CHAPTER VI

Life support

1 a. measuring radiation levels

Ionizing radiation in space comes in three main types. The first is Galactic Cosmic Rays. Astronomers believe that these rays originate mainly in supernovae, although they also appear to come from quasars and solar flares from stars outside the Solar System. Every star reaches a point in its lifetime when the hydrogen in its core has all been converted to helium. This starts a series of reactions which forces the core to collapse in on itself. When a star with a mass 10 times that of the Sun collapses, a vast amount of energy is released in an explosion. A shock wave travels from the core and blows apart the star. Positively charged nuclei of atoms are spewed into space. These highly energetic nuclei travel through space almost as quickly as light.

The second type of radiation that astronauts and space colonists must be concerned with is solar protons. The protons originate in the sun. For reasons not fully understood by scientists, the sun sometimes ejects magnetic energy in the form of solar flares. Solar flare activity is linked with sunspots and the Sun's eleven year cycle. During a flare, temperatures range from 10 to 20 million degrees Kelvin. The high temperatures accelerate particles in the solar atmosphere. One of the most astounding things about solar flares is the amount of energy released in a single eruption. A flare usually releases 10²⁷ ergs/sec. During the course of the entire flare, the released energy would be the same as that given off by the simultaneous explosion of several million, 100-megaton hydrogen bombs! This energy takes the shape of many things, including solar protons. The protons travel through space in the solar wind  which has a velocity of approximately 400 km/sec.

The third type of radiation is high energy electrons and protons trapped by the Earth's magnetic field. The areas of trapped radiation are called Van Allen belts. Protons surrounded by an inner and outer belt of electrons form a belt which circles the Earth like a doughnut. NASA discovered these belts in 1958 during the Explorer I mission. They are referred to as the inner and outer Van Allen radiation belts, after James Van Allen who designed Explorer I. The inner region is centered at about 3000 km above Earth and has a thickness of about 5000 km. The outer region is centered at about 15,000 -- 20,000 km above the surface of the Earth and has a thickness of 6,000 -- 10,000 km. Typically, manned space flight (such as the Shuttle) stays well below the altitude of the van Allen radiation belts. Safe flight can occur below altitudes of 400 km or so. The particles in Van Allen belts come from solar flares, magnetic storms, and collisions of cosmic rays with particles in the Earth's atmosphere.

All three forms of radiation can be extremely dangerous to astronauts, especially when they are performing extravehicular and extra-colonial activities (EVAs). The risk of radiation sickness will also increase on longer voyages to places like Mars.

Ionizing radiations in space

  The detection and measurement of radiation is one of the most important functions the colonists will perform in determining if radiation and/or radioactive contamination is present inside or outside the settlement. Since humans can not sense ionizing radiation with their natural senses, they will rely on instruments for detecting and measuring radiation. They must be familiarized with the proper operation and use of the instruments they have and intend to use even before reaching the orbital colony. That is why both traditional and new radiation measurement methods will be used on the Space colony. 

Portable instruments, often called “survey meters”, will play a major role in radiological protection inside the Settlement. They are primarily used to detect contamination and to determine radiation field intensities. Many radiation safety decisions, such as the need for decontamination, shielding, personnel monitoring, change in work procedures, etc., - will be based on radiological survey result using survey meters. The majority of portable instruments are ionization chambers or Geiger-Mueller counters. 

Ion chambers are the simplest of all gas filled detectors. Their normal operation is based on the collection of all the charges created by ionization of radiation within the gas through the application of an electric field. In the presence of an electric field, the drift of the positive and negative charges represented by the ions and electrons constitutes an electric current. Assuming that recombination is negligible, and all charges are efficiently collected, the steady-state current which is produced is an accurate measure of the radiation.

One of the important applications of ion chambers is in the measurement of gamma ray exposure and exposure rate. 

Portable ion chambers of many designs will commonly be used as survey instruments for radiation monitoring purposes. The typically consist of an air volume of several hundred cm3 from which the saturated ion current is measured using a battery powered electrometer circuit. Walls are typically air-equivalent, and are usually made of plastic or aluminum. These instruments will give relatively accurate measurements of the exposure from gamma ray energies inside the colony. 

Another device efficient in measuring radiation levels is the Geiger-Mueller (G-M) counter, which is probably the best known radiation detector. It is popular because it is simple in principle, inexpensive to construct and purchase, easy to operate, sensitive and reliable as a detector of ionizing radiation. It will be particularly useful for radiation protection surveys.  

Simply constructed, a G-M counter consists of a type of gas (usually helium, neon or argon). A positive high voltage source is then connected between the shell and the wire. Any incident particle that ionizes at least one molecule of the gas will initiate a succession of ionizations and discharges in the counter. 

These GM survey meters will be used for detecting alpha, beta, and gamma radiation. With the detector window facing the radiation source and held very close to it, all three radiations can be detected. With a solid metal part of the detector (probe) facing the source of  radiation, only gamma radiation will be detected. The detection of either alpha and/or beta radiation suggests the presence of radioactive contamination.     

X-ray imaging is also an important technique which will be used in variety of applications such as nondestructive evaluation, radiology in medicine, astronomical observations, X-ray diffraction for materials studies, and others. The ability of X-rays to penetrate deep in to matter allows investigation of interior components with possibility of real-time dynamic studies. However, while significant advances have been made in X-ray sources as well as image processing steps, the X-ray detectors will remain a limiting step in many of applications. Important requirements for the X-ray detectors used in such applications include large area (~ 20 cm x 20 cm), high resolution (100-200 um), wide dynamic range (10~), high sensitivity, compact design, and low cost. Ability to provide real-time images is an additional requirement in some applications. To address this situation, we have proposed to develop a solid state, large area, high resolution imaging detector by combining the semiconductor film (lead iodide, PbI2) technology being developed at RMID with the large format amorphous silicon (a-Si:H) readout technology. The detectors would be capable of performing static as well as dynamic imaging.      

The Space Settlement will also serve as a huge laboratory for conducting a variety of experiments concerning radiation and radiation measurements technology. Some of these experiments will continue those of the ISS scientists.A good way to measure exterior radiation levels and their effects on astronauts is using a replica of human torso, similar to Fred, but with improved characteristics. Fred is NASA's Phantom Torso traveling in the International Space Station. This replica of a human torso is composed of 35 one-inch layers, each carrying passive dosimeters to measure the total radiation that travels through the torso. Real-time radiation levels will also be measured in the Phantom's brain, stomach, heart, colon, and thyroid. Fred's "skin" is made of Nomex, a non-flammable material used in the suits worn by NASCAR drivers. Two more passive dosimeters in the "skin" measure external radiation doses. The data from the internal detectors can then be compared with data from the external detectors. This experiment can provide information on how to better protect the astronauts and can also be used in measuring radiation levels in the immediate proximity of the space colony.

Two other solutions for measuring radiation, which are used onboard the International Space Station (ISS), could serve very efficiently the space settlement’s needs. One of them is the German Space Agency’s Dosimetric Mapping System. An improved version of the system will be designed to measure the different types of radiation that are penetrating the outside of the Settlement. Dosimeters specific to various types of radiation will be placed in the areas of major interest, such as residential and industrial areas.  These dosimeters will record radiation levels for long periods of time. High energy particles entering the Space Colony will be measured by the tracks they leave behind in the Nuclear Tracking Detector Packages. Two Dosimetry Telescopes will be placed in the industrial area, where they will measure ions streaming into the Settlement, while 12 thermoluminescence dosimeters will measure the neutron dose.

The third measuring solution, the Bonner Ball Neutron Detector, comes from the Japanese Space Agency, NASDA. Its primary function is to measure neutron radiation. Because neutrons pass through an astronaut's skin and may damage the bone marrow, we will dedicate experiments to recording data on neutrons. The Bonner Ball consists of 6 spheres filled with Helium 3 and connected to the control unit by a wire. Each sphere is covered with polyethylene, the material used to protect sailors in nuclear submarines. Neutrons enter each sphere where they react with the Helium to form electrons. These electrons travel in a current down the wire into the control unit where this current's strength is recorded. Scientists will collect information which will allow them to assess the risk astronauts experience while traveling through the exterior layers of the Space colony.

1 b. Effects oflong term exposure to radiation

The radiation environments encountered in space are different from the natural background radiation on Earth and are complex in nature. Both bacteria and eukaryotes have evolved a series of mechanisms to respond to similar damages on Earth.

As we have already shown, the space radiation environment is largely comprised of positively charged particles such as protons and helium ions and negatively charged electrons. The Earth's magnetic field serves as a shield against charged particle radiations. The primary sources of radiation in space are traditionally classified into trapped particle radiation, galactic cosmic radiation, and solar particle radiation.

The galactic cosmic radiation (GCR) is the major radiation in interplanetary space and is comprised primarily of charged particle radiation. Of the different charged particles that make up the GCR, 87% are protons, 12% are helium ions, and 1% are heavier ions that are of high energies. Iron is the most important of these heavier ions due to its abundance and the amount of energy each iron ion can deposit as it interacts with matter.

The sun contributes in a dynamic way to the space radiation environment. Solar particle events (SPE) are large intermittent emissions of protons, helium, and sometimes heavier ions from the sun. The frequency of SPE varies within the solar cycle.

 The different charged particle radiations in space have biological consequences that are dependent upon the spatial distribution of the energy they impart to the cell or tissue. As charged particles pass through matter, they slow down. The energy deposited is a function of the energy of a given particle, and the greatest amount of energy deposited by a particle comes at the very end of its track. Protons are generally sparsely ionizing radiations until they reach the very end of their tracks, while the heavier ions are densely ionizing at the beginning of their path and become more so as they slow down.

For short excursions outside the Space settlement, such as have previously occurred, the small dose increments might be expected to have little or no effect on astronauts. However, longer-duration space travel, such as to the moon or different celestial bodies, may be another story. Radiation doses may be sufficient to cause measurable increases in cancer or mutation risk. However, radiation-induced cancer and mutations are rare effects at any dose, and large populations are required to measure effects with statistical reliability. It may be possible, though not terribly likely, that some radiation doses in space may be sufficient to cause acute radiation sickness. This is a deterministic effect of radiation, with a threshold dose for symptoms of about 250 mSv at a high dose rate. For protracted exposure at a lower dose rate in space, the threshold dose is substantially greater, perhaps up to 1 Sv. The NCRP estimated that if a major solar particle event occurred during a visit to the moon, it could give the astronauts doses to their skin of 6 Sv (600 rem) with bone marrow doses of close to 0.9 Sv (90 rem).

Cells, tissues, and whole organisms have evolved a myriad of responses to the types of damage that can be caused by charged particle radiations. The early responses to charged particle exposures include recruitment of DNA repair machinery, changes in gene expression, the initiation of programmed cellular responses such as apoptosis, and alterations in the tissue microenvironment.

Included among the initial types of damage that result in DNA following exposure to charged particle radiations are base damage, single-strand breaks, and double-strand breaks. Bacteria and eukaryotes have highly complex systems for the repair of these alterations, which can also result from naturally occurring errors in replication, changes that result from ongoing oxidative metabolism, and exposure to chemicals of various kinds. Following exposure to sparsely ionizing radiations, base damage and strand breaks are widely scattered throughout the cell nucleus. For densely ionizing radiations such as iron ions, the alterations are often clustered. Most of the initial damage to DNA is efficiently removed prior to the next cell division cycle by processes including nucleotide excision repair and double-strand break repair. It has been suggested that the clustered damages associated with densely ionizing radiation exposures may recruit multiple repair pathways to the site of damage. The resulting "traffic jam" may lead to an alteration of the efficiency of repair.

The programmed cell death pathway may be important in maintaining tissue integrity in the space radiation environment by removing damaged cells before they can divide. Virtually all cells in multicellular organisms have evolved a system of altruistic suicide that is often referred to as programmed cell death or apoptosis. This process is critical to normal development and tissue homeostasis. Apoptosis is regulated by a series of proteins that function as either effectors or suppressors of the process. Through a complex series of heterodimeric and homodimeric interactions, these proteins act as a "rheostat" to promote or suppress apoptosis. The amounts of the various components of the "rheostat" are altered in response to exposure to both sparsely and densely ionizing radiations. One of the key players in the regulation of the apoptotic process is the p53 gene, which has been referred to as the "guardian of the genome". P53 is expressed in response to ionizing radiation exposures and serves to downregulate one of the natural suppressors of apoptosis, bcl-2. Cells which have lost the ability to initiate the normal apoptotic pathway appear to accumulate mutations more readily following exposure to sparsely and densely ionizing radiation.

In the context of organized tissues, there are additional factors that mediate responses to charged particle radiations. The extracellular matrix (ECM) and the cytokine environment provide signals that help maintain tissue integrity and normal development of the organism. The ECM influences cell morphology, mediates proliferative capacity, and regulates gene and protein expression. The ECM can promote cancer progression and incidence. Tissues respond to charged particle radiations by rapidly remodelling the ECM. The time course and characteristics of the remodelling are different in different tissue compartments. The long-term effects of this remodelling are fertile areas of investigation.

In conclusion, biological systems have evolved a series of mechanisms at the cell and tissue level to respond to the types of damages that occur as a consequence of exposure to the various components of the space radiation environment. In large part, these responses evolved to protect the integrity of the organism.

Still radiation can cause immeasurable damage by penetrating the skin and destroying cells. Many possible problems can ensue, depending upon the severity of the damage. Temporary sterility in men and women, bone-marrow damage, radiation burns, cancer, chromosome breakage, and damage to the central nervous system are all possibilities. Although these run the gamut from mild to serious for those of us on Earth, they all spell trouble in space. If an colonist on the Space Settlement becomes ill, he may not be able to complete all necessary tasks and may have impaired judgment. That is why prevention and protection procedures must be efficiently conceived and fully operable.

1 c. Radiation prevention and protection

As said, a significant difficulty for manned missions outside of the Earth's magnetosphere, including colonization related activities, asteroid exploration, and space-based mining and manufacturing, is the hazard of crew exposure to particulate radiation. Crew radiation shielding must become an active problem for investigation.

Two types of radiation are particularly significant and must be reduced as possible: solar flare protons, and high-energy galactic cosmic rays (GCR). Solar flare protons come in bursts, lasting a day or so, following an energetic solar event. The proton flux is omnidirectional; although the source of the radiation is solar, the actual radiation comes from all directions, and hence the orbital colony must be shielded in all directions, and not just in the direction of the sun. In the absence of shielding, a single large solar flare would likely be fatal to the crew, either immediately or as a result of cancers induced by the radiation dose. Cosmic rays are a continuous background consisting of extremely high energy heavy nuclei, and are also omnidirectional. While the GCR background is not immediately fatal, the integrated GCR dose over long missions will approach or exceed the recommended maximum allowable whole-body radiation dose.

The dangerous components in both solar flare and GCR radiation consists of positively charged particles. Neutral radiation (gammas, neutrons) are a negligible component of the radiation ambient; negative particles (electrons), while present, can be easily shielded. The positive particles, however, are extremely penetrating, and require massive shields. In the case of GCR, a small amount of mass shielding has no benefit, or even negative benefit over no shielding at all, since the impact of GCR nuclei on a light shield will produce secondary radiation considerably more intense than the original GCR.

Since the particles involved are charged, an alternative solution to the problem of shielding is the use of active electromagnetic shields. The simplest such device would be the magnetic dipole shield. The magnetic field of the Earth is a good example of a magnetic shield, and is responsible for the relatively benign radiation environment on Earth. A magnetic shield makes use of the fact that a charged particle's trajectory in a magnetic field is curved. As a particle enters the region of high magnetic field, its trajectory will curve away from the region to be protected. The advantages of a magnetic shield to crew safety and health are obvious.

An additional advantage of the magnetic shield is that no secondary radiation is produced by interaction of the shielded area with the incident radiation.

The limit to the mass needed to produce a magnetic field is determined by the tensile strength of materials required to withstand the magnetic self-force on the conductors. For the minimum structure, all the structural elements are tensioned, and from the virial theorem, the mass required for withstand magnetic force can be estimated as:

where  is the density of the structural material, S is the tensile strength, B the magnetic field, V the characteristic volume of the field, and  the permeability of vacuum.

An alternative to the magnetic shielding is to use an electrostatic shield. Since both solar flare protons and heavy nuclei in GCR radiation are positively charged, shielding would simply require adding a positive charge to the object to be shielded sufficient to repel the particles. To shield against solar flare protons would require an electrostatic potential of on the order of 1 E8 volts; shielding against cosmic ray nuclei as well would require as much as 1 E10 volts.

Unfortunately, the situation is complicated by the interplanetary plasma. Attempting to simply charge the colony in Earth orbit would result in electrons being attracted by it. This would discharge the settlement very quickly. In this case, to maintain a charge of 2.E8 volts would require a power of 1 E7 kilowatts.

Con-centric spheres of opposing charge to repel both positive and negative particles, would reduce the discharging, but maintaining the required voltage difference over a small distance is beyond the range of current technology.

Another solution would be using a hybrid of the magnetic shield and the electrostatic shield, the "plasma shield." An electrostatic charge is applied to the vehicle (or habitat) shell to repel the positively charged radiation; a magnetic field then prevents the plasma electrons from discharging the vehicle. At large distances the shield is charge neutral, since the magnetically confined electrons exactly neutralize the charge on the shell. Since electrons are lighter than protons by a factor of 1860, the magnetic field required for the plasma shield is reduced over that for a simple magnetic shield by the same ratio, and hence the weight associated with the field generation and structure. This ratio is even more favorable for shielding from cosmic rays.

The required electron confinement time tau to maintain the charge, assuming a maximum allowable energy expenditure of 10 kW (for the 5m. radius torus assumed), is 100 minutes. With the assumed plasma density n of 2.E9 e-/cm3, the confinement product n tau is 1 E13/cm3-sec. Magnetic containment systems for fusion applications have demonstrated n tau products in excess of E14 /cm3-sec at considerably higher temperature, so maintaining the charge is not unreasonable.

The plasma shield will be made even more effective if it is used in combination with a passive mass shield, since the mass shield is most effective for low energy particles.

Still the most efficient and simple way of protecting against radiations and solar flares is using an electromagnetic shield. This topic is detailed in the next chapter (“Electromagnetic shielding”).

The choice of material and thicknesses for best radiation blocking are dictated primarily by structural and thermal considerations. Metals (which meet all these considerations) are generally opaque to UV, X-ray and gamma-ray radiation.

Recent advances in high-temperature superconductors mean that it is reasonable to consider superconductors operating at 77K or higher on the orbital colony. This is a range which will allow use of passive cooling, where the temperature is achieved by directly radiating excess heat to space, a considerable advantage over use of superconductors requiring liquid He temperatures.

Extremely high strength to weight composite materials could be the best solution. Since the limit to magnetic field strength is produced by the tensile strength of materials required, composite materials with strength to weight ratios five times (Kevlar 49) to 7 times (PBO) higher than that of steel allow considerable weight reduction in the tension members.

The most important enabling technology, which must be available on the orbital colony, will be the ability to form high-temperature superconductors into wires, process which will take place deep inside the industrial core of the settlement. While magnetic shielding can be done using conventional (low temperature) superconductors, the pay-off in simplicity and weight of higher temperatures is so great as to be mission-enabling. Clearly, advances in the critical current and the transition temperature will also allow significant gains to be made as well. A second required technology which must be demonstrated is the cooling of wires to the superconducting transition temperature using passive cooling, essentially shielding the wire from the sun and allowing it to radiate to deep space.

However, the skin of the forward fuselage of the orbital or mining modules will be  made of 'conventional 2024 aluminum alloy', while the crew compartment will be constructed of 2219 aluminum alloy plate. The windows will be comprised of either 2 or 3 panes of glass, depending on the window location, with the panes between 0.25 and 1.3 inches and made of either aluminosilicate or fused silica, similar to those found on today’s shuttles.

Spacesuit and spacecraft windows will be specifically designed to block most of the UV radiations that pass through.

An important requirement is that little or no magnetic field should penetrate into the inhabited region, due to concern about the hazardous effects of long-term exposure to magnetic fields. However, considerably simpler engineering designs can be made if some magnetic field is allowed to penetrate into the shielded region.

In cases of emergency, well-shielded areas that can sustain life for a few days until the particles die down can work as shelter from unusual powerful solar flares. A good place for such special radiation-isolated areas would be in the center of the ship, surrounded by the water tanks.

The moon may also represent a source of radiation which must be taken into account during the mining operations. The majority of radiation on the moon is in the form of charged particles (protons and helium nuclei) from the sun. Most of the rest is ultraviolet radiation (UV). UV, of course, will not penetrate even a small thickness of lead, and neither will charged particles. On the other hand, these radiations will not penetrate other materials, such as rock, plastic, and so forth. It's not necessary to use lead for shielding on the moon because it's too heavy. The use plastic will be more efficient. As for the thickness, it depends on the energy of the incoming protons—a few cm may suffice, or maybe as much as a few tens of cm.

d. Electromagnetic shielding

As we said before, electromagnetic shielding is the most convenient way of protecting against ionizing radiations in space. The principle is in fact simple: the magnetic shield is based on the fact that a charged particle's trajectory in a magnetic field is curved. When the particle enters the region of high magnetic field, its trajectory will be curved away from the region we want to protect from radiation.

For example, let’s consider the Alpha particles () as radiating factor. They represent 8% of the maximum amount of ionizing particles found in space. Their mass (m₁) is 4, their speed (v) is of approximately 1000 Km/s and their electric charge (q) is 2e. The figure below shows the particle’s change of trajectory when entering a magnetic field zone.

We notice that in all cases the trajectory of the particle is tangent to the magnetic field zone in point P. This can also be shown using a geometrical demonstration, based on the drawing below:

Knowing the electromagnetic induction of the field (), the mass (), the speed () and the charge (q) of the Alpha particle, we can determine the Lawrence force () and the radius of the particle’s circular trajectory ().

Let’s assume that  R=R₀ (the radius of the magnetic field). For generating and maintaining a certain magnetic field around the torus we will use a series of close wound bobbins placed on the exterior margins of the torus, powered by photovoltaic panels. The distance between coils can be calculated by taking into account the electromagnetic induction we wish to generate.

We can determine the inductance of a singe-layer coil according to the Wheeler formula, which states:

We can also find the amperage needed to maximize the efficiency of the electromagnetic field.

  ;  - the Solar power per square meter

 ; - the radius of the electromagnetic field

Taking into account that the coils will be entirely exposed to the ionizing radiations, we have chosen the radius of a coil (R₀) to be half of its length (l).

; S- the surface of the coil face to the Sun

; P – the power generated on a coil; - the efficiency of the photovoltaic panel

; n – the number of turns (n=10⁴)

The determined amperage is very low and thus it is very easy to generate. The electromagnetic field created by the sysem of coils will be functioning at satisfactory efficiency and will protect the torus from ionizing radiations.

For obtaining a more intense electromagnetic induction using the same amperage and  without having to increase the length of the coil systems we could use multi-layered coils, which consist in a number of concentric common coils. We will be able to generate a more intense electromagnetic field with almost the same use of energy.

Still there will be points found in less intense electromagnetic field somewhere between the coils, but they will not raise any problem because of their simetric repartition.  

2. Artificial gravity

a. Means of creating pseudogravity

After studying the effects of the 0 gravity habitats, we reached the conclusion that artificial gravity is extremely necessary for the health and the normal life course of the colonists.

While the Space Settlement is spinning, the floor of the space station would apply a centripetal force on the persons to keep them traveling in a circular path, thus an object in circular motion with and angular velocity  around a circle of radius R experiences a centripetal acceleration  which will be the pseudo constant g, similar on Earth.

Abnormalities in free-fall motion reveal abnormalities in the gravity itself. To facilitate a side-by-side comparison of various gravity environments, it's useful to specify a few standard tests:

• Drop a body from an initial height h.
• Hop vertically from the floor with an initial relative velocity v.

Drop

The figure shows the motions of an observer and of a particle which drops from a height h.

In the inertial frame:

Before striking the floor, the particle travels a linear distance in the inertial frame:

, and subtends an angle of:

If the observer had not dropped the particle it would have traveled the same distance on a circular path subtending an angle of:

This is the angle that the observer subtends while the particle is falling.

In the observer's rotating frame of reference, the particle will strike the floor at an arc distance from the observer:

, where positive is east (prograde) and negative is west (retrograde). The particle always deflects to the west, because:

The angles  and  depend only on the initial height h and the floor radius r. If the expressions are rewritten in terms of the ratio, they become:

Smaller ratios of h to r result in smaller angles, smaller angle differences, and a more vertical path as seen from the rotating frame.

The angular velocity  and centripetal acceleration A_cent influence the speed at which the particle falls, but not the path it follows. The elapsed time will be:

Hop

The figure below shows the motion of a particle that hops vertically from the floor with an initial relative velocity v.

First we write the tangential velocity dependency of the radius

The resultant force is 0 thus,

For our particular case:

From here we calculate the normal velocity:

Now we can calculate the composed velocity from:

Here we calculate the distance between detachment and the landing points:

The time between the detachment and the landing moment:

and

We can calculate

b. The effects of artificial gravity and zero-gravity on human metabolism

Zero gravity has diverse effects on the human body, some of which lead to significant health concerns. We can easily conclude that it would be much healthier for crews to provide artificial gravity for long duration space habitation. This means rotating the habitat to produce artificial gravity by use of the centrifugal force.

For very small habitats, rotating them produces artificial gravity which results in some very noticeable differences with real gravity due to the Coriolis Effect. When you drop an object, it does not fall straight now, but falls by a curve (according to the perspective of the person inside the rotating habitat).

While standing up, your upper body will find itself significantly leaned over if you are in a small habitat rotating fast. For larger habitats, these effects are diluted to where they are humanly unnoticeable. If we want artificial gravity in spacecraft or small habitats and strive for a most economical design, then we need to understand the significance of rotation on humans. The analogy to the comfort of sailors on ships at sea is appropriate. Large ships are more comfortable than small ones.

Based on experiments on people in centrifuges and slow rotation rooms, it appears that the maximum rotation rate appears to be around 4 revolutions per minute.

The main reason for lowering radius would be simply economics in an early space habitat in that lower radius means less material needed, including designs for stress. However, in a scenario using asteroidal or lunar material whereby the costs of material in orbit is much lower; we will opt for larger habitats and Earth-normal gravity.

Space stations in low Earth orbit have not used artificial gravity for several reasons: so that they could be smaller and cheaper; many of the experiments to be conducted by the station were in microgravity.

For connecting the spent fuel tanks to produce a space station situated in orbit, we can just put a long cable between them and rotate the structure.

Studies indicate that familiarity with gravity is learned in infancy. An infant at 4 months begins to realize that a rolling ball cannot pass through an obstacle, but are not yet aware that an unsupported ball will fall. When they have 5 months, they discriminate between upward and downward motion. At 7 months, they show sensitivity to gravity and the “appropriate” acceleration of a ball rolling upward or downward. By adulthood, falling objects are judged to move naturally only if they accelerate downward on a parabolic path. These judgments are based not on mathematical reasoning, but on visual experience.

These common-sense ideas, rooted in the experience of terrestrial gravity, permeate architectural theory. A habitat design for a gravitational environment distinctly different from Earth’s requires a fundamental reexamination of terrestrial design principles. The goal is not to mimic Earth, but rather, to help the inhabitants adapt to the realities of their rotating habitat. In artificial gravity, the effects of Coriolis acceleration and cross-coupled rotation arise only during relative motion within the rotating habitat.

One phenomena which is taken for granted on Earth but cannot be in space, is vestibular perception. It might be possible, through experience in a properly designed habitat, to acquire a transformation tendency to vestibular perception from visual, acoustic, haptic, or other perceptions. The goal is not to induce motion sickness by the mere sight of some visual cue. Rather, it is to provide visual or other reminders that motion relative to these cues will result in certain inescapable side effects, inherent in the artificial gravity. These perceptual cues would act as signals, triggering adaptive coordination in the inhabitants. From the designer’s point of view, a consistent vocabulary of such signals would have to arise from convention. From the inhabitants’ point of view, these conventions might to some extent be taught, but the unconscious transformation to a vestibular image would rely on association based on direct experience.

It is ironic that, having gone to great expense to escape Earth gravity, it may be necessary to incur the additional expense of simulating gravity in orbit because the consequences of long-term exposure to weightlessness.

(*)

A conclusion after all these is that artificial gravity can approach Earth-normalcy within any non-zero tolerance, provided that the radius and tangential velocity are large and the

angular velocity is small.

3. Atmosphere

a.Effects of the artificial gravity on the atmosphere

The spinning motion of the Settlement around its symmetry axis causes different atmospheric pressure values in different points of the colony, depending on their distance to the center of the torus. The atmospheric pressure will decrease from the exterior circumference of the torus to its center, following the law deduced in this chapter.

Towards the OY axis we consider a very thin disc of air of mass dm, found in mechanical equilibrium under the action of the forces of pressure which simulate the effects of gravity on the atmosphere. The “disc” is shown in the figure below:

We can apply the fundamental principle of dynamics for the state of equilibrium:

   [1]

We can also express the dm mass as:

                [2]

The equation of state for the gaseous disc is:

         [3]

resulting in

                           [4].

According to relations [2], [3] and [4], relation [1] becomes a differential equation:

                     [5]

In the mathematical relation above, p is the air pressure at distance y towards the center of the Settlement, dp – the pressure rise according to the dy dsitance, μ – the molar mass of the air, ω – the angular speed of the torus around its axis, T – the average termodinamic temperature inside the colony, which is assumed to be constant and equal to 293 K (corresponding to 20^oC), R_g - the universal gas constant (8310 J Kmol^-1 K^-1). The equation can be solved by performing an integral calculus:

               ,                                         [6],

C is an integration constant. Its value can be determined by requiering the pressure at ground level (y=R;, R – the major radius of the torus; R=4011m) to be similar to that on Earth (p = p₀  10⁵ Pa).

                           resulting in                                          [7]

By interpolating relation [7] in relation [8] we obtain:

          [8]

We can transorm the logarithmic function into a exponential dependency. Therefore, relation [8] becomes:

 [9],

Relation [9]  puts forward in an adequate form the variation of the air pressure inside the Settlement according with the distance from the residential surface, measured towards the center of the torus, along a transport column leading to the center of the orbital station.

We notice that the pressure inside the 0 gravity body is not null.

                       [10]

T_rot is the rotation period of the settlement around its simmetry axis (T_rot=127s).

It appears that the pressure inside the central body of the colony is eligible for sustaining life in case part of the population is evacuated and sheltered there, as it exceeds the air pressure on top of the highest mountains on Earth.

Phisiological implications of atmosphere

Creating an atmosphere that can sustain life is extremely important, but at the same time extremely difficult, because there are many problems to consider.

Pressure and its influence on blood absorption of gasses is one of the major problems, because of its’ physiological implications.

High pressures create embolia, the gass absorption being stopped and we do not need that. This is the reason why we calculated a normal air pressure in the settlement of ½ atmospheres, in order to make the blood gas absorption easier. This also creates a smaller amoung of gass that has to be generated or imported to the station.

Atmosphere Composition

In order to preserve acceptable living conditions we have to recreate Earth’s atmospheric pressure, keeping the molar fractions of the gasses constant.

Earth’s atmosphere consists of: 20% O₂ , 78 %N₂, and 2% other gasses (volumes).

Oxygen’s molar fraction is:  20/100=0.2 (volume percents equal mole percents because a mole of any gas in the same environment conditions occupies the same volume; for example: in normal conditions at 0^o Celsius (273K) and 1 atm a mole of any gas occupies a volume of 22.4 L or dm³  according to Avogadro’s law). Nitrogen’s molar fraction is 0.78, and other gasses’ molar fraction is 0.02.

 The total volume of the space station is 19754175000 m³ (the volume of the torus) +      815125000 m³ (the central body’s volume), for a total of 20569300000 m³.

- number of moles

- number of moles of air needed in the settlement’s conditions

 of air

Oxygen’s molar fraction is: x_O2=0.2

Number of kmoles of oxygen is : kmoles of oxygen 

               Nitrogen’s molar fraction is : x_N2=0.78

Number of kmoles of nitrogen needed : kmoles of nitrogen

Number of kmoles of other gasses: kmoles of other gasses

Chemical generation of Oxygen

 In order to preserve the gaseous pressure in the station, we will have to constantly monitor the oxygen, nitrogen balance and volume.

Some of the Station’s oxygen will be generated  different ways, from two different types of substances: from lunar and asteroidal ores that contain metal oxides, using the separation methods presented in chapter 3, and from heated lunar ice water, by its electrolysis:

2* |cathode (-)        2H₂O(liquid) +2e^-=> H₂ (gas)+2OH^-(aqueous) [reduction]

                     anode (+)    2H₂O(liquid) -4e^- => O₂(gas)+4H⁺ (aqueous) [oxidation]

 Total process:

      2H₂O  => 2H₂ + O ₂ 

This reaction needs 285,5 kJ per mole of water. ∆H_reaction= 571 kJ

This is also a source of hydrogen.

Oxygen is also used for the fabrication of ozone (ozein= to smell), it’s triatomic allotropic state O₃.It can be obtained with UV lamps or by the cryogenic liquefaction of air. This can have a plentitude of uses: medical uses and water disinfectant (see waste management). It’s a very powerful oxidizing agent, and it must be produced close to its source of application.

 Hydrogen generation

Hydrogen generation is made from thermal extraction and electrolysis (see separation methods). Another method would be from large ammonia transports, by decomposing it into elements: 2 NH₃=>N ₂ +3 H _2, altering the equilibrium created with the reverse reaction (by Le Chatelier’s principle). Asteroids contain also hydrogen volatiles from which we can obtain the hydrogen.

Nitrogen generation

This gas is extremely important (a little rare), being one on the gasses we have to transport in large amounts from Earth, under the form of ammonia, so that we will be able to use the entire cargo.

Lunar ice water which was newly discovered to have amounts of nitrogen dissolved in it. This is another source of  N ₂. The reason for this surprising fact could be the meteor and asteroidal impacts in the past; another space nitrogen source is asteroid volatiles containing nitrogen gas along other gasses.

The lack of some volatiles can determine major problems. Nitrogen is one of the most important because nitrogen sources are few and the necessary quantities are great. Once created the biogeoecosystem the import of ammonia will stop, because the circuit will be closed, and matter will not be lost any more.

f.  CO₂ concentration control and removal

Carbon Dioxide Elimination

Biological elimination is made by plants, which take the carbon dioxide form the atmosphere and they use it as their own food.

We are aware of the importance of photosynthesis in the carbon dioxide elimination process, but we have to take safety measures, and find a backup system of elimination of CO₂.Accidents may happen with the plant population. We can use the dioxide to form water and methane with hydrogen, and the compounds formed can be used to form water and in this manner to reform the cycle.

Carbon Dioxide Reduction System (CRS)

In this cycle, CO₂ reacts with hydrogen and forms methane and water:

CO₂ + 4H₂  => CH₄ + 2H₂O + Q

This reaction can happen in a reactor, in catalytical conditions. The water vapour formed in this manner is condensed on a cold surface, so that the gas stream is composed only by methane. Water obtained this way can be collected and the methane separated in a combustible gas chamber or pipe.

The water can support the process of electrolysis, and it is decomposed in Oxygen and hydrogen. Oxygen is released at the anode and is collected and seprated, and hydrogen molecules are formed at the cathode. This last gas is used at the restart of the cycle.

METAL OXIDES

Silver oxide reacts with CO₂ and forms a silver carbonate. Also Magnesium and lithioum oxides are viable to take part in this process, but the highest chemisorbtion of CO is made by Ag. 

Ag₂O + CO₂ => Ag₂CO₃ (in an aqueous environment)

SOLID AMINE WATER DESORBED

This is an elimination method that uses an ion exchange resin that has the proprety of being able to chemically bond CO₂ molecules to its structure. The total elimination of the gas can be made in vacuum or even space, when tha dioxide molecules are dispersed.

ION EXCHANGE ELECTRODIALYSIS

This method has the same principle as the ne mentioned above, but it is at the same time different. The compounds formed at the surface contact between the ion-exchange resin and the dioxide are carbonates, that can be easily eliminated in an electrical field, and at the same time the resin is regenerated.

THE 4 BED MOLECULAR SIEVE (4BMS)

This device has a water side and a chemically active side. In the active side, on of the beds has the function of actively adsorbing water molecules, and at the same time the air is passed to the bed and the CO₂ is adsorbed.  The other beds have the purpose of desorbing the water, which is eventually returned to the first phase of the cycle.

THE SABATIER PROCESS

This process is based on the burning of CO₂ in H to produce Oxygen and methane gas. The process is exothermic (323K/mole CO₂) because of the destruction of the two double C=O bonds.

                                              CO₂ + H₂ =>CH₄ + O₂ + Q

THE BOSCH PROCESS

This is another process of transforming CO₂ in other products. In this case the products are solid black C and gaseous O₂. This reaction generates 431K per mole of CO₂.

                                                             CO₂ => C + O₂  + Q

7. Measuring toxicity levels and contamination prevention

Preventing contamination involves eliminating the risk factors which could lead to the incapability of the organisms to function within their normal adaptation limits.

Measuring toxicity levels inside a fully operative ecosystem will surely not be an easy thing to achieve. For estimating the distribution and level of toxicity we must first study the response of the different communities of humans, animals and plants based on a specific biochemical, physiological or behavioral endpoint.

For determining if exposure to a certain toxicant substance will result in adverse responses for the Settlement’s biotope we must first calculate the dose, the time and the frequency of exposure.

Therefore all habitats onboard the Space Settlement must be permanently monitored and carefully studied. To achieve this, periodical tests must be conducted upon both aquatic and terrestrial organism, including plants, invertebrates and vertebrates. This complex monitoring system will be based on highly sensitive chemo-sensors which will constantly examine the chemical composition of air and water vapors and send the precise results to the central data logger (trace contaminant control) for further analysis.

Still the best way of preventing contamination and thus endangering the artificial ecosystem will be creating a strict set of rules concerning the use, waste and recycling of the different materials onboard the Settlement. Therefore, the distribution, exploiting and dumping of materials will have to respect a certain cycle; meanwhile, several norms concerning the industrial activities and the industrial waste management will help in preventing chemical contamination.

The different substances onboard the Settlement will have to follow the cycle presented below:

e. Ventilation and ventilation devices

Because we have a perfect isolated habitat we need a very good ventilation to replenish oxygen, dilute the concentration of carbon dioxide and water vapor, preventing the infiltration of dust and atmospheric pollutants, and minimize unpleasant odors. Thereby we will stop the effects of a poor air quality which can lead to headaches, respiratory difficulties, sinus congestion, fatigue, throat and eye irritation and poor concentration. For the houses’ interior we can use the Indian Teepee principle.

The exhausted air will be replaced with fresh air found at the temperature of the torus, which is drawn into the building via low level louvers and doorways, thus providing vertical air movement, which is the most natural and efficient way to ventilate buildings.

Vertical air movement occurs due to lower density, warm air rising as it expands becoming more buoyant. As cool air, which is dense and therefore heavier, enters the building at low level it pushes the warm air upwards thus developing convection currents. For the artificial “wind”, in the residential zone and also in the

agricultural one, we can use common fans with aluminium palettes for high efficiency.

f. Temperature and humidity control

We must have automatic temperature control systems all over the torus and the central body for  maintaining a constant normal temperature. A sensor will monitor the temperature inside the habitable area and the agricultural area. If a temperature variation appears it communicates with the controller, which will be linked to a microchip which is able to increase or decrease the required temperature with a margin of safety of maximum +/- 0.5°C.

A Dehumidifier is an appliance that removes moisture from the air. Most of the dehumidifiers work like refrigerators and air-conditioners. They have cooling coils. Water vapor is condensed and removed from the air going through the dehumidifier. This requires a lot of energy to condense water vapor and the higher the background humidity level, the more energy it takes.

Other types of dehumidifiers are made with the help of a silica gel impregnated on a desiccant wheel with a fast heating coat made out of paper or fiber-glass. This wheel is like a deep porous material that forces the air to get to the desiccant substance. This chemical compound attracts the water molecules in its pores, taking all the moisture from the air and incorporating it.

Low humidity also can be harmful since excessive evaporation can irritate the mucous membranes of the nose and bronchi, thus we need a device for creating humidity. Studies show that for a person wearing light clothes, the ideal conditions of well-being occur when the environmental temperature is between 23...25°C, and the relative humidity is between 40...60%. Also, in some industrial processes the humidity favors we can avoid various inconveniences consisting in the formation of electrical charges.

Besides the natural humidification which has lot sources, we must use artificial ones too. A type of artificial humidifier would be the one which nebulizes the water producing a fine mist that is blown into the torus by a small fan incorporated in the machine. The mist then evaporates immediately, humidifying the air. The mist outlets can be orientated in every horizontal direction.

All these features will make an efficient and versatile atmosphere control, suitable for creating an agreeable way of life.

VI.4. Flora

a. Plant growing and maintaining process

Plants will be needed to produce O₂ and food from simple substances like CO₂ and H2O and they are essential for life support on the station. But plants also need themselves conditions to live. The most important factors that influence plant growth are nutrients (minerals, C, H, N, O, P, S), the soil and climateric conditions (temperature, light, humidity, atmosphere composition). Plant processes (like photosyntesis, circulation and respiration) are of major interest for plant growing as well as for humans (photosyntesys produces oxygen and organic compound such as glucose, intense respiration consumes oxygen etc. *see nutrition in plants). If one of these functions is altered, the result will be abnormal growing or even death.

The soil is very important to plants, because it offers both support and almost all nutrients. Because natural soil takes millions of years of development making manufacturing almost impossible and its transportation from Earth would be very expensive, artificial soil will be used with similar properties as the natural one. The soil is in fact a solution; which contains both organic and inorganic molecules.

Since nutrients are by nature inorganic, the organic component is not strictly necessary ( in nature is a continuous source of inorganic compounds, but the station will be a closed system, so the organic detritus will be recycled and transformed in simple, inorganic substances, which will be returned back to the soil).

The artificial soil will have two components: a biotic one (plant roots and other organisms, needed to maintain the soil balance) and an abiotic component. The abiotic component will comprise a polymer (which will have a structure and consistency resembling with a sponge - like the natural soil-  providing support and space for water and other dissolved compounds -like nutrients), sand (silica)-small quantities, calcar (CaCO₃)-small quantities, nutrients and organic detritus (in small quantities). An average depth of 5-7 meters will be sufficient for all type of plants grown on the station. The soil will stay on a bed of rubber (10 cm deep), which is impenetrable for all substances solved in earth. Water will be held in small spaces by capillarity (all spaces with a diameter smaller than 0.5 mm). Nutrients will be held by solving in water and by their attraction to the negative charged membrane of the root absorbing cells.

The  nutrients are divided into two major groups: macronutrients (which are required in large amounts - approx. 1 mg per gram of dry mass: C, H, O, N, P, S, K, Ca) and micronutrients (100 microg per gram of dry mass: Cl,Fe,Mn,B,Zn,Cu,Ni,Molybdeum). These nutrients can be obtained initially from the Moon and the Earth and then integrated into natural cycles to be reused by the plants.

1.   Sources of nutrients

2.   Carbon source: => plants use CO₂ as source of carbon. CO₂ will be obtained from respiration of humans, animals and plants.

3.   Oxygen source: => for glucose (monozaharide) and polyzaharides or derivates (fructose) obtained from it the main source of oxygen is CO₂. In respiration, oxygen is taken from O₂ - produced by plants themselves. Even if O₂ is consumed during plant respiration and pho torespiration (a special type of respiration that occurs when photosynthesis is blocked), the quantity of oxygen produced during water hydrolysis (first part of photosynthesis) is much higher than the quantity used for respiration, thus resulting a surplus that may be used by humans and animals.

4.   Hydrogen source: => the main source of hydrogen is water or the free H⁺ ions from the soil.

5.   Phosphorus source: => acids :(H₂PO₄)- , (HPO₄)₂^-; salts: K₃PO₄, Na₂PO₄.

6.   Potassium source: => K⁺ from potassium salts: KCl, K₂SO₄ , KI solved in water

      (Ionized form; e.g. for potassium and  clorure, free ions of K⁺ and Cl^-).

7.   Calcium source: => Ca₂⁺ from salts (CaSO₄, CaCl₂) or fine divided Ca.

8.   Nitrogen source : => nitrogen will be taken from (NO₃)-, (NH₄)+, NH₃ and from the artificial atmosphere through nitrogen fixation.

9.   Iron, Zinc, Copper, Nickel, Manganese, Magnesium : => from fine divided metal or their salts (FeCl₂, FeCl₃, CuSO₄, ZnSO₄ etc.).

10. Boron source: => (BO₃)₃^-, B4O₇.

11. Molybdenum source: => fine divided molybdenum.

12. Chlorine source: => chlorine will be obtained from salts in their ionized forms (K⁺, Cl^-, Na⁺- Cl^-).

13. Sulfur source : => (SO₄)₂-, from salts or acids, solved in water.  

Nutrients are absorbed by plants in their ionized form (K+, Cl-, Mn₂+, Mg₂+, Fe₂+, Fe₃+, Cu₂+, Ca₂+, (NO₃)-, (SO₄)₂- or as gases (CO₂,O₂) or liquids (H₂O) through osmosis. Generally, nutrients are available for plants in their most oxidized form (carbon as CO₂, hydrogen as water, phosphorous as phosphate, nitrogen as nitrate, and sulfur as sulfate). In addition to CO₂ and O₂, plants are able to take up other compounds through their leaves such as some sulfur oxides from the atmosphere. Plants can also be fertilized by spraying their leaves with a nutrient solution (copper, manganese and iron are more efficiently absorbed from such foliar spraying than from the soil), but the pH of the solution and the concentration of nutrient ions within must be carefully adjusted (in very large quantities, iron is toxic for plants and a very low pH prevents ion absorption), and the plants must be sprayed at the right “time of day”. Plants can adapt to nutrient - deficient soils by directing their roots to patches of soil where the nutrients they lack can be found.

Plant roots manifest a certain degree of selectivity. However, the mineral composition of plants often reflects the composition of the soil and water in which they grow, meaning that some minerals that are not necessary for plants can accumulate in their body. Plants growing on mine tailings, for instance, may contain gold or silver, and the nutritional value of fruits and vegetables may vary depending on the composition of the soil. But that means also that some elements that humans and animals need (like selenium or natrium) can be absorbed by the plants from the soil and then used in alimentation; they can provide a plentiful source of elements (provided that the soil contains these elements).

As it results from the table, nutrients deficiencies may cause severe disturbances in plant metabolism. Any deficiency should be treated immediately after observed, otherwise the plant will die.

Light is essential for plants and they cannot live without it. It influences circulation and its absence prevents photosynthesis.Light is one type of electromagnetic radiation, a form of energy that behaves like both a particle and an oscillating wave, straining the human ability to represent natural phenomena realistically.

 As a particle, each unit of EM radiation is called a photon. It travels at a velocity (c), which is 3x(10)8 meters/sec in vacuum; the radiation also vibrates with a frequency of a vibration per second and has a wavelength of lambda. The photon may be considered a packet or quantum of energy. But not all the light is used by plants. Only red ad blue light is absorbed and the rest is reflected (that’s why the color of the plant is green - the only visible color which is not absorbed).

The optimum intensity for plants is around 20,000 - 25,000 Lx, higher or smaller values lowering photosynthesis. To the plants from the station only red and blue light will be given, by filtering normal light through red or blue glass.

b. Fluorescent plants

There are two types of light that may be used: artificial and natural light, each one with is advantages and disadvantages. Artificial light can be obtained from illuminating systems such as ordinary lightballs and has a high intensity, but consumes a lot of energy. Natural light can be obtained from some bacteria, mushrooms, fishes and coelenterates (only the bacteria are of interest) or from the plants themselves if they are genetically modified. The light produced by bacteria (from genus Photobacterium: Photobacterium phosphorous and Photobacterium leiognath) is withe-green and cold (it doesn’t contain infrared and ultraviolet rays) and of small intensity, so a huge quantity of such bacteria would be needed and is an oxygen consumer. The mechanism which will produce light is the following: a substance (called generically luciferin) is oxidized with molecular oxygen to luciferase, from this process resulting light.  Substances from the luciferin group are: luciferil-sulphate, 2-benzil luciferin etc.

                                          luciferil-sulfokinase

Luciferil-sulphate + O₂ ——————————————————————> LH₂ luciferin

                                                         +ATP (cofactor)    

So, the bacterium grown on a nutritive medium (glucose and nutrients) in presence of oxygen can be used to produce inexpensive, small intensity light.

The light producing plants are genetically manipulated plants to which the luciferase enzyme (responsible for glowing) gene has been added. The nature of the light is similar to the light produced by the bacterium from the Photobacterium genus. The technique used is cloning the gene into a plasmid which permits their expression in plants treated with it. Plants obtained from the genetically modified plant will have the same properties as their parents (they will glow too).

VI.5. Food factor and Agriculture

In order to be able to conceive a permanent existence of a rather dense population on our proposed Space Settlement we began by imagining the model of a microclimate similar to that found on Earth. We then tried to artificially compensate for the lack of all those elements which are not to be naturally found on our station.

a. Food composition and preparation

Correct nourishment is a basic condition for a healthy population. Health does not mean only “not being ill”, but also a physical, mental and social state of well-being.

Nourishment is the first among the eight principles which define a healthy way of living. That’s why achieving a project of such magnitude implies special care and studies in order to find solutions to all human necessities.

Agriculture is the field which provides the essential raw materials to the food industry, therefore only by creating the conditions for getting quality produce can we ensure the necessary base of the food processing.     

In this respect, we could also get rid of everything that has been harmful to people on Earth (tobacco, alcohol etc.) and direct our attention to healthy produce.

The nutritive substances are divided after their function in:

·    nutrients with energetic role: glucids and proteins, which provide the vital energy

·    nutrients with plastic role: proteins, used to repair cellular structures

·    nutrients with catalytic role: vitamins, minerals, that influence metabolic reactions. 

The optimal proportion between proteins, lipids and glucids (or carbohydrates) is 1:2.5-3.5:0.8. The quantity needed by a person varies after the “due body weight “. Due body weight, in kilograms, is equal to person’s height in centimeters minus 100 (+-10%) - for men and minus 110 for women. Thus, for a person 160 cm tall, a due body weight is 60 kg +- 6kg. A correct amount of protein to be consumed in a day is approx. 1g per kg of due body weight. Thus, a person with 60kg needs to consume about 60+-6 g of protein to satisfy body’s daily needs. Any excess of protein is converted to fat, provided energy requirements are met by other components. Using the ratio 1:2.5-3.5:0.8, the required quantity of lipids and carbohydrates can be calculated: 150-210 g of fat and 30 to 50 g of carbohydrate. 

The needed energy is expressed in calories (1 cal = the quantity of heat required to raise the temperature of 1g of water with 1 grade). All body activities require energy, and daily needs vary with people due body weight and activities. For example, an adult with less activity needs about 2500 kcal, while a worker needs 5000 kcal and a performance sportive 8000 kcal. Energetic requirements are also higher for children: 4000-4500 kcal.    

How much a healthy human requires protein per day? Opinions are divided: while the WHO protein figure translate into 56g of protein a day for a (75 kg) man and 48g for a(64 kg) woman, the recommendations of the UK Department of Health and Social Security (DHSS) are slightly higher: 68g a day for a sedentary or moderately active men, and 54g a day for women, but the quality is important. The quality of protein is measured by comparing the proportions of essential amino acids in a food with the proportions required for good nutrition. The closer the 2 numbers are, the higher the protein quality. Egg and milk proteins are high - quality proteins that are efficiently used by the body and are used as reference standards against which other proteins can be compared. Meat protein is of high protein quality, whereas several proteins from plants used as major food sources are relatively deficient in certain essential amino acids, e.g., tryptophan and lysine in maize (corn), lysine in wheat, and methionine in some beans. In a mixed diet, a deficiency of an amino acid in one protein is made up by its abundance in another; such proteins are described as complementary; e.g., the protein of wheat and beans combined provides a satisfactory amino acid intake. Under such circumstances, a greater total amount of protein must he consumed to satisfy requirements.

Regardless of their source, aminoacids that are not immediately incorporated into new protein are rapidly degraded and they are not stored.

All dietary proteins (proteins that can be used by humans) are digested and absorbed in the bloodstream as individual aminoacids. The body requires 20 different aminoacids, and only 8 can be synthesized. The daily needs of protein are calculated based on body weight, extra growth on infants require larger quantities. Pregnancy, lactation, tissue repair after injury, recovery from ilness, increased physical activity is other conditions requiring more dietary protein. Generally, a diet where 12% of the energy is supplied as protein is adequate.

Fats-or lipids-are a class of organic substances that are not soluble in water. In simple terms, fatty acids are chains of carbon atoms with hydrogen atoms filling the available bonds. Most fat in our bodies and in the food we eat is in the form of triglycerides, that is, three fatty-acid chains attached to a glycerol molecule.

Fat’s value as a “fuel” for our body increases with the increase in the amount of hydrogen per gram of carbon in its molecule, with the increase in the energy-contributing constituents. Chemically, the best are long-chain fully saturated fatty acids, that is to say, solid fats of animal origin. Only fats with the length of the chain above 10 carbon atoms are suitable to be utilized by our cells and tissues without conversion. These fats are directed straight to the blood stream via the lymphatic system, and they do not have to be converted and made suitable by the liver, as is the case with inferior fats (with shorter chains), or all other constituents of consumed and digested foods. Long chain fatty acids are the best medication for those suffering from liver diseases. Chemically and factually long chain fatty acids are the best “fuel” for our bodies.
By eating animal fats we not only receive concentrated energy, but we also receive all the fat- accompanying elements needed to obtain this energy, in the necessary quantity and proportion. The human body metabolizes animal fats easily and such metabolism is energetically economical. The digestive system is designed to slowly deliver the building blocks and energy containing matter.

Carbohydrates are widely distributed in plants and animals, where they fulfill both structural and metabolically functions. In plants, glucose C₆H₁₂O₆ is synthesized during photosynthesis, while animals obtain it from plants or other animals. Animals can synthesize some carbohydrates from fat and protein but these quantities are much under their needs.

Most carbohydrates in the food form glucose, galactose and fructose. These are transported to the liver via the portal vein, where galactose and fructose are converted into glucose. Glucose is specifically required by many tissues, but does not have to be provided directly from food since other compounds like starch, fructose, galactose are transformed in glucose either during digestion (starch) or in liver (fructose, galactose). A minimum daily intake of carbohydrates is about 50g to prevent ketosis and loss of muscle protein. 

Vitamins are substances that act as catalytic substances. In their absence, some products cannot be synthesized, producing severe diseases to humans (loss of nocturnal sight, heart diseases, anemia, etc.)

The necessary vitamins are: A, B1, B2, B6, B12, C, D, E, K, and PP. Some can be solved in water (B1,B2,B6,B12,PP,C) and others in fats (A,D,E,K). Vitamin A can be found in fresh vegetables (especially carrots), milk, liver, butter, cheese and eggs; 12mg are required daily. Vitamin B1 is found in meat, cereals, vegetables, milk, liver; 1-2mg/day. Vitamin B2 can be found in almost all foods; 1-2mg/day. Vitamin B6 can be found in cereals, vegetables, and meat. Vitamin B12 is found in pork and beef meat, eggs and fish; 2mg/day. Vitamin C can be found in fresh fruits and vegetables (tomatoes); 70mg/day. Vitamin D is found in cheese, yogurt, milk, cream, liver, eggs, fish, fish oil; 1-2 mg/day. Vitamin E can be found in margarine, seeds, fresh vegetables, wheat, vegetal oils; 20mg/day. Vitamin K is found in fresh vegetables, liver, produced by intestinal bacteria; 4mg/day. Vitamin PP can be found in dried vegetables, cereals, eggs, milk, and liver. Vitamins are generally present in plants and they are less abundant in animals.

Although water isn’t a nutrient, it has a very high importance because it represents the medium were all reactions take place and in which most substances are solved. The daily need of water is around 1.5-2 l/person, but this value can be much higher if transpiration is high (for example, when temperature is high). Water can be taken directly or from other products (the value required comprises the total water ingested).

 Minerals have catalytic proprieties or they take part as components in some compounds (like iron in hemoglobin). Minerals are: P, Ca, Fe, Zn, Cu, Cl, Na, K, S, Se, Ni, Mn, and Mg.

As no single food contains all these elements, we have to use a variety of foodstuffs. In the case of living on a space station, there are two possibilities of ensuring the nourishment of the population.

One could be the classical way similar to that which we are familiar with on Earth. This presents, however, a variety of problems, connected to the diversity of the required technical means, complex methods and storage facilities. Another way would be a balanced vegetarian diet, without cholesterol and fats for the benefit of the human body. Furthermore, as the evolution of civilization aims at the creation of a new type of man, with higher aspirations but less time, we suggest a re-thinking and re-designing of the food industry, so that it would serve the interests of the individual, offering him the necessary state of health and comfort.

In this respect, we recommend the use of Soya as the basic raw material to obtain various foodstuffs ranging from diary produce to those having the taste of meat. Millet paste could successfully replace eggs. 

A vegetarian diet can offer man the benefit of protein of superior quality such as glucose and lipids which are not harmful, nut-oil, seeds, olives, fiber, vitamins and total mineral salts.

This is the ideal we should pursue to avoid many of the causes of illness nowadays. Setting as our objective a healthy diet, the designing and construction of the technical facilities helps to achieve the above purpose.

On as pace station, crops an be grown on the seven levels used for agriculture, provided with red spectrum lights, adequate ventilation, system of keeping constant temperature and air humidity, as well as the polymer texture used as crop supports.

Crops must be treated with natural and synthetic fertilizers to get quality produce. Once the plants have grown, they are harvested and stored in appropriate spaces, until they are processed.

But, people’s mentality being what it is, perhaps some may experience frustration in the absence of those useful domestic animals with whom they were used on Earth (poultry, livestock). Fish breeding facilities are also possible and from a psychological point of view.

In conclusion, the diet onboard L.E.D.A. will comprise a mixture of aliments from the following classes:

·    Fruits and vegetables

·    Cereals

·    Milk and milk products

      ·       Meat and eggs

Since cultivation will be reduced on the station, only the foods with the best quality will be grown.

 b. Food depositing and quality control

In the area designed for industrial activities, the technical equipment for processing the agricultural and animal produce will be of major importance. They will ensure the mechanical and thermal treatment used in the process of getting both raw materials and the final produce.

We must design this equipment having in view the special conditions required when working in a space station environment, the necessity of recycling the residues, eliminating the effect of vibrations, noise, and odor pollution. The final products must be properly stored in special locations from which they will be delivered according to the demand.

The quality of the products is reflected in the quality of the population’s state of health, therefore monitoring quality is essential during the entire production cycle.

VI.6. Water management

Most forms of life require water for their survival. On the Space Settlement, we will need to find ways of producing and effectively recycling the water for plants and humans.

From: Wydeven, T., and Golub, M.A., Generation Rates and Chemical Compositions of Waste Streams in a Typical Crewed Space Habitat,  NASA Ames Research Center, Moffett Field, CA (1990) and Webb, P., Ed., Bioastronautics Data Book, NASA SP-3006, National Aeronautics and Space Administration, Washington, D.C. (1964).

a. Water Production

Initially, water will have to be extracted from the Moon, in the form of ice, the ice melted using solar energy and then purified. Also, the first spaceships arriving at the station will need to carry water supplies. On the settlement, water will be constantly recycled, since there are no viable water sources in space, apart for The Moon and The Earth, and the cost of supplying the station with all the necessary water from these places is too great.

Plants and animals eliminate water through breathing and excretion.

 Excess humidity in the air will need to be condensed and the water recycled.

b. Water storage

Water will be stored in a cluster of interconnected tanks located at the center of the space station. The connections of the tanks will be fitted with valves and pumps. When water from the tanks is used, the remaining water must be distributed evenly in order to avoid oscillations due to inertia.

The storage area will need to be large enough to hold a few days’ supply of water in the case of an emergency (about 54250 tons for a week, which means that the whole storage area should have a volume of 54250 cubic meters).

Since “gravity” increases as we advance towards the outer regions of the station (the inhabited area), water will flow naturally (or with little energy consumption) to where it is needed. However, sewage water will have to be pumped to the purification plant and then into the storage tanks using electric pumps.

c. Water quality control

A water processing facility will be placed next to the storage tanks. It should be able to handle a flow of 7750 cubic meters a day. Water purification methods include physical, chemical and biological purification and each method will be used at different stages of the process.

1. Physical purification involves the removal of solids from liquids using filters. Water is forced through a membrane under pressure, leaving impurities behind. Cross flow membrane filtration methods will be used to separate salts and organic matter from the water. The finest membranes will be able to filter particles as small as 0.001 microns (reversed osmosis). That includes most salts, bacteria, viruses, and metal ions.

2. Chemical purification consists of adding chemicals to the water. The chemicals act as biocides or prevent the formation of certain reaction products. Oxidizing agents can be added for disinfection or to neutralize reducing agents and reducing agents should be added to reduce oxidizing agents.

The most common chemical used for disinfection is chlorine. However, it is not a suitable solution for the space station because of its tendency to form toxic chlorine gas or to react to chloramines and chlorinated hydrocarbons. To prevent this, we could add chlorine dioxide (ClO2) to the water, as it is an effective biocide in very low concentrations. It reacts to amino-acids in the cytoplasm and kills the microorganism. The by-product of this reaction is chlorite.

Ultra-violet radiation can be used for disinfection, as well as ozone, iodine or silver. UV radiation treatment should be applied to water being stored in the tanks, since it prevents the division of cells and therefore the multiplication of microorganisms.

3. Biological purification involves the use of microorganisms, mainly bacteria to decompose remaining organic materials dissolved in the water.

4. A very useful method for preventing the water contamination by removing organic constituents and residual disinfectants is the activated carbon filter. This is a favored technique because of its multifunctional nature and the fact that it adds nothing detrimental to the treated water. Another advantage is that this method not only improves taste and minimizes health hazards; it also protects other water treatment units such as reverse osmosis membranes and ion exchange resins from possible damage due to oxidation and organic fouling. There are two principles by which activated carbon removes contaminants from water: absorption and residual disinfectants removed by catalytic reduction.

Water quality will be monitored to ensure against disease. The supply will conform to regulations concerning chemical, inorganic and organic matter concentration.

The EPA current drinking water standards (units are milligrams per liter (mg/L) unless otherwise specified):