Building with mars mud

[Ionmars]

Building with mars mud – 15 posts/14 sketches:

(1) What is mars mud? I use this term for a Mars ISRU building material consisting of a mixture of Mars  rocks, sand, water, and thickener. Its function would be similar to concrete as used on Earth, a product useful for laying a foundation or making natural marscrete building blocks. It would work well where the range of ground temperature is -30 to -80 C, but would fail miserably on Earth where subsurface temperature is mostly above 0 degrees C. Transforming mars mud into natural marscrete involves no chemical hardening to form a rock-like material; its ability to provide structural strength depends on the water component turning quickly into its solid state and remaining frozen at all times. This seems reasonable in Mars’ natural environment.

Mars mud is good for building foundations and for forming a GCR radiation shield (because it contains water).

[Ionmars]

(2) What type of building project on Mars would call for mars mud? The example I suggest here is using Starship hulls on Mars to set up an initial settlement. They would be employed as initial human habitats, greenhouse modules , machine shops; laboratory modules, and inter-module hallways.

In a recent reply to a query “Could Starship be used in horizontal position on Mars?” Elon replied “no.” Nevertheless, I believe SpX would evaluate the feasibility of any approach that might accelerate Mars development. In this thread I present a technique employing mars mud and careful handling of SS that might be feasible. (I am a late starter to this horizontal approach and only now do I believe it could be a desirable option.)

In the sketch below, 12 whole starships are laid together in horizontal position. This arrangement may be termed a high density neighborhood, an approach  that follows from the thread “Modular Mars.” The advantages are  (a) it facilitates covering the whole community with a  blanket of protective regolith, (b) it enhances inter-module mobility and communications, and (c) it reduces the volume of regolith-derived material required to provide protective covering for residents during the early phase of settlement.

Note 1. I assume the area where a neighborhood is planned would be cleared of rocks and made level in advance. Ground could be leveled either one space at a time or for the whole neighborhood at once.

Note 2: Color-coded images of individual starships were copied from Brendan 8-7-30, SpaceX prototypes, Thread 11.

[Ionmars]

(3) Employing Starships in horizontal position requires delicate handling to compensate for SS not being designed for horizontal positioning. First, ships need to be fully pressurized to withstand Mars gravity and other forces that would tend to collapse it. Second, a special harness is required to hold SS in position while installation proceeds.

The sketch below shows strong points in the SS hull that could be utilized as primary points of support.  They would be supplemented with additional supports at other locations along the hull. Strong points occur where the thrust puck, the middle dome, and the upper dome are welded to the hull, which are the only locations (AFAIK) where structural elements extend across the middle of the propellant tanks. In addition, I assume (speculate) one or more structural elements in the crew or cargo section would also extend across the diameter of the ship; for example, a circular floor extending across the crew section.

[Ionmars]

(4)  The sketch below shows a metal lifting beam (upside down T) resting along the upper surface of SS. Flexible straps pass though openings in the beam and encircle the ship. A ratchet latch on each strap enables it to be tightened around SS circumference and locked in place. Four of these straps are positioned over the four strong points and additional straps are positioned at selected locations between the four straps and at the ends of the ship.

The actual locations of straps would be determined by analyzing  weight distribution along the length of the ship. A margin of support would be calculated such that any one strap could be removed and the remaining straps would easily hold the ship in place.

When all straps are locked in place, the lifting beam with  SS attached can be lifted by a crane and the spatial  position of SS adjusted accurately. (Crane not shown in the sketch.)

[Ionmars]

(5)  To begin installation, SS would be held about 25 cm above its pre-selected location over cleared level ground. The sketch below is a side view of a part of the hull held in place by one strap at a strong point on the left and two supplemental straps. An initial pile of warm mars mud is squirted, pushed, or emplaced under the hull at its lowest point near the ground. It lies close to the strap at a strong point, but does not touch it.  After a few minutes pf contact with extremely cold ground, it solidifies into icy natural marscrete.

The mud must not touch the strap because it would freeze to it and render the strap unmovable.

[Ionmars]

(6) The next step is to remove the first supplemental strap. This is done by unlatching it and pulling it through the T-beam to one side of the ship. (The strap would be reused for the next SS to be installed.) Then the initial mud pile is extended toward the next strap by shooting in more mud, but stopping short of the strap. When the extended mud pile hardens, it would be capable of supporting SS in the space previously held up by a strap. It would exert a small force against the SS hull because of 10% expansion of freezing water.

[Ionmars]

(7) The sketch below shows extended frozen mud piles between all four strong point straps and both ends of the ship. Supplemental straps have been replaced by frozen mud piles to temporarily support SS.

Note that the area at the lower crew section has less mud applied so as to leave room for crew to attach an inter-vessel interface ring. (Interface rings would join together adjacent Starships and create a hallway extending through the entire 12-vessel neighborhood.)

[Ionmars]

(eight) A cross section end view shows frozen mud piles that support sections of SS. Note that piles of dry regolith were placed beside the mud piles to restrain the horizontal movement of unfrozen mud. This is a conservation measure to limit the use of washed Mars mud, which is a relatively expensive material compared to raw untreated regolith. (Washed mud is composed of regolith components that have been flooded with water to dissolve and remove perchlorates that potentially could react with the steel hull of SS.)

[Ionmars]

(9) (Combined with #7 - Skip to #10.)

[Ionmars]

(10) End view of one ship and the side view one interface ring attached (welded) to it. This particular ring is 6.5m in diameter and will support a large portal 5m x 5m and its door frame. The corresponding hallway running through each ring would also be 5m. Other ring sizes could be smaller, supporting a hallway width as narrow as 2.5m, depending on the size of material  planned to pass through. Each ring is fashioned from the skirt of one ship by reducing its diameter to the specified size and cutting curves to match the curvature of the SS hull.

[Ionmars]

(11) This sketch indicates how an interface ring joins two adjacent ships lying side-by-side. Frozen mud piles support the underside of each ship.

[Ionmars]

(12)  At this point we fulfill the second purpose of building with mars mud, namely to enclose each SS in an “igloo” arch. The first two SS are completely enclosed inside a hardened water-rich shell capable of protecting residents from GCR radiation and small meteorites. Two meters of frozen mud over the top surface of each SS with an additional 1-2m layer of raw regolith should provide sufficient  compressive strength to allow modest-sized construction equipment to pass overhead to finish covering all ships comprising the neighborhood.

Added: To clarify, when shooting mars mud around the hull, I have in mind very thin layers. For the first layer over the top of SS I think 25cm should be sufficient. Although SS is under pressure (tension) ISTM desirable to minimize compressive force on the hull. When this first layer freezes, it needs enough strength to hold the second layer, perhaps 50 cm. Each successive layer builds up the strength of the arch over SS until it can support the weight of equipment overhead, perhaps 3 to 4 m in total.

[Ionmars]

(13) End view of ramp building in layers. Allow each application of mud to harden and expand before the next layer is applied. For laying untreated regolith, the accumulated depth would be  the depth required to support equipment passing overhead at any one time.

[Ionmars]

(14) Once the ramp is built, mud delivery equipment (concrete truck and small pump) could shoot mud from a the top of the row of SSs down along the sides of each vehicle; it would be an efficient procedure utilizing moderate sized construction equipment during the early settlement phase. Laying down protective top layers could proceed in priority order: (a) 2-4m thick pathway over the hallway to gain access to all ships; (b) crew section because they already have some rad protection and additional cover will make them habitable long-term; (c) CH4 tanks because they just need rad protection to become pressurized humanity nodules; (d) Lox tanks are last because they require extra work inside to make them habitable. (CH4 header tank, downcomer, and multiple plumbing lines need to be closed off or repurposed.)

In an initial settlement period, establishing  a neighborhood using moderate sized bulldozers, dump trucks, tampers, and cranes might take the best part of one synod. Later, larger equipment could accelerate the process.

[Ionmars]

(15) After all 12 ships are installed and covered, we will have created a 55 x 110m flat area atop the neighborhood. Can’t be a landing pad and probably not another neighborhood, so perhaps a solar farm.

[Ionmars]

(Continued)
Terms I used in this thread:

Mars mud: a mixture of sand, rocks or gravel, thickener, and liquid water.
Washed mars mud: mars mud ingredients that have been flushed with water to remove soluble perchlorates.
Natural marscrete: mars mud frozen solid.
Thickener: an ingredient to keep water suspended in mars mud while it is freezing.
Mars mud truck: a vehicle that can mix ingredients and deliver mud to a work site; analogous to a concrete truck on Earth.
Mars mud pump: a device to pump mars mud through a hose to a selected location; analogous to a concrete pump.

[Ionmars]

(Continued: water ingredient)
Some experiments would be required to find the best combination of ingredients for mars mud. For example, physical characteristics of rocks and regolith will vary from place to place and the  best percentage of water ingredient will probably also vary. But concrete on Earth usually contains 15 to 20 percent water and may be good for a first experiment.

[Ionmars]

(Continued: thickener)
I speculate that water in a mixture of sand and gravel will tend to fall through the mixture and accumulate at the bottom of a container. To keep water suspended for a few minutes while freezing takes place, a thickener may be added to the mixture. On Earth, a concrete mixture with excess water may be thickened with hydroxy-propyl-methyl cellulose (HPMC). However, Mars’ atmosphere contains molecule-sized particles of iron oxide and other particulates not found on Earth at this microscopic size. This dust is so exceedingly fine that it might serve as a thickener for mars mud; It could possibly fill the interstices between larger particles and help hold them together.

Mars atmospheric particles could be captured during a process carried out for other purposes. For example, when atmospheric CO2 is utilized for industrial or greenhouse applications, it needs to be cleaned of dust particles that could foul equipment or harm people. This could be accomplished in a settling chamber where natural wind speed is slowed to a low velocity that allows it to settle out. Another process could be an electrostatic precipitator where dust accumulates on electrified wires. Fine dust could be collected in bags and added to a batch of  mars mud.

Before Mars particulates can be tested as a thickener, it may be necessary to import HPMC from Earth for this purpose.

Update 9-17-20: In Reply #74, Slarty1080 presented an article reporting experiments showing that atmospheric particles could indeed serve as a binding agent in making mars blocks from regolith. Implicitly, it would serve as a binder/thickener in mars mud.

[Ionmars]

(Continued: mud truck)

To save on mass delivered to Mars, a Mars mud truck could serve two functions. The first function would be mud delivery and the second would be mixing the ingredients. Sometimes a concrete truck on Earth is used to mix ingredients inside the concrete mixing chamber while the truck is moving. In some concrete truck designs a spiral rotating blade inside the concrete chamber does the mixing.

For mixing mars mud, a rotating blade mixing chamber would be heated continuously, perhaps with methalox burners, to maintain the water ingredient in liquid state. In addition, the chamber would be pressurized to prevent instantaneous sublimation. To further reduce sublimation, warm mud  would be quickly transferred to the mud pump and applied as soon as possible. The long tube conveying mud to its intended location would also be heated to prevent premature freezing. Sublimation from the mud pile should cool the surface rapidly so that a frozen crust would form before the interior of the mud pile is frozen. Further freezing should proceed from the ultra-cold ground upwards, within minutes.

Two images below show (1) components of a mixing concrete truck and (2) a concrete truck combined with a concrete pump.

[Pete]

A couple of questions:
* What are the structural characteristics of frozen Mars Mud? Tensile and compressive strength, brittleness, thermal conductivity etc...
  Please compare to the characteristics of alternates, such as Sintered Regolith, Sulfur-Regolith composite, etc.

* Why build a bunch of Starships specifically so they can land *and return*, then bury them in the ground.

* Does Stainless Steel make a good structural material for the resultant building you are constructing?
  Specifically, what benefit does it provide over an inflated pressure vessel of similar dimensions but 1/20th the mass?
  The Starship will provide *very poor* lateral strength against buckling without the addition of more structural supports, which could be used in the same role for other structures of similar dimensions.
 
* Is it better to use the whole, virtually intact Starship for structure, or better to ship more specialized construction tools and materials?