Leaving the confines of Earth to colonize Mars will be a daunting task with numerous new challenges. Questions range from how to design the appropriate flight plan to arrive safely on Mars to the psychological makeup of the traveling astronauts. One important question that has evolved recently is the design of the initial Martian habitat. The most important element when considering habitat design is to establish the purpose for the mission to Mars. Early on in the quest to travel to Mars the principal goal was for scientific purposes, largely establishing whether or not life had ever existed on Mars or currently exists on Mars. However, over time this motivating factor has begun to shift towards developing a permanent human presence on Mars. Clearly habitat design will demand different boundary conditions between a mission designed to last 6-18 months and a mission designed to last indefinitely. This post will apply a permanent stay boundary condition in the discussion regarding Martian shelter design.
One of the first issues in Martian colonization is the preparation element. One concern with current preparation is the nature of how the “need” methodology is designed for Martian colonization simulations conducted on Earth. Most colonization simulations take place on Earth in remote locations like various deserts (Mars Desert Research Station) or in Arctic areas (Flashline Mars Arctic Research Station) and are undertaken with the correct spirit and attitude, but appear to have significant design problems. The characteristics that are correct involve the isolated environment and limited resource availability and capacity. However, the usefulness of a simulation stems from the commonalities that can be demonstrated between the actual environment and the simulated environment. In this mindset these colonization simulations fail at least on the following levels, if not more:
- The task schedule described in these simulations for the participating crewmembers seems inaccurate relative to what colonists on Mars will be doing. In simulations tasks revolve around maintenance of machinery, simulated research and shelter-based chores. There is no construction of additional shelter elements, which will comprise significant amounts of time for colonists or farming. To be fair some simulations were conducted with a research mindset over colonization (18-month stay before a return); however, with the current momentum for Mars missions shifting from research return missions to permanent stay colonization, construction of additional shelter elements using Martian based resources (in-situ) and developing an independent food production system should take precedence over research and chores.
- Food consumption is too “well-developed”. In these simulations “colonists” have a wide selection of food available, most of which will not be available on Mars. It stands to reason that there will be some initial variety born from the food transported with the colonists (albeit most of this, if not all of it, will be dehydrated or freeze dried due to the travel time between Mars and Earth). However, this initial source food will be consumed over a brief period of time and less hardy choices will be relied upon for a significant time period afterwards. The “food” study aspects of these simulations do not properly represent starting or transition points. This misrepresentation reduces the probability of collecting accurate information pertaining to how biological functions would change over time and how colonists would have to adjust when consuming significantly fewer calories.
- Modes of transportation operate on diesel or gasoline instead of electricity or methanol as they would on Mars.
- Water extraction and consumption is not practiced in the same manner as will need to occur on Mars. There is no water extraction from simulated ice, no atmospheric extraction, limited water recycling and no experimentation involving water synthesis from the Sabatier reaction. Consumption is managed a little better with personal hygiene restrictions, but unclear parameters regarding actual biological consumption.
These are just some of the limitations that create problems in developing an accurate understanding of the physical, mental and psychological elements that will be required for colonizing Mars. Without addressing these concerns conducting similar future simulations may be more harmful versus not performing any simulations at all because it is more dangerous to create a targeted strategy born from inaccurate boundary conditions and situations than not create a targeted strategy at all.
While both food and water consumption and development strategies will be discussed in much greater detail in another blog post it is important to note that there are questions to whether or not colonization proponents are overestimating the ease of water use, thus underestimating the probability of water stress and shortage for Martian colonists. It is to be expected that water use for personal hygiene will be restricted (showers will be allowed every x number of days based on a rotating schedule baring emergency, dish washing could use UV treated sponges verses water and soap, etc.). Water use will also have to be rationed for personal use (both direct consumption and in food preparation) and this rationing will need to be effectively measured for too many seem to believe that biological water expenditure will be similar to that on Earth, which does not appear to be effective reasoning. Numerous external vehicle activities (EVAs, although one could rename this exercise as ECA (external colony activities)) and multiple hours of exercise per day will place an excess workload on colonist, which should demand greater water and food consumption over the minimum survival amount, a value that most calculations utilize.
Energy for the colony should be derived almost entirely from electricity with the best option being some form of small modular nuclear reactor with breeding capacity. Such a reactor will not produce significant waste so disposal will not be a major issue and the reactor will be able to provide a near 100% capacity rate, something that no other energy medium situated on Mars can achieve. Reactor location is still tentative because of uncertainty relative to how radiation could negatively impact colonists versus the necessary length of transmission lines. If there is a concern regarding potential radiation exposure then reactors can be placed in a nearby crater to offer partial shielding.
Solar power is a popular selection for some colony advocates, but it really is a non-starter because of inconsistencies derived from day-night intermittency, CO2 fog at higher latitudes, dust storms, lower absolute solar radiance on Mars versus Earth, among other things. The only way solar would work is with large amounts of energy storage and only batteries would be available in the short and mid-term significantly limiting storage options and viability due to weight considerations because these batteries would have to be sent from Earth. In addition these batteries would have inconsistencies in their energy storage rates because of the demand for redundancy (most energy consuming elements for the habitat operate 24/7 to ensure survival), but only unused energy can be stored. Finally there are potential oxidation and maintenance issues as well.
There has also been some concern about solar panels being strong enough to withstand wind gusts on Mars, but with the lower atmospheric pressure Martian wind velocities rarely exceed a 4 m/s equivalency on Earth. Thus, only the abrasion resistance is important due to sand particles traveling up to 32 m/s.1,2 Lifting the solar panels above the saltation point (20 cm) can increase abrasion resistance, but the panels will still have to be cleaned constantly creating additional external environment work for the colonists and consume additional resources.3 Therefore, based on all of these issues any proposal to utilize solar power as a primary source of energy is highly questionable. Note that these low equivalency wind velocities as well as its own intermittency eliminate the viability of wind power as well.
Use of solar power as a secondary source of energy is also highly questionable because of intermittency issues. For example in the event of a failure of the small modular reactor for solar to be an adequate backup energy provider the failure would have to occur during the day with clear skies under limited energy demands. Basically the conditions for the successful administration of solar power as a backup source are too narrow to justify its use. If one could develop an effective Martian energy storage system then solar as a backup could become viable, but currently such an infrastructure is not viable due to its dependency on Earth batteries.
The debate between an underground shelter and an above ground shelter is worthwhile for each has advantages and disadvantages. The chief advantage of an underground shelter is additional radiation and dust storm protection. However, the chief disadvantage is digging through the regolith to develop the appropriate underground region to house the habitat. Drilling through the regolith is difficult for two reasons: first, there are almost no easily available fossil fuels on Mars so operational times for drilling equipment would be almost entirely dependent on fossil fuels sent from Earth. One could use methanol as a fuel source, but that would complicated and require large amounts of prep work before sending colonists. Second, Martian regolith is heterogeneous with fragments of glass, coral and other obtuse shaped miscellaneous objects which can significantly interfere with the drilling process by damaging drill bits and other important machine elements.4
Fortunately there are two possible strategies to avoid this problem of regolith drilling. First, regolith does have various iron oxides strewn through it, which opens the possibility of using an electrical attractant or magnetism to thin a significant portion of regolith within a localized area possibly, but not likely forgoing the digging process entirely.4 The chief concern with this method is isolating the regolith to the specific target area due to iron oxides being widely spread throughout all of the regolith.
Second, the underground shelter can be centralized in a lava tube that already has an eroded surface opening so no digging is necessary. In such a scenario a crane/elevator system may be needed to safely lower objects sent from Earth down into the shelter area. Unfortunately while this second possibility sounds promising no organization has even attempted to land a rover in an lava tube, let alone succeeded, thus the prospects of successfully landing a habitat structure (inflatable or not) in a lava tube is a bridge too far in optimism at this point in time.
Another concern with building an underground shelter is the potential for a lack of similar elevation water availability. Some lava tubes double as ice caves, which would have significant sources of water, but where these ice caves are located exactly is not entirely clear.5 Therefore, without identifying at least one easily accessible ice cave, underground shelters would more than likely have less atmospheric and regolith based water sources available versus surface shelters. The best subsurface colonization site would demand three elements: 1) easy surface-subsurface access, preferably from a pre-existing natural opening; 2) a source of ice, which can be converted into drinkable water; 3) sufficient ceiling height and outer area to allow for habitat expansion; unfortunately such goldilocks sites are far and few between at the moment.
For surface-based sites there are three popular locations for initial habitat construction: within the equatorial region of 30 N to 30 S, the edge of the southern polar cap and the northern polar cap.3,6,7 One of the concerns with the reasoning that went into determining these habitat locations is the contradiction between the operations of the habitat and colonists versus the features of the habitat location. In the past when these locations were considered the mission objective was a short stay for scientific purposes; however, how do they rate when the mission objective is changed to a permanent colony? For a permanent colony only two elements are of critical importance: water availability and dust storm frequency.
Other elements of consideration can be easily compensated for depending on the design of the habitat. For example sunlight exposure through changes in inclined angle of incidence is irrelevant if artificial lighting is used. Due to the general sunlight patterns on Mars, the development of an artificial lighting system is appropriate because one will be required anyways to ensure continued flora growth. Other individuals believe that close proximity to sites of scientific interest is important; that belief may be important if individuals were not colonizing Mars, but instead simply traveling for the purpose of research, but in the case of colonization scientific study is far down the list of important considerations for the initial habitat.
While sites closer to the equator will foster external environments with greater temperatures and will reduce internal power requirements for heating, potential water availability decreases as the habitat moves away from the poles. Therefore, colony planners appear to have an energy-water tradeoff decision. Using small modular nuclear reactor(s) to power the colony, energy becomes much less of an issue versus water, thus with regards to this issue the initial colony should be situated closer to one of the poles. Humidity is also an important consideration for it will influence the rate of atmospheric water extraction as well as biological cooling within the contained environment of a space suit during external activities.
Another important factor is the frequency and intensity of dust storms. Dust storms have a higher probability of occurrence in the regions of Hellas, Noachis, Argyre and the Syria, Sinai and Solis Plani in the Southern Hemisphere and in the regions of Chryse-Acidalia, Isidis-Syris Major and Cerberus in the Northern Hemisphere.2,3,8 In general the greatest storm activity takes place between latitudes 20 S and 40 S.8,9 Therefore, based on storm activity potential a colony site in the Northern Hemisphere appears superior to the Southern Hemisphere.
Finally while a polar location appears superior to an equatorial location, a polar landing from Martian orbit is more difficult and offers fewer orbital support options. Therefore, test flights will have to generate an appropriate dynamic for landing successfully otherwise a more equatorial location may need to be selected by default to ensure the safety of the colonization crew. Also note that while targeting has improved from 62 by 174 miles (100 by 280 kilometers) for the 1976 Viking mission to just 4 by 12 miles (6 by 19 km) for the Curiosity rover,10 colonization may demand further improvement due to the limited ability to move the habitat after landing. Overall despite the landing concern the best surface colonization site appears to be near the pole on the Northern Hemisphere.
There are numerous types of habitat design, but with the advancement of plastics and deployment technologies, inflatable habitats seem to be the superior design type. The chief advantage of an inflatable habitat is high space to weight ratio. Increasing the amount of space available for the first habitat is obviously important for psychological and flexibility reasons without significantly increasing launch costs. Another advantage is the lack of complexity in the deployment and functionality for inflatables removing the possibility of requiring secondary structures within the habitat for structural support further reducing costs associated with excess weight despite the fact that various light-weight metals like aluminum would likely comprise these secondary structures.
The chief problem with an inflatable habitat is that it will more than likely provide significantly less radiation shielding either inherently or over time. For example one means to address this concern is to dope laminates into the plastics that makeup the habitat; laminates make excellent shields against debris and even radiation, but when they absorb energy they delaminate, which can create structural abnormalities that are difficult to identify and repair, thus making the doping risky.11 However, this radiation problem can be alleviated through augmenting radiation shielding with additional elements like regolith or human feces.
If an inflatable habitat is utilized space compression will allow for the implementation of a tiered system creating a 1st and 2nd floor. The figures below illustrate one possible layout that can be applied to these two floors incorporating the rooms discussed above.
Figure 1: First Floor of Possible Martian Colonization Habitat
Figure 2: Second Floor of Possible Martian Colonization Habitat
1 – Outer Hatch
2 – Grey Room/Airlock
3 – Inner Hatch
4 – Primary Life Support Area
5 – Infirmary
6 – Ladder to the 2nd Floor
7 – Secondary Sleeping Quarters
8 – Kitchen
9 – Water Storage
10 – Primary Food Growth Chamber
11 – Filtration/Secondary Life Support Area
12 – Machine Shop
13 – General Meeting and Group Planning Area
1 – Communication Room
2 – Refrigeration Storage
3 – Secondary Food Growth Chamber
4 – Ladder to the 1st Floor
5 – Meditation Room
6 – Sleeping Quarters
7 – Bathroom / Evacuation Area
8 – Research Area 1
9 – Research Area 2
There are two points of consideration for the above figures. First, there are no dimensions on the figures because creating dimensionality requires continuous hands-on experience and access to various habitat structures for testing, something that is not available to me, thus to apply dimensions in any real detail would be rather arbitrary. Second, lacking the dimension specifics may have created what some would argue is an unrealistic expectation to the “carrying capacity” of the habitat. However, the above figures represent elements that could be present in the habitat creating a debate forum between parties for a hierarchical classification of importance among these possibilities. One point of reference is that the Flashline Mars Arctic Research Station has an internal volume of approximately 416.6 m^3, which is a good starting point for debate, but realistically this is probably the minimum volume that should be used. Finally the lines in the figures do not represent physical barriers (walls), but instead are include as space demarcation elements.
One critical aspect of shelter design and operation that has been explored in simulation conditions is the organization and functionality of the crew.12,13 Due to the isolated nature of the crew and the proposed diversity of their assignments it seems important that there be a common area where group meetings could be conducted for debriefs and meals could be fixed and consumed to decompress and bond. Note that these meetings are not designed to be formal. The connections established and reinforced in these group activities will be important to reaffirm trust as well as reduce stress and simple errors during the course of the colonization. It is not surprising that trust is increased when people hear about other people doing a good job at their assigned tasks as well as discuss problem solving strategies with other colonists.12
This group meeting dynamic appears in some simulation environments, but is foregone in others for individual reporting to the commanding officer, a tactic that is less efficient. Overall consistency and casualness are key elements for developing psychological stability and normalcy for new Mars colonists. Also it would also be useful if the central area had a large message board, either a tablet computer or standard white board, that would be used as a display listing the planned activities for the given day and other important announcements.
Formal reports will be required on occasion, but should be limited to only scheduled reports, baring emergency, to limit unnecessary work and also limit stress. For example the only daily report would be the engineering check-in report, which would detail the technical status of all primary life support systems. Informal reports and briefings during meals should suffice for most of the day’s activity.
Expected formal weekly reports would entail:
- the Commander's check-in report (on crew’s overall health, performance and main habitat system status);
- science reports (experiments and preliminary results obtained);
- EVA reports (after each EVA: on duration, range, activity, results, interpretations, etc.);
- Commander’s future report detailing the necessary tasks to be undertaken over the next week;
As mentioned above initial colonization must focus on survival over science. Mars is not going anywhere nor is the environment going through a state of radical flux, therefore, holding off on scientific endeavors for at least six to nine months after landing is rational and appropriate. In fact the first three to four months after landing on Mars easily could involve doing very little “outside of colony work” for immediate tasks would involve required routine operational establishment, life support deployment, exercise, establishing a food growth system and allowing the body to acclimate to the ambient conditions of the Martian habitat including new levels of food and water consumption, which should be significantly diminished from those enjoyed on Earth. A secondary important task after landing would be establishing an autonomous security control system to track any potential external wall breaches and other problems with recycling or synthesis systems to reduce the amount of redundancy involved in colonists checking for these problems during the average day.
Obviously any habitat will require an area devoted to food growth. Numerous individuals envision constructing greenhouses inundated with natural light, but the viability of such a design is questionable. First, the use of natural light to cultivate flora is complicated by the longer Martian day and compounded with the reduced intensity of light exposure, which is approximately 48% versus that on Earth based on distance from the sun and thickness of the atmosphere. Therefore, there are longer consecutive periods of darkness and a longer, but weaker period of light. Some argue that there are numerous occasions of photosynthetic saturation on Earth for various plants, thus less intense natural light would act similar to more diffuse light and would not be a significant detriment to growing plants on Mars.14 Unfortunately light derived photosynthetic saturation is largely a product of long duration exposure to direct sunlight at optimal angles and is rarely a limiting factor to growth of plants on Earth and would be nearly irrelevant on Mars.
Instead of creating an exteriorized greenhouse environment to grow food, lighting can be provided through light emitting diodes (LEDs) at specific wavelengths to encourage growth. Some studies have been conducted regarding the potency of non-while light on planet growth finding that monochromatic red or blue, depending on the particular species, work the best.16-19 There are conflicting reports regarding the usefulness of exposure to monochromatic green light.20-22
The trickiest part to growing most food on Mars will be soil management. Unfortunately native Martian soil will be unable to reliably support food growth for years even after the initiation of a dedicated terraforming program. One solution is to transport soil from Earth to Mars and use that soil as a base inside the habitat (with appropriate temperature and pressure) for a food growth environment. The concern with this strategy, beyond cost, is the base construct of soil is more than just dirt and during the sojourn from Earth to Mars important organic compounds and supporting bacteria more than likely will be lost or altered in such a way that the soil is no longer useful. One potential means to circumvent this problem is cryogenically freezing important bacteria samples prior to takeoff and thawing them for soil insertion during the greenhouse seeding process.
Another popular solution is to forego soil use altogether and grow food through hydroponics. While hydroponics manages the soil concern of food growth on Mars it raises concerns regarding water use. Even with high rates of recycling, water scarcity will be an issue on Mars and growing food through hydroponics will place further stress on that scarcity. Also although soil is not used, a special nutrient mixture is required and it may be difficult to mass synthesize this mixture on Mars after the initial sample is consumed without having some base to work from that must either be created on Mars or sent from Earth.
Another option for food growth is aeroponic growth. Aeroponics attempts to optimize plant growth through the use of a pressurized water mist doped with nutrients sprayed on the entire exposed root system of the plant. One of the chief reasons aeroponics is successful is it does not require soil, which can provide growth inefficiencies due to poor drainage or lack of porosity limiting root aeration leading to reduced growth. NASA has even suggested that aeroponic-based food production through an ultrasonic technique will result in similar yields to conventional growth at 45% greater rates of growth despite using 99% less water and 50% fewer nutrients. However, this conclusion must be tempered with the fact that the comparison is more than likely (it is not really specified) being made against crops raised through flood irrigation and fertilizer saturation, two common yet incredibly inefficient agriculture techniques, thus the actual benefits of aeroponics over more responsible farming is more muted.
The most significant detriment to aeroponics in normal conditions is a higher probability of pathogenic death due to root exposure, but this concern is somewhat mitigated due to the natural aseptic environment on Mars limiting the absolute probability of exposure. Additional sanitary elements can be added to an aeroponics system to limit contamination from colonists. A secondary problem may be synthesis of additional nutrient compounds for the mist for traditional farming develops nutrients from organic compounds and bacteria.
Significant research has been conducted by NASA and other NASA sponsored outside researchers since the early 1990s resulting in several effective water droplet nebulizer technologies and a low mass polymer aeroponic apparatus.23 Some inflatable growth chambers have also been developed for flora growth in space. With that said some argue that a growing area is not necessary in a Martian habitat because aeroponic structures could be incorporated within various other parts of the habitat resulting in more efficient use of overall available space. While aeroponics is viewed by some as the future of food growth in space no serious long-term aeroponic experiments have been conducted in space, so most of the supposed benefits remain theoretical.
Random deployment of aeroponic systems throughout the habitat seems inefficient due to lighting condition confliction. Regardless of growth medium, plants will benefit from exposure to a different wavelength of light over standard white light. As noted above monochromatic blue and red lights have all demonstrated positive growth influences on plants and some positive results have been recorded for green, typically ordering from red to blue to green.20 Therefore, it stands to reason that all potential crops should be exposed to either a red or blue light source preferably from a LED. However, consistent exposure to red or blue light during wakeful hours could have a detrimental effect on the crew. Due to the possible lighting conflict as well as potential sanitation issues localization of food growth to isolated areas of the habitat principally responsible for food growth is advisable.
A problematic element surrounding potential aeroponic use in a Martian habitat is the lack of experimentation for such a system on Earth. Recall above that numerous “Martian Simulation” experiments have been conducted, but none have extensively utilized aeroponics in an isolated environment to support food production. If aeroponics is viewed as a valid option for providing food on Mars why have these simulation experiments failed to incorporate such a testable strategy?
Depending on the final strategy for food growth on Mars one idea for expanding stability and growth potential is to design a small indentation in the habitat that can be filled with water to develop a makeshift aquatic environment for raising fish and other life. While the specific details regarding what could be grown in such a pool will be left for another blog post two possible food candidates are loach and azolla because the azolla can fix nitrogen and suppress any weed growth while loach can survive in higher toxic environments (like high salt) with little detriment or consumption toxicity. Such a survival ability could be important because there will more than likely be periods where the water in this farming pool will be less than ideal and changing consistently it will be difficult to due higher priorities for water.
There are numerous questions associated with potential changes in sleep patterns on Mars. Astronauts on the International Space Station (ISS) use small-individualized compartments, similar to phone booths, to ensure personalization and space constriction. However, on the ISS the microgravity conditions allow these units to be vertical because with insignificant localized body forces the astronauts are able to sleep in any position without negative biological effects. On Mars gravity is only 1/3 that of Earth, but still significant enough that effective sleeping will more than likely require lying down. This requirement limits the usefulness of the phone booth designs utilized on the ISS. Two other options are ceiling/wall hammocks or using the floor of the inflatable habitat as an air mattress of sorts. While hammocks are viewed as a popular option there is a question of how much body, especially back, support they offer over the long-term. Thus, either long-term testing of hammock sleeping in a reduce gravity simulation environment (simulations typically utilize patients sleeping a an angled incline (30-45 degrees) has to be conducted or sleeping on the floor should be used due to uncertain safety concerns.
Another issue with sleep methodology is that experts acknowledge that sleeping environments must remain as homogenous as possible to increase probability of consistent high-quality sleep. Basically physiologically the body and mind must generate an understanding that this “area” of the environment is reserved for sleep not machine work, cooking, laboratory study, etc. Due to the shorter duration of stay (normally 3-9 months) on the ISS, astronauts can get away with more disrupted sleep patterns whereas colonizing Mars will demand a more stable sleep pattern, thus colonists should have some form of personalized sleeping quarters.
Sleeping quarters will need to have opaque shielding over the walls to eliminate any outside light sources, use LED lighting and will also more than likely have to be soundproofed in some manner because of the constant and excessive noise produced by the life support system. Not surprisingly colonists will sleep in shifts to ensure that multiple people are awake over a given time period to handle any emergency situations. Despite the planned shift sleeping the life support system will have a centralized yellow alert alarm that will act similar to a smoke detector when alerting colonists to a potential problem and a red alert alarm system that will act similar to a tornado siren to breach the soundproofing. In addition because of the soundproofing it may be beneficial to have a rudimentary intercom system between the main meeting area and the sleeping area.
As alluded to earlier there is the concern of noise pollution in the habitat, both during the day and night, due to the constant operation of the motors and pumps corresponding to life support function, other machine systems and in-situ processes. One possible strategy to deal with excess noise is to isolate the source limiting the resource and time requirements for soundproofing for all other necessary areas of the habitat. While this strategy could be effective, it typically does not consider the secondary redundant life support elements. Fortunately secondary life support elements should not be a large problem relative to noise production because they will only be on-line if the associated primary element is off-line. Also there will also be sources of external noise like dust storms, which will make soundproofing sleeping areas a high priority. Final designs will have to select between soundproofing the primary life support area, the sleeping area or both.
Whether or not private rooms will be made available or sleeping arrangements will be partnered to save space is a decision that will need to be made before the mission commences. A practical way to determine if partnering is a plausible idea is to have potential candidates sleep in the same room during isolation tests to determine whether specific sleeping habits are tolerable. If yes, then partnering is possible. Finally different forms of LED lighting could be incorporated to improve sleeping capacity and duration both during the process of falling asleep or/and during waking hours. Soft blue-enriched white light is thought to be the best option so far based on existing research.24
Another important element in habitat design that a number of people seem to neglect is whether or not to include a specific area for medical treatment. One response for this exclusion is that such a space is not necessary because there are only a limited number of medical conditions that could befall an individual on Mars versus Earth. For example the lack of pathogenic microorganisms nearly eliminates the possibility for infection (recall that all individuals and equipment will be sterilized prior to launch and the landing area should be thoroughly sterilized via UV bombardment). However, the reduced gravity will increase the probability of bone and muscle injuries due to apoptosis and bone degeneration. The additional demands of exercise could also increase the probability of muscle injury. It is difficult to apply experiences in exercise and the corresponding rate of injury potential from the ISS to Mars because of the difference in intensity of the exercise and the duration required due to length of stay. Therefore, it is unclear whether or not bone/muscle injuries can occur to such an extent that will require surgery (ACL tears, bicep tears, etc).
Without a prepared environment what will happen if someone needs an operation? Can another area of the habitat be prepared accordingly to create an appropriate operation theater? It is difficult to envision the creation of an appropriate area for surgical and other advanced medical procedures from the manipulation of another area largely because of the methodology in handling the blood and sterilization procedures required for successful surgical practice. Note that the probability of an individual sustaining an injury that requires surgery early in the colonization process is unlikely, but the probability of such an injury will increase with time. Therefore, the construction of an appropriate and stable location to conduct surgeries should be high on the priority list of habitat add-ons after initial deployment, but may not be required as a part of the initial habitat design.
The gray zone is the preparation area for EVA activities and separates the internal habitat from the external Martian environment (think of it as an expanded airlock space). Entry and exit will take place through pressurized hatches with the one leading to the surface of Mars denoted as the external hatch and the one leading to the internal habitat denoted as the internal hatch. There will be obvious safety precautions so that both hatches cannot be open at the same time (basically if one is open or opening the other cannot be opened) to ensure the purity of the internal atmospheric pressure by preventing disruption of the colony pressure, temperature and oxygen environments as well as the infiltration of dust that could damage instruments and other machinery. When designing this space the most important elements are airlock volume, airlock-suit interaction, power consumption, compression ratio, pump down rate and thermal cooling rate/method. Of course when the external hatch is opened there will be atmospheric mixing between the gray zone and the Martian atmosphere including the incursion of dust. To address dust in the gray zone a system of blowers will be used to transfer dust to a separate internalized compartment that can release the dust back into the Martian atmosphere.
There are numerous detrimental effects that afflict Earth-born humans in a significantly reduced gravity environment including, but not limited to: 1) Renal stone formation; 2) Diminished immune response; 3) accelerated bone and muscle loss; 4) changes to cardiac and vascular function and architecture.25 Clearly since Mars is a significantly reduced gravity environment these changes will afflict potential colonists although not at speeds equal to those experienced in space itself. One of the chief strategies for reducing the impact of these negative outcomes is a rigorous exercise program.
The lack of gravitational force near to what humans experienced during birth and early stages of development influences bone mineralization, reabsorption, matrix formation due to the lack of the “recognized” external body force that the bone structure developed around.26,27 These problems significantly increase the probability of osteoporosis. On the ISS force applied during foot exercises are dramatically reduced (25% for walking and 46% for running) versus the same exercises on Earth28 and one must expect a slightly reduced reduction on Mars. However, since these changes appear dependent on gravity, both from a standpoint of magnitude and direction, if muscle contractions are large enough intense exercise can act as an effective countermeasure.29,30
Exercise systems currently in use on the ISS are designed for saving space in that the equipment folds into the wall, similar to a Murphy bed, which is smart design. A similar design will need to be utilized for the Martian habitat as well, although a direct copy design could be difficult for an inflatable environment. However, the equipment should be upgraded to higher quality harness systems to increase musculo-skeletal loading. The loss of both slow twitch and fast twitch (type I and II respectively) muscle fibers, with slow twitch losses occurring much faster, demands more effective treadmill systems as well.31,32 In addition to treadmills, various resistance bands, at various levels of resistance, will be utilized as a light-weight, but effective means for tensile strength loading. A lingering question regarding exercise is whether or not a separate room should be reserved for this equipment versus incorporating it into another room?
Most would immediately answer that due to space considerations secondary incorporation would be a better choice over creating a specific space reserved for exercise. However, where would such incorporation take place? Clearly foldout equipment would need to be placed away from sleeping areas, life support, research areas, any areas designed for food growth and more than likely the communication areas (due to desires of privacy and quiet when talking with family, friends and associates on Earth). For most habitat designs this leaves the central meeting room, the gray area and the machining area.
The machining area may not be a practical decision because of necessary work on various tasks. Recall that each colonist will have to exercise a certain amount (usually 2-3 hours) per day to reduce detrimental effects from the limited gravity and it would not be advisable to skip specific sessions. The capriciousness of use for any type of machining or repair, its typical critical nature and unknown time allotment required for the repair will create situations of conflict with scheduled exercise times. The gray area suffers from a similar problem although EVAs can be scheduled creating less uncertainty in time confliction, thus this problem is not insurmountable. Fortunately the general meeting area does not have these types of problems and by default is the best place to incorporate the exercise equipment if it is not given its own area. This hybridization is rather easy to organize with appropriate scheduling assigning specific time to colonists and avoiding exercising during meal and meeting times.
One of the interesting debates concerning habitat development is how to address the psychology of living on Mars. Some believe that incorporating windows will be an important element to maintaining a healthy psychological makeup by providing a connection to the outside world.33,34 However, would such a strategy really provide said benefit for Martian colonists? Having a connection to the outside world/nature is only relevant when there is meaning behind that connection, i.e. when it provides inspiration or support. Any Martian colonists looking out a window will only see a barren rather monochromatic landscape unable to support life… how can such an experience provide benefit? There is also the belief that pictures of nature provide positive psychological benefits, which research supports.33 However, the research focused on individuals in isolation who would later leave that isolation, Martian colonists will not leave Mars, so would this reality lead to such pictures causing psychological detriment over benefit due to colonists lamenting about what they left behind?
Another strategy to produce a connection to nature could be a meditation room. One viewpoint towards food production, which will be expanded on in a later blog post, is for colonists to develop a simple aquatic farming system. The system would consist of a small pond with specific types of fish, algae and other simple life. Periodically this system would be farmed for food and could provide some rudimentary waste neutralization. In addition to providing food such a pond could act as a basis for a more Earth-like environment in the habitat. Some transported soil could be added to the pond environment to allow grass seeding, flowers and/or a very small garden as well as a pump system for the pond to produce a small waterfall (this could also provide better oxygenation of the pond itself); such features would produce an environment that would have a positive psychological effect on colonists.
In addition to providing a “little bit of Earth” on Mars, the room could provide a specific environment for individuals to regain focus and concentration after a bad day or persistent psychological deterioration due to task monotony. Such an environment would improve psychological, mental and physical health improving survival probability across the board. The space used for such an environment would not be significant in the habitat itself or could be “outsourced” to an externally constructed environment built after landing.
However, despite the outlined potential benefits of any of the above systems or others that were not mentioned, one could argue that these techniques to foster psychological benefits are superficial. They only provide benefit to the psychologically weak who are unable to cope with leaving Earth and settling on Mars. Pick the right colonists and adding such psychologically associated features would be a waste of time, space, resources and money. Whether or not this assessment is correct is debatable, thus leading to the aforementioned statement about the debate that will surround any psychological support elements being added to initial habitat design.
While one general goal of a colonization mission should be to mitigate as much critical communication between Earth and Mars as possible with the proper occupational and training selection of candidates, it will be important to design an effective facility to properly carry out interactions between Earth and Mars. The principle reason that one needs to limit critical communication is that there will be an 8-18 minute delay for radio communication depending on the proximity between Earth and Mars in their orbits.35 Video communication will be even longer, which will further limit the effectiveness of real-time support, thus colonists should have the experience and knowledge required to address situations that would have critical time constraints. This time delay also basically eliminates a practical Internet between Earth and Mars for it will take approximately 18-40 minutes to register a single mouse click.36 Cache storing is possible, but it will require a lot of additional work for little benefit.
However, communications between Mars and Earth will also involve non-critical information exchanges either on a professional level (official progress reports to a Mission Control-type organization) or causal/personal level (exchanges between colonists and family/friends). The feasibility and reliability of this communication will be based on two separate elements: inclusion of Ka-Band frequencies (18-40 GHz) relays and incorporation of new Mars-orbit satellite relays focusing on X-band frequencies (7-12.5 GHz).
A secondary important issue to judge communication between Mars and Earth apart from the time delay is the line of sight (LOS) problem where the Sun will produce significant levels of interference potentially eliminating most standard forms of communication for long periods of time. This problem will demand, but not require, modification of the Deep Space Network (DSN). One means for modification is launching numerous satellite relay points various Lagrangian Points. This modification can also provide an early warning system for various types of solar radiation. Unfortunately basic maintenance of the DSN has been generally deferred since the 1990s, thus it is questionable whether or not any improvements will ever be made.
The communication room could also double as a form of entertainment room with a large lightweight projector screen and two or three lightweight computer tablets. The tablets should be loaded with numerous different computer games from simple games like solitaire and scrabble to more complicated games like real-time or turn-based strategy games. The variety of games installed can be determined by gathering survey information from the colonists prior to takeoff. These games should be installed onto the computer so that they do not require Internet access because as mentioned above Internet connections on Mars are very improbable in the first few decades.
While research will be a secondary element in the primary stages of the colonization, it is practical to consider the design of scientific research areas in the habitat. The three most important research subjects on Mars will be biology, geology and chemistry, all requiring significantly different and sometime contrasting study environments. For example geologist will require low illumination and dust availability versus a particulate free and high illumination environment for biologist. Some of these elements are so contrasting that lab sharing is an unlikely solution. Also limiting the number of scientific tools could be a double-edged sword for fewer tools mean less clutter and maintenance, but would also demand more strict cooperation between researchers when using these tools. Overall it appears that research importance should trend from biology as the most important to chemistry then finally geology, so preparations should reflect this importance.
The first colony should have a rudimentary form of machine shop that can be used to facilitate repairs on damaged habitat features or EVA suit parts. For example EVA suits themselves will eventually become unusable, especially if exposed to additional impact damage produced during dust storms. How will damaged EVA suits be replaced? Expecting a “new” shipment from Earth is unrealistic, thus colonists will need to have materials and knowledge to make necessary repairs. However, there needs to be very strict coordination between Earth and the Mars colony regarding re-supply for EVA suits that sustain so much damage that they cannot be repaired. Also a machine shop should store the necessary tools to repair various habitat systems and life support elements.
In addition to the machine shop colonists must create an in-situ resource utilization (ISRU) processing area. Fortunately the major ISRU elements (water and oxygen) can be funneled through the life support system where other ISRU elements (various metals and building materials) can be synthesized in an area external to the primary habitat. Most previous Martian return mission or colonization plans have focused on ISRU to synthesize fuels, both for space travel and surface travel, over other elements. For a colonization mission using electrified modes of transportation with methanol as an emergency backup, there should be less focus on synthesizing fuel from ISRU processes. The need for producing fuel is also diminished in the interim of a colonization mission due to less need for scientific exploration. Instead the focus will be on producing complementary water, oxygen and additional masonry building materials.
Concerning ISRU processes one of the most common proposals for a Martian mission is to use electrolysis on available water, largely derived from settlement at one of the poles, to produce hydrogen and oxygen. While this strategy is used on the ISS, it has never made much sense on a long-term scale for Mars colonization because of the high value of water, the almost non-existent ability to re-supply from Earth and the limited benefit from the produced elements due to other existing synthesis strategies. Hydrogen has little value in initial habitat settlement of Mars. Some view hydrogen as a potential energy source through the use of fuel cells, but this idea makes little sense because there are numerous more efficient means to power the habitat and transportation vehicles, like small modular nuclear reactors, which eliminates the need for fuel cells.
Using hydrogen as a transportation fuel source is also contingent on vehicle design. Hydrogen synthesis is only relevant if methanol is going to be utilized as a transport fuel for rovers. The idea revolves around using electrolysis to create a feedstock of hydrogen for the Sabatier reaction to partially recover some water and produce methane, which is later converted to methanol. However, transport rovers that utilize electrical batteries can be used over hydrocarbon/methanol-based rovers. One could argue a concern about a loss of the battery crippling an electrical rover, but similar crippling events could also come from the loss of various other machine parts utilized by either hydrocarbon-based rovers or electrical rovers, thus the seriousness of such a concern is mitigated by the random fail probability that embodies it. The goal of designing a transport rover is simply to reduce this fail probability to as small a number as possible while maintaining efficient operation. Overall it seems more probable that running out of a methanol fuel would be more troublesome than having a battery malfunction in probability of occurrence. Without any use as a fuel, either for electricity or transportation, production of hydrogen derived from water electrolysis loses its principle purpose.
Oxygen is another product of electrolysis and is an essential element for survival. Unfortunately oxygen production through electrolysis is inefficient because it involves the consumption of another important resource. A secondary method for creating oxygen would involve simply splitting the abundant CO2 in the atmosphere into carbon and oxygen. Such a process will take large amount of energy, but fortunately this energy would be available from a small modular nuclear reactor for it will produce much more energy than the initial habitat will need to survive. Oxygen concentration can further be supplemented through plant and cyanobacteria photosynthesis. However, it is important to note that photosynthesis derived oxygen will more than likely not be sufficient alone. The above analysis has mitigated the importance of electrolysis for the express purpose of synthesizing hydrogen and oxygen, thus there is little point to utilizing it during the colonization of Mars.
Early in Martian mission designs there was the potential need for a cryogenic storage area to store methane, hydrogen and other gases that would be utilized as potential rocket fuel to coordinate a return mission back to Earth. For a colonization mission the importance of the cryogenic storage area is reduced, especially if transportation is electrified over hydrocarbon-based. Any synthesized and/or collected hydrogen will be almost instantly inserted into a Sabatier reaction bed for the purpose of synthesizing water. Methane and other hydrocarbon-based gases do not need to be stored for any legitimate purpose.
However, the colony must have some form of refrigeration capacity for storing food as the efficiencies of harvesting food will not be maximized to the point where there will be zero potential food waste without a refrigeration system. Refrigeration will also be needed to store medical samples and generate ice for dealing with minor injuries. Also it is important to note that water treatment and recycling systems will be mandatory for any habitat, but it must be acknowledged that the lower Martian gravity will increase the rate of time for particles to be taken out of suspension in the recycled water. Realistically this increased time should only significantly affect passive filtration systems, but dependence on active filtration systems will increase energy demands, thus simulations need to be run to determine which system should be incorporated for a given specific process.
An additional element that has been noted in simulations with habitat operation is that storage space is highly coveted for scientific samples from biological and geological study, scientific instruments and personal items.12,13 On Mars storage will not be such a large concern in the interim because there should be a very limited level of scientific exploration/analysis for the first several months. During the process of acclimation one goal may be the construction of an external storage “shed” type structure apart from the initial habitat to alleviate future storage stressors. Digitizing documents would also be standard, not only to save space, but simply due to a general lack of paper.
One potential problem with habitat construction could come from the electrically active atmosphere. While the nature of the concern is strictly theoretical due to a lack of Martian exploration and lack of electrical charging measurements, differential charging in relation to electrified dust (recall that regolith possesses iron oxides) could create electrical discharges between different objects that could damage electronics or interfere with communications at inopportune times.39
The internal habitat environment should have a single atmospheric pressure eliminating the need for internal airlocks ensuring a more simple and efficient build as well as easier travel within the habitat. Despite a single atmospheric pressure, internal gas partial pressures can be adjusted appropriately (CO2 dominating in greenhouse areas and O2 in other areas of the habitat).
All of the primary life support elements should be located within same general area with secondary redundant life support elements individually spread throughout the habitat in case something happens to the core area housing the primary life support elements. The equilibrium values that will be generated by the life support systems will be set prior to launch based on estimated necessities for survival. The ISS has demonstrated a good standing for most of the life support elements that will be utilized on Mars.
Another consideration regarding the placement of primary life support and even secondary life support units is addressing possible radio frequency and electrical magnetic field interference (RFI and EMI). Sufficient RFI will interfere with communications, which given the specific windows of operation for an early Martian colony losing communications with Earth could be crippling. EMI originate largely from power distribution systems due to their large currents and can have a devastating effect on microcircuitry. RFI shielding typically consists of metal membranes or foils whereas EMI neutralizing actually involves simple physical separation of generators and targets. Overall to avoid RFI communication systems should be within their own room and properly shielded.
Although it is a topic that is uncomfortable to discuss what happens if one of the colonists experiences a psychological break and becomes unstable and potentially homicidal? In this potential scenario there must be some form of security measures applied to protect the life support system from sabotage. However, this security must also be lenient enough that if a colonist perishes through non-malicious events that it does not prevent surviving colonists from accessing the life support systems when necessary.
One possibility would be to control the security system from Earth, but would the frequent communication blackouts that occur between Mars and Earth create life or death problems? Unfortunately this system is handicapped by the emergency situation during a communication blackout because any override system would defeat the main purpose of having security control on Earth in the first place. One possible way around this dilemma is to only have the emergency override active when the signal from Earth is down. A second security possibility is to require two positive voice and retina identifications to enter the life support chamber. It is highly unlikely that two individuals would experience psychological breaks at similar times and conspire together to eliminate the rest of the colonists.
There are two aspects of temperature control in a Martian habitat. First, there must be external thermal insulation and reflective foils to eliminate the colder influence of the outside environment, which will frequently be too cold for human survival outside a space suit. Second, there must be a form of internal thermal control to reject or reprocess waste heat to eliminate temperature spikes inside the habitat. This secondary element will normally be controlled by the life support system and there is less need for a secondary redundant system backup because if life support fails there will be bigger immediate concerns than additional waste heat in the habitat.
In additional to controlling temperature, internal moisture control also will be an important element. Increased water vapor will come from colonist perspiration and flora/fauna (depending on the type of insects and/or fish raised in the habitat). If not controlled the excess water vapor will condense on colder surfaces within the habitat. This water condensate will increase failure probability for microelectronics and increase oxidation rates for various metals and other composites. One method to address condensation would be to utilize atmospheric condensers or humidifiers to pull water from the air and water condensate from solids while remembering to strategically place these units away from areas with agents, which require water consumption. On a side note fire elimination will more than likely involve an extinguishing chemical versus water.
Concerning the layout of the habitat shown above in figures 1 and 2, placement of the infirmary on the first floor is entirely practical because most serious injuries will take place either during EVAs or when exercising (both activities occur on the “first” floor and moving these individuals up or down a ladder is unnecessary and could aggravate the injury. First floor placement also makes sense for the purpose of equipment transport. Some form of secondary sleeping quarters should also be made available on the first floor to accommodate injured individuals for it makes little sense to locate the infirmary on the first floor to limit unnecessary transportation to those suffering from certain injuries, but then expect those same individuals to engage in that transportation for the purpose of sleeping and rest.
Due to the heavier equipment that will be transported for the purpose of exercise placement of the exercise area on the first floor is appropriate for weight barring and some of the associated jarring movements, which will occur during exercise. Also as mentioned placement on the same floor as the infirmary is important to lessen injury in transportation. Locating the machine shop operation on the first floor also makes sense again for transportation reasons because most of the operations in this room will involve elements that either originate from outside the habitat (various gases and materials) or interacts with the ambient atmosphere (EVA suits).
The general design of the habitat is to concentrate most of the noise and work production on the first floor due to ease of movement and continuity. Therefore, with most of the habitat-produced noise taking place on the first floor it would make sense to locate the sleeping quarters on the second floor to limit noise infiltration. In addition the sleeping quarters should be placed as far away proximity wise from the primary life support system. In the figures the sleeping quarters are placed in close proximity to some of the secondary life support systems (located on the first floor), but it is more important to ensure a sufficient distance between the primary and the secondary life support systems versus distance between the secondary life support system and the sleeping quarters because in most situations, hopefully all situations, he secondary life support system should not be producing any noise, thus close proximity to the sleeping quarters will not be an issue.
The research area is placed on the second floor to reduce noise and foot traffic in efforts to improve efficiency. Transportation of exterior objects for study is less of an issue because objects will be smaller and lighter. The research area will also be split into multiple sections because as stated above different types of research will demand different types of environmental conditions that could contrast with each other.
Due to collision dynamics of dust and other particles in the atmosphere all organic matter would be best shielded by plastic with additional doped agents for radiation protection; however, structures that will not house organic matter for a long period of time or at all can be constructed from more traditional methods like bricks. Most early brick housing on Earth involved the use of adobe bricks, which are basically dried blocks of sand and/or clay. One of the chief advantages of adobe bricks if their high thermal mass, which provides resistance to rapid environmental temperature changes similar to those that occur on Mars between the day and night. However, unfortunately the Martian day is typically not warm like the Earth day (-50 C versus 10-30 C), thus the thermal properties of abode bricks to store heat with a slow release time has limited usefulness. Another concern with using bricks is the optimal process on Mars involves kiln-like treatment (very high temperatures usually stemming from a chemically generated fire in an oxygen rich atmosphere, i.e. vitrification). Despite the inability to benefit from its thermal properties and the extra processing steps, adobe brick construction is more than likely still the best method for early additional external construction.
Another method of building construction involves either rammed soil cement or cast soil cement. Rammed soil cement is a rather old and widely demonstrated technique that involves mimicking the natural process of sedimentation with soil mixing with water and cement before being shoveled into the proper shape. Applying a significant amount of force and tamping the mixture finish the brick.4 Cast soil cement uses a soil, water and gypsum slurry mixture that is used in wall molds and later dried.4 The gypsum mixture is used to stabilize the slurry. Unfortunately there are two problems with both of these synthesis techniques. First, both require the use of large amounts of water to create appropriate scale sized buildings and water is a pressing resource on Mars. Second, it would be difficult to create these bricks without extensive external work periods, which may not be appropriate in the current Mars environment. Water consumption is also a strong reason for the prohibition of concrete as a building material.
Processing raw materials on Mars for habitat augmentation will be an important element in increasing comfort and safety. The silicate, calcium oxide and other oxides (sodium and potassium) within the sand on Mars can be used to create glass (thermal fusion), but the iron oxide will have to be removed first otherwise the glass will become black glass, which has reduced strength and purity. However, the lower gravity will require a greater processing time during the molten stage to allow for complete bubble removal.38 Glass fibers can also be added to concrete and other building material to improve tensile strength.
The chief problem with glass is without augmentation from laminates the glass will more than likely be too brittle to stand against changes in pressure differentials, which could occur at any life support malfunction or hiccup.11 Basically if the glass is too brittle then if the pressure of the habitat changes in any significant manner the glass could break. However, the concern with laminate doping in glass, as mentioned above, is that laminate absorbs impact energy, which can lead to delaminating resulting in the increased probability of microfractures in the glass eliminating the advantage of the laminate doping in the first place and again these microfractures are difficult to identify without destroying part of the structure, which defeats the entire point of inspecting the structure.
The primary electrical components will range from macro-structures like high voltage and amperage breaker panels and transformers for power conditioning to micro-structures like microprocessors and transistors. Typical building codes for electrical systems should be applied where switch panels have unobstructed access within a secure unit, transformers exist outside the building to reduce fire probability and resultant damage and other major power conditioning equipment is separated from main living areas. “Cold plating” equipment (placing it outside the pressurized environment/habitat) is a debatable issue. Such a strategy is utilized for the International Space Station, but for a Martian colony placing necessary equipment in an isolated secured area of the habitat may be more appropriate because of greater lead times for EVA preparations between Mars and the ISS.
Finally one of the elements that some supporters seem to forget is that it is difficult to imagine a “cheap” Martian colonization mission because of necessary redundancy. With the element of uncertainty and the inability for rescue (remember that Biosphere 2 had numerous catastrophic failures that were remedied due to nearby support), redundancy is the key to increasing safety probability and generating a successful mission. Redundancy encompasses two features: “like redundancy” (multiple copies of the same element) and “unlike redundancy” (single copies of multiple elements that perform the same general function). For example at least two elements for each life support system should be included in the initial colonization habitat unit. Due to necessary redundancy, planning for a colonization mission to Mars must demand intelligent and practical decisions involving where to spend money without cutting corners. The real “cost prohibitive” aspect of a Martian mission would be to do it again because the first one failed due to not properly supplying the initial habitat. This reality is why strict scrutiny needs to be applied to all proposals, but especially those who expect to only spend 4-10 billion dollars on an initial Martian colonization mission.
Overall there are a number of issues that need to be addressed when designing and deploying a suitable habitat for Mars colonization and obviously that discussion must go into greater detail than this post. Some groups optimistically believe that a colonization mission could take place as early as 2020, but such a mindset is dangerous with the lack of long-term information that currently exists regarding habitat construction and functionality. While it is incredibly difficult to address all of the important issues on Earth due to the differences in gravity, one significant current concern is that most of these manageable issues are not being properly addressed in Earth based “Martian simulations”. It seems that most of these simulations are concerned with only addressing one or two elements, if any at all, which could be a mistake because results derived from these simulations may be significantly impacted by creating inappropriate control conditions, which will not be seen on Mars, especially in food supply/growth. Theory should always be addressed rationally; it would be very helpful for further consideration of Martian colonization strategies if simulation studies were designed to incorporate more Martian-like characteristics. Numerous questions still remain, but addressing these simulation issues would be a significant positive step in creating a more accurate simulation experience and developing better preparatory information concerning a Mars colonization mission.
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