Flex House

By IonMars

10-15-2014

When I was 11 years old the Boy Scouts of America was a challenging organization where community volunteers worked together to create healthy outdoor experiences for boys. In those days I eagerly participated in camping trips and voraciously read the field manuals on my own volition. I became enamored with the idea of becoming a capable survivalist who could live off the land with nothing but his own skills and a good knife.

Boy ScoutsI never quite realized my own lofty goals of free-living as I found that my frail body needed lots of well-made clothing and my skills weren’t quite equal to the task of fire making without matches. So I accepted tents, sleeping bags and canned foods out of practicality, but in my heart I knew I was cheating.

And so it is with surviving on Mars. I set out with high goals of applying in-situ resource utilization (ISRU) procedures on the vey first steps off the Mars Colonial Transporter. In version 1 of “Pioneer House Building” I described how we would immediately set out to cut basaltic stone into building blocks and how we would use those blocks to build a standard house employing a temporary scaffold. Mortar wouldn’t work because rapid volatilization would prevent any water-based cementicious product from curing, so we would sinter the edges of stone blocks together using a methane torch. I took a step back when I realized that sintering the edges of blocks by heat treatment might be difficult to achieve without cracking some of the stones. The problem could be ameliorated but the solution was unproven.

I searched for a company that distributes a product that could substitute for mortar on a Mars construction site. Finally a few companies heard my call and offered epoxy resins that could function under conditions of near-zero atmospheric pressure. After examining the product specifications I devised new procedures for building the same Mars house using these resins.  The products required curing for the best part of a day at a temperature range of 65 to 122 degrees F. This would take place on a planet where nighttime temperatures plunge to -80 degrees C or lower, which meant that extreme measures would be required to maintain the surface temperature of the stone blocks during the curing period. These measures would include warming the blocks in an oven before stacking them onto a house wall and laying a heating blanket over the blocks during curing. These procedures were difficult to carry out and still required some additional equipment.

Like a practical-minded Boy Scout I came to acknowledge that it might be prudent to dodge the complexities of building a house out of ISRU materials until new techniques can be tested or until the colony is well established,.  A more widely accepted idea for Mars construction is that of hauling all house-making materials from Earth on the first few colonizing trips. This alternative is anathema to a thrift-minded individual because it adds billions of dollars in extra hauling costs.  Building with ISRU might be delayed unless we can devise and test on Earth the ISRU construction techniqes like sintering so we can be certain of performing the procedures properly on the first attempt. However, when I pursue non-ISRU approaches I know in my heart that I will be cheating,

 

A Flexible House Plan

 A flexible Mars house will provide a simple house plan that can be adapted to many circumstances. It could be built in the first stage of colony development using construction materials from Earth. Some alternative Earth materials are carbon steel, aluminum, aluminum alloys, plastics, or composites. Some of these construction materials could also be produced at a later date on Mars, but the earliest and easiest to produce may be meteoric iron–nickel alloy. If we find that this alloy is not suitable, then carbon steel from magnetite or hematite, or plastics mined and processed on Mars may also be employed. The detailed engineering plans will be modified to reflect the chosen material.

Regardless of which materials are used, which techniques are employed, or when construction occurs in the development of a colony, all Mars Flex houses will follow certain design principles to address common problems to be found on Mars, as follows:

  1. All the Flex houses will adopt the Roman arched roof, as shown in Mars houses in other articles to date. This design feature provides the compressive strength needed during construction.  When well-sealed it also provides the tensile strength to withstand interior air pressure when colonists live in the house.
  2. All Flex houses will be covered by a protective layer of regolith, currently set at a depth of 2-1/2 meters over the ceiling.
  3. All Flex houses will feature vertical sidewalls that provide efficient use of floor space by people. This assumes that regolith piled along the exterior of the sidewalls will be stacked as high as the walls and extend at least 5 meters in the horizontal direction.
  4. All Flex houses will use structural ribs, namely, joists, studs and rafters and will be covered by sheets of material. (Houses constructed of stone blocks or bricks will comprise a separate class of houses.)
  5. All Flex houses will employ a double shell construction to address the potential problems of cold walls and condensation.

The problem of cold walls will become particularly poignant on Mars. Nighttime temperatures on the surface will plunge to temperatures of -80 to as low as

Temp Gun-120 Degrees C and the planet subsurface will maintain a low temperature continuously.  A house built of any material will lie in direct contact with a very cold surface. Materials of high thermal conductivity, such as aluminum, iron or steel will more readily transfer low temperatures to the interior of the habitat (or conduct heat away from the interior). The first concern will be that someone would inadvertently touch with bare hand a surface that is at a dangerously cold.  A badly burned hand could result; in a worse case moisture from a body part could freeze instantly and glue the person to the surface.

In an environment where low temperature cannot be easily noticed or avoided, an instrument that can detect extreme low temperature without touching a surface will be a handy tool to have on hand. One example of such a tool is the industrial infrared thermometer (IR gun) produced by ThermoWorks Company. Model IR-GUN-S is shown in the picture; it operates by pointing and shooting at an object to instantly read its surface temperature at a safe distance. One can also scan across a wall surface looking for a preset low temperature that will sound an alarm1.

 

Mold Prevention

A second concern is that cold walls in proximity to warm moist indoor air could produce condensation or even frost on the wall surface. Condensation, if not controlled, is likely to lead to the growth of mold colonies. Mold is a form of fungus that thrives in wet, damp or humid environments. There are over a thousand different varieties of indoor mold, and the presence of a moderate amount of mold is not harmful. Most health problems arise only when there is a build-up of high mold concentrations.

Mold spreads by generating spores that are able to survive for long periods even in harsh, dry environments, such as the interior of a Mars Colony Transporter. A person can smell mold spores in an old car when the heating system is first started up after an off-season of disuse. Some mold is prevalent everywhere all the time, so attempting to make an Earth home or Mars home totally mold-free will be nearly impossible, but high concentrations can be averted2.

Fungi Growth
One species of toxicogenic mold is Stachybotrys chartarum or Stachybotrys atra, popularly known as "black mold." It is a greenish-black fungus that requires a moist environment in which to grow such as flood-damaged buildings. Its mycotoxins are potent, but only a few strains of are toxigenic3.

A second type of toxic mold is Aspergillis, a family of molds. The mycotoxins produced by toxigenic strains of Aspergillis are less potent than stachybotrys, but infestations of Aspergillis mold are more common. Aspergillis may be found in any mold-friendly environment such as surface condensation.

To prevent colonies of mold from growing in Mars houses we must prevent condensation from forming on the walls. We will design the Flex House to meet this objective. We will implement a system of ventilation that will blow warm air across the walls, which is analogous to a car’s defroster system blowing air across the windshield. It will feature a double shell that comprises all exterior parts: the floor, walls and ceiling of the habitat. The outer shell will be in contact with the regolith that surrounds the habitat on all sides and the inner shell will be 10 to 15 cm from the outer wall except where it is attached to the structural ribs between the two shells. Warm air will be continuously blown between the two shells to heat the outer wall to a temperature that is between the inside and outside temperatures. The inside shell will provide a more temperate surface that is human-friendly.

The drawing below shows the end view of a Flex house, revealing the circulation pattern of warm air between the inner and outer shells. The main distribution duct is built into the floor and air from this duct flows under the floor to the sidewalls, continues up the walls, across the arched ceiling and into a return air duct. We will not expect condensation to form under the warm floor, however, the air will cool down as it flows around the cold external shell. If any condensation were to form in the inter-shell spaces in the ceiling, then we will increase the thermostat setting, or if necessary, install heating devices such as electric heaters between the shells comprising the walls and ceiling.

 Air Circulation

In this example the Flex house will be constructed from I-beams and sheets made of carbon steel and imported from Earth. High quality steel may compete with aluminum because its greater weight may be compensated by its higher strength so that structural elements may be smaller and thinner. By efficient design of theses structural elements we will realize additional savings in materials to be imported from Earth. 

The drawing below shows a plan view of the below-floor airflow and ductwork. No additional materials are employed for ductwork because the spaces between the floor joists (I-beams) will serve a second purpose as ductwork. The floor joists (side-to-side beams) will terminate near the middle of the house. This will leave a long space from one end of the house to the other that will comprise the main air Flex House Airflowdistribution duct. The sides of the main duct will consist of additional length-wise beams that are welded to each of the lateral floor joists.

As shown in the drawing, the heating and air conditioning system (HVAC) will be located on one end of the house. (On Mars the HVAC system will be combined with a Life Support System [LSS].) A large blower will push heated air from this system into the main duct. As the air passes down the duct it will enter each of the between-joist side ducts by means of holes cut into the metal sides of the main duct. These holes will increase in number and size as air flowing down the main duct loses its pressure. The total area of the holes will be calibrated to allow the same volume of air to pass into each of the side ducts regardless of reduced air pressure. (See the drawing of under-floor ventilation.)

The heated air will flow from the main duct through the side ducts, then up the walls through the space between steel wall studs that align with the floor joists. The air will then flow through ceiling ducts formed by steel rafters that align with the wall studs. The air will exit into a large return air duct in the ceiling as shown in the previous end view of Flex house airflow. The main return air duct will run the full length of the house and return to the HVAC system. 

 

Under Floor VentilationAs heated air circulates from the floor up the walls and across the ceiling it will be cooled continuously by the cold outside shell as well as warming it. Additional heaters may be installed in the inter-shell spaces in walls and ceiling to maintain a temperature high enough to prevent condensation

Another function of the circulating air will be to help maintain a comfortable temperature for inhabitants inside the inner shell. The warm inner floors and wall will warm the house interior by convection, but additional electrical heaters may be required in cool spots.  

Note that the inner shell of the house should be comprised of a series of panels that cover the spaces between beams. The panels should be attached to the beams with screws or bolts so that they may be removed for occasional inspections and repairs.

 

House Sizes and Usage

 

Three Sizes of FLex House
Besides flexibility in the choice of building materials and the source of those materials, colonists may choose among many sizes of house to be constructed. The drawing below shows three sizes that will be appropriate for a start-up Mars colony. The base number indicates the interior width of each house in meters.

Flex House Layout The first size, 80 m2 (861 ft2), is comparable to a city apartment on Earth. It is the size that was used in the example above concerning air circulation and is the same size as the house featured in the articles “Pioneer House Building” Versions 1 and 1.1 that was constructed from basaltic stone blocks (not a Flex houses). An example of how the floor area could be used was given in those articles.  

The second (Base 6) house size contains 300 m2 (3220 ft2) of living space and is comparable to a suburban house on Earth. It is a little longer and wider than the apartment and features two stories that double the area.  It also features an attic for storage or for HVAC equipment that is not counted in the floor space.

The third (Base 8) apartment house contains 720 m2 (7750 ft2) of living space. It is comparable to a small apartment building on Earth. It is a little longer and wider than the Base 6 house size and features three floors of living area. The attic is not counted as living area but could be used for storage, HVAC equipment, or additional living space. While the larger houses expand the living area considerably for a small colony, they also greatly increase the materials that must be imported from Earth. Once the Mars steel industry is established this will be much less of an issue.

The adjacent drawing presents an example of a Base 6 House floor plan. It shows how it could be designed and the space on the first floor utilized. This is a scaled drawing where each square represents one meter. Double shell construction is indicated by the two notes in bedroom 3 (BA3) that label the inside of the wall as the interior shell and the outside of the wall as the exterior shell. (The space between shells is not explicitly shown.) In this example the total wall thickness is 12 cm, which includes the thickness of each shell and the space between them.

A central hallway runs the full length of the house. One side of the hallway is a structural wall to support the cross beams running from one sidewall to the center. These beams will serve as floor joists for the floor above.

The two rooms on one end of the house (EVA1 and EVA2) are for entering and exiting the habitat. EVA1 is for the use of a colonist in a spacesuit who requires a completely airtight room separate from the rest of the house. This room is a depressurization chamber with its own ECLSS system so that the air pressure and oxygen levels can be controlled as the colonist goes through his depressurization drill. This drill is required to accommodate him to the spacesuit pressure and O2 level as opposed to the levels in the habitat. Room EVA2 is for a colonist who will employ a Mars EVA Vehicle (MEV) during his time on the surface. The MEV may be a truck or a utility vehicle with a side access hatch. The MEV and the habitat will employ the same air pressure and O2 levels so no depressurization drill and no special room is required. The box attached to the room is a flexible crawlway from the house to the vehicle. It  features a hatch/doorway that attaches firmly and airtight to the vehicle. 

The main hallway runs from the EVA rooms through the entire house to the “back door,” which exits into a hallway intersection module. (See “Pioneer Hose Building” for a description of basic features like a hallway intersection.) The hallway lies directly over the main air distribution duct, which can be accessed by means of removable floor panels. 

NASA Control
On one side of the hallway are four bedrooms (BR1 - BR4) equipped with bunk beds and cabinets for clothes and personal items. On the opposite side of the hallway are a storage room and a lounge equipped with a kitchenette. The lavatory is equipped with four toilets, four showers, two double washbasins, two washers and two dryers. In this example 12 colonists are provided with relatively comfortable surroundings, better than a submarine.  

The one workroom is a robot remote control center. Colonists will use this facility to control the robots operating on the surface. The robotics operators will deliver orders to the robots using radio signals from computers or utilize remote telemanipulators. They will receive orders from a MEV driver on the surface who is the construction Supervisor. Robots will perform many tasks on Mars’ surface so as to reduce the exposure of humans to GCR, micrometeorites, extreme cold, and extreme low air pressure. It will not be necessary for humans to perform all of the construction tasks, but they will need to supervise operations and perform any unexpected procedures that the robots are not designed to implement. 

Next to the robot control room is a stairway leading up to the second floor. It may be similar to the first floor but could also be dedicated to more commodious living spaces, perhaps for more senior personnel. Likewise, the attic space may be used entirely for equipment or could be designed to meet the floor space requirements of the head of the colony. About 25 people will likely live in a Base 6 house.

 

Summary

In this article IonMars shares personal thoughts from his Boy Scout youth that if you are not using ISRU at the beginning of Mars colonization you are “cheating.” Nevertheless, a flexible house plan (Flex house) will be constructed from materials imported from Earth or materials produced on Mars after industries have been established. Each Flex house will exhibit an arched roof covered by regolith. It will have vertical sidewalls and will feature double shell construction. Air will circulate between the shells to prevent condensation, which in turn will prevent mold colonies from forming. The structural elements of floor joists, wall studs, and ceiling rafters will be placed in alignment so as to facilitate air circulation around the house. Three practical sizes of houses will be 6, 8, and 10 meters wide and feature 1, 2 or 3 floors. An example floor plan exhibits amenities for 12 persons living in a compact space. Robot operators will utilize one room where they will control the robots operating on the surface.

 

References 

  1. “Industrial Infrared Thermometer” (Undated) ThermoWorks, Retrieved 9-28-2014 from http://www.thermoworks.com/products/ir/ 
  2. “Toxic Mold Basics” (undated) , Legal Encyclopedia, Retrieved 9-28-2014 from  http://www.nolo.com/legal-encyclopedia/toxic-mold-basics-29685.html
  3. B. D. Nelson. (2001) “Stachybotrys chartarum: The Toxic Indoor Mold,” The American Phytopathological Society. Retrieved 9-28-2014 from http://www.apsnet.org/publications/apsnetfeatures/Pages/Stachybotrys.aspx