General Structural Engineering

The vision here is only possible after decades of expansive development on the moon. It assumes a wealth of both sophisticated robotic equipment and available power. The sections for each significant structure and piece of equipment will explain their design in greater detail. Here we shall outline the principle architectural approaches.

Atrium Hab exterior showing reinforcing ribs, beams across glazing

Living spaces on the moon have to be pressure vessels placed mostly underground. In the vision here, exterior walls are made of basalt or glass materials that have been melted into panels, beams, and pipes, which are then joined with more melted basalt until monolithic shapes are produced. The pressure of the atmosphere is contained by  cables of basalt fiber incorporated into channels within the arches and beams. Panels and beams also have mats or webbing of glass fiber pressed into them while molten. Underground sections of habitats have a layer of packed gravel surrounding exterior walls and floors, and may have a grid of rods stabilizing them which penetrate deep into the ground outside.

Fused quartz glass is used in the arched glazing of the atrium habs and all the windows. Where sky is visible outside windows, a separate layer of glass is offset from the layer that supports the pressure of the air by a few meters. That layer ensures that meteoroids that impact there explode on the outer layer, and if they penetrate that, the force of the explosion is dispersed over such a large area that no cracks or significant leaks result. Such measures are appropriate in structures meant to endure centuries, which is the only kind of construction that makes sense for major habitats.

Each hab portrayed has been designed for proper thermal control, low radiation exposure, plentiful sunlight, consistently good air and water quality, and a pleasant auditory environment (meaning damping of echoes). That is explained in each hab’s section. Here we will look at internal design. That is what impacts how people will build things of their own inside the habs.

The interior of the Big Atrium hab, showing the arches and tall columns down the middle, the many levels of floors between them, and the radiation blind arches on either side


97% of your time is going to be spent indoors. Nature for you is only the small and limited gardens of the habs. This is why each habitat is made as large as possible, and then slowly filled in afterwards. Each cubic meter is precious. Habitat planning is like urban planning, if the basic happiness of every resident of a city depended on urban planning.

Planning is done in a manner similar to shopping malls, except aiming for inspiring and life-giving. The major structures are created such that maximum freedom remains for the minor structures, while still preparing distribution of critical resources so they are shared and monitored optimally. In order to maximize the amount of shared space, which allows the greatest range of activity for everyone, individual dwellings and most business spaces are restricted to the minimum adequate volume. There is great aesthetic freedom though, because there is little need to think about structural strength, utilities are provided, and there is no weather. Just use your space carefully.

Everything possible is done to allow the indoors of the habs to substitute adequately for the outdoors on Earth. Habitats always have places where you can see from end to end of them. They have very large screens that display views of nature or city streets, either recorded or streamed from Earth. Those are the size of Jumbo-trons but with the resolution of Retina displays. Some are back-lit with sunlight piped in by fiber-optic cable, so that images have enough light to be vivid, even when showing bright scenes like beaches or clouds scattered in a blue sky. Organic shapes are used in public architecture where possible. (Note that some shapes portrayed in the town right now are far more linear than planned for one or both of the following reasons: first, organic shapes and detailing greatly increase the number of points needed for software to display things, which means it takes longer for your computer to draw, and that becomes impractical beyond a certain point; second, creating such details takes a lot of time, and hopefully will become more feasible once the project has grown and more people are contributing to it. Portraying the giant screens will also have to wait for both the programming and the computing power needed to become available.)

Water and Air

Besides the need to optimize space, the imperative to ensure the quality and security of these resources is the the other reason why dwellings are clustered in small neighborhoods. Each neighborhood of 20 to 30 dwellings shares one main tank of water. Self-directed robots fill the tanks of each dwelling from that tank, and empty each one’s waste water tank.  This way the quality of the water going in is ensured in the process, usage is known exactly, and each batch of waste water is checked for hazards individually before it gets added to any common reservoir. Activities that greatly impact air quality are also mostly done in one central area of each such neighborhood – cooking, laundry, handicrafts. Filtration of air is more efficient and complete when one large, well-appointed kitchen, one laundry area, and one workshop are all placed together for the neighbors to share. Large heavy-duty systems for this have room to work, and their noise and vibration can be properly damped, keeping the ambiance pleasant. Doing domestic tasks by hand is almost always optional – there are robots for that. So, the system works well.

Controlling humidity takes a lot of effort. Clothes dryers and ventilation hoods over ovens and stoves draw off moisture constantly. Most cooking vessels are made of glass and stirring is done with electric devices built into the vessel’s lid, or with the sort of magnetic stirring rods used in chemistry labs. That way the lids rarely need to be removed during cooking, and vents in the vessels are connected straight to tubes that go straight to the filters and dehumidifiers. Shower stalls are required to have filter and dehumidifier devices attached that are so aggressive, the bathroom fans of today buzz like a bumblebee by comparison. This makes the option of not including a shower in your home, and instead using the luxury showers, hot tubs, and saunas of your neighborhood, preferable to many. Moss and aerial plants are cultivated over as much roof and wall area as possible, to eliminate echoes and absorb water that would otherwise become condensation. Mold can become hard to control in an enclosed ecosystem, and can become very unhealthy as well as unpleasant. Preventing condensation and keeping humidity below 50% is vital to keeping mold and dust mites down to healthy levels. 

The chemicals used in cleaning, maintenance, and repairs are carefully chosen and amounts applied are carefully measured. They must be minimally irritating to all living things in the ecosystem. They must degrade gracefully with no possible hazardous byproducts resulting from combining with other chemicals in the environment. All things are manufactured to be highly durable. They aren’t made with things as ephemeral as paint – anything that needs a coating is coated with an enamel, or anodized or galvanized. Sometimes things are taken outside to be processed. That’s where garbage and human waste is incinerated, where things are welded. And of course, all manufacturing of any consequence happens on the surface, including furnishings, household goods, and dwellings themselves.

The wealth of robots and electricity

Each neighborhood also shares a suite of robots which together can handle almost any menial labor. This makes sharing facilities much smoother. The town has always had a large population of robots – that’s why it’s possible at all – and it is a manufacturing hub of robots for all space applications. It isn’t very expensive to give each neighborhood a few, and it is smart for environmental control. To ensure things like mold don’t take hold, it’s really better to have a robot assigned to cleaning, not a human.  Robots always follow the best protocol and are extremely thorough. They always remember to clean filters, they never use the wrong chemical. They don’t burn food or let it go bad. If they have nothing better to do they will continually, obsessively clean. They can be programmed to use far more elbow grease than a limited human can, instead of using more or stronger cleaners. When the volume of air for each resident is measured in cubic meters, these are very good things.

The town also gets so much power beamed to it from space solar power stations, residents go looking for ways to use more of it. People commonly add mechanisms to their homes that fold and unfold entire rooms as needed – space is expensive, power is cheap, and so are most of the components, since they are locally made in highly automated processes. View screens that cover entire walls are typical. Plant lights are everywhere, and tanning beds, and miniature HVAC systems. The waste heat from all this has to be handled by the habs’ heat pumps and radiators, but there is plenty of power for them too.

Farming is almost entirely handled by robotic equipment. Soil is not in plentiful supply. The environment in farming areas must be meticulously managed. Thus there are many labor-intensive practices that are part of lunar farming, and they are only practical because there are robots specially made to do it. Development of new soils, new cultivars, the integration of new organisms, and the constant testing and adjusting that is part of the monumental effort to create a new ecosystem that is truly closed and independent of Earth, requires constant detailed monitoring, logging, and testing. The robots are the key.

In farm areas, the amount of electricity used at night to give the plants the light they need is massive, even with high efficiency LED lights and light spectra optimized for growth, flowering, and fruiting. It is so much, that to remove the need to also pump out all the waste heat that goes with that light, the lights are placed out on the surface and piped in by fiber-optic cable by a system very similar to the light tubes described below. During the day, the light coming in is natural sun, and heat pours in with it. In that case there is nothing for it but to pump the excess heat into thermal mass and then radiate it away using radiators on the surface. This also requires a massive amount of electric power. Thanks to space solar power stations, this isn’t a problem at all. 

Sunlight and Windows

large parabolic mirrors that focus light onto a lens leading to fiber optic cables, delivering sunlight to the outlet of the cable tens of meters away

The roofs of all the gallery habs, which are the long narrow ones running down the slope of the crater wall, are covered with hundreds of light tubes. Their parabolic mirrors track the sun, focus it on a lens, and pipe its light down long fiber-optic cables into the habs, all day long. This is the only way to pipe in sun while eliminating all exposure to the kinds of space radiation that can both penetrate meters of shielding and potentially cause serious health problems over many years of exposure. The light is then spread out as it leaves the light fixture indoors, creating a diffuse light most akin to twilight, except brighter. At night the same cables are used to pipe in light from powerful LED bulbs that are patched in to them between dusk and dawn. An imitation of Earthly nights is created throughout the month-long lunar day-night cycle by tilting the mirrors slightly out of the sun during the day, and turning off the lights for stretches at night. 

Sun is obtained this way in order to protect you from radiation. Thus is the nature of all windows on the moon. A calculation must always be made that offers the best views and most light in exchange for the least radiation. Wherever you can see the sky, galactic cosmic rays are coming at you. They are atoms stripped of their electrons and accelerated to a large fraction of the speed of light. When they pass through matter, their positive charge causes them to rip electrons off nearby atoms as they pass, leaving a trail of free radicals behind them. When they strike another atom, a shower of new particles is created. Most of those particles are charged, and as long as they pass through enough further material, the attraction or repulsion between them and the surrounding matter drains them of their energy until they get absorbed into some other atom. But a few of them are neutrons. Because they lack a charge and are moving too fast to be absorbed, they will keep right on going until they hit something again, and will likely have enough energy to create a new shower of particles, some of which will also be neutrons. The cascade doesn’t stop until the energy of the original particle has been dispersed among enough secondary particle to slow down to a speed where the neutrons get absorbed by something. For that to happen, you want 700 grams of material over every square centimeter between you and the sky. That’s 10 lbs per square inch. If there is much less than that, the neutron cascades, in particular, will still be going and will hit you. We aren’t really sure what it would do to you after years of exposure, but it really just doesn’t sound good. When neutrons like this hit strands of DNA, for instance, they just blow them apart. Not the kind of thing the body can repair. People get exposed to ionizing radiation at low levels all the time and our bodies have repair mechanisms for that. The human body has never been exposed to radiation like this, down here under a hundred kilometers of air (which adds up to 1000 g/cm2). Maybe we can take it. Maybe not. Astronauts on the ISS have taken it for up to a year at a stretch or up to 2 years on multiple missions at different times. Once your time in space stretches to decades, that could be a different matter.

Interestingly, if you can’t have at least 700 g/cm2, your next best option is to have as little material as possible between you and the great beyond. Preferably no more than 20 g/cm2, which is more than enough for a layer of glass that can hold in an atmosphere. That way, if a particle passes through you, odds are good it will do just that – pass by, leaving a trail of charged molecules where it stripped electrons off them. That isn’t nearly as bad as if it hits something and shatters it.

long curved window reinforced with an exterior truss, looking over the crater floor

That is the thinking behind the other light and window designs used in the habs. Some see only a small sliver of sky, and keep you protected behind enough material to block everything outside of that. If you can see the ground, that’s okay, it absorbs this radiation. It’s the sky you need to worry about. As long as the fraction of your surroundings that is sky is low enough, the dose is sustainable. All the windows looking over the crater use this approach. They are in deep recesses surrounded by thick layers of regolith laid over the structure of the habs. Sky is only visible through them from certain angles or if you are very close to it, and the guess is that the amount of sky is small enough to be safe.

On the edges of the radiation shielding are areas where the amount of material between you and the sky is in the peak cascade particle thickness of about 100 to 300 g/cm2. From those directions you get quite an elevated dose of this particular kind of particle radiation, however the area with that thickness is small. The image with the red truss matrix shows one of the places in the tubular habs where you are most exposed. You probably shouldn’t spend much time there. Most of the tube hab volume exposes you far less or not at all.

There is a reverse variant of this kind of window, one that is in a window well. That kind has a mirror angled at 45 degrees just outside it. At this location on the moon, the big advantage of that is that the Earth is in  the sky, almost at the zenith, and it barely moves from there ever because the moon is tidally locked to it. The Earth is always visible in those windows, definitely the most beautiful thing visible on the moon, no contest.

It would be feasible to use a similar trick to block direct views of the sky from other windows with direct sky views, especially the tube habs. Instead of seeing the sky directly, a mirror could be positioned to reflect in the sky above it, and behind that mirror, a large mass of regolith could be placed to block radiation from the sky behind. It would work but requires a large structure, would block views of the crater from a lot of angles due both to the mass itself and due to the pillars that would be needed to hold it up, and large sections of sky would remain visible, though from smaller areas. If evidence indicates radiation is a problem, in particular through the very large windows of the tube habs, it might be the best solution. In any case, mirrors like this are planned for everywhere that a view of the Earth can be had this way. It is just tricky to get the software to actually show the reflection of the Earth this way, and so that plan is on the back burner for now.

Geometry of radiation blind arches - 50 cm wide, set 50 cm apart, 7 m tall with the last 2.5 narrowing to a point, gently arched, it takes 130 in 2 sections to cover the roof of the Big Atrium hab

The atrium habs – the long straight ones sunk into the ground on the crater rim – are covered with a large number of close-set arches with glazing in between. That cover is being called a radiation blind, as it uses a principle similar to the use of recessed windows to reduce the dangerous radiation to a hopefully safe level. Although half of the roof is only separated from the vacuum by a layer of glass, from anywhere in an atrium only a few narrow sections of sky are visible to a person inside. The rest of your view is blocked, usually by several arches, or by a thickness of rock (which the arches are made of) several meters long, passing through most of the height of an arch. The area in your view where the line of sight passes only through the 100 to 300 g/cm2 that is most dangerous is made very limited by the geometry of the arches. 

Humans require at least a minimum of sunlight and exterior views to be happy. In a place where they are deprived of almost all of nature, providing as much of this as possible is worth great expense. A healthy and sustainable community may not be possible without it.