3 Life Support3.1 Pseudo-Gravity GenerationIt has already been demonstrated that humans can’t live in microgravity for more than a coupleof years without seriously deconditioning their health. The main long-term physiological effectsof the weightlessness are:• Some muscles weaken, atrophy rapidly and eventually get smaller. Hence, astronauts canlose up to 20 percent of their muscle mass in a time frame of 11 days.
• The loss of bone tissue is approximately 1.5 percent per month especially from the lowervertebrae, hip and femur. The rapid change in bone density is dramatic, making bonesfrail and resulting in symptoms which resemble those of osteoporosis.• Astronauts lose fluid volume (up to 22 percent of their blood volume). Because it has lessblood to pump, the heart will atrophy. A weakened heart results in low blood pressureand can produce a problem with “orthostatic tolerance”, or the body’s ability to sendenough oxygen to the brain without the astronaut’s fainting or becoming dizzy 9.
Therefore, we have to create aboard our space settlement an artificial gravity environment asa countermeasure to the negative low gravity effects on humans. To that end, we will inducea rotational motion to the cylinder, which will generate the centrifugal force that will act onevery object inside the settlement and will be oriented from the center to the exterior of thecylinder (Figure 31). This way, the centrifugal force will reproduce the gravity on Earth andwipe out the malignant effects of microgravity.30Figure 31: The exertion of centrifugal forceThus,G = Fcf (3.1)where G represents the gravitational force and Fcf the centrifugal force. Their expressions are:G = mg (3.2)Fcf = mv2R(3.3)where m is the mass of the object which the two forces act on, g is the gravitational acceleration,v is the linear velocity of the space station and R represents the cylinder’s base radius.
Butv = ?R (3.4)where ? is the angular velocity. Using the relation (3.4) in (3.3) results:Fcf = m?2R (3.5)We substitute (3.5) and (3.
2) in (3.1) and we have:mg = m?2RWe simplify by m:g = ?2R or R =g?2(3.6)where g = 9.80665m/s2(at sea level).It has been discovered that the most harmful effects on inner ear appear at rotation rates thatexceed 2 revolutions per minute (2rpm).1rpm =2?rad60sIt means that:? <4?rad60s=? ? < 0, 209(3)rad/sBy substituting the above equation in (3.
6), we obtain:R > 223.8mThis way, we have demonstrated that the minimal outer cylinder’s base radius is 223.8 meters.The precise radius’ value will be determined by taking into account the required surface forsatisfying all the people’s needs, as explained in Section 2.3.313.
2 Air ManagementWhile people take fresh air for granted on Earth, keeping the air clean and maintaining theappropriate atmospheric composition and pressure on a space station is a complex process ofcrucial importance that has to be permanently and carefully controlled.3.2.
1 Atmospheric compositionThe atmospheres of the industry area, agricultural area and “city” will be separated by a reinforcedsmart glass wall, thus the three zones will have atmospheres of different compositions.Therefore, in the residential and industrial areas, the atmosphere composition will be constantand very similar to the Earth’s one. By contrast, in agricultural zone, the atmosphere of everylevel will differ from one another, depending on the plant species grown there.Figure 32: Composition of Earth’s atmosphereIn the agricultural area and the “city”, the air purification system will solely have regenerateoxygen and reduce the carbon dioxide concentration resulted from inhabitants’ respiration, andto remove the dust, bacterias and odors. We have found two feasible solutions to tackle thisproblem; biological and chemical.The biological system consists of large amounts of Chlorella algae placed on various supportsthroughout the spacecraft. We’ve chosen this very species of algae due to its extreme photosynthesisefficiency, so that only 8m2 of exposed Chlorella can remove carbon dioxide and replaceoxygen within the sealed environment for a single human 10. This system has the disadvantageof not precisely controlling the oxygen-carbon dioxide equilibrium.
The chemical solution consists of engines that pull the air through filters that contain small capsulesof sodium peroxide and activated charcoal. Sodium peroxide reacts with carbon dioxidein order to produce sodium carbonate and oxygen:2 Na2O2 + 2 CO2 2 Na2CO3 + O2When sodium peroxide is completely consumed, sodium carbonate reacts with water vapourand carbon dioxide, as shown below:Na2CO3 + CO2 + H2O 2 NaHCO3Charcoal has the role of absorbing odors and gaseous pollutants. The major drawback of thissolution is that filters have to be regularly changed, giving consideration to the depleting of thesodium peroxide.We have heedfully surveyed the two choices and concluded that roughly 85% of the air will be32purified using the biological system and the rest of 15% will be cleaned by the chemical system.In the industrial area, besides the process depicted above, we will use more complicated systemsin order to remove from air toxic pollutants, such as carbon monoxide, nitrogen dioxide, nitrogenmonoxide, sulfur dioxide and so forth. For instance, using Selective Catalytic Reduction,dangerous nitrogen oxides are reduced up to nitrogen and water in the presence of a vanadiumoxide catalyst and at 300 degrees Celsius:4 NO + 4 NH3 + O2V2O5 4 N2 + 6 H2O2 NO2 + 4 NH3 + O2V2O5 3 N2 + 6 H2O113.
2.2 Air pressureOn Earth, the atmospheric pressure is caused by the weight of air above the Earth’s surface.Since Earth’s atmosphere extends to 100000 km height on average, we will be compelled tocreate an artificial atmospheric pressure within the spacecraft.
We will therefore pump air intothe space settlement until it reaches the pressure of 101325 Pa, the average value of atmosphericpressure at sea level. The quantities of gases that have to be introduced can be easily calculatedusing the Ideal Gas Law:P V = nRTwhere P is the sea level air pressure, V represents the total volume of the empty space insidethe spacecraft, n is the number of moles of gas, R is the Ideal Gas Constant, roughly equal to8.314 JmolK , and T is the absolute temperature. It is important to only use the SI base unitsduring the calculation.3.
3 Water ManagementWater is the most essential human need, hence providing enough water for the inhabitants isa fundamental goal. Besides, water plays an important role in almost every agricultural andindustrial process. All of these require huge amounts of water daily, so the water managementhas to be based on reusing and recycling, and to seldom be changed.3.3.1 Water ProductionAs previously mentioned, it is desirable to renew the water aboard our spacecraft from time totime in order to enhance the quality of water which is of such great importance to the citizens.This action will be performed gradually, as new obtained water arrives to The Iris.
The main way to obtain water is by extracting ice from Moon’s crust. This process will becarried out by robots, as explained in detail in Section 5.3.2.Another way to obtain water is by reducing ilmenite, an ore that lunar soil abounds with.
Apart from water, this reaction forms a very useful product (Fe), and an expensive one, namelytitanium oxide:FeTiO3 + H2 TiO2 + Fe + H2O12Water can also be produced aboard our space settlement as a by-product of the air purificationprocesses in the industrial area, like the ones described in the previous section.3.3.2 Water RecyclingWe will use plenty of water purification methods so as to assure that water quality is at highstandards. The industrial zone will have a water supply system separated from that of the33residential and agricultural areas since they demand different water properties. Additionally,production of drinking water and distilled water (used in the medical field) will contain extrapurification systems.Microfiltration, Ultrafiltration, and NanofiltrationAll of these types of filtration are based on the same principles: water passes through a semipermeablemembrane that removes undissolved particles. The sizes of membrane’s pores vary from0.
1µm at microfiltration to almost 0.001 µm at nanofiltration. However, nanofiltration alsoinvolves the applying of pressure (nearly 7 atmospheres) on one side of the membrane. Thesemethods will be utilized in every water supply system on The Iris.Figure 33: Water filtration system comparisonImage Credit:https://www.eurowater.com/products/standard products/nanofiltration plants.aspxReverse OsmosisAs the above graph shows, the reverse osmosis almost completely demineralizes water, thus wecan replace the classic and inefficient Ion Exchange method.
Osmosis is a naturally occurring phenomenon where a less concentrated solution tends to migrateto a more concentrated solution. Reverse Osmosis is the process of Osmosis in reverse, andrequires applying of great pressure on the more concentrated solution, as illustrated in thescheme below.34Figure 34: Reverse OsmosisImage Credit: https://puretecwater.com/reverse-osmosis/what-is-reverse-osmosisThis method will not be used in the industrial area, in order not to make water too corrosiveand to enable us to obtain a certain hardness for each factory.DisinfectionAlthough the filtration membranes don’t allow the micro-organisms through, it is mandatoryto also use a disinfection process in every water supply system in order to prevent any watercontamination . The ultraviolet disinfection is very effective, killing any pathogens, but it leavesno residual disinfectant to inactivate the potential micro-organisms that may appear in thedistribution system. To tackle this problem, we will add chloramines during a second disinfectionstep, whose residual disinfectants are long-lasting and don’t readily form trihalomethanes andhaloacetic acids13.
This way, the negative effects of classic chlorine disinfection are avoided.