Rock Street, San Francisco

3 Life Support
3.1 Pseudo-Gravity Generation
It has already been demonstrated that humans can’t live in microgravity for more than a couple
of years without seriously deconditioning their health. The main long-term physiological effects
of the weightlessness are:
• Some muscles weaken, atrophy rapidly and eventually get smaller. Hence, astronauts can
lose 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 lower
vertebrae, hip and femur. The rapid change in bone density is dramatic, making bones
frail and resulting in symptoms which resemble those of osteoporosis.
• Astronauts lose fluid volume (up to 22 percent of their blood volume). Because it has less
blood to pump, the heart will atrophy. A weakened heart results in low blood pressure
and can produce a problem with “orthostatic tolerance”, or the body’s ability to send
enough 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 as
a countermeasure to the negative low gravity effects on humans. To that end, we will induce
a rotational motion to the cylinder, which will generate the centrifugal force that will act on
every object inside the settlement and will be oriented from the center to the exterior of the
cylinder (Figure 31). This way, the centrifugal force will reproduce the gravity on Earth and
wipe out the malignant effects of microgravity.
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Figure 31: The exertion of centrifugal force
Thus,
G = Fcf (3.1)
where G represents the gravitational force and Fcf the centrifugal force. Their expressions are:
G = mg (3.2)
Fcf = m
v
2
R
(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. But
v = ?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?2R
We 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 that
exceed 2 revolutions per minute (2rpm).
1rpm =
60s
It means that:
? < 4?rad 60s =? ? < 0, 209(3)rad/s By substituting the above equation in (3.6), we obtain: R > 223.8m
This 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 for
satisfying all the people’s needs, as explained in Section 2.3.
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3.2 Air Management
While people take fresh air for granted on Earth, keeping the air clean and maintaining the
appropriate atmospheric composition and pressure on a space station is a complex process of
crucial importance that has to be permanently and carefully controlled.
3.2.1 Atmospheric composition
The atmospheres of the industry area, agricultural area and “city” will be separated by a reinforced
smart glass wall, thus the three zones will have atmospheres of different compositions.
Therefore, in the residential and industrial areas, the atmosphere composition will be constant
and very similar to the Earth’s one. By contrast, in agricultural zone, the atmosphere of every
level will differ from one another, depending on the plant species grown there.
Figure 32: Composition of Earth’s atmosphere
In the agricultural area and the “city”, the air purification system will solely have regenerate
oxygen and reduce the carbon dioxide concentration resulted from inhabitants’ respiration, and
to remove the dust, bacterias and odors. We have found two feasible solutions to tackle this
problem; biological and chemical.
The biological system consists of large amounts of Chlorella algae placed on various supports
throughout the spacecraft. We’ve chosen this very species of algae due to its extreme photosynthesis
efficiency, so that only 8m2 of exposed Chlorella can remove carbon dioxide and replace
oxygen within the sealed environment for a single human 10. This system has the disadvantage
of not precisely controlling the oxygen-carbon dioxide equilibrium.
The chemical solution consists of engines that pull the air through filters that contain small capsules
of sodium peroxide and activated charcoal. Sodium peroxide reacts with carbon dioxide
in order to produce sodium carbonate and oxygen:
2 Na2O2 + 2 CO2 2 Na2CO3 + O2
When sodium peroxide is completely consumed, sodium carbonate reacts with water vapour
and carbon dioxide, as shown below:
Na2CO3 + CO2 + H2O 2 NaHCO3
Charcoal has the role of absorbing odors and gaseous pollutants. The major drawback of this
solution is that filters have to be regularly changed, giving consideration to the depleting of the
sodium peroxide.
We have heedfully surveyed the two choices and concluded that roughly 85% of the air will be
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purified 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 systems
in order to remove from air toxic pollutants, such as carbon monoxide, nitrogen dioxide, nitrogen
monoxide, 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 vanadium
oxide catalyst and at 300 degrees Celsius:
4 NO + 4 NH3 + O2
V2O5 4 N2 + 6 H2O
2 NO2 + 4 NH3 + O2
V2O5 3 N2 + 6 H2O11
3.2.2 Air pressure
On 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 to
create an artificial atmospheric pressure within the spacecraft. We will therefore pump air into
the space settlement until it reaches the pressure of 101325 Pa, the average value of atmospheric
pressure at sea level. The quantities of gases that have to be introduced can be easily calculated
using the Ideal Gas Law:
P V = nRT
where P is the sea level air pressure, V represents the total volume of the empty space inside
the spacecraft, n is the number of moles of gas, R is the Ideal Gas Constant, roughly equal to
8.314 J
molK , and T is the absolute temperature. It is important to only use the SI base units
during the calculation.
3.3 Water Management
Water is the most essential human need, hence providing enough water for the inhabitants is
a fundamental goal. Besides, water plays an important role in almost every agricultural and
industrial process. All of these require huge amounts of water daily, so the water management
has to be based on reusing and recycling, and to seldom be changed.
3.3.1 Water Production
As previously mentioned, it is desirable to renew the water aboard our spacecraft from time to
time 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 be
carried 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, namely
titanium oxide:
FeTiO3 + H2 TiO2 + Fe + H2O12
Water can also be produced aboard our space settlement as a by-product of the air purification
processes in the industrial area, like the ones described in the previous section.
3.3.2 Water Recycling
We will use plenty of water purification methods so as to assure that water quality is at high
standards. The industrial zone will have a water supply system separated from that of the
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residential and agricultural areas since they demand different water properties. Additionally,
production of drinking water and distilled water (used in the medical field) will contain extra
purification systems.
Microfiltration, Ultrafiltration, and Nanofiltration
All of these types of filtration are based on the same principles: water passes through a semipermeable
membrane that removes undissolved particles. The sizes of membrane’s pores vary from
0.1µm at microfiltration to almost 0.001 µm at nanofiltration. However, nanofiltration also
involves the applying of pressure (nearly 7 atmospheres) on one side of the membrane. These
methods will be utilized in every water supply system on The Iris.
Figure 33: Water filtration system comparison
Image Credit:
https://www.eurowater.com/products/standard products/nanofiltration plants.aspx
Reverse Osmosis
As the above graph shows, the reverse osmosis almost completely demineralizes water, thus we
can replace the classic and inefficient Ion Exchange method.
Osmosis is a naturally occurring phenomenon where a less concentrated solution tends to migrate
to a more concentrated solution. Reverse Osmosis is the process of Osmosis in reverse, and
requires applying of great pressure on the more concentrated solution, as illustrated in the
scheme below.
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Figure 34: Reverse Osmosis
Image Credit: https://puretecwater.com/reverse-osmosis/what-is-reverse-osmosis
This method will not be used in the industrial area, in order not to make water too corrosive
and to enable us to obtain a certain hardness for each factory.
Disinfection
Although the filtration membranes don’t allow the micro-organisms through, it is mandatory
to also use a disinfection process in every water supply system in order to prevent any water
contamination . The ultraviolet disinfection is very effective, killing any pathogens, but it leaves
no residual disinfectant to inactivate the potential micro-organisms that may appear in the
distribution system. To tackle this problem, we will add chloramines during a second disinfection
step, whose residual disinfectants are long-lasting and don’t readily form trihalomethanes and
haloacetic acids13. This way, the negative effects of classic chlorine disinfection are avoided.