person since there is more area requiring oxygen.  The partial pressure is also a concern.  If there is more additives in the air it might create a higher pressure, but there would be less oxygen for consumption, which creates a factor for concern.  The more physical and strenuous the activity is, the more oxygen that will be needed to be burned, to provide energy to accomplish the task. 

            If the oxygen needs are not met, or the blood becomes more alkaline than normal, due to too much carbon dioxide being expelled, people can become dizzy, or nauseated.  Some of the other side effects are headaches, appetite loss, insomnia, and extreme fatigue. (http:/www.nationalgeographic.com/everest/human_toll_content.html)  These symptoms would be detrimental to the mission of the crew and hinder them significantly.  The blood circulation could speed up and it could collect in the brain and cause swelling, which would cause disorientation.  Another place fluid may gather is in the lungs, which would further impair oxygen absorption in the blood.  This would become a cyclic process with each furthering the difficulties experienced.  These symptoms are generally easily diagnosed so that damage is unlikely to occur.  If any of the above symptoms are mentioned the person should be asked to walk a straight line, if they fail to do so then they are experiencing hypoxia and need treatment. (http:/www.nationalgeographic.com/everest/human_toll_content.html)  The main problem is that it impairs the higher functions of the brain, which is difficult to notice, since it would not be self-evident to the person.  (Human Physiology, W. B. Youmans)  The organs that are most active are the most susceptible to problems, and prolonged deprivation could result in the loss of ability to respond to stimuli, which could be irrecoverable.

            With time the body is capable of adjusting moderately.  Added iron in the body to produce more red blood cells to carry oxygen is an adjustment that can be made.  The enythrocyte levels will increase in proportion to the decrease in the oxygen tension in the blood.  The body can only accommodate to a point however. 

            Pressurization is a concern due to the necessity of it to hold the body together.  Since it is pressurized internally, there has to be outside pressure to maintain the balance so no damage is done.  At very light to no external pressure the body would explode because of the forces in the body not having any containment.  The other determinant is the partial pressure of oxygen needed for biological consumption.  This provides part of the basis for pressurization.  Without this human habitation is impossible.

            Radiation is a factor due to the mutation it could cause in the DNA structure and in causing disease.  Exposure and dosage levels then have to be regulated to prevent harm.  Sources of radiation are the sun, nuclear power supply, and the Marian environment.  The main cause for worry is from the sun during transit.  This provides for the longest most unrelenting exposure to higher levels.  The exact levels are rather ambiguous.  There has not been much research done in this area.  Many different systems have been developed with different measuring systems.  The maximum dose permitted by nuclear facilities is 20 mSv/yr. (millisievert per year). Supposedly 37 kBq/m2 (kilobecquerel per meter squared) does not require decontamination.  (October issue of Science Magazine)  A sievert is defined by

,

where H is the equivalent in J/kg (joules per kilogram) and D is in Gy (grey which is joule per kilogram).  A becquerel is disintegration per second, which translates to MBq (megabecquerel) being equivalent to 27 ug (micrograms) of radium. (Principles of Physiologic Measurement, James N. Cameron)

            Exposure to some radiation is inevitable, people are exposed daily to it on earth.  The yearly dosage for people is 100 mSv at sea level.  People that have an X-ray are exposed to 500-700 uSv/yr/person (uSv is microsievert).  These are all acceptable levels and cause only minor damage that the cells are capable of repairing on their own.  The problem arises when the damage goes beyond the capabilities of the cells to repair.  If the dosage level is around three to five sieverts there is a 5% increased chance for death.  If the person is exposed to 100Sv they will go into shock and die within 24 hours of exposure. (Professor Longworth)  These levels are not likely to be reached at any time during the mission.  The exact levels are not really known however.  This will have to be a risk the crew will have to take and all precautions possible taken to minimize the exposure to any potentially high sources to the best of their capability.  One place where radiation will not be of any concern is in the food supply.  The food being exposed to radiation will not affect its composition and will not lead to contamination through digestion. The only way it could cause any trouble is if it were touched by radioactive dust.  As long as it is sealed away there will not be any trouble. (Gerlard, 1952)

            The weather is a consideration based upon how it will affect energy needs, and the difficulties it poses to people.  The higher temperature range is acceptable for humans at approximately 17 degrees Celsius, but the lower ranges especially at night is deadly at below 100 degrees Celsius.  (http:/nova-standford.edu/projects/mgs/late.html)  These temperatures of exposure would lead to hypothermia and frostbite immediately.  Protective regulated clothing would be necessary to prevent harm from the cold.  The sand storms might be problematic, in causing irritation to the skin because of the strength of the winds.  The light atmosphere does not allow for very heavy particles to be suspended however, preventing major damage.

            Nutrition is going to be a challenging affair to maintain for the duration of the mission.  Depending on the person and their personal metabolic energy consumption varying caloric requirements are needed for the individual.  The basal requirement can range anywhere from 1200 to 1800 Calories per day.  In terms of body weight that is one Calorie per kilogram hour, and in terms of body surface it is 40 Calories per square meter hour.  Some factors that can influence energy needs are the external temperature, a person needs more energy to warm the body in cold weather.  If the person is thin they have a much higher metabolic rate than short people around 50% greater.  Males also have a higher basal metabolic rate by about 6-7%.  (Anatomy and Physiology, Edwin B. Steen)  Then other factors have to be included, because the body cannot run itself all day on nothing.  Those were the basal requirement, so any activity needs to be included for the energy requirements.  Nowhere is it mentioned on where it would be best to obtain these necessary calories that the body needs.  It is assumed that a healthy balanced diet is what is to be followed.  This could prove to be difficult on the mission since fresh supplies of food are not readily available in most cases if at all.

 

Determination of Calorie requirement                                            Cal (above basal needs)

Sedentary                                                                                 500-700

Light work (profession in business)                                              700-1200

Moderate (mechanics)                                                                1200-1500

Heavy (laborers, lumberjacks, athletics)                                       1500-4000

Sleep                                                                                        500

(The Living Body)

If the proper vitamin and mineral requisites are not met, many problems can occur.  These are essential to the body.  If these needs are not met, the person will fail in the capacity that is required of them.  The body will become weakened and not perform as it should.  It will also hasten any other problems there might be with the person, and cause further difficulties.  The main worry of space missions is bone density loss.  If the vitamins and minerals the body needs to produce and maintain the bones are not taken then this could cause it to be more severe than it has to be.  The main additional supplements that will alleviate this problem are vitamin C, calcium, magnesium, and phosphorus.  These helps to preserve the strength in the bones even though it will be subjected to low gravity conditions for length periods of time.  The main minerals that must be in the person’s diet are vitamin D, K, C, B1 (thiamin), A, E, and the other variations of D and B are what are known to be required by the body.  The minerals that are needed for the body are calcium, phosphorus, sodium, chlorine, potassium, magnesium, sulfur, iron, iodine, are the major requirements with traces of these needed copper, zinc, manganese, fluorine, and cobalt.  Magnesium is also beneficial for the muscles in retaining strength and tone.  Some of the problems of deficiencies of vitamins and minerals are mentioned in Human Biology. 

            Another primary necessity is water.  There is of great concern on the supply that will be available to the crew during the entire length of the mission.  For a crew of six people a minimum requirement for two years of non-recycled water is 4380 gallons.  This is not taking into consideration the need for more when the body is being exerted, or requirements for maintaining plants and sanitation.  With these other factors the water requirements are very high.  A hazarded estimation would be over 10,000 gallons of water.  This is why recycling is necessary, to cut down on the requirement that must be taken with the crew and save on the weight.

            There are many other issues that need to be addressed for the safety of the crew.  These are the main points of concern that had evidenced themselves.  A more extensive study would be needed to address all the issues of concern and ensure the welfare of the crew.