Suspension Bridge Martian City Roof Design

tahanson43206 · 2025-11-10 19:12:43

This post is inspired by a vision of Calliban for open air cityscapes that look like Amsterdam.

This vision depends upon the presence of a roof so far above the street level that LED lighting systems can create a plausible simulation of Earthly blue sky and clouds moving slowly across the scene.

This topic is available for NewMars members who might wish to add link, images or text about how this concept might be implemented on Mars, and how life in such an environment might look, sound and feel.

(th)

tahanson43206 · 2025-11-10 19:13:33

This post is reserved for an index to posts that may be contributed by NewMars members.

Index:

Post #3: Image of the longest suspension bridge on Earth.
Post #4: Calliban on basalt
Post #6: Calliban sketch's of suspension dome
Post #5: kbd512 with images of cast/worked basalt objects plus discussion
https://newmars.com/forums/viewtopic.ph … 32#p235432

(th)

tahanson43206 · 2025-11-10 19:17:12

This post shows a suspension bridge between Europe and Asia at Turkey.

The central span is over a mile long (2 kilometers). That is on Earth! The same span would be easier to achieve on Mars.

A requirement is for the roof to be overlaid with regolith to counter 1/2 bar atmospheric pressure inside the habitat, and to provide radiation protection.

The underside of the roof would be fitted with LED lighting systems to simulate blue sky and clouds moving as they might appear on Earth.

Such a roof could easily simulate the dark sky scene, with every sun, planet, galaxy and other visible object.

images?q=tbn:ANd9GcSJAblWlYId6pJcQ5t1uuf9qKVNy7urtzdWde8APSWSzQ&s

(th)

Calliban · 2025-11-11 17:59:45

tahanson43206 wrote:

For Calliban re new Suspended Roof topic...
https://newmars.com/forums/viewtopic.php?id=11235
Of all our members, it seems to me you may be best qualified to add substance to this new topic.
I am hoping your previous work on cast iron would extend to this structure.
It seems likely you would need stronger material for the cables, and that would require energy, but a city like this is going to happen only if there is sufficient energy available to splurge on metalurgy. Assuming you have enough energy, am i correct in thinking a city scape using suspended roofing with regolith cover for pressure balance and radiation protection would make sense?
The alternative is to dig underground, and it seems to me that unless huge natural cavities are found, it would ** always ** take more energy for excavation than would be required for the suspended roof concept.
(th)

One material that we have examined in the past is cast basalt. This has compressive strength of 300-500MPa. This is about the same as the tensile strength of low alloy steel. From the data in the attached article, I estimate that between 1.5-2MJ of heat are needed to transform 1kg basalt from a room temperature solid to a castable liquid. Basalt has density 3t/m3, whereas low alloy steel is 7.8t/m3.
http://www.rmag.soil.msu.ru/articles/478.pdf

Low alloy steel has an energy cost of about 30MJ/kg if produced from ore rather than recycled metal. On Mars, it will all be produced from ore for a long time to come. This means that 1 cubic metre of cast basalt has about 2.5% of the energy cost of the equivelant volume of steel. We also need a lot less equipment to produce cast basalt. An electrically heated furnace and a set of moulds to cast the ceramic members.

Cast basalt tiles could then be glued together using a thin film of epoxy resin to produce a tibrel vaulted roof. If the tiles are polished after casting, then the epoxy film could be as thin as 0.1mm thick. The vault would then be covered in a thick berm of compressed graded regolith.

Last edited by Calliban (2025-11-11 18:26:50)

tahanson43206 · 2025-11-11 18:35:13

For Calliban re cast basalt as a building material. In the context of a Suspended Roof system for Mars (as distinct from a roof that depends upon support from below such as a tibrel vaulted roof), would cast basalt have the strength needed to support suspension cables.

This topic is designed and intended to provide a venue for development of designs using suspension to hold a roof against Mars gravity. We have a topic in Architecture where the idea of a tibrel vaulted roof might be developed.

(th)

Calliban · 2025-11-12 16:04:52

TH, see images below.

In this example, cables support a steel frame ceiling. The frame is covered first with a layer of coarse rocks and then a layer of compacted regolith fines. Finally, bulk regolith is heaped ontop to a depth of about 5m. The weight of the regolith and frame is transfered to the cables prior to pressurisation. The cables transfer load to the cast basalt ring on top of the stone retaining wall. Circumferential compressive forces balance the tensile forces in thebasalt fibre cables.

Once pressurised, the internal pressure would largely cancel out the downward weight of the frame and regolith overburden. At this point, tensile stresses in the cables and shearing stresses in the frame, are largely cancelled out. This removes any longterm fatigue problems.

The LED screen (or blue transluscent sheet?) would hang from the underside of the steel frame. This would presumably be a lightweight structure.

I'm not quite sure why we would build a roof this way, rather than as an entirely compressive shell structure. Can you think of advantages that a cable supported structure would have over a parabolic compressive shell?

Last edited by Calliban (2025-11-12 16:14:32)

kbd512 · 2025-11-13 09:55:14

Cast basalt's tensile strength is 30-40MPa, roughly half that of any variety of oak wood. While it doesn't absorb water at all and is highly resistant to most acids and bases, which is great for chemical processing and brine transport, it's not particularly fond of large thermal shocks or very cold temperatures or impact loading. Those drawbacks may mean very little for this application or they might become stumbling blocks on Mars since we're operating outside of the normal environmental extremes encountered on Earth. Here on Earth steel mills frequently use cast basalt as a liner for chemical processing piping and waste stream removal. Some sewers and runoff systems also use basalt liners.

Basalt can be cast or carved into plates / bowls / coffee mugs, too:

Mexico makes their traditional molcajetes from hand-carved basalt.

I've seen sinks / wash basins, bathtubs, and various decorative pieces carved from basalt as well. Presumably, all tile flooring, sinks / tubs / toilets / shower stalls / drain pipes for bathrooms and kitchens, and most types of ceramic kitchenware could be made from cast basalt.

For structural applications, are there examples where cast basalt was selected for use here on Earth, just to show that it can be done and has been done before?

How might we improve upon basalt's tensile strength and other mechanical properties to something approaching a plain Carbon steel, if that's possible to do?

Could we add small amounts of Carbon Fiber to greatly enhance tensile strength?

We'd be processing the materials in an Oxygen-free near-vacuum atmosphere.

If that's not possible, can internally pressurized structures be kept in near-uniform compression using externally-applied loads, and how difficult is this to do in practice?

It seems as if that requires very careful engineering and construction, like weighing-out the overburden used to bury a basalt structure to guarantee the applied load matches the engineering calculations. How generous are the "fudge factors"? Maybe we can carve tunnels into bedrock and then use cast basalt tiles as abrasion and chemically resistant liners? That would mimic how we already use cast basalt as pipe liners here on Earth.

You have to heat up the basalt, and presumably the mold, to around 1,300C to pour it like liquid Iron. I don't know how fast you can cool molded basalt without cracking. Pure Iron melts at 1,538C. Inconel and stainless start to melt at temperatures remarkably similar to basalt. They retain much more of their room temperature strength at higher temperatures than plain Carbon steels, but their alloy content, which reduces high temperature oxidation, actually depresses their melting points. That's not a major difference in melting temperature between basalt and Iron, even though you also have to source coking coal or Hydrogen to make steel. I can see how sourcing other materials to make steel would easily consume a huge amount of energy, though. Steelmaking on Mars could end up being far more energy-intensive than it is here on Earth, so there's sound engineering and economic logic behind choosing a construction material with fewer processing steps and energy inputs. The actual energy savings may be more modest than Earth-based energy input averages would suggest, though, and it's likely to be the case that making any bulk construction material on Mars is energy intensive.

If we have to make cast basalt structures thicker and therefore heavier to approximate the tensile strength values of steels, then how much energy do we save?

Is the entire logistical tail required to make cast basalt easier to acquire and use for structural applications?

Either way, we're starting from scratch here. We obviously wouldn't be welding or cutting as much, nor splitting water to source Hydrogen to make steel, but we might need quite a few molds for all the castings (standardization is obviously key here), grinding and polishing to exact dimensions, adhesives with special properties to work in extreme cold to seal the structure, and specialized construction techniques to support above-ground structures before internal pressure can be applied.

Steel has been a staple of construction for the past two centuries, but that's because we have easy access to the energy inputs to mass produce it here on Earth. Perhaps a modern Mars civilization will be built with stone instead of steel.

Calliban · 2025-11-13 21:02:00

Basalt fiber has a tensile strength ranging from 2.8 to 3.1 GPa. This beats most maraging steels, for a material with only about 1/3rd the density! For larger castings, the strength is a lot less. This is likely because cooling introduces stress fractures into the material, which is quite brittle. Tensile stress must be kept sufficiently low to ensure that any stress fractures remain smaller than critical crack length. This allowable stress will be much lower than the UTS of the material. Still, the compressive strength of 300-500MPa is impressive.

I wonder if we could make rails out of this stuff? They would need a steel strip upper surface to interface with the wheels. But the compressive strength is plenty for a railway line. Food for thought. If this material cannot cope with thermal transients, then that would be its undoing on Mars. High manganese steel should retain ductility even at Martian nighttime temperatures. But the energy cost is much higher. Steel making on Mars will be much easier if we find fossil methane or hydrogen in traps beneath its surface. There are hints that that may be the case. But the presence of large deposits is speculative at this point,

Last edited by Calliban (2025-11-13 21:14:58)

tahanson43206 · 2025-11-14 07:34:26

This topic is about a suspension roofing system for a very large pressurized volume on Mars.

Following up on post #8... taking into the account the lower flexibility of basalt bonds compared to steel, but pursuing the idea of fabricating fibers into cable able to withstand tension during the build phase, is it possible to weave cable of basalt threads?

As Calliban described the building we are considering earlier in this topic, it appears that the tensile strength of the cable is most needed during construction, before atmosphere is pumped into the volume after it is sealed.

If a city is constructed with a central span of 2 kilometers, and side spans of 1 kilometer each, and a length of many kilometers, the cables will have to carry their load for an extended period of time. Eventually as pressure builds inside the volume, the load carried by the cables will ease.

The question offered by this post is: Can basalt be woven into a cable strong enough to carry this load for several Martian years? The load on the cable can be reduced by NOT laying regolith on the bridge surface until ** after ** pressure starts to build. The Regolith radiation and pressure compensation layer can be spread evenly across the bridge surface as pressure builds.

It is going to take a long time to build pressure inside a structure of this size, so there will be plenty of time to distribute the regolith evenly across the surface.

The strength of the basalt cable would be in reserve in case a blowout occurs somewhere in the structure. An example of a cause for such a blowout is the arrival of a space vessel that has gone off course with a trajectory that intersects the roof over the city. Such an incident should be avoided of course, but an human agent might wish to inflict harm on the occupants of the city.

Unfortunately, humans have a history of engaging in destruction as well as construction.

(th)

tahanson43206 · 2025-11-14 18:26:52

In other topics, and on multiple occasions, Calliban has written about basalt as a structural material with attractive properties.

In this post, I asked Google to look up basalt used for cable, and it came back with multiple applications, including cable.

AI Overview A cable woven from basalt thread is a high-strength, heat-resistant, and durable product used for insulation, reinforcement, and protection in various industries like aerospace and automotive. This material is made by melting volcanic rock, spinning it into fine fibers, and then weaving or braiding them into a protective sleeving or fabric to guard against high temperatures, chemicals, and fire. Key properties and uses High heat resistance: Basalt fibers can withstand temperatures up to \(1,000^{\circ }C\) (\(1,832^{\circ }F\)), making them ideal for applications like exhaust systems and engine components.Chemical and corrosion resistance: The material is resistant to chemicals and corrosion, which makes it suitable for use in harsh environments, such as chemical plants or in the protection of sub-station cables.Electrical insulation: Basalt is a good electrical insulator, providing protection against both electrical arcing and high-voltage surges.Strength and durability: It offers excellent tensile strength, even at high temperatures, and maintains its integrity and functionality under extreme conditions.Flexibility: The braided or woven structure of the cable makes it flexible and conformable to irregular shapes, such as pipes or wires.Safety and environmental benefits: Basalt fiber is non-toxic and non-carcinogenic, and since it's made from a common volcanic rock with no additives, it is considered a more sustainable alternative to some synthetic materials. Examples of applications Aerospace: Protection for engine components, fuel lines, and other sensitive parts in aircraft and spacecraft.Automotive: Insulation for exhaust pipes, turbochargers, and engine components to improve performance and longevity.Industrial: Reinforcement for hoses and pipes, thermal insulation for high-temperature equipment, and electrical cable protection in sub-stations and other industrial settings.Construction: Reinforcing mesh for tunnels and shotcrete walls.
Marine: High-strength ropes for anchoring offshore structures like fish farms.

(th)

tahanson43206 · Yesterday 09:50:49

The concept of a suspension supported roof for a very large building on Mars is looking more and more feasible.

The report by Gemini in post #10 supports observations by Calliban and kbd512, that basalt has qualities that appear to lend themselves to a project on this scale.

The posts for the suspension cables need to be built upon bedrock.

however, as GW Johnson has pointed out numerous times, we do not have any direct knowledge of subsurface conditions at Mars.

On the other hand, we ** do ** have plenty of radar data from satellites flying overhead, so perhaps there is a way to tease bedrock depth from all that data. Another possibility is sound wave data. A great deal of data has already been accumulated by Mars rovers with suitable sensing devices.

Perhaps something can be deduced from that data.

In any case, it seems to me that the construction practices worked out on Earth over the centuries would apply on Mars.

Excavation is one way to reach bedrock, and pile drivers is another.

A laser cutter might prove useful in removing material from the surface of an excavation.

What I am thinking about here is a V shaped cutter, with lasers cutting a V shaped section to whatever depth the lasers can handle. The V shaped wedge can be removed with a pry bar, and the next cut performed.

Louis provided a location for "Sagan City" near one of the early landers. That is as good a place as any to look to see if a long wide pressurized building might be sited.

I'll add that as soon as the first human is on Mars for more than a brief visit, there needs to be traffic control for arriving and departing space vessels or delivery packages that might land anywhere without strict controls.

Because humans have an unfortunate tendency to engage in conflict, that trait might as well be addressed from the beginning of the enterprise.

A city the size of the one imagined in this topic will be vulnerable to human activity. The planet itself will be about as non-threatening as any location in the Solar System might be.

(th)

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#1 2025-11-10 19:12:43

Suspension Bridge Martian City Roof Design

#2 2025-11-10 19:13:33

Re: Suspension Bridge Martian City Roof Design

#3 2025-11-10 19:17:12

Re: Suspension Bridge Martian City Roof Design

#4 2025-11-11 17:59:45

Re: Suspension Bridge Martian City Roof Design

#5 2025-11-11 18:35:13

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#6 2025-11-12 16:04:52

Re: Suspension Bridge Martian City Roof Design

#7 2025-11-13 09:55:14

Re: Suspension Bridge Martian City Roof Design

#8 2025-11-13 21:02:00

Re: Suspension Bridge Martian City Roof Design

#9 2025-11-14 07:34:26

Re: Suspension Bridge Martian City Roof Design

#10 2025-11-14 18:26:52

Re: Suspension Bridge Martian City Roof Design

Marine: High-strength ropes for anchoring offshore structures like fish farms.

#11 Yesterday 09:50:49

Re: Suspension Bridge Martian City Roof Design

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