III. Life Support

            The earth’s extreme range of environments has already proven how frail the human body is.  Without sophisticated gear, human beings cannot venture into the depths of the oceans, the expanses of deserts, and the high altitudes of mountains. This fact is doubly important for life in space, as the needs of humans must be provided for, and to accomplish such a task plants with millennia-old lineages will be combined with just out of the womb technology to create a viable environment in Æther.

 

III.A Radiation

            Radiation in outer space can be differentiated into two kinds: nonionizing radiation and ionizing radiation.  Nonionizing radiation consists of long-wavelength electromagnetic radiation, which is defined as electric and magnetic energy, or fields, traveling through space.  The sun emits nearly all of the electromagnetic radiation found in the solar system; the radiation intensity is approximately 1390 W/m2 near the earth.  However, an object in orbit around the earth also has to take into account the radiation intensity emitted by the earth, 225 W/m2 [ref 1].

Ionizing radiation is defined as high-energy particles and short wavelength electromagnetic-radiation that separate electrons from their atoms upon close passage.  It includes gamma radiation, X radiation, alpha particles, beta particles, neutrons, protons, and heavy nuclei.  Two primary sources of ionizing radiation in space are Solar Cosmic Rays (SCR) and Galactic Cosmic Radiation (GCR).  SCR are composed of protons, electrons, and other heavy nuclei with energies of 107 to 109 eV.  SCR coincide with very large solar flares that occur once or twice during the eleven-year solar cycle.  SCR are responsible for rapid increases in radiation doses in a short amount of time, and advance notice of only a few hours to several minutes can be given for solar events.  GCR is a continuous stream of particles consisting of high-energy protons, alpha particles, and heavy nuclei called HZE radiation.  GCR is also influenced by the 11-year solar cycle, at sunspot maximum GCR is at its minimum due to the stronger interplanetary magnetic field. Conversely, at sunspot minimum GCR is at its maximum.  In absence of solar-flare activity GCR constitutes about 90 percent of the radiation absorbed [ref. 2].  Although GCR is small in quantity, it possesses high energies that enables it to penetrate deeply.

 

III.A.1 Measuring Radiation

            The amount of radiation that is absorbed can be quantified through the use of dosimetry. The SI unit for absorbed dose is the gray (Gy): 1 Gy = 1 J/kg.  However, equal doses of different types of radiation have differing effects on the material that is absorbing the radiation.  This can be tied to the quality factor of the radiation, which is expressed in relative biological effectiveness (RBE).   RBE is defined as the number of Gy of X-ray radiation that produces the same result as 1 Gy of the given radiation.

Table 3.1

Radiation

RBE

X rays

1

5 MeV γ rays

0.5

1 MeV γ rays

0.7

200 keV γ rays

1

Electrons (β rays)

1

Protons

2-10

Neutrons

2-10

α particles (He nucleus)

10-20

 

            Thus, the effective dose can be given as the product of RBE and Gy.  Effective dose is measured in Sievert (Sv) in the SI unit system: 1 Sv= 1 J/kg = 100 rem. On earth, an average human receives a dosage of 1.7 mSv [ref 1].

 

III.A.2 Effects of Radiation

            When a high-energy particle enters the body, it can either undergo direct interaction with the atoms of the body, thus producing many ions, or it can undergo indirect interaction with the atoms and produce secondary radiation.  The secondary radiation that is produced when high-energy particles interact with atoms or molecules in the human body is called Brehmsstrahlung radiation.  Brehmsstrahlung radiation occurs when high-energy particles are deflected and decelerated by charged particles.  This secondary radiation also ionizes the surrounding tissue.  In both cases, the ionizing effects of the radiation are proportional to the energy absorbed by the surrounding tissue.  The ions produced can produce free radicals, such as the highly reactive and unstable OH molecule.  A free radical can attack other compounds in the body to form even more free radicals and thus has far reaching consequences.  A dose of 0 to 0.5 Sv will result in no obvious effects, while doses from 0.5 to 1 will cause radiation sickness in 5-10% of exposed personnel.  A dose of 10 Sv will most likely kill all who are exposed [ref 1].

Somatic damage affects the exposed organism during its lifetime and can be classified as acute or long-term effects.  Acute effects of radiation are caused by exposure to high doses of radiation in a short time frame, it is indicated by the symptoms of radiation sickness such as nausea, vomiting, discomfort, a decrease in the number of white blood cells, loss of appetite, and fatigue.  If exposed to doses higher than 2 Sv, one can also expect diarrhea, hemorrhaging, and hair loss.  Effects of prolonged exposure to low doses of radiation include cancers of the lung, breast, digestive system, and leukemia.  One can expect an increase in 2% to 5% chance of contracting cancer for every 0.5 Sv.

Radiation can also inflict genetic damage; this type of damage harms the offspring of the exposed organism through damage of the genes and chromosomes.  The genetic effects in animals and other forms of life caused by ionizing radiation are well documented.  Radiation exposure to nonhuman forms of life resulted in abnormalities and mutations that were evident in immediate and remote offspring.  The frequency of genetic effects due to radiation exposure has a linear relationship with the dose and does not seem to have a threshold. The radiation dose needed to double the mutation rate in humans has been calculated to be higher than 1 Sv [ref 4].

Exposure to radiation of fetuses during 16 to 25 weeks of pregnancy results in adverse neuro-developmental effects such as mental retardation, reduced IQ, and seizure disorders.  Exposure during the gestational period (8-15 weeks) results in even more damage, as it is the most sensitive time for neurological developments.  The above-mentioned three abnormalities, as well as microcephaly (the abnormal smallness of the head) occurred in children born to the survivors of the atomic bomb detonations in Japan during the Second World War [ref 4].

Setting health standards for exposure to radiation is difficult, as the effect of heavy nuclei on human tissue is not well known. Currently, some scientists advocate that any amount of radiation causes some damage, even down to low doses. Other scientists, however, believe that there a threshold exists below which no radiation risks occur.  Until more scientific evidence that can settle the matter with confidence is introduced, it would be safer to assume that even low doses of radiation pose danger to human life.  The 1993 National Council on Radiation Protection and Measurements (NCRP) recommendations were 1 mSv annual dose limit for continuous exposure and a 5 mSv annual dose limit for infrequent exposure.

 

III.A.3 Radiation Protection

            There are two main types of radiation protection: active shielding and passive bulk shielding.  Active shielding includes a magnetic field that deflects charged particles from the crew area and a magnetic/electrostatic plasma shield that uses an electrostatic shield to protect the interior from positively charged particles while a magnetic field confines electrons from the space plasma to provide charge neutrality [ref 5].  An advantage of active shielding is that it can be dynamically controlled, which could then be matched with dosimetric monitoring of solar flare activity [ref 2]. However, a dilemma exists with active shielding; to produce a powerful shield with a low energy cost one must turn to the use of superconductors, but along with the introduction of superconductors into the system comes the costs and problems associated with it [ref 5]. Clearly, the disadvantages of active shielding, such as higher masses required for adequate shielding from radiation and the inability to deflect heavier particles with high kinetic energies have precluded active shielding from use in Æther; but a dynamically controlled active shield could be used in an integrated system, and turned on when the influx of light particles from solar-flare activity is high.

Passive bulk shielding deflects or stops radiation before damage to sensitive electronics, living tissue, and structural components can be done.  Aluminum is most commonly used in today’s spacecraft for passive shielding, as it is both lightweight and high density [ref 1].  However, the idea that by adding more and more aluminum one can eventually protect Æther’s interior from all radiation is wrong.  As the thickness of the aluminum shield is increased, the possibility that secondary radiation would be produced increases.  Because of Brehmsstrahlung radiation lighter elements such as oxygen, carbon, and hydrogen and their compounds are more effective shields for HZE radiation than are heavier elements such as lead, which is commonly used on earth. Water and polyethylene have excellent shielding efficiency per unit mass, and their use in other applications may also have a secondary role in maximizing shielding mass.  For example, distributing drinking water over large surface areas would contribute to the total radiation shielding mass.  A shield made of lunar soil would require a thickness of 5 meters in order to provide protection equal to the earth’s atmosphere.

The residential area radiation shielding will consist of a lunar regolith/ice layer 4 meters thick.  The lunar regolith/ice layer will consist of a crushed lunar regolith matrix and ice supported by an aluminum framework, the total density of the structure would be around 500-3000 kg/m2.  Lunar soil consists mostly of SiO2, TiO2, Al2O3, MgO, CaO, and FeO [ref 1].  The light elements, such as silicon, oxygen, and aluminum, will provide an excellent shield for both GCR and SCR.  The addition of ice to the shielding will also aid in shielding against incoming particles as well as diffusing the ions that are created from the interactions of radiation and the passive shield, thereby preventing the ions amalgamating into and weakening the crystal structure of the aluminum framework [ref 9].  The titanium hull will be the next layer of radiation shielding.  A layer of Copper Tungsten alloy would be placed on the inside of the titanium hull to provide protection against deeply penetrating heavy nuclei from GCR and solar flares.  The CuW alloy contains 90% tungsten and 10% copper by weight density (the equivalent of 75% atomic weight tungsten and 25% weight copper).  Such an alloy layer shows a twofold to fourfold increase in shielding efficiency over an aluminum shield [ref  7].  CuW alloy is prepared by the liquid-phase sintering of mixed elemental powders during which part of the tungsten dissolves in the copper liquid.  The product is a two-phase material consisting of rounded tungsten grains and a matrix of copper-tungsten containing up to 17% tungsten [ref 8]. The resultant CuW alloy would possess a density of 17,000 to 18,000 kg/m3, and panels would be formed from CuW alloy and placed in the interior of the titanium hulls. The Water Ballast System will also be configured to provide the final layer of radiation shielding.

The windows that permit sunlight into the residential area of Æther will also have to filter out the undesired wavelengths.  This can be achieved through the use of selectively transparent glass, which absorb some wavelengths while allowing others to pass through. Selectively transparent glasses can be manufactured by depositing a thin layer of metal onto the glass.  Thick glass in itself is opaque to the long wavelengths of infrared radiation, while leaded glass would also provide protection against X and gamma radiation. A “sandwich” would be made with leaded glass on the outsides and a layer of water in between.  This layer of water could be laced with aqueous solutes that decrease the amount of radiation that reaches the colonists.  The aluminum mirrors that work in conjunction to reflect light into the habitable areas will also be able to absorb some harmful radiation. During times of heightened solar flare activity, radiation shutters made of CuW-Al panels could be drawn over the windows and residents would be advised to stay inside radiation shelters.

 

III.B Pseudo-Gravity

As Æther is in a free falling orbit around earth, there will exist a microgravity environment within it.  This environment is undesirable for long-term habitation since humans cannot adapt to weightlessness.  The human body reacts to the conditions associated with weightlessness in a series of interrelated responses that begin in the gravity receptor tissues, fluids, and weight bearing structures.

The gravity receptors refer to the otolith organs in the inner ear; mechanical receptors in the muscles, tendons, and joints; and pressure receptors in the skin.  The otolith organs are part of the vestibular apparatus in the inner ear. The otolith organs comprise of protein and calcium carbonate crystals embedded in a gel, they respond to gravity by triggering hair cells which provide a sense of balance.  The two otolith organs are the saccule, which senses motion in the vertical plane; and the utricle, which senses motion in the horizontal plane.  Combined, the saccule and the utricle give the human body the means to deduce acceleration in any arbitrary direction in three-dimensional space [ref 27].  On earth, the acceleration caused by gravity always causes a signal to be sent from the otolith organs.  Mechanical receptors and pressure receptors respond to the weight associated with body parts in the presence of gravity. However, in conditions of weightlessness the otoliths no longer feel a downward pull on the head, and muscles have to contract and relax in different ways to bring about movement of the limbs and other body parts.  The absence of these signals can result in visual-orientation illusions and feelings of spontaneous reorientation.  The signal changes due to gravity cause a space sickness that has symptoms not unlike those of terrestrial motion sickness.  Impaired concentration, loss of appetite, stomach awareness, and vomiting are not uncommon, but only last for the first two to three days of weightlessness.

Weightlessness also causes havoc in the body’s fluid systems, as the body is 60 percent water by weight.  On earth, fluids inside the body have weight and are normally pulled towards the ground, creating hydrostatic pressure [ref 27].  This hydrostatic pressure primarily influences the distribution of fluids by affecting how much blood leaks from arteries and into the interstitial space in between cells.  Under weightlessness conditions, this hydrostatic pressure is not present and redistribution of bodily fluids occurs [ref 27].  Each leg loses about one liter of fluid in the first day of micro gravity conditions, this fluid is redistributed to the upper body. Renal, hormonal, and mechanical mechanisms that regulate fluid and electrolyte levels are affected by the shift in fluids.  The kidney filtration rate increases by almost 20 percent, while some space travelers have suffered from a special type of anemia indirectly caused by loss of plasma [ref 27].

Muscle and bone loss is also associated with long periods. Structural elements experience drastic changes in conditions of weightlessness, as they no longer have to bear the weight associated with organs on earth.  Some skeletal muscles also atrophy as different muscles are used for traversing through a weightless environment.  Muscles also switch over to fast-twitch muscle fibers, which are used for rapid movements, rather than slow-twitch fibers, which are used for support against gravity’s pull.  Bone mass in the lower vertebrae, hips and upper femur decreases by one percent per month while in space, and other bones lose calcium at a faster rate.  The lost calcium in the bones ends up causing elevated calcium levels in the bloodstream, leading to potential formation of kidney stones and calcification in soft tissues.  Some bone loss is permanent, and those who spend long durations in weightlessness may find life with 1-g filled with peril of broken bones [ref 28].

            Partial remedy of these symptoms can be achieved through exercise and the use of light-emitting diode (LED) blankets, which prevents bone and muscle atrophy by submerging the body in 680, 730, and 880 nm light [ref 29]. However, the least discomfort can be achieved by rotating the colony to produce a psuedo-gravity that mimics gravity on earth.  Rotational motion results in the constant change of direction of an object’s velocity. Since acceleration is defined as the change in velocity over time, acceleration is required to produce rotational motion.  This acceleration is perpendicular to the tangential velocity and points radially inward, and is called the centripetal acceleration.

 fig. 3.1

Rotational motion produces a “pull” radially outwards that many are tempted to call the centrifugal (“center-fleeing”) force, but in fact no such force exists.  Consider the example of two passengers in an automobile that is rounding a curve.  As most people who have ridden in a car know, there is a tendency for the passenger to be pushed away from the center of the turn; this is caused by the passenger’s tendency to go straight, which is a result of his or her inertia.  Likewise, a constant rotation of the colony will utilize the colonist’s mass to produce pseudo-gravity.  It is also helpful to think of pseudo-gravity as a result of the colony edge pushing radially inwards against a colonist. 

 

 fig. 3.2

If ac=v2/r and v= ωr, we can find an equation for ac in terms of ω, or the angular velocity.  Since the desired psuedo-gravity is 9.8 m/s2, the equation for revolutions per minute in terms of radius would be .  The graph of this function can be seen in figure 3.3. 

 fig. 3.3

 

            However, in a reference frame that rotates at a constant angular speed, there exists another psuedoforce known as the Coriolis force.  The Coriolis force affects any object that moves linearly within a rotating system.  If the object moves from Ra radially towards Rb, where Ra is a with a smaller radius compared to Rb, the direction of the Coriolis pseudoforce is counter to the direction of rotation.  If the object moves radially from Rb to Ra, then the pseudoforce acts in the direction of rotation.  Likewise, if an object moves tangentially in direction of rotation, the pseudoforce is radially outwards, in other words the object gets heavier.  If an object moves tangentially counter to the direction of rotation, the pseudoforce is radially inwards, and the object becomes lighter [ref 1].  One can clearly see that the Coriolis pseudoforce is undesirable.  Symptoms of vertigo, disorientation, and nausea are a result of excessive Coriolis pseudoforces.  Also, since frequent commuting between the habitable areas and the microgravity industrial areas will occur, special care must be given to the prevention of disorienting effects that can hinder the quality of life and produce undesirable results.  Generally, the Coriolis pseudoforce decreases as the radius becomes larger and the angular velocities associated with producing pseudogravity become smaller. All humans can tolerate a rotation rate of 1 rpm or less, and this should be taken into account when deciding the size of the colony.

            Since Æther will have a major radius of 2000m, the angular velocity will be 0.07 rad/s; and the rotation rate will be 0.6685 rpm, well within the allowable limits.  The rotation of Æther will be achieved by spinning it with thrusters positioned at the outermost edges of the torus.  To calculate the thrust needed, the equations τ =Ia and

τ = rFsinθ must be used, where τ equals the torque, I is the moment of inertia of Æther, a is the angular acceleration, r is the radius, and F is the force.  Thus Ia=rFsinθ, and solving for force yields F=(Ia)/(rsinθ). The moment of inertia for Æther can be approximated using a rough model (see Appendix A) and is roughly 7.868x1017 kg·m2.  Although spinning will commence during construction of Æther, for this calculation it is assumed that Æther is at rest at the starting point.  Thus, if the spin time is to be 30 days, or 2592000 seconds, the angular acceleration a would be 2.7x10-8 rad/s2.  The radius r would be 2255 meters, since the thrusters would be placed at the edge of the torus, and assuming they are perpendicular to the radius of the torus, sinθ would equal 1. Thus, thrusters with the combined force of approximately 9.42x106 N would be needed to spin the colony.

 fig. 3.4

 

However, the thrusters will also be employed for maintaining the rotation of the colony, since variances in angular momentum will occur when objects move from the center to the torus.  Thus the thrusters should be of a durable and reliable nature, preferably ion thrusters, since they are able to generate low thrust at high efficiencies and are also very reliable.

 

III.C Atmosphere Management

            Atmosphere management concerns the atmospheric revitalization and contaminant control of the colony atmosphere.  The five main tasks of atmosphere management will be atmosphere control and supply, temperature and humidity control, trace contaminant control, and colony ventilation. Atmosphere revitalization in the colony will have two main steps, CO2 concentration and removal, and O2 generation.

 

III.C.1 CO2 Concentration and Removal

CO2 concentrations must remain at a low level in order for normal life to occur.  The adverse effects of high concentrations of CO2 include headaches, mental depression, hearing losses, dizziness, increased cardiovascular activity, nausea, and eventually unconsciousness.  The partial pressure of CO2 on earth is 0.0318 kPa. Allowable levels of CO2 concentration are 1.01 kPa during short missions and 0.40 kPa for long missions such as an assignment to the International Space Station.  In order to prevent CO2 buildup due to human respiration (1 kg of CO2 per day), methods of removing it from the atmosphere must be utilized [ref Designing for Human presence in space]..

Four ways to remove CO2 from the colony atmosphere are absorption (chemical or electrochemical reaction with a sorbent material, adsorption (physical attraction to a sorbent material), membrane separation, and biological consumption. The main technology in use today that utilizes absorption for CO2 removal is LiOH absorption, however, LiOH absorption is not acceptable for long-term (over 2 weeks) use as it is not a regenerable process and the chemical reaction cannot be reversed. Molecular Sieves adsorb CO2 due to its microscopic pores, which allow O2 and N2 to pass through, but trap CO2.  Molecular sieves are able to hold large amounts of CO2 due to their large surface area.  Other technologies used to concentrate and remove CO2 from spacecraft interiors include solid amine water desorption, electrochemical depolarization concentrator, and air polarized concentrator.

4 bed molecular systems (4BMS), which utilize 5A zeolite molecular sieves for trapping CO2, have already been flight proven on Skylab, and can be expected to perform for 10 years without failure [ref http://www.ae.utexas.edu/~campbell/fatmass/pdr2.htm].  4BMS operates in a cycle, with equal amounts of time needed for adsorption and desorption of CO2. However, a vacuum environment is needed for the desorption of CO2.  2 bed molecular systems (2BMS), utilize carbon molecular sieves and is projected to have half the weight and power requirements of 4BMS, however, this technology is still in its early stages of development.

Solid amine water desorption utilizes heated solid amine to absorb/desorb CO2.  However, potential amine degradation leads to reduced CO2 capacity and toxic vapors, and thus this technology was not considered for use in the colony.

Electrochemical depolarization concentration (EDC) uses electrochemical reactions to remove CO2 from the air, the net effect is the production of water from hydrogen and oxygen, the production of DC power and heat, and the concentration of carbon dioxide.  EDC has the advantages of being able to operate in cyclic or continuous mode, easily alter the CO2 removal rate, and produce DC power. However, the possibilities of H2 leakage must also be considered as well as the heat load and O2 demands.  Air polarized concentrators (APC) work on the same technology as EDC, except it negates the need for H2, however, in doing so, it becomes a power consumer.  An APC can easily be run with H2, in effect becoming an EDC. APC/EDC combination was finally chosen as the technology to concentrate CO2 onboard the colony.  Not only does this combination offer great flexibility as to the power draw and safety issues of the system, it also fits quite nicely into a bio-regenerative system because of its continuous operation mode.

 

III.C.2 O2 Generation

            The O2 partial pressure at sea level is 21.4 kPa.  O2 partial pressure must be maintained near this level to avoid negative the physiological effects of decreased night vision, convulsions, unconsciousness, impaired memory and coordination, and death of nerve tissue [ref Designing for Human presence in space].  Traditional, non-biological methods of generating O2 onboard space missions mostly involve the electrolysis of water, electrolysis of water vapor, or electrolysis of CO2.

            On the space colony, O2 generation will be the task of the plants onboard.  The plants could also be used for CO2 removal from the colony atmosphere; however, since faster plant growth rates can be achieved with a concentrated CO2 atmospheric level, CO2 removal and concentration will be left to the EDC/APC systems onboard.

            However, there is a loss of approximately 0.10 moles of CO2 if plants are introduced into the colony CELSS, since humans exhale about 0.85 moles per mole of O2 consumed, and plants consume about 0.95 moles of O2 for every mole of O2 produced. Variations in CO2 consumption and O2 production rates also exist due to the fact that plants do not experience constant plant growth, but rather experience periods of accelerated growth when CO2 consumption is at a higher level. Plants also stop producing CO2 and start consuming O2 because of cellular respiration during periods when there is no illumination.  High growth rates must be considered along with high yields as high temperatures 298 K (25º C) promote rapid growth but lead to low yields, while cooler temperatures 293 K (20 º C) promote higher yields but hinder rapid growth. Therefore, to ensure a stable means of oxygen generation while utilizing plants as the method of O2 generation, several methods are recommended, such as providing multiple plant growth areas that are illuminated at different times of the day, to ensure a steady source of oxygen night and day; altering illumination or temperature levels to control photosynthetic rates; and using a system of gas storage.

            To compensate for times when plant O2 generation is below required levels, artificial means of generating O2 must be considered.  As mentioned above, artificial means of generating O2 mostly involve the electrolysis of water, electrolysis of water vapor, or electrolysis of CO2.  An advantage of electrolysis is that the H2 produced from this electrochemical reaction could be fed into the EDC/APC system, in effect “closing the loop.”

            Several systems considered for O2 generation onboard the colony are Static Feed Water Electrolysis (SFWE), Solid Polymer Water Electrolysis (SPWE), and Water Vapor Electrolysis (WVE).  SFWE was rejected because of its use of asbestos, SPWE and WVE both are technologies that possess many desirable attributes. SPWE is a mature technology that is being used onboard the International Space Station for its Oxygen Generation Assembly.  Integration of both SPWE and WVE would not be too difficult as SPWE could receive water from the CHX subsystem, and WVE could directly electrolyze atmospheric air.  The drawback of SPWE are that it is sensitive to water contamination, while the drawback of WVE is that it interferes with the humidity control of CHX.  Thus, WVE was finally chosen as its problems can easily be rectified.

 

III.C.3 Temperature and Humidity Control

            Condensing heat exchangers (CHX) have been widely used to remove moisture and heat at the same time from the atmosphere of space missions by using coolant-cooled fins to condense humid air and then removing the condensation via “slurper holes” [ref 1].  By using fins to maximize the surface area, faster rates of heat exchange with a minimum of volume can be achieved.  First, atmospheric air is drawn into the system, and its humidity and temperature are recorded.  Then the air is passed through high efficiency particulate atmosphere (HEPA) filters to remove microbial and dust contaminants ranging from 0.5 to 300 microns in size.  At the water-cooled air fins of the CHX the temperature of the airflow is brought below the dew point, thus causing the air to be super-saturated with water vapor.  Water then condenses and is carried by the airflow to the slurper holes, where it will leave the main stream of air, along with some air.  Control of the amount of water to be removed from the atmosphere is determined by the flow rate through the CHX [ref 40].  The heated coolant will then dump its heat into space via the radiators. The condensed water will be purified and then used as tap water or fed into the agricultural areas.

 

III.C.4 Trace Contaminant Control

            Trace gasses in the colony atmosphere will pose a threat since even the smallest amounts of harmful gas would create an unacceptably high concentration in the relatively small volume of the colony. Sources of trace gasses could include outgassing, CELSS processes, and evaporation of volatile substances, and special concern for those elements should be taken during the design stage. Trace contaminants which may be pose a threat in space missions include acetone, C3 to C8 aliphatic saturated aldehydes, hydrogen chloride, isoprene, methylhydrazine, perfluoropropane and other aliphatic perfluoroalkanes, polydimethylcyclosiloxanes, dichlorofluoromethane (Freon 21), chlorodifluormethane (Freon 22), trichlorofluoromethane (Freon 11), dichlorodifluoromethane (Freon 12), 4-methyl-2-pentanone, chloroform, furan, hydrogen cyanide, carbon monoxide, benzene, acetaldehyde, methanol, indole, hydrogen, nitromethane, hydrazine, nitrogen dioxide, mercury, ammonia, and others [refs 40, 41].

The technologies available for active contamination monitoring include gas chromatography/mass spectrometry (GC/MS), infrared dispersion/spectroscopy, and ultraviolet spectroscopy [ref 40].  Then technologies such as particulate filters, activated charcoals, chemisorbant beds, and catalytic burners are used to purge the atmosphere of undesired contaminants [ref 1].

The first component of GC/MS is a gas chromatograph, which uses gaseous diffusion to identify different components of the airflow, while the second component of GC/MS is a mass spectrometer, which utilizes the different deflections caused by a magnetic field to analyze molecular weights.  GC/MS is a proven system both on space missions and during earth-bound field use, and can identify virtually all chemicals encountered via analysis of the data obtained through both components.

Infrared dispersion/spectroscopy would be used in conjunction with GC/MS during analysis of organic contaminants to verify its conclusions and provide further data.  Infrared dispersion/spectroscopy operates on the principle that different molecules absorb different wavelengths of an infrared beam that is shone through it. By analyzing the resultant complex spectrum with Fourier transforms, the components of the air sample can be determined.  The infrared dispersion/spectroscopy technique pairs nicely with GC/MS since it can determine the nature of a contaminant that does not possess a unique molecular weight [ref 40].

            Removal techniques would utilize all of the purging technologies. First the air would be passed through several HEPA filters to trap dust particles and microorganisms, these would preferably be placed in an easily accessible place, so that they can be exchanged for fresh ones once they have reached the end of their lifespan.  Then the contaminated air is passed over activated charcoal beds, which adsorb ammonia and water-soluble contaminants [ref 1]. These beds can be “recharged” via desorption during exposure to vacuum and heat.  A catalytic oxidizer based on palladium oxidizes hydrocarbons not adsorbed by the charcoal beds, while LiOH post- and presorbant beds adsorb acids [ref 1, 40].  The CHX can also remove soluble contaminants as the water condenses and drops to the bottom of the exchanger [ref 40].

 

III.C.5 Colony Ventilation

            To ensure proper mixture of oxygen into the atmosphere, removal of heat, and the removal of carbon dioxide and trace contaminants, a minimum air velocity inside the colony is needed.  Maintaining a proper ventilation system is also crucial to supplying the atmospheric management subsystems with air from the colony atmosphere.  Due to the generation of a pseudogravity via the spinning of the colony, a natural convection current will ensue, driven by the temperature differential between the heated interior of the torus and the relatively cooler region closer to the center of the colony torus.  Intakes outfitted with blowers should be positioned on the middle supporting strip bisecting the glass sky so as to vent the waste air.

 fig. 3.5

The air velocity created by the vents should not be so excessive as to cause drafts (>0.2 m/s) but should be above the recommended 0.08 m/s required for adequate removal of carbon dioxide and other substances toxic in various amount [refs 1, 40].  Computational fluid dynamics (CFD) methods will be required for determining the requisite airflow.

 

III.D Waste and Water Management

            Solid and liquid organic waste onboard the colony will have to be treated and converted into useful substances so that an accumulation of unwanted mass is avoided.  Waste onboard the colony will mostly consist of feces, urine, food preparation byproducts, packaging, etc.  Collection of wastes would be differentiated between organic and inorganic wastes. Organic wastes would be processed in order to return the inherent carbon to plants, while inorganic wastes would be vigorously recycled.

            Water is essential for human life, as humans use water for nutrition and cleansing.  Additionally, many manufacturing and research processes will require the use of water.  Like all other vital materials on Æther, recycling will be needed to provide enough fresh water.  Due to the vitality of water, emergency supplies should also be kept on hand. Since the sewage system on Æther will be powered by a flow of water, reclaiming and reusing that water is of vital importance.

 

III.D.1 Waste Collection

            A lot of organic waste will occur during harvesting and food processing, when the inedible parts of a plant are discarded. Waste also occurs when in the house in the form of bodily excretions and discarded materials or food.  Thus, collection facilities should be in place to properly dispose of this waste.  Collection of feces and urine will be through earth-like toilets that would utilize “gravity” action and will use a flow of water to carry away the waste. Colonists will be encouraged to presort their organic and inorganic trash.  The organic trash could then go into paper or biodegradable plastic bags, while the inorganic trash could go into a communal collection bin.  The organic trash would then be fed into the waste processing system while inorganic matter would be sent to the recycling facilities.

 

III.D.2 Waste Processing

            Most organic wastes onboard the colony would be inedible plant mass such as roots, stems, and leaves.  Processing of this material can either be bioregenerative recovery of the plant nutrients or total oxidation of the plant matter. Bioregenerative recovery of the plant matter was selected in order to maximize the nutrients gained from the growing of plants.  Nutrients that can be derived from inedible plant matter include carbohydrates, proteins, and lipids.

            Cellulose, the primary structural component of cell walls in plants, is a polysaccharide of glucose.  Many methods exist to hydrolyze cellulose into glucose, which could then be added to the human diet, but most of them involve chemicals or high temperatures that also decompose the resultant glucose.  Cellulase is a group of enzymes, which hydrolyze cellulose, cellulases are most common in fungi and microbial sources.  Pretreatment of the plant matter is necessary before efficient hydrolysis of cellulose can occur, since cellulose in plants is “sealed” with lignin and commonly found in the presence of hemicellulose [ref 1]. These additional substances inhibit enzyme contact with cellulose and only after they have been removed can cellulose conversion rates of over 50% be achieved [ref 1].  The ideal method for removal of lignin and hemicellulose is thought to be hot water treatment.  Approximately 0.4 g of edible glucose can be obtained from 1 g of plant material using this process.

            Human wastes primarily consist of urine and feces. The first step in processing this waste is collection and segregation.  Urine would probably be collected along with feces via the colony sewage system.  This waste stream would then be routed to a processing facility, which would break down the waste into various substances.  Preprocessing would include separating the solids from the liquids, which could be achieved through sedimentation tanks or centrifuges. There are several processes available for solid waste treatment, Super Critical Wet Oxidation (SCWO), wet oxidation, combustion, electrochemical incineration, Waste Management-Water Systems (WM-WS), and anaerobic or aerobic bioreactors [ref 1].

SCWO oxidizes organic compounds using water in its supercritical state.  Basically, in a SCWO reactor, the aqueous waste is heated and pressurized in the presence of oxygen, and organic compounds are completely oxidized to CO2, H2, and N2 as the reactor temperature and pressure are brought above 922 K and 25.3 MPa. Advantages of SCWO include short waste residence time, ease of inorganic salt segregation, and production of potable water [ref 1].  Due to the corrosive nature of CELSS waste and the high temperatures and pressures involved, the reactor would have to be constructed out of a corrosion resistant metal such as titanium or its alloys [ref 30].

Wet oxidation is similar to SCWO in that it also heats and pressurizes aqueous waste in the presence of oxygen.  However, the pressures and temperatures involved are not as drastic (14 MPa, 473-573 K).  The disadvantages of this system are that the organic compounds are not totally converted into CO2 and other simple compounds, so there is a small amount of ash residue [ref 1].

Combustion involves the rapid exothermic oxidation of organic matter.  The oxidation of organic matter can either happen in an oxygen excess environment (incineration), or in an oxygen-deprived environment (Starved Air Combustion). Both of these processes leave behind ash residue [ref 1].

Electrochemical incineration has the potential to degrade organic substances into carbon dioxide, nitrogen, and hydrogen gas through an electrolysis process.  Electrochemical incineration operates at a low temperature of 422 K, does not consume atmospheric oxygen, and has lower power requirements [ref 1].  However, this technology is in the early stages of development at this point, but the future definitely looks promising.

Another waste management technology is Waste Management-Water Systems (WM-WS).  WM-WS has the advantage of being more efficient in microbial control than other systems, and operates at 920 K with catalytic oxidation [ref 1].  Like electrochemical incineration, little could be found out about WM-WS, but it looks to be a promising system.

WM-MS, electrochemical incineration, and SCWO are all promising systems in development.  At this time, insufficient data is available in determining which system would be the most suitable to process organic waste, but SCWO seems to be the technology farthest along in development, as it is already being developed for the destruction of chemical wastes on earth.  After being processed through SCWO, the waste feed is then routed to the agricultural sections, where it will be analyzed, adjusted, and used as a nutrient source.  SCWO will also serve as the one of the primary sources of recycled water, along with the CHX system.

 

III.D.3 Recycling

Recycling of inorganic materials would utilize processes similar to those on earth.  Glass would be separated into different types according to chemical composition, crushed, melted, and then remanufactured.  Glassware could also be reused before being remanufactured, saving energy costs.  Tin cans, which are actually made of steel and only have a thin plating of tin, are first detinned and then melted down and reused.

 

III.D.4 Water Storage

            After collection from the CHX and SCWO systems, the recycled water would then be tested for purity and then stored inside the WBS.  During the period of emergency, all unnecessary water consumption would be prohibited.  To adequately provide for water needs during emergencies, enough water to sustain 100,000 individuals for 7 days should be stored.  Given the fact that one individual consumes approximately 20 kg of water per day [ref 40], the total amount of water to be stored at any given time should be 1.4x104 L.  To prevent the growth of unwanted microorganisms inside the WBS tanks, ozone should be utilized as a biocide.

 

III.D.5 Water Quality Monitoring

            In order to ensure the safety of machines and humans, the water supply must abide by water quality guidelines.

(units are mL/g, unless otherwise stated)

 

Total Solids

100

pH

6.0-8.5

Ammonia

0.5

Arsenic

0.01

Barium

1.0

Cadmium

0.005

Calcium

30

Chlorine

200

Chromium

0.05

Copper

1.0

Iodine

15

Iron

0.3

Lead

0.05

Magnesium

50

Manganese

0.05

Mercury

0.002

Nickel

0.05

Nitrate

10

Potassium

340

Selenium

0.01

Silver

0.05

Sulfate

250

Sulfide

0.05

Zinc

5.0

Cations

30

Anions

30

Carbon dioxide

15

Bacteria (Colony Forming Units/100mL)

1

Total Acids (µg/L)

500

Cyanide (µg/L)

200

Halogenated Hydrocarbons (µg/L)

10

Total Phenols (µg/L)

1

Total Alcohols (µg/L)

500

Total Organic Carbon (µg/L)

500

[ref 40]

            These pollutants should be monitored by an automatic system that would divert the unacceptable water to processing systems. There exists chemical, thermal, light, and mechanical methods to disinfect water [ref 40].  Mechanical filtration would be useful for separating nonsoluble and large particle contaminants and thus would come at the very beginning of the disinfection system.  Since thermal and light means of disinfecting water mostly affect biological contaminants, the tainted water would first be subjected to heat and UV irradiation treatment before being subjected to chemical treatment.  Chemical means to disinfect water include iodine, ozone, and silver.  Since silver and iodine are both contaminants, ozone was chosen to disinfect water.  Mechanical filtration, thermal processing, UV irradiation, and ozone treatment are all technologies proven on earth and should not pose significant problems during implementation.

 

III.E Plants and Algae

Photosynthesis can fulfill the need for food production, atmospheric regeneration, waste management, as well as water management, since it produces edible biomass; oxygen from atmospheric carbon dioxide; simple compounds such as nitrogen and carbon dioxide from biodegradable substances; and potable water from transpiration in plant leaves.

Two kingdoms of organisms that carry on photosynthesis are Protista and Plantae.  Green and blue-green algae belong to the kingdom of Protista and have several aspects such as rapid growth, controllable metabolism, high harvest index, gas exchanges compatible to human needs, ease of cultivation, and high reliability that make them attractive for use in a life support system.  Although algae does contain all the essential amino acids, sufficient lipids, and nearly all the essential vitamins, it is lacking in carbohydrates and difficulties remain in converting it into an edible form, although the same techniques for hydrolyzing plant cellulose into glucose using cellulase are involved here.  However, plant cellulose and algae cells should not be hydrolyzed for glucose if the process proves to be too costly [ref 1].

Higher plants have the advantages of transpiring water, which makes water purification much simpler; of being the basis for much food normally eaten by humans and providing most of the nutrients needed by humans; of being capable of removing some volatile and liquid contaminants produced by humans or machinery; and of providing an aesthetically pleasing environment to the colonists.  However, different crops of higher plants require different temperatures and photoperiods, complicating the task of growing higher plants.  The objective in designing the agricultural sections should be to provide the optimal environment for growing crops. Non-food crops such as cotton, flax, mulberry, flowers, etc. would also be grown for aesthetic and clothing purposes.

 

III.E.1 Illumination

            Since the process of photosynthesis relies on the light energy, providing proper illumination in the agriculture areas is of vital importance.  In Æther, solar and artificial lighting will be utilized for growing plants.  The green color of some algae and most plants is due to the presence of chlorophyll-a and chlorophyll-b pigments, which absorb 420-448 μm (red) and 643-661 μm (blue) wavelengths but reflect the green wavelengths.  Thus, to provide proper illumination, only blue and red light sources are needed, however many light sources contain red, green, and blue wavelengths.  Solar lighting uses the solar light available in outer space, while artificial lighting utilizes man-made light sources to illuminate the plants.  Like humans, plants cannot live if exposed to the massive amounts of radiation that accompany the visible electromagnetic spectrum, since the plants will be grown inside the shielded torus of Æther this should not be a problem.

However, in the lower level of the habitat section, either indirect solar lighting or artificial lighting will have to be used, since the lower level does not directly receive solar light.  Indirect solar lighting involves the collection and transportation of light with the use of mirrors, lenses, and optical fibers. The primary goal in designing a solar light collection system is to filter out the unnecessary wavelengths and supply light at the required intensities.  Selectively transparent coatings or lenses can be used to filter out undesirable frequencies such as infrared and ultraviolet.  Artificial lighting seems to be the better method, since indirect solar lighting would require large structures to collect and transport light [ref 1].

There are many types of artificial lighting, from fluorescent tubes and high-pressure sodium lamps to light-emitting diodes (LEDs). Interest in the latter is particularly high due to their low heat generation, high electrical efficiency, low mass, and low volume.  Red and blue LEDs in conjunction may provide adequate lighting for plant growth [ref 19].

            Solar lighting augmented with artificial lighting will be utilized in the agricultural areas on the primary floor, while the agricultural areas on the lower level will be entirely lit by LEDs.

 

III.E.2 Nutrient Delivery

            Plants can derive their nutrients from either soil substrates or from water-based solutions. Soils can be either earth-like or synthetic.  The advantages of using earth-like soils are not readily apparent; among other things, they require a large amount of mass, do not offer a readily adjustable nutrient concentration, and could possibly lead to microbiological contamination. Synthetic soils consist primarily of zeolites, which enable it to store and slowly release the desired nutrients over a long period of time.  These attributes enable plants in synthetic soils to only require periodic watering, as all of its nutrients will be provided for by the soil.  The design goal for zeolites is to store enough nutrients to provide for three or more seasons [ref 1].

            Substrate-less nutrient delivery systems include hydroponics and aeroponics.  In hydroponics, the roots are placed in an aerated, circulating, liquid system that provides the plant with water, nutrients, and oxygen.  Thus hydroponics allows for precise control of pH and nutrient concentration of the solution, since the nutrient flow can be monitored and adjusted [ref 1].  An additional advantage of substrate-less nutrient delivery systems is that since the plant can easily obtain an adequate amount of nutrients from the delivery system, it does not grow large roots and instead devotes its energy to growing the upper stem.  However, proper growth of plants may require the use of supports, and hydroponics requires more mass because of the equipment involved and also requires more supervision.  Aeroponics is like hydroponics in many ways with one major difference, the nutrient is applied to the plant roots in the form of a spray rather than a liquid flow.  Since it utilizes a spray, aeroponics requires less solution per plant than hydroponics.  However, the major problem of nozzle clogging exists in aeroponics, and for the present, hydroponics seems to be the better choice. 

 

III.E.3 Atmosphere

            The atmosphere should be carefully designed to maximize growth, and attention should be given to atmosphere composition, temperature, humidity, ventilation, and toxicant levels [ref 1].

            While the goal of the CELSS is to provide an environment that is as Earth-like as possible, the opposite may be true when determining the atmosphere composition in the plant growth chambers.  Plants generally do well when the O2 partial pressures are reduced, and when CO2 partial pressures are increased.  C4 pathway plants have an optimal CO2 concentration of about 350 ppm, while C3 plants have a higher optimal concentration of approximately 1000 ppm [ref 1].  However, the specific optimal CO2 concentration is dependant on the plant grown and on the specific stage of its growth cycle; thus only very similar plants should be grown in the same chamber.  Carbon dioxide concentration can be accurately determined by using infrared analyzers, which operate on the principle that carbon dioxide absorbs specific infrared wavelengths; however, some computational processing is necessary to distinguish the signal from the background infrared radiation.  The APC/EDC systems would serve as the source for plant chamber carbon dioxide, but contingency carbon dioxide should be stored via cryogenic or pressurized methods in case of emergency.

            Preserving a stable temperature is important for plant growth as they contain enzymes that operate at an optimal temperature.  Most plants prefer a temperature range of 285-301K, but specific temperatures vary with species, carbon dioxide concentration, irradiance intensity, and photoperiod.  Plants also require air moment so that leaves do not overheat; cooling airflow can be provided by centrifugal blowers that intake fresh air and also exhaust hot air into a sensor array that monitors the atmosphere of the growth chamber [ref 20].

            Transpiration is a major process that impacts photosynthesis, and is impacted by the humidity of the atmosphere.  High humidity levels are preferable since they reduce transpiration rates; therefore the water needs of the plants are reduced.  Yet plants also need an adequate transpiration rate that can sufficiently cool off the leaves.  Thus humidity controls should be linked to temperature monitoring of plants.

 

III.E.4 Modules

            Taking the varied requirements of plants into account, plants will be grown in self-contained modules that can be easily reprogrammed for different species.  These modules would also allow the repair and cleaning of different sections of the plant growth area without having to disrupt a large number of plants.

 

III.F Food and Agriculture

            Human diets must contain certain amounts of carbohydrates, certain amino acids, fats, calcium, iron, iodine, fluorine, potassium, zinc, vitamin A, vitamin B1, vitamin B2, vitamin B12, niacin, folic acid, vitamin C, vitamin D, vitamin E, vitamin K, as well as trace amounts of other minerals.

 

III.F.1 Food Production

Due to the higher efficiency of plant and algae based agriculture, the using plants or algae based products to fulfil the requirements of as many nutrients as possible is desirable; fortunately, a carefully planned vegetarian diet is able to cover all the nutritional needs of a human.  A list of the crops selected for the DaedalusaL4 project include “Acorn Squash; Apple; Aubergine; Banana Squash; Barley; Beetroot – ‘Table beet’; Blackberries; Blackcurrants, Broccoli (Super Dome, Minaret, Green Comet, Purple Sprouting); Butternut squash; Cabbage; Carrots; Cauliflower; Chickpea; Chillies; Chives; Courgette; Corn; Cotton; Cowpea – ‘Black/Yellow-Eyed Pea’; Cucumber (Lemon, Amira, Orient Express, Vert de Massy, De Bouenil); Fennel; Flax; Garden peas; Garlic; Ginger; Grapefruit; Grapes; Hops; Horseradish; Hubbard Squash; Kale (Winterbor, Ornamental); Lemon; Lentil; Lettuce (Arctic King, Brune d’Hiver, North Pole, Rougette du Midi, Rouge d’Hiver, Winter Density, Winter Marvel); Maize; Melon (Cantaloupe, Persian, Santa Claus, Casaba, Crenshaw, Honeydew – Earlidew, Watermelon); Millets; Mint; Mushrooms; Nectarines; Oats; Onions; Orange; Oregano; Parsley; Peaches; Peanut; Pear; Pepper – sweet; Peppercorn; Pinto beans; Plums; Potato (Huckleberry, Blossom, Yukon Gold, Russet Burbank, White Rose, Round White, Round Red); Pumpkin; Quinoa; Radish; Rape seed –  Canola; Raspberries; Rice; Rye; Sage; Seaweed; Sesame; Snow peas; Sorghum; Soybean; Spinach; Strawberry; Sugar beet; Sunflower; Sweet potato; Swiss chard; Thyme; Tomatillo; Tomato (Sun Gold, White Wonder, Evergreen, Costoluto, Genovese, Big Rainbow, San Marzano); Turmeric; Turnips; Watercress; Wheat” [ref 6].  Additional crops that would be of benefit to the colonists are Taro, Quince, Cassava, Amaranth, Pomegranate, Papaya, Passion Fruit, Mango, Loquat, Kiwi, Apricot, Avocado, Pokeweed, Breadfruit, Pineapple, Chayote, Okra, and Zucchini. While this list certainly does not contain all of the potential crops, it certainly contains enough crops to cover all the nutrients needed while making possible a wide variety in diet. These crops should be grown in “stagger” fashion, so that their produce would be available all year long.  An additional food source would be the trees grown for aesthetic purposes, which could supply nuts and fruits such as Pecan, Pistachio, Cashew, Hickory, Walnut, Acorn, Almond, and Cherry.  Maple trees could also be grown so that their syrup can be harvested.

            While plants are a more efficient method of obtaining protein, the culinary benefits of the inclusion of animals into the diet cannot be overlooked.  Many important cultural dishes heavily rely on meat or fish, and the psychological benefits from the inclusion would also be great.  However, some animals, particularly cows and lamb, do not present an efficient method of procuring protein, thus leaving the colonists with only small and fast reproducing animals, which have a much higher efficiency than cows and lambs.  Fish, too, are generally much more efficient in terms of mass of feed needed for increase in body mass.  Chickens, shrimp, prawns, catfish, grass carp, and tilapia are all excellent candidates for inclusion into the colony diet.  The mass penalties imposed by the aquaculture are primarily due to the large amounts of water needed [ref 1], however, they could be integrated into parks and serve a dual role of fulfilling aesthetics and agricultural needs at the same time.  Seaweed, eaten by many cultures, can also be grown inside the aquaculture ponds.

Another group of animals that meets the criterion of being small and being able to reproduce quickly is rodents.  Although the mere thought of eating rodents may deflate most reader’s appetites, it must be noted that eating squirrels and rabbits, both of which are considered rodents, is generally accepted.  Culinary taste onboard Æther may evolve to a point where the use of rodents in dishes is tolerated, but initially rodents may have to be processed into an unrecognizable form in order to induce people to eat them.

Unfortunately, some conflicts will arise between the colonists’ innate tastes and the ability to cater to those tastes using foods grown on Æther.  The European and North American reliance on dairy products [ref 48], for example, will conflict with the scarcity and high price of such desired goods.  Fortunately, some other cultures, such as Hinduistic Indian, do not rely heavily on animal products and their dietary needs should not pose a problem. It is hoped that the colonists will be able to maintain their traditional diets while at the same time being able to sample different foods from all over the world.

            The development of acceptable substitute will be of great concern to colony nutritionist who will strive to create the most appealing of diets while restricted by the number of raw materials. Substitutes are already used on earth, including many products made out of soy and peanuts.  However, recent advances in biochemistry that have lead to the identification of organic compounds responsible for the taste for wine give hope to the possibility that authentic-tasting steaks or burgers can be synthesized from the crops grown in Æther.

 

III.F.2 Food Preparation

            The need for preparation of different foods falls into three general categories, little to no processing, primary processing, and secondary processing [ref 1].  Foods that require little to no processing are either fruits or vegetables that may be eaten raw, and thus only require washing, peeling, or cutting before being served.  Foods that require primary processing include juices, flour, and cooked foods. The processes needed involve pressing, grinding, and cooking.  Foods may be irradiated to ensure death of pathogens before being served.

 

III.F.3 Food Storage

            If raw materials or processed foods are not to be consumed immediately, refrigeration is necessary to prevent spoilage.  Three methods to achieve refrigeration are: phase-change, thermoelectric, and thermoacoustic.  Phase-change refrigerators are in common use today, however they rely on coolants that may be harmful to humans, and their pumps are suspect to failure.  Thermoelectric modules (TEMs) rely on the peltier effect, which arises when a current is sent through a circuit made of dissimilar conductors, to absorb heat on one side and release it on the other.  Most TEMs are made from telluride bismuth, and thus are expensive to manufacture; coupled with the problems of expansion and contraction, this factor make the construction of large scale TEMs quite difficult. Thermoacoustic cooling relies on the pressure, temperature, and displacement oscillations caused by an audio driver to cool objects [ref 44].  By placing the audio driver at one end of a coolant-filled metal tube, and a heat absorbing porous conductor near it, a simple but reliable thermoacoustically driven refrigerator can be built.  Thus, heat will be pumped towards the end of the tube with the audio driver when it is turned on, and the coolant used can be human-safe helium. However, adequate noise precautions must be put in place beforehand, since audio drivers producing 180 decibels are needed in order to produce sufficiently low temperatures. Thermoacoustical refrigeration would be the technology of choice, since it does not use harmful coolants, is reliable, and improvements are being made on efficiency.

            Biodegradable packaging based on either cellulose or bioplastics should be used to lower the amount of unrecyclable waste.  Edible rice (or wafer) has been used for quite some time on earth, and may prove to be useful in Æther.  Plastic and metal containers should be reused and not thrown away after the first use.

 

III.G Fire Prevention, Detection, and Suppression

Fire is the most undesirable mishap to happen in a spacecraft. The confined interiors of any space habitat have the effect of greatly increasing the lethality of a fire. Methods of reducing losses due to fires include prevention, detection, and suppression.  Fire prevention is implemented during the design phase and minimizes the probability that a fire will occur onboard by using nonflammable materials in construction.  Fire detection systems should be able to quickly sense the presence of a fire and also be able to accurately locate its whereabouts in Æther.  After the fire has been detected it can be suppressed by breaking the “fire triangle” of temperature, oxygen, and fuel.

 

III.G.1 Fire Prevention

The use of flammable materials in everyday objects should be avoided so as to prevent the accumulation of such substances. Prevention of fires can be done by not utilizing napped (fuzzy) finishes on clothing; designing garments so that a minimum of loose clothing is used; manufacturing carpets and other textile items out of flame resistant or flame retardant material; reducing the number of ignition sources; separating flammable material with non-flammable material; isolating flammable material from ignition sources; creating flame barriers through the use of non-flammable materials such as metals and ceramics; using metallic coatings on substrates; and coating flammable surfaces with Fluorel® [ref 10].  Flammability tests should be conducted on the items used in the construction of Æther, these tests include upward flame propagation to test if the material can self-extinguish and will not propagate the fire through debris; heat and visible smoke release rates; flash point of liquids to determine the lowest temperature at which a liquid forms an ignitable mixture with air near the surface of the liquid; fire point of liquids, to determine the lowest temperature at which a fire becomes self-sustained, the fire point is usually a few degrees above the flash point; and electrical wire insulation flammability [ref 11].  Undoubtedly there will be many more tests, and many of them will be concerning the materials used in the industry and research areas of Æther.

 

III.G.2 Fire Detection

Traditionally, space habitats have utilized the inherent human sense of as smell to detect the presence of fire.  However, in a voluminous space settlement, fires may break out where humans are not nearby to detect its presence, thus automatic fire detectors must be present in all parts of the colony [ref 13].  Current methods of fire detection sense the presence of smoke or flame.

Smoke detectors are usually employed in ventilation ducts while flame detectors are installed in open areas.  Two types of smoke detectors are photoelectric detectors and ionization detectors.  Obscuration detectors, scattering detectors, and condensation nuclei counters are all classified as photoelectric detectors.  Obscuration detectors rely on the fact that when particles pass between a light source and a receiver a fraction of the light is obscured. Scattering detectors operate on the principle that when a particle passes through a laser beam light is scattered at an angle inversely proportional to the particle’s size. This scattered light is then collected and analyzed by a receiver.  Condensation nuclei counters detect smaller particles by increasing their size in the presence of 100% humidity.  Ionization detectors have a radiation source (which is americium-241 in most household smoke detectors) that ionizes the air with alpha particles, this ionized air is then forced in between a positive and a negative electrode by a convective flow. Under normal circumstances with no smoke particles, the ionized air is attracted to the electrodes and a electrical current results; however, the increased mass due to smoke particles attached to the ionized air reduces the velocity of the particle-air pair and the convective flow carries the pair out of the electrode chamber, thus creating no electrical current.  Another way smoke particles affect the electrical current of the detector is by neutralizing the ionized air, either way, the reduced current caused by smoke particles sets off an alarm.  Ionizing detectors are more efficient at detecting flaming fires, while photoelectric are more efficient at detecting smoldering fires [ref 12].

Flame detectors are triggered by the ultraviolet, visible, and infrared radiation that fires produce.  Monitoring of all wavelengths (UV, visible, and IR) is desirable so that false alarms are kept to a minimum.  Integrated UV, IR, and visible sensors have already been fabricated using CMOS technology, and will undoubtedly be available for use in the future.

 

III.G.3 Fire Suppression

Once a fire has been detected, it should be expediently extinguished.  However, the methods used to extinguish the fire should not harm the surrounding equipment and the environment of Æther.  Some fire suppressants that could be considered are CO2 and water.

CO2 is an effective fire suppressant and is normally stored as a liquid at room temperature with high pressures.  When liquid carbon dioxide is released from an extinguisher, the liquid immediately changes to a gas because of the pressure difference.  This process is highly endothermic and helps in cooling the fire.  Additionally, carbon dioxide is denser than normal air, and will suffocate the fire by depriving it of oxygen.  Carbon dioxide will not leave behind a residue, can easily be recaptured through atmospheric control systems, is not electrically conductive, and does not decompose into other substances.  However, carbon dioxide is not suited for use in habitable areas because inhaling large amounts of it is dangerous to humans.  Therefore, carbon dioxide will only be used in the industry/research areas and only after everyone has been evacuated.  Venting the area on fire, and thus depriving it of oxygen, could be put to use if the situation became extreme.

Water based fire suppression systems fall into two categories, sprinklers and fine water mist systems, with the two differing only in the droplet size.  Sprinklers generate droplets of size 1mm while fine water mist systems produce 0.1mm to 0.01mm droplets [ref 31].  Since sprinklers have no advantage whatsoever over fine water mist systems, only fine water mist systems were considered.  Fine water mist system droplets have a large surface area that aids in the absorption of heat, quickly lowering the temperature to below the fire point.  Heavy smoke particles are also precipitated by the mist, which uses relatively little water when compared to conventional deluge/sprinkler systems.  Unlike carbon dioxide, water mist is not toxic upon inhalation.  The challenge in making fine water systems feasible for use is producing nozzles that can generate the desired mist of water.  The nozzle opening must be small enough to produce the droplets, yet large enough to escape clogging from impurities present in the water supply.  However, this challenge is easily overcome, especially with the large amounts of research being conducted by the military, which needs to purge itself of Halon.

Water will be used in most locations, but carbon dioxide suppression systems will be implemented in vital places where humans are not normally present, such as the areas which house CELSS machinery.

 

III.H Power

The Æther space colony will require a vast amount of electrical power to function seamlessly. The issues needed to be discussed are power distribution, generation, and storage.

 

III.H.1 Power Distribution

            Copper wires will be used to distribute power throughout Æther, and wire diameters would have to be large enough to prevent fires from breaking out due to excess heat caused by resistance of the wire.  High voltages will be used to distribute power, so that the current can be minimized, thus reducing energy loss due to resistance.  Power from the photovoltaic cells or from the flywheel storage units will first be converted into AC then sent through primary transmission lines at high voltages.  The voltage then is “stepped down” to the voltage used by household appliances at local transformers.

 

III.H.2 Power generation

            Æther will have a centrally located hexagonal solar panel with sides of 900 meters that has a hexagonal shaped hole with sides of 380 meters in the center plus two rectangular panels with length of 600 meters and width of 300 meters below the hexagon.  The total combined surface area of all the panels is 3.45 million m2, thus enabling the space colony to soak up 5.3 million kilowatts, but due to solar cell efficiencies of approximately 13%, that only means 689 thousand kilowatts that the colony can actually use.  

 fig. 3.6

 

III.H.3 Power Storage

There are many cutting-edge technologies available for power storage on Aether.  These technologies include flywheels, ultracapacitators, and fuel cells.

 

III.H.3.a Flywheels

            A flywheel is an electromechanical system that stores energy by spinning a disk at high speeds.  When power is needed the rotational energy of the disk is used to turn a dynamo.  A high efficiency can be achieved by keeping bearing and air friction at minimal levels, thereby reducing energy loss.  The vacuum housing can also serve as a shield when calamities develop.  The flywheels use superconduction magnets as low-friction bearings to support the disk using magnetic forces so that there is no contact or friction and no lubricants involved.  Active magnetic bearings dynamically respond to different situations in order to prevent contact and thus friction is largely avoided. By using permanent magnets on the flywheel and a current-generating coil, the conversion from electrical to mechanical energy efficiency values can reach up to 90% [ref 43].  Since the energy stored is a function of the disk’s rotational speed, the ultimate strength of the material that the disk is composed of will determine how effectively energy can be stored. Current research has focused on using carbon fiber composites, which possess excellent strength but also have the additional benefit of disintegrating into dust rather than shrapnel, which would only require the use of a light Kevlar shield [ref 43].  The development of disks composed of ultra-strong “bucky-ball” nanostructures could enable even more efficient storage of energy in a given volume.  Flywheels will be used for long-term energy storage.

 

III.H.3.b Ultracapacitors

            A capacitor  usually consists of conducting plates or foils separated by thin layers of dielectric material with the plates on opposite sides of the dielectric layers oppositely charged by a source of voltage and the electrical energy of the charged system stored in the polarized dielectric.  Selection of the proper dielectric is crucial as the electrical properties of the dielectric will ultimately determine the maximum storable charge.  Several materials considered for low-mass, high-energy storage include thin film polymers and ceramics [ref 43].  Capacitors are useful in that they can be recharged quickly at periodic intervals, thus proving useful in a hybrid system where photocells would be used in high illumination conditions and the excess power being stored in capacitors; however, capacitors gradually lose charge over time and are not ideal for long term energy storage.

 

III.H.3.c Fuel Cells

            Currently, the most widely used fuel cell is the hydrogen-oxygen fuel cell.  The hydrogen has enters the gas chamber on the left, and oxygen enters on the right. The porous electrocatalyst anode strips two electrons from hydrogen in an oxidation reaction.  The potassium hydroxide electrolyte in the middle is an ion-exchanging medium, allowing only H+ ions to cross, while at the same time prohibiting O2- to flow the other way.  A circuit is connected from anode to cathode, allowing the oxygen to gain electrons in a reduction reaction.  The hydrogen ions join the oxygen ions to produce water and some thermal energy [ref 43]. 

 

            All of the above mentioned systems would be implemented on Æther since different ones have the most advantages in certain situations.  However, the main power storage method used will be the flywheel for its high efficiency levels, emergency power could be distributed from a reliable source based on batteries or fuel cells during times of duress.

Habitability

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