III. Life Support

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

III.A Radiation

            Radiationin outer space can be differentiated into two kinds: nonionizing radiation andionizing radiation.  Nonionizingradiation consists of long-wavelength electromagnetic radiation, which isdefined as electric and magnetic energy, or fields, traveling throughspace.  The sun emits nearly all of theelectromagnetic radiation found in the solar system; the radiation intensity isapproximately 1390 W/m² near the earth.  However, an object in orbit around the earth also has to take intoaccount the radiation intensity emitted by the earth, 225 W/m² [ref1].

Ionizingradiation is defined as high-energy particles and short wavelengthelectromagnetic-radiation that separate electrons from their atoms upon closepassage.  It includes gamma radiation, Xradiation, alpha particles, beta particles, neutrons, protons, and heavynuclei.  Two primary sources of ionizingradiation 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 10⁹eV.  SCR coincide with very large solarflares that occur once or twice during the eleven-year solar cycle.  SCR are responsible for rapid increases inradiation doses in a short amount of time, and advance notice of only a fewhours to several minutes can be given for solar events.  GCR is a continuous stream of particlesconsisting of high-energy protons, alpha particles, and heavy nuclei called HZEradiation.  GCR is also influenced bythe 11-year solar cycle, at sunspot maximum GCR is at its minimum due to thestronger interplanetary magnetic field.Conversely, at sunspot minimum GCR is at its maximum.  In absence of solar-flare activity GCRconstitutes about 90 percent of the radiation absorbed [ref. 2].  Although GCR is small in quantity, itpossesses high energies that enables it to penetrate deeply.

III.A.1 Measuring Radiation

            The amount of radiation that is absorbed can bequantified 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 ofradiation have differing effects on the material that is absorbing theradiation.  This can be tied to thequality factor of the radiation, which is expressed in relative biological effectiveness(RBE).   RBE is defined as the number ofGy of X-ray radiation that produces the same result as 1 Gy of the givenradiation.

Table 3.1

            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

            Whena high-energy particle enters the body, it can either undergo directinteraction with the atoms of the body, thus producing many ions, or it canundergo indirect interaction with the atoms and produce secondaryradiation.  The secondary radiation thatis produced when high-energy particles interact with atoms or molecules in thehuman body is called Brehmsstrahlung radiation.  Brehmsstrahlung radiation occurs when high-energy particles aredeflected and decelerated by charged particles.  This secondary radiation also ionizes the surroundingtissue.  In both cases, the ionizingeffects of the radiation are proportional to the energy absorbed by thesurrounding tissue.  The ions producedcan produce free radicals, such as the highly reactive and unstable OHmolecule.  A free radical can attackother compounds in the body to form even more free radicals and thus has far reachingconsequences.  A dose of 0 to 0.5 Svwill result in no obvious effects, while doses from 0.5 to 1 will causeradiation sickness in 5-10% of exposed personnel.  A dose of 10 Sv will most likely kill all who are exposed [ref1].

Somatic damageaffects the exposed organism during its lifetime and can be classified as acuteor long-term effects.  Acute effects ofradiation are caused by exposure to high doses of radiation in a short timeframe, it is indicated by the symptoms of radiation sickness such as nausea,vomiting, discomfort, a decrease in the number of white blood cells, loss ofappetite, and fatigue.  If exposed todoses higher than 2 Sv, one can also expect diarrhea, hemorrhaging, and hairloss.  Effects of prolonged exposure tolow doses of radiation include cancers of the lung, breast, digestive system,and leukemia.  One can expect anincrease in 2% to 5% chance of contracting cancer for every 0.5 Sv.

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

Exposure toradiation of fetuses during 16 to 25 weeks of pregnancy results in adverseneuro-developmental effects such as mental retardation, reduced IQ, and seizuredisorders.  Exposure during the gestationalperiod (8-15 weeks) results in even more damage, as it is the most sensitivetime for neurological developments.  Theabove-mentioned three abnormalities, as well as microcephaly (the abnormalsmallness of the head) occurred in children born to the survivors of the atomicbomb detonations in Japan during the Second World War [ref 4].

Setting healthstandards for exposure to radiation is difficult, as the effect of heavy nucleion human tissue is not well known.Currently, some scientists advocate that any amount of radiation causessome damage, even down to low doses.Other scientists, however, believe that there a threshold exists belowwhich no radiation risks occur.  Untilmore 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 tohuman life.  The 1993 National Councilon Radiation Protection and Measurements (NCRP) recommendations were 1 mSvannual dose limit for continuous exposure and a 5 mSv annual dose limit forinfrequent exposure.

III.A.3 Radiation Protection

            Thereare two main types of radiation protection: active shielding and passive bulkshielding.  Active shielding includes amagnetic field that deflects charged particles from the crew area and amagnetic/electrostatic plasma shield that uses an electrostatic shield toprotect the interior from positively charged particles while a magnetic fieldconfines electrons from the space plasma to provide charge neutrality [ref 5].  An advantage of active shielding is that itcan be dynamically controlled, which could then be matched with dosimetricmonitoring of solar flare activity [ref 2].However, a dilemma exists with active shielding; to produce a powerfulshield with a low energy cost one must turn to the use of superconductors, butalong with the introduction of superconductors into the system comes the costsand problems associated with it [ref 5].Clearly, the disadvantages of active shielding, such as higher massesrequired for adequate shielding from radiation and the inability to deflectheavier particles with high kinetic energies have precluded active shieldingfrom use in Æther; but a dynamically controlled active shield could be used inan integrated system, and turned on when the influx of light particles fromsolar-flare activity is high.

Passive bulkshielding 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 passiveshielding, as it is both lightweight and high density [ref 1].  However, the idea that by adding more andmore aluminum one can eventually protect Æther’s interior from all radiation iswrong.  As the thickness of the aluminumshield is increased, the possibility that secondary radiation would be producedincreases.  Because of Brehmsstrahlungradiation lighter elements such as oxygen, carbon, and hydrogen and theircompounds are more effective shields for HZE radiation than are heavier elementssuch as lead, which is commonly used on earth.Water and polyethylene have excellent shielding efficiency per unitmass, and their use in other applications may also have a secondary role inmaximizing shielding mass.  For example,distributing drinking water over large surface areas would contribute to thetotal radiation shielding mass.  Ashield made of lunar soil would require a thickness of 5 meters in order toprovide protection equal to the earth’s atmosphere.

The residentialarea radiation shielding will consist of a lunar regolith/ice layer 4 metersthick.  The lunar regolith/ice layerwill consist of a crushed lunar regolith matrix and ice supported by analuminum framework, the total density of the structure would be around 500-3000kg/m².  Lunar soil consistsmostly of SiO₂, TiO₂, Al₂O₃, MgO,CaO, and FeO [ref 1].  The lightelements, such as silicon, oxygen, and aluminum, will provide an excellentshield for both GCR and SCR.  Theaddition of ice to the shielding will also aid in shielding against incomingparticles as well as diffusing the ions that are created from the interactionsof radiation and the passive shield, thereby preventing the ions amalgamatinginto and weakening the crystal structure of the aluminum framework [ref 9].  The titanium hull will be the next layer ofradiation shielding.  A layer of CopperTungsten alloy would be placed on the inside of the titanium hull to provideprotection against deeply penetrating heavy nuclei from GCR and solarflares.  The CuW alloy contains 90%tungsten and 10% copper by weight density (the equivalent of 75% atomic weighttungsten and 25% weight copper).  Suchan alloy layer shows a twofold to fourfold increase in shielding efficiencyover an aluminum shield [ref  7].  CuW alloy is prepared by the liquid-phase sintering of mixed elemental powdersduring which part of the tungsten dissolves in the copper liquid.  The product is a two-phase materialconsisting of rounded tungsten grains and a matrix of copper-tungstencontaining 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 thetitanium hulls. The Water Ballast System will also be configured toprovide the final layer of radiation shielding.

The windows thatpermit sunlight into the residential area of Æther will also have to filter outthe undesired wavelengths.  This can beachieved through the use of selectively transparent glass, which absorb some wavelengthswhile allowing others to pass through.Selectively transparent glasses can be manufactured by depositing a thinlayer of metal onto the glass.  Thickglass in itself is opaque to the long wavelengths of infrared radiation, whileleaded 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 waterin between.  This layer of water couldbe laced with aqueous solutes that decrease the amount of radiation thatreaches the colonists.  The aluminummirrors that work in conjunction to reflect light into the habitable areas willalso be able to absorb some harmful radiation.During times of heightened solar flare activity, radiation shutters madeof CuW-Al panels could be drawn over the windows and residents would be advisedto stay inside radiation shelters.

III.B Pseudo-Gravity

As Æther is in afree falling orbit around earth, there will exist a microgravity environmentwithin it.  This environment isundesirable for long-term habitation since humans cannot adapt toweightlessness.  The human body reactsto the conditions associated with weightlessness in a series of interrelatedresponses that begin in the gravity receptor tissues, fluids, and weightbearing structures.

The gravityreceptors refer to the otolith organs in the inner ear; mechanical receptors inthe muscles, tendons, and joints; and pressure receptors in the skin.  The otolith organs are part of thevestibular apparatus in the inner ear.The otolith organs comprise of protein and calcium carbonate crystalsembedded in a gel, they respond to gravity by triggering hair cells whichprovide a sense of balance.  The twootolith organs are the saccule, which senses motion in the vertical plane; andthe utricle, which senses motion in the horizontal plane.  Combined, the saccule and the utricle givethe human body the means to deduce acceleration in any arbitrary direction inthree-dimensional space [ref 27].  Onearth, the acceleration caused by gravity always causes a signal to be sentfrom the otolith organs.  Mechanicalreceptors and pressure receptors respond to the weight associated with bodyparts in the presence of gravity.However, in conditions of weightlessness the otoliths no longer feel adownward pull on the head, and muscles have to contract and relax in differentways to bring about movement of the limbs and other body parts.  The absence of these signals can result invisual-orientation illusions and feelings of spontaneous reorientation.  The signal changes due to gravity cause aspace sickness that has symptoms not unlike those of terrestrial motionsickness.  Impaired concentration, lossof appetite, stomach awareness, and vomiting are not uncommon, but only last forthe first two to three days of weightlessness.

Weightlessnessalso causes havoc in the body’s fluid systems, as the body is 60 percent waterby weight.  On earth, fluids inside thebody have weight and are normally pulled towards the ground, creatinghydrostatic pressure [ref 27].  Thishydrostatic pressure primarily influences the distribution of fluids byaffecting how much blood leaks from arteries and into the interstitial space inbetween cells.  Under weightlessnessconditions, this hydrostatic pressure is not present and redistribution ofbodily fluids occurs [ref 27].  Each legloses 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 andelectrolyte levels are affected by the shift in fluids.  The kidney filtration rate increases byalmost 20 percent, while some space travelers have suffered from a special typeof anemia indirectly caused by loss of plasma [ref 27].

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

            Partialremedy of these symptoms can be achieved through exercise and the use of light-emittingdiode (LED) blankets, which prevents bone and muscle atrophy by submerging thebody in 680, 730, and 880 nm light [ref 29].However, the least discomfort can be achieved by rotating the colony toproduce a psuedo-gravity that mimics gravity on earth.  Rotational motion results in the constantchange 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 thetangential velocity and points radially inward, and is called the centripetalacceleration.

 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 anautomobile that is rounding a curve.  Asmost people who have ridden in a car know, there is a tendency for thepassenger to be pushed away from the center of the turn; this is caused by thepassenger’s tendency to go straight, which is a result of his or herinertia.  Likewise, a constant rotationof the colony will utilize the colonist’s mass to produce pseudo-gravity.  It is also helpful to think ofpseudo-gravity as a result of the colony edge pushing radially inwards againsta colonist. 

 fig. 3.2

If a_c=v²/rand v= ωr, we can find an equation for a_c in terms of ω,or the angular velocity.  Since thedesired psuedo-gravity is 9.8 m/s², the equation for revolutions perminute in terms of radius would be .  The graph of this function can be seen infigure 3.3. 

 fig. 3.3

            However,in a reference frame that rotates at a constant angular speed, there existsanother psuedoforce known as the Coriolis force.  The Coriolis force affects any object that moves linearly withina rotating system.  If the object movesfrom R_a radially towards R_b, where R_a is awith a smaller radius compared to R_b, the direction of the Coriolispseudoforce is counter to the direction of rotation.  If the object moves radially from R_b to R_a,then the pseudoforce acts in the direction of rotation.  Likewise, if an object moves tangentially indirection of rotation, the pseudoforce is radially outwards, in other words theobject gets heavier.  If an object movestangentially counter to the direction of rotation, the pseudoforce is radiallyinwards, and the object becomes lighter [ref 1].  One can clearly see that the Coriolis pseudoforce isundesirable.  Symptoms of vertigo,disorientation, and nausea are a result of excessive Coriolispseudoforces.  Also, since frequent commutingbetween the habitable areas and the microgravity industrial areas will occur,special care must be given to the prevention of disorienting effects that canhinder the quality of life and produce undesirable results.  Generally, the Coriolis pseudoforcedecreases as the radius becomes larger and the angular velocities associatedwith producing pseudogravity become smaller.All humans can tolerate a rotation rate of 1 rpm or less, and thisshould be taken into account when deciding the size of the colony.

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

τ = rFsinθ must beused, where τ equals the torque, I is the moment of inertia of Æther, ais the angular acceleration, r is the radius, and F is the force.  Thus Ia=rFsinθ, and solving forforce 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 duringconstruction of Æther, for this calculation it is assumed that Æther is at restat the starting point.  Thus, if the spintime is to be 30 days, or 2592000 seconds, the angular acceleration awould be 2.7x10^-8 rad/s².  The radius r would be 2255 meters, since the thrusters would beplaced at the edge of the torus, and assuming they are perpendicular to theradius of the torus, sinθ would equal 1.Thus, thrusters with the combined force of approximately 9.42x10⁶N would be needed to spin the colony.

 fig. 3.4

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

III.C Atmosphere Management

            Atmosphere management concerns the atmosphericrevitalization and contaminant control of the colony atmosphere.  The five main tasks of atmosphere managementwill be atmosphere control and supply, temperature and humidity control, tracecontaminant control, and colony ventilation.Atmosphere revitalization in the colony will have two main steps, CO₂concentration and removal, and O₂ generation.

III.C.1 CO₂Concentration and Removal

CO₂concentrations must remain at a low level in order for normal life tooccur.  The adverse effects of highconcentrations of CO₂ include headaches, mental depression, hearinglosses, dizziness, increased cardiovascular activity, nausea, and eventuallyunconsciousness.  The partial pressureof CO₂ on earth is 0.0318 kPa.Allowable levels of CO₂ concentration are 1.01 kPa duringshort missions and 0.40 kPa for long missions such as an assignment to theInternational Space Station.  In orderto prevent CO₂ buildup due to human respiration (1 kg of CO₂per day), methods of removing it from the atmosphere must be utilized [refDesigning for Human presence in space]..

Four ways toremove CO₂ from the colony atmosphere are absorption (chemical orelectrochemical reaction with a sorbent material, adsorption (physicalattraction to a sorbent material), membrane separation, and biologicalconsumption. The main technology in use today that utilizes absorption for CO₂removal is LiOH absorption, however, LiOH absorption is not acceptable forlong-term (over 2 weeks) use as it is not a regenerable process and thechemical 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 largeamounts of CO₂ due to their large surface area.  Other technologies used to concentrate andremove CO₂ from spacecraft interiors include solid amine waterdesorption, electrochemical depolarization concentrator, and air polarizedconcentrator.

4 bed molecularsystems (4BMS), which utilize 5A zeolite molecular sieves for trapping CO₂,have already been flight proven on Skylab, and can be expected to perform for10 years without failure [refhttp://www.ae.utexas.edu/~campbell/fatmass/pdr2.htm].  4BMS operates in a cycle, with equal amounts of time needed foradsorption and desorption of CO₂.However, a vacuum environment is needed for the desorption of CO₂.  2 bed molecular systems (2BMS), utilizecarbon molecular sieves and is projected to have half the weight and powerrequirements of 4BMS, however, this technology is still in its early stages ofdevelopment.

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

Electrochemicaldepolarization concentration (EDC) uses electrochemical reactions to remove CO₂from 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 carbondioxide.  EDC has the advantages ofbeing able to operate in cyclic or continuous mode, easily alter the CO₂removal rate, and produce DC power.However, the possibilities of H₂ leakage must also beconsidered as well as the heat load and O₂ demands.  Air polarized concentrators (APC) work onthe 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 becomingan EDC. APC/EDC combination was finally chosen as the technology to concentrateCO₂ onboard the colony.  Notonly does this combination offer great flexibility as to the power draw andsafety issues of the system, it also fits quite nicely into a bio-regenerativesystem because of its continuous operation mode.

III.C.2 O₂ Generation

            TheO₂ partial pressure at sea level is 21.4 kPa.  O₂ partial pressure must bemaintained near this level to avoid negative the physiological effects ofdecreased night vision, convulsions, unconsciousness, impaired memory andcoordination, and death of nerve tissue [ref Designing for Human presence inspace].  Traditional, non-biologicalmethods of generating O₂ onboard space missions mostly involve theelectrolysis of water, electrolysis of water vapor, or electrolysis of CO₂.

            Onthe space colony, O₂ generation will be the task of the plantsonboard.  The plants could also be usedfor CO₂ removal from the colony atmosphere; however, since fasterplant growth rates can be achieved with a concentrated CO₂atmospheric level, CO₂ removal and concentration will be left to theEDC/APC systems onboard.

            However,there is a loss of approximately 0.10 moles of CO₂ if plants areintroduced into the colony CELSS, since humans exhale about 0.85 moles per moleof O₂ consumed, and plants consume about 0.95 moles of O₂for every mole of O₂ produced.Variations in CO₂ consumption and O₂ productionrates also exist due to the fact that plants do not experience constant plantgrowth, but rather experience periods of accelerated growth when CO₂consumption is at a higher level.Plants also stop producing CO₂ and start consuming O₂because of cellular respiration during periods when there is noillumination.  High growth rates must beconsidered along with high yields as high temperatures 298 K (25º C) promoterapid 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 utilizingplants as the method of O₂ generation, several methods arerecommended, such as providing multiple plant growth areas that are illuminatedat different times of the day, to ensure a steady source of oxygen night andday; altering illumination or temperature levels to control photosyntheticrates; and using a system of gas storage.

            Tocompensate for times when plant O₂ generation is below requiredlevels, artificial means of generating O₂ must be considered.  As mentioned above, artificial means ofgenerating O₂ mostly involve the electrolysis of water, electrolysisof water vapor, or electrolysis of CO₂.  An advantage of electrolysis is that the H₂ producedfrom this electrochemical reaction could be fed into the EDC/APC system, ineffect “closing the loop.”

            Severalsystems considered for O₂ generation onboard the colony are StaticFeed Water Electrolysis (SFWE), Solid Polymer Water Electrolysis (SPWE), andWater Vapor Electrolysis (WVE).  SFWEwas rejected because of its use of asbestos, SPWE and WVE both are technologiesthat possess many desirable attributes.SPWE is a mature technology that is being used onboard the InternationalSpace Station for its Oxygen Generation Assembly.  Integration of both SPWE and WVE would not be too difficult asSPWE could receive water from the CHX subsystem, and WVE could directlyelectrolyze atmospheric air.  Thedrawback of SPWE are that it is sensitive to water contamination, while thedrawback of WVE is that it interferes with the humidity control of CHX.  Thus, WVE was finally chosen as its problemscan easily be rectified.

III.C.3 Temperature and Humidity Control

            Condensingheat exchangers (CHX) have been widely used to remove moisture and heat at thesame time from the atmosphere of space missions by using coolant-cooled fins tocondense humid air and then removing the condensation via “slurper holes” [ref1].  By using fins to maximize thesurface area, faster rates of heat exchange with a minimum of volume can beachieved.  First, atmospheric air isdrawn into the system, and its humidity and temperature are recorded.  Then the air is passed through highefficiency particulate atmosphere (HEPA) filters to remove microbial and dustcontaminants ranging from 0.5 to 300 microns in size.  At the water-cooled air fins of the CHX the temperature of theairflow is brought below the dew point, thus causing the air to besuper-saturated with water vapor.  Waterthen condenses and is carried by the airflow to the slurper holes, where itwill leave the main stream of air, along with some air.  Control of the amount of water to be removedfrom the atmosphere is determined by the flow rate through the CHX [ref40].  The heated coolant will then dumpits heat into space via the radiators.The condensed water will be purified and then used as tap water or fedinto the agricultural areas.

III.C.4 Trace Contaminant Control

            Tracegasses in the colony atmosphere will pose a threat since even the smallestamounts of harmful gas would create an unacceptably high concentration in therelatively small volume of the colony.Sources of trace gasses could include outgassing, CELSS processes, andevaporation of volatile substances, and special concern for those elementsshould be taken during the design stage.Trace contaminants which may be pose a threat in space missions includeacetone, 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 [refs40, 41].

The technologiesavailable for active contamination monitoring include gas chromatography/massspectrometry (GC/MS), infrared dispersion/spectroscopy, and ultravioletspectroscopy [ref 40].  Thentechnologies such as particulate filters, activated charcoals, chemisorbantbeds, and catalytic burners are used to purge the atmosphere of undesiredcontaminants [ref 1].

The firstcomponent of GC/MS is a gas chromatograph, which uses gaseous diffusion toidentify different components of the airflow, while the second component ofGC/MS is a mass spectrometer, which utilizes the different deflections causedby a magnetic field to analyze molecular weights.  GC/MS is a proven system both on space missions and duringearth-bound field use, and can identify virtually all chemicals encountered viaanalysis of the data obtained through both components.

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

            Removal techniqueswould utilize all of the purging technologies.First the air would be passed through several HEPA filters to trap dustparticles and microorganisms, these would preferably be placed in an easily accessibleplace, so that they can be exchanged for fresh ones once they have reached theend of their lifespan.  Then thecontaminated air is passed over activated charcoal beds, which adsorb ammoniaand water-soluble contaminants [ref 1].These beds can be “recharged” via desorption during exposure to vacuumand heat.  A catalytic oxidizer based onpalladium oxidizes hydrocarbons not adsorbed by the charcoal beds, while LiOHpost- and presorbant beds adsorb acids [ref 1, 40].  The CHX can also remove soluble contaminants as the watercondenses and drops to the bottom of the exchanger [ref 40].

III.C.5 Colony Ventilation

            Toensure proper mixture of oxygen into the atmosphere, removal of heat, and theremoval of carbon dioxide and trace contaminants, a minimum air velocity insidethe colony is needed.  Maintaining aproper ventilation system is also crucial to supplying the atmosphericmanagement subsystems with air from the colony atmosphere.  Due to the generation of a pseudogravity viathe spinning of the colony, a natural convection current will ensue, driven bythe temperature differential between the heated interior of the torus and therelatively cooler region closer to the center of the colony torus.  Intakes outfitted with blowers should bepositioned on the middle supporting strip bisecting the glass sky so as to ventthe waste air.

 fig. 3.5

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

III.D Waste and Water Management

            Solidand liquid organic waste onboard the colony will have to be treated andconverted into useful substances so that an accumulation of unwanted mass isavoided.  Waste onboard the colony willmostly consist of feces, urine, food preparation byproducts, packaging, etc.  Collection of wastes would be differentiatedbetween organic and inorganic wastes.Organic wastes would be processed in order to return the inherent carbonto plants, while inorganic wastes would be vigorously recycled.

            Wateris essential for human life, as humans use water for nutrition andcleansing.  Additionally, manymanufacturing 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, emergencysupplies 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

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

III.D.2 Waste Processing

            Mostorganic wastes onboard the colony would be inedible plant mass such as roots,stems, and leaves.  Processing of thismaterial can either be bioregenerative recovery of the plant nutrients or totaloxidation of the plant matter.Bioregenerative recovery of the plant matter was selected in order tomaximize the nutrients gained from the growing of plants.  Nutrients that can be derived from inedibleplant matter include carbohydrates, proteins, and lipids.

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

            Humanwastes primarily consist of urine and feces.The first step in processing this waste is collection andsegregation.  Urine would probably becollected along with feces via the colony sewage system.  This waste stream would then be routed to aprocessing facility, which would break down the waste into varioussubstances.  Preprocessing would includeseparating the solids from the liquids, which could be achieved throughsedimentation tanks or centrifuges.There are several processes available for solid waste treatment, SuperCritical Wet Oxidation (SCWO), wet oxidation, combustion, electrochemicalincineration, Waste Management-Water Systems (WM-WS), and anaerobic or aerobicbioreactors [ref 1].

SCWO oxidizesorganic compounds using water in its supercritical state.  Basically, in a SCWO reactor, the aqueouswaste is heated and pressurized in the presence of oxygen, and organiccompounds are completely oxidized to CO₂, H₂, and N₂as 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 saltsegregation, and production of potable water [ref 1].  Due to the corrosive nature of CELSS waste and the hightemperatures and pressures involved, the reactor would have to be constructedout of a corrosion resistant metal such as titanium or its alloys [ref 30].

Wet oxidation issimilar to SCWO in that it also heats and pressurizes aqueous waste in thepresence of oxygen.  However, thepressures and temperatures involved are not as drastic (14 MPa, 473-573K).  The disadvantages of this systemare that the organic compounds are not totally converted into CO₂and other simple compounds, so there is a small amount of ash residue [ref 1].

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

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

Another wastemanagement technology is Waste Management-Water Systems (WM-WS).  WM-WS has the advantage of being more efficientin microbial control than other systems, and operates at 920 K with catalyticoxidation [ref 1].  Like electrochemicalincineration, little could be found out about WM-WS, but it looks to be apromising system.

WM-MS,electrochemical incineration, and SCWO are all promising systems indevelopment.  At this time, insufficientdata is available in determining which system would be the most suitable toprocess organic waste, but SCWO seems to be the technology farthest along indevelopment, as it is already being developed for the destruction of chemicalwastes on earth.  After being processedthrough SCWO, the waste feed is then routed to the agricultural sections, whereit will be analyzed, adjusted, and used as a nutrient source.  SCWO will also serve as the one of theprimary sources of recycled water, along with the CHX system.

III.D.3 Recycling

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

III.D.4 Water Storage

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

III.D.5 Water Quality Monitoring

            Inorder to ensure the safety of machines and humans, the water supply must abideby water quality guidelines.

[ref 40]

            Thesepollutants should be monitored by an automatic system that would divert theunacceptable water to processing systems.There exists chemical, thermal, light, and mechanical methods todisinfect water [ref 40].  Mechanicalfiltration would be useful for separating nonsoluble and large particlecontaminants and thus would come at the very beginning of the disinfectionsystem.  Since thermal and light meansof disinfecting water mostly affect biological contaminants, the tainted waterwould first be subjected to heat and UV irradiation treatment before being subjectedto chemical treatment.  Chemical meansto disinfect water include iodine, ozone, and silver.  Since silver and iodine are both contaminants, ozone was chosento disinfect water.  Mechanicalfiltration, thermal processing, UV irradiation, and ozone treatment are alltechnologies proven on earth and should not pose significant problems duringimplementation.

III.E Plants and Algae

Photosynthesiscan fulfill the need for food production, atmospheric regeneration, wastemanagement, as well as water management, since it produces edible biomass; oxygenfrom atmospheric carbon dioxide; simple compounds such as nitrogen and carbondioxide from biodegradable substances; and potable water from transpiration inplant leaves.

Two kingdoms of organismsthat carry on photosynthesis are Protista and Plantae.  Green and blue-green algae belong to thekingdom of Protista and have several aspects such as rapid growth, controllablemetabolism, high harvest index, gas exchanges compatible to human needs, easeof cultivation, and high reliability that make them attractive for use in alife support system.  Although algaedoes contain all the essential amino acids, sufficient lipids, and nearly allthe essential vitamins, it is lacking in carbohydrates and difficulties remainin converting it into an edible form, although the same techniques forhydrolyzing plant cellulose into glucose using cellulase are involvedhere.  However, plant cellulose andalgae cells should not be hydrolyzed for glucose if the process proves to be toocostly [ref 1].

Higher plantshave the advantages of transpiring water, which makes water purification muchsimpler; of being the basis for much food normally eaten by humans andproviding most of the nutrients needed by humans; of being capable of removingsome volatile and liquid contaminants produced by humans or machinery; and ofproviding an aesthetically pleasing environment to the colonists.  However, different crops of higher plantsrequire different temperatures and photoperiods, complicating the task ofgrowing higher plants.  The objective indesigning the agricultural sections should be to provide the optimalenvironment 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

            Sincethe process of photosynthesis relies on the light energy, providing properillumination in the agriculture areas is of vital importance.  In Æther, solar and artificial lighting willbe utilized for growing plants.  Thegreen color of some algae and most plants is due to the presence ofchlorophyll-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, onlyblue and red light sources are needed, however many light sources contain red,green, and blue wavelengths.  Solarlighting uses the solar light available in outer space, while artificiallighting utilizes man-made light sources to illuminate the plants.  Like humans, plants cannot live if exposedto the massive amounts of radiation that accompany the visible electromagneticspectrum, since the plants will be grown inside the shielded torus of Ætherthis should not be a problem.

However, in thelower level of the habitat section, either indirect solar lighting orartificial lighting will have to be used, since the lower level does notdirectly receive solar light.  Indirectsolar lighting involves the collection and transportation of light with the useof mirrors, lenses, and optical fibers.The primary goal in designing a solar light collection system is tofilter out the unnecessary wavelengths and supply light at the requiredintensities.  Selectively transparentcoatings or lenses can be used to filter out undesirable frequencies such as infraredand ultraviolet.  Artificial lightingseems to be the better method, since indirect solar lighting would requirelarge structures to collect and transport light [ref 1].

There are manytypes of artificial lighting, from fluorescent tubes and high-pressure sodiumlamps to light-emitting diodes (LEDs).Interest in the latter is particularly high due to their low heatgeneration, high electrical efficiency, low mass, and low volume.  Red and blue LEDs in conjunction may provideadequate lighting for plant growth [ref 19].

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

III.E.2 Nutrient Delivery

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

            Substrate-lessnutrient delivery systems include hydroponics and aeroponics.  In hydroponics, the roots are placed in anaerated, circulating, liquid system that provides the plant with water,nutrients, and oxygen.  Thus hydroponicsallows 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-lessnutrient delivery systems is that since the plant can easily obtain an adequateamount of nutrients from the delivery system, it does not grow large roots andinstead 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 requiresmore supervision.  Aeroponics is likehydroponics in many ways with one major difference, the nutrient is applied tothe plant roots in the form of a spray rather than a liquid flow.  Since it utilizes a spray, aeroponicsrequires less solution per plant than hydroponics.  However, the major problem of nozzle clogging exists inaeroponics, and for the present, hydroponics seems to be the betterchoice. 

III.E.3 Atmosphere

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

            Whilethe goal of the CELSS is to provide an environment that is as Earth-like aspossible, the opposite may be true when determining the atmosphere compositionin the plant growth chambers.  Plantsgenerally do well when the O₂ partial pressures are reduced, andwhen CO₂ partial pressures are increased.  C₄ pathway plants have an optimal CO₂concentration of about 350 ppm, while C₃ plants have a higheroptimal concentration of approximately 1000 ppm [ref 1].  However, the specific optimal CO₂concentration is dependant on the plant grown and on the specific stage of itsgrowth cycle; thus only very similar plants should be grown in the same chamber.  Carbon dioxide concentration can beaccurately determined by using infrared analyzers, which operate on theprinciple that carbon dioxide absorbs specific infrared wavelengths; however,some computational processing is necessary to distinguish the signal from thebackground infrared radiation.  TheAPC/EDC systems would serve as the source for plant chamber carbon dioxide, butcontingency carbon dioxide should be stored via cryogenic or pressurizedmethods in case of emergency.

            Preservinga stable temperature is important for plant growth as they contain enzymes thatoperate at an optimal temperature.  Mostplants prefer a temperature range of 285-301K, but specific temperatures varywith species, carbon dioxide concentration, irradiance intensity, and photoperiod.  Plants also require air moment so thatleaves do not overheat; cooling airflow can be provided by centrifugal blowersthat intake fresh air and also exhaust hot air into a sensor array thatmonitors the atmosphere of the growth chamber [ref 20].

            Transpirationis a major process that impacts photosynthesis, and is impacted by the humidityof the atmosphere.  High humidity levelsare preferable since they reduce transpiration rates; therefore the water needsof the plants are reduced.  Yet plantsalso need an adequate transpiration rate that can sufficiently cool off theleaves.  Thus humidity controls shouldbe linked to temperature monitoring of plants.

III.E.4 Modules

            Takingthe varied requirements of plants into account, plants will be grown inself-contained modules that can be easily reprogrammed for differentspecies.  These modules would also allowthe repair and cleaning of different sections of the plant growth area withouthaving to disrupt a large number of plants.

III.F Food and Agriculture

            Humandiets 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.1Food Production

Due to the higher efficiency ofplant and algae based agriculture, the using plants or algae based products tofulfil the requirements of as many nutrients as possible is desirable; fortunately,a carefully planned vegetarian diet is able to cover all the nutritional needsof 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); Butternutsquash; Cabbage; Carrots; Cauliflower; Chickpea; Chillies; Chives; Courgette;Corn; Cotton; Cowpea – ‘Black/Yellow-Eyed Pea’; Cucumber (Lemon, Amira, OrientExpress, 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; Pintobeans; Plums; Potato (Huckleberry, Blossom, Yukon Gold, Russet Burbank, WhiteRose, 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” [ref6].  Additional crops that would be ofbenefit 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 certainlydoes not contain all of the potential crops, it certainly contains enough cropsto 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 wouldbe available all year long.  Anadditional food source would be the trees grown for aesthetic purposes, whichcould supply nuts and fruits such as Pecan, Pistachio, Cashew, Hickory, Walnut,Acorn, Almond, and Cherry.  Maple treescould also be grown so that their syrup can be harvested.

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

Another group of animals that meetsthe criterion of being small and being able to reproduce quickly isrodents.  Although the mere thought ofeating rodents may deflate most reader’s appetites, it must be noted thateating squirrels and rabbits, both of which are considered rodents, isgenerally accepted.  Culinary tasteonboard Æther may evolve to a point where the use of rodents in dishesis tolerated, but initially rodents may have to be processed into anunrecognizable form in order to induce people to eat them.

Unfortunately,some conflicts will arise between the colonists’ innate tastes and the abilityto 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 desiredgoods.  Fortunately, some othercultures, such as Hinduistic Indian, do not rely heavily on animal products andtheir dietary needs should not pose a problem. It is hoped that the colonists will be able tomaintain their traditional diets while at the same time being able to sampledifferent foods from all over the world.

            Thedevelopment of acceptable substitute will be of great concern to colonynutritionist who will strive to create the most appealing of diets whilerestricted by the number of raw materials.Substitutes are already used on earth, including many products made outof soy and peanuts.  However, recentadvances in biochemistry that have lead to the identification of organiccompounds responsible for the taste for wine give hope to the possibility thatauthentic-tasting steaks or burgers can be synthesized from the crops grown in Æther.

III.F.2 Food Preparation

            Theneed for preparation of different foods falls into three general categories,little to no processing, primary processing, and secondary processing [ref1].  Foods that require little to noprocessing are either fruits or vegetables that may be eaten raw, and thus onlyrequire washing, peeling, or cutting before being served.  Foods that require primary processinginclude juices, flour, and cooked foods.The processes needed involve pressing, grinding, and cooking.  Foods may be irradiated to ensure death ofpathogens before being served.

III.F.3 Food Storage

            If raw materials or processed foods are not to beconsumed 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 theyrely on coolants that may be harmful to humans, and their pumps are suspect tofailure.  Thermoelectric modules (TEMs)rely on the peltier effect, which arises when a current is sent through acircuit made of dissimilar conductors, to absorb heat on one side and releaseit on the other.  Most TEMs are madefrom telluride bismuth, and thus are expensive to manufacture; coupled with theproblems of expansion and contraction, this factor make the construction oflarge scale TEMs quite difficult.Thermoacoustic cooling relies on the pressure, temperature, anddisplacement oscillations caused by an audio driver to cool objects [ref44].  By placing the audio driver at oneend of a coolant-filled metal tube, and a heat absorbing porous conductor nearit, a simple but reliable thermoacoustically driven refrigerator can bebuilt.  Thus, heat will be pumpedtowards the end of the tube with the audio driver when it is turned on, and thecoolant 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 producesufficiently low temperatures.Thermoacoustical refrigeration would be the technology of choice, sinceit does not use harmful coolants, is reliable, and improvements are being madeon efficiency.

            Biodegradablepackaging based on either cellulose or bioplastics should be used to lower theamount of unrecyclable waste.  Ediblerice (or wafer) has been used for quite some time on earth, and may prove to beuseful in Æther.  Plastic and metalcontainers should be reused and not thrown away after the first use.

III.G Fire Prevention, Detection, andSuppression

Fire is the mostundesirable mishap to happen in a spacecraft.The confined interiors of any space habitat have the effect of greatlyincreasing the lethality of a fire.Methods of reducing losses due to fires include prevention, detection,and suppression.  Fire prevention isimplemented during the design phase and minimizes the probability that a firewill occur onboard by using nonflammable materials in construction.  Fire detection systems should be able toquickly sense the presence of a fire and also be able to accurately locate itswhereabouts in Æther.  After the firehas been detected it can be suppressed by breaking the “fire triangle” oftemperature, oxygen, and fuel.

III.G.1 Fire Prevention

The use offlammable materials in everyday objects should be avoided so as to prevent theaccumulation of such substances.Prevention of fires can be done by not utilizing napped (fuzzy) finisheson clothing; designing garments so that a minimum of loose clothing is used;manufacturing carpets and other textile items out of flame resistant or flameretardant material; reducing the number of ignition sources; separatingflammable material with non-flammable material; isolating flammable materialfrom ignition sources; creating flame barriers through the use of non-flammablematerials such as metals and ceramics; using metallic coatings on substrates;and coating flammable surfaces with Fluorel® [ref 10].  Flammability tests should be conducted onthe items used in the construction of Æther, these tests include upward flamepropagation to test if the material can self-extinguish and will not propagatethe fire through debris; heat and visible smoke release rates; flash point ofliquids to determine the lowest temperature at which a liquid forms anignitable mixture with air near the surface of the liquid; fire point ofliquids, to determine the lowest temperature at which a fire becomesself-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 willbe 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 thepresence of fire.  However, in avoluminous space settlement, fires may break out where humans are not nearby todetect its presence, thus automatic fire detectors must be present in all partsof the colony [ref 13].  Current methodsof fire detection sense the presence of smoke or flame.

Smoke detectorsare usually employed in ventilation ducts while flame detectors are installedin open areas.  Two types of smokedetectors are photoelectric detectors and ionization detectors.  Obscuration detectors, scattering detectors,and condensation nuclei counters are all classified as photoelectricdetectors.  Obscuration detectors relyon the fact that when particles pass between a light source and a receiver afraction of the light is obscured.Scattering detectors operate on the principle that when a particlepasses through a laser beam light is scattered at an angle inverselyproportional to the particle’s size.This scattered light is then collected and analyzed by a receiver.  Condensation nuclei counters detect smallerparticles 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 airwith alpha particles, this ionized air is then forced in between a positive anda negative electrode by a convective flow.Under normal circumstances with no smoke particles, the ionized air isattracted to the electrodes and a electrical current results; however, theincreased mass due to smoke particles attached to the ionized air reduces thevelocity of the particle-air pair and the convective flow carries the pair outof the electrode chamber, thus creating no electrical current.  Another way smoke particles affect theelectrical current of the detector is by neutralizing the ionized air, eitherway, the reduced current caused by smoke particles sets off an alarm.  Ionizing detectors are more efficient atdetecting flaming fires, while photoelectric are more efficient at detectingsmoldering fires [ref 12].

Flame detectorsare triggered by the ultraviolet, visible, and infrared radiation that firesproduce.  Monitoring of all wavelengths(UV, visible, and IR) is desirable so that false alarms are kept to aminimum.  Integrated UV, IR, and visiblesensors have already been fabricated using CMOS technology, and willundoubtedly be available for use in the future.

III.G.3 Fire Suppression

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

CO₂is an effective fire suppressant and is normally stored as a liquid at roomtemperature with high pressures.  Whenliquid carbon dioxide is released from an extinguisher, the liquid immediatelychanges to a gas because of the pressure difference.  This process is highly endothermic and helps in cooling thefire.  Additionally, carbon dioxide isdenser than normal air, and will suffocate the fire by depriving it of oxygen.  Carbon dioxide will not leave behind aresidue, can easily be recaptured through atmospheric control systems, is notelectrically conductive, and does not decompose into other substances.  However, carbon dioxide is not suited foruse in habitable areas because inhaling large amounts of it is dangerous tohumans.  Therefore, carbon dioxide willonly be used in the industry/research areas and only after everyone has beenevacuated.  Venting the area on fire,and thus depriving it of oxygen, could be put to use if the situation becameextreme.

Water based firesuppression systems fall into two categories, sprinklers and fine water mistsystems, with the two differing only in the droplet size.  Sprinklers generate droplets of size 1mmwhile fine water mist systems produce 0.1mm to 0.01mm droplets [ref 31].  Since sprinklers have no advantagewhatsoever over fine water mist systems, only fine water mist systems wereconsidered.  Fine water mist systemdroplets have a large surface area that aids in the absorption of heat, quicklylowering the temperature to below the fire point.  Heavy smoke particles are also precipitated by the mist, whichuses relatively little water when compared to conventional deluge/sprinkler systems.  Unlike carbon dioxide, water mist is nottoxic upon inhalation.  The challenge inmaking fine water systems feasible for use is producing nozzles that cangenerate the desired mist of water.  Thenozzle opening must be small enough to produce the droplets, yet large enoughto 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 beused in most locations, but carbon dioxide suppression systems will beimplemented in vital places where humans are not normally present, such as theareas which house CELSS machinery.

III.H Power

The Æther space colony will require a vast amount ofelectrical 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 powerthroughout Æther, and wire diameters would have to be large enough to preventfires from breaking out due to excess heat caused by resistance of thewire.  High voltages will be used todistribute power, so that the current can be minimized, thus reducing energyloss due to resistance.  Power from thephotovoltaic cells or from the flywheel storage units will first be convertedinto AC then sent through primary transmission lines at high voltages.  The voltage then is “stepped down” to thevoltage used by household appliances at local transformers.

III.H.2 Power generation

            Ætherwill have a centrally located hexagonal solar panel with sides of 900 metersthat has a hexagonal shaped hole with sides of 380 meters in the center plustwo rectangular panels with length of 600 meters and width of 300 meters belowthe hexagon.  The total combined surfacearea of all the panels is 3.45 million m², thus enabling the spacecolony to soak up 5.3 million kilowatts, but due to solar cell efficiencies ofapproximately 13%, that only means 689 thousand kilowatts that the colony canactually use.  

 fig. 3.6

III.H.3 Power Storage

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

III.H.3.a Flywheels

            A flywheel is anelectromechanical system that stores energy by spinning a disk at highspeeds.  When power is needed therotational energy of the disk is used to turn a dynamo.  A high efficiency can be achieved by keepingbearing and air friction at minimal levels, thereby reducing energy loss.  The vacuum housing can also serve as ashield when calamities develop.  Theflywheels use superconduction magnets as low-friction bearings to support thedisk using magnetic forces so that there is no contact or friction and nolubricants involved.  Active magneticbearings dynamically respond to different situations in order to preventcontact and thus friction is largely avoided.By using permanent magnets on the flywheel and a current-generatingcoil, the conversion from electrical to mechanical energy efficiency values canreach up to 90% [ref 43].  Since theenergy stored is a function of the disk’s rotational speed, the ultimatestrength of the material that the disk is composed of will determine howeffectively energy can be stored.Current research has focused on using carbon fiber composites, whichpossess excellent strength but also have the additional benefit ofdisintegrating into dust rather than shrapnel, which would only require the useof a light Kevlar shield [ref 43].  Thedevelopment of disks composed of ultra-strong “bucky-ball” nanostructures couldenable even more efficient storage of energy in a given volume.  Flywheels will be used for long-term energystorage.

III.H.3.b Ultracapacitors

            A capacitor  usually consists of conducting platesor foils separated by thin layers of dielectric material with the plates onopposite sides of the dielectric layers oppositely charged by a source ofvoltage and the electrical energy of the charged system stored in the polarizeddielectric.  Selection of the properdielectric is crucial as the electrical properties of the dielectric willultimately determine the maximum storable charge.  Several materials considered for low-mass, high-energy storageinclude thin film polymers and ceramics [ref 43].  Capacitors are useful in that they can be recharged quickly atperiodic intervals, thus proving useful in a hybrid system where photocellswould be used in high illumination conditions and the excess power being storedin capacitors; however, capacitors gradually lose charge over time and are notideal 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 onthe left, and oxygen enters on the right.The porous electrocatalyst anode strips two electrons from hydrogen inan oxidation reaction.  The potassiumhydroxide electrolyte in the middle is an ion-exchanging medium, allowing onlyH⁺ ions to cross, while at the same time prohibiting O^2- toflow the other way.  A circuit isconnected from anode to cathode, allowing the oxygen to gain electrons in areduction reaction.  The hydrogen ionsjoin the oxygen ions to produce water and some thermal energy [ref 43]. 

            Allof the above mentioned systems would be implemented on Æther since differentones have the most advantages in certain situations.  However, the main power storage method used will be the flywheelfor its high efficiency levels, emergency power could be distributed from areliable source based on batteries or fuel cells during times of duress.