Tango III : A Space Settlement Design

Engineering Life

"Looking outward to the blackness of space, sprinkled with the glory of a universe of lights, I saw majesty - but no welcome. Below was a welcoming planet. There, contained in the thin, moving, incredibly fragile shell of the biosphere is everything that is dear to you, all the human drama and comedy. That's where life is; that's where all the good stuff is."
Loren Acton, USA

Life Support System

The already mentioned very hostile conditions of space make it necessary not only to design and create a physical habitat for people to live in and be shielded from the rigors of space, but also that the elements that we humans need in order to survive must be supplied.

We will need a stable and comfortable climate, air to breathe, food to eat and our waste must be disposed of. None of these elements in the form we consume them exist in space.


The primary references are, of course, spacecraft that have faced the same elementary and life threatening problems. in general, spacecraft have used what are called physico chemical life support systems. Because missions aren't generally very long, they use consumables to generate the necessary fluids. Oxygen is carried on tanks, water is also taken on board and electricity is generated by fuel cells. Carbon Dioxide is absorbed by Lithium hydroxide canisters that are changed periodically. Waste is stored or dumped into space. Food is carried on board.

Space stations, projected and existing, use partially regenerative systems but will be refurbished periodically. Their size will be comparably small.

A life support system for the space colony

In our space settlement, as in the case of any long range mission (like the projected Mission to Mars) the problem is completely different and the above solutions are inadequate, for it would be impossible to carry so many consumables on board or to have to resupply the colony periodically.

The life support system for the colony must be regenerative, that is, not based on consumables. It must be designed in such a way that the components are recycled or regenerated and don't need to be resupplied or just need minimal adjustments.

In particular, it would be desirable to engineer a bioregenerative system, that is, a system that incorporates biological components in the synthesis, purification and regeneration of basic life support commodities.

A good example of a bioregenerative system is the Earth itself, where in a large scale the natural equilibrium is preserved.

Spacecraft like the Space Shuttle are still based on physico chemical LSSs

The concept of a CELSS

NASA's acronym for these systems is CELSS (Controlled Ecological Life Support System).

This system would provide basic and continuous life-support requirements, such as food, drinking water, and breathable atmosphere, by using plant as the central recycling component.

Higher plants in life support system will be utilized in food production, CO2 uptake, and O2 release and, in concert with microbial systems, will support water purification.

A regenerative life support system will provide an enhanced crew environment (i.e., fresh food and the psychological benefits of growing plants).

The plants in a CELSS will be grown in a hydroponic solution (a nutrient solution without soil ) in a " medium soil " such as lunar soil or in some combination of nutrient delivery systems.

They are selected in a complex process involving dwarf varieties (for space limitations), productivity and ability to adapt to a "Greenhouse" environment.

The disadvantages of a CELSS are not insignificant. They require an energy input on par with physico-chemical systems in the production of plant material (biomass) and in the production of low grade heat that ultimately must be removed from the system.


Background on CELSS

Very few scientific studies have really been made on CELSS. The famous Biosphere II experiment tried to replicate a self contained environment inside a sealed glass structure in the desert, but not many of its results were made public.

NASA sponsors an EPCOT study with Kraft Co. called "The Land", where visitors are barged through canals that show hydroponics based plant systems.

At Kennedy Space Center, NASA has recently concluded studies on the same topic in its Biomass Production Chamber. The University of Purdue through NSCORT has performed several studies on the topic.

As it can be seen, although very important efforts have been made as to engineer a definite solution, the nature of the experiment (results only come after several months, huge facilities are needed, etc.) makes realization of that goal with a certain degree of certainty problematic.

Very Large Scale vs. Small Scale

In the Space Colony, the CELSS will basically consist in a controlled plant based bioregenerative system similar to the earth's environment. The main idea of building huge habitats is to try to replicate our terrestrial ecosystem in a small scale version.

The two proposed designs show their main differences with respect to their LSSs. Whereas the ring's atmosphere, although large enough to generate a breathable environment is relatively small. The cylinder's huge volume seems to guarantee natural equilibrium of the system, providing natural buffers to self regulate eventual disbalances.


Food requirements

Food requirements by the population should not differ at all from those on Earth. Colonists should be maintained healthy and active, and no differences should be made between the two proposed designs.

Psychological considerations

Although algae based systems can be designed to comply with most requirements, if we want as usual to be consistent with our established goals of a permanent presence in space all aspects must be considered.

Limiting severely the variety of settlers' diet will be a negative factor in their choice of volunteering for the colony and psychologically disturbing.

The vegetarian diet

Whether or not to take meat producing animals is a problem. Although it will represent a cost in terms of initial transportation, some sort of Noah's arc should be considered so that species breed and reproduce once they are introduced in the colony. It would be interesting to study which of them prosper in the new environment.

As a first hand preliminary analysis we would say that the ring type colony is perhaps too confined and that settlers could be encouraged to follow a vegetarian diet, whereas in the cylinder space is available for cattle to breed. It is in the cylinder, the evolutionary type of space settlement, that the earth like conditions must be engineered at any costs. The natural buffers provided by it are especially helpful to breed animals.

Crops to be chosen

Plants to be utilized in the CELSS for both systems will have to fulfill all of the above functions and also be able to generate some edible mass.

They must also be resistant, produce high yields and complement each other in order to provide a balanced diet.

Ideally, a great variety of crops will be grown in the Space Colony, especially in the cylinder where more space is available. However, some of them will provide a basis to sustain life. These will be the main crops in the system, and they must be carefully selected to meet the above criteria.

NASA NSCORT at the University of Purdue have conducted extensive studies and they recommend three potential crops for CELSS : potato, soybeans and peanuts.

Agricultural methods

The Space Colony again provides the designer with the possibility of unique ways of doing things. In the case of agriculture, it would be possible to redirect sunlight in such a way that more illumination was received, use photosynthetic acceleration, increase the temperature in certain areas, utilize intensive planting methods, etc.

Close control of agricultural parameters could be exercised, in such a way that ideal conditions would be ensured so that plants growth and yield would be maximized.

The Computer Controlled Greenhouse

In order to investigate the conditions under which the plants would grow in the space colonies, our study group designed and built a computer controlled greenhouse. In it, the NASA suggested crops peanut, soybean and potato were planted in a hydroponic soil. Temperature and humidity were constantly monitored by means of the computer system and results will be compared with similar plants that were grown on sample test beds open to the atmosphere, both on soil and hydroponics.

The following sections refer to the biological investigation on the planted crops and the design , construction and operation of the system.

The peanut

Nutritional aspect: The peanut is an oil seed which contains around 45% to 50% of oil, and approximately 27% to 33% of proteins, together with some carbohydrates ( 12 % to 18% ), minerals and group B vitamins.

Peanut oil is excellent for cooking. It has a low content of the principal saturated acids

Peanuts are ready to be harvested when the streams start to fade and the leaves get yellow and fall.

The potato has the advantage of keeping them in a warehouse in times of abundance, without being degraded, always when the place is dry and ventilated. This tubercle is sometimes used for cattle food ,but it has to be boiled before, or peeled because the crude skin contains a toxic substance.

The skin varies in color from brownish white to deep purple, the flesh normally ranges in color from white to yellow, but it may be purple.

The potato has been converted in one of the most important vegetables for man. Potatoes are highly digestible, they also supply vitamin C, aminoacids, proteins, thiamin, and nicotinicocid .

The Greenhouse

To be able to develop this investigation we built a Greenhouse in our school's laboratory. This Greenhouse was intended to be isolated from external atmospheric conditions in terms of temperature and humidity.

Felipe and Sandra monitor the control station while Charito oversees planting

These parameters would be monitored and maintained by the system, by means of special sensors connected to the computer. The designed software keeps track of the above mentioned environmental variables and switches on and off the subsystems accordingly.

The Soil

The first problem has to do with the type of soil that would be used, taking into account that hauling huge quantities of organic soil to the Space Colony from earth would be costly and inefficient.

The obvious alternative is using a hydroponic system for anchorage. The most likely candidate is the lunar soil or regolith. This, however, means that nutrients should be supplied to the plants, for regolith is totally devoid of any organic elements.

In the space colony water, that will probably have to be made in situ with hydrogen brought from elsewhere, will be a precious commodity and will thus have to be infinitely recycled.

So, knowing that plants have to be watered and liquid effluents recycled, the solution developed consists in circulating partially treated water effluents into the plat system in order to supply them with organic nutrients. At the same time, water is purified through plant transpiration. This generates an ecosystem that maintains the effluents with a low level of contamination. The low level of contamination that persists in the water is an organic contamination which is useful as a natural fertilizer of the plants.

In order to simulate this in our school's laboratory, water was circulated from a small tank containing algae, aquatic plants and fish. All of these were directly transplanted from the adjoining River Plate. We had to be careful so as not to not to surpass the maximum level of contamination because if this level was to be surpassed, this ecosystem would have been totally destroyed.

With respect to the regolith base, as no moon stones were available (KSC ships a lunar simulant upon request) volcanic gravel was used as a substitute. For practical purposes results are comparable.


Flexible construction materials were used, which at the same time act as insulators from the external weather conditions. The framework of the Greenhouse was built of aluminum rods. Once this frame was built, the insulating material which actually embodied the walls and the real structure were polycarbonate sheets .

Collecting samples for the tank at the River Plate

The Computer Control System

The role of the computer interface was basically to monitor the environmental variables, namely temperature and humidity, detect when critical values were overcome and switch on and off watering and heating devices accordingly.

A program to control the devices through the parallel port was devised for the experiment.


There were three control devices.

Heating : Air was preheated and later insuflated into the Greenhouse. The heating job was achieved by making the air flow inside an air pipe which was heated with an electrical resistance. A fan, installed at the beginning of the pipe, pushed the air into it, and through the pipe, into the Greenhouse.

Watering The device which controlled the humidity watered the Greenhouse with the mini lagoon's water. The water was pumped out of the tank and a valve opened, to permit the flow of water.

Lighting : The illumination inside the Greenhouse, to favour the photosynthesis of the plants, should be continuous .Inside the Space Colony, this could be done by maintaining the mirrors in such a way that they always illuminate the same place. In the Greenhouse this was achieved with cold lamp illumination.


The sensors and the devices were connected to the computer by means of the computer's parallel port. As this Computer's parallel port has 8 data lines and the sum between the sensors and the devices is six, this computer's port is enough for the complete control of the Greenhouse. Each data line can receive or send, either a logical 1 or 0. In the case of the sensors, the data line, should send the data, and in the case of the devices, they should receive the data. The logical data that the port sends and receives, must be: if it is a logical 1, 5 volts; and if it is a logical 0, 0 volts. So as not to have problems with the different tensions, we took this tension from the same computer.

The temperature sensor, is a bimetal which is graduated with a screw up to the desired temperature. When the plates touch each other, electricity flows through it and then, if we have it connected to one of the connection terminals (5 volts) as the plates touch each other, we'll have in the other connection terminal, 5 V too. And then, if this last connection terminal is connected to a data line, we will then have a logical 1 at this point. When the program senses this logical 1, it will then know that it should order the pump and the valve to activate themselves.

The fan and the electrical resistance, both work at 220 V. This tension cannot be directly managed by the computer.

What was then done, was to design an interface which received data from the computer and switched on these 220 volt devices.

As regards the humidity sensor, what was done was to directly measure the electrical conductivity between two points. As all we wanted to know was if this humidity (conductivity) reached an acceptable minimum, we designed an electronic circuit consisting of a transistor whose base was directly connected to one of the terminals and the other terminal, was connected to 5 volt. When this transistor stops conducting, it means that the conductivity is low and at the same time the transmitter stops having tension and if we connect the transmitter to the data line, we can say that when it conducts we have a logical 1 ( there is humidity) while if it does not conduct there is no humidity.

Again, the program must interpret this data, and if the conduction was low, make the pump and the valve work. As in the case of the resistance and the fan, we must have an interface, that interpreting the 5 volt, actions the 220 volt devices.

Therefore the interface will be the same but connected to another data line.

The software was designed in QuickBasic, because it is an easy to handle language that manages data transfer in a straightforward way. The program reads the port's status and according to the signal that the sensors emit, will decidewhat to do with the watering, the temperature or the illumination.


After having finished the investigation and construction of the Greenhouse, we proceeded to plant the seeds

This planting was done in four different places, that is, inside the Greenhouse 2 different crops were planted, one in soil and the other in volcanic gravel.

These same crops were planted outside the Greenhouse, in specially designed tubs or barrels and which being outside the Greenhouse, received the normal weather conditions. Like this, on the one hand we have the comparison between crops in soil in the Greenhouse, with the soil crops in normal atmospheric conditions; and on the other hand , hydroponics crops in normal conditions and hydroponics crops inside the Greenhouse.

In this way and doing a statistical control of the plants growth, we expect to learn, even though we had previously studied the ideal conditions for the crop, that there will be conditions that will have to be modified to improve the growth of the plants.

Preliminary conclusions

We have realized, for example, that in the first step, we had a great growth in both crops in Hydroponia and after some days, that growth became stagnated. We then found out that what was happening was that we were undernurturing the Hydroponics crops.

To solve this problem we took the sediment which had been formed in the artificial lagoon and we used it as a fertilizer. This, produced a reactivation in the growth. And in this way we achieved a homogeneous performance in the crops grown inside the Greenhouse, taking into account that the crops grown in soil inside the Greenhouse, grew in the same proportion.

The test crops grown under normal conditions, had a relatively good growth, while in the ones grown in volcanic gravel, performance was poor.

We should make clear that each one of these four crops, included soybean , peanut and potato seeds.

These crops grow well under similar climatic conditions. This gave us the possibility of having to generate only one atmosphere.

During the first step of the Greenhouse's functioning, the water (commanded by the computer) was switched automatically on very frequently but, as time went by, this frequency diminished till it was stabilized in a low watering average. We can conclude from this, that as this is a closed system, the internal humidity inside maintains itself in constant condensation and evaporation cycles. The only factor which involves a loss in the humidity volume is the growth and absorption that the plants produce. In this way, the flow of necessary watering will be proportional to the volume of liquid absorbed by the plants.

Further conclusions will be formulated as the experiment progresses and more comparative results are obtained. These will yield some clues as to the real advantages of using permanent illumination and controlling temperature and humidity.

Waste processing

The confinement of the colony's atmosphere makes it essential to monitor pollution levels very carefully. Because the atmosphere will be perpetually recycled and no fresh air can be incorporated into it, industries and other pollution prone activities or processes must be carefully watched over.

The same can be said about waste management and water purification. Waste must be completely recycled and those products which produce non recyclable waste should directly not be used.

Sewage treatment method:

As it was stated repeatedly, the Space Colony offers the possibility of designing energy intensive processes that will take full advantage of solar energy availability. The sewage disposal method engineered here also profits from the fact that artificial gravity below the surface level will be more than 1g and so deposition and sedimentation processes occur more rapidly. The water treatment plant will rotate with the structure and operate at more than 1 g.

Water treatment

Water will become a precious commodity. Unless the Lunar south pole yields some water, it will have to be fabricated in situ from lunar oxygen and imported hydrogen. Because of this, total water recycling will become imperative.

The water is supposed to receive not only a physical process but also chemical and biological treatment.

The first step consists in screening out large objects ( gravel, garbage, leaves , feces, etc ) .

During the second step the stream of water is pumped into a tank (grit chamber) also called clarifiers, where suspended organic solids settle to the bottom. The purpose is to take out every single particle that could remain suspended in water. Extra artificial gravity is going to be used to accumulate them at the bottom. These are pumped into a sludge digester where millions of anaerobic bacteria transform it. The Water Treatment Method

Some of the products that are formed during this process are:

Fuel: Much of the organic materials are decomposed producing biogas (mainly methane, CH4)

Livestock feed: as it is formed by organic macromolecules such as proteins, fats it is used as food for cattle and chickens (if they make the trip)

Soil conditioner: It improves the ability of soil to retain nutrients and hold oxygen and moisture.

Fertilizer: As it contains large amounts of nitrogen and phosphorous it has some value as fertilizer.

Building material: Bricks can be produced with sludge.

The reverse osmosis is used to take out part of the nitrates and phosphates that are dissolved in water. It consists in a semipermeable membrane through which water is forced under very high pressure.

Finally heat and Ultraviolet rays (plentifully available in space) are used to avoid microbiological contamination. An important group of microorganisms that could be found in water are: fecal coliforms. These bacteriae do not resist high temperature (110° C) so that is why water is passed through a thermostatic serpentine.

Total water: 27,64 kg per person per day.

Human water needs

Food preparation water          0,76Kg 

Drink                           1,62Kg 

Hand / face wash                4,09Kg 

Shower water                    2,73Kg 

Dish wash                       12,50kg 

Urinal flush                    0,49Kg 

Even though these are the available figures, we consider them to be insufficient. Because of that is we decided to consider 35Kg of water per capita per day as a more likely and conservative estimate.

As the colony will have 10000 inhabitants, the amount of water needed for all of them is: 350000kg. ( 350000 dm3 = 350 m3 ). Since this quantity does not include the watering or some sort of irrigation system, 1000m3 will be finally considered a fair estimation.

This water would be stored in four open tanks of 10 x 5 x 5 m, which are reduced enough, even for the ring colony. Every house will have their own reserve tanks.

Waste Management Techniques

Waste will be totally recycled. The same methods that are applied on Earth cannot be used in the Space Settlement : incineration because of the toxic fumes; composting, because a big space is needed to leave the organic material to decompose, sanitary landfields, because they can change the soil composition deteriorating it, etc

Possible materials to be recycled include :

Paper: Paper is certainly going to be recycled. The method is easy enough to be carried out in space. Recycling a ton of papers saves 17 trees, which are a very valuable oxygen resource in the colony.

Glass: Glass can be easily recycled. Several new systems can use 100% of recycled glass to make new bottles and jars.

Plastics: Plastics have to be recycled because they resist breakdowns by sunlight or bacteria. They cannot be burnt because they release toxic chemicals to the atmosphere.

Some hazardous wastes that cannot be recycled can be detoxified using bacteria or a controlled incineration.

Estimation of the number of trees needed to produce O2 atmosphere for 10000 inhabitants

Taking into account that every tree consumes 50 g of CO2 / day and considering that the reaction yields 100% :

6 CO2 + 6 H2O ------------------> C6H12O6 + 6O2

264 g CO2 ___________________ 192 g O2

50 g CO2 ____________________ x=36.36 g

36.36 g of O2 are produced per day.

A man needs 0.63 kg of oxygen per day.

1 tree _______________ 0.036 kg/dia

x _______________ 0.63 kg O2

x = 17.5 trees per person

Multiplying by the number of inhabitants we would need 175000 trees in order to generate the atmosphere for 10000 inhabitants.

Estimation of the number of trees needed to absorb CO2 generated by 10000 inhabitants

As man liberates 1 kg (1000 g) of carbon dioxide per day and each tree consumes approximately 50 g per day, some excess CO2 would remain in the atmosphere:

17 trees per person x 50 g CO2= 850 g CO2

So in order to absorb the full 100 g of CO2 liberated by each person :

Ntrees = 1000 g/ 50 = 20 trees per person which results in 200000 total trees.



Oxygen :                         0,63Kg

Food solids:                     0,62Kg

Water in food:                   1,15Kg

Food prep water:                 0,76Kg

Drink:                           1,62Kg

Metabolized water:               0,35Kg

Hand/ face wash water:           4,09Kg

Shower water:                    2,73Kg

Urinal flush:                    0,49Kg

Clothes wash water:             12,50Kg

Dish wash water:                 5,45Kg

TOTAL:                          30,60Kg

Effluents :

Carbon dioxide:                      1Kg

Respiration & perspiration wate r:   2,28Kg

Food preparation, latent water:      0,036Kg

Urine :                              1,50Kg

Urine flush water:                   0,50Kg

Feces water:                         0,091Kg

Sweat solids:                        0,018Kg

Urine solids:                        0,059Kg

Feces solids:                        0,032Kg


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