Wind Cave of Cyrus, The

Windcave on Cyrus
Image from Steve Bowers


"Wind Cave" is one of the better known Caverns of Maha, a moon in the Cyrus system. Its fame is assisted by its picturesque environment and currently-chic hotels. Many of the Caverns also seek to emulate its design, which is adaptable to a range of retroist groups and technology levels. Wind Cave currently imposes rules on residents of 'no technological items requiring manufacturing techniques or materials post-dating 100 BT, (that is, approximately 1869 c.e. using the dating system common at that time)'; 'residents are expected to behave as if limited to <100 BT human physiologies,' and 'visitors should not utilize advanced technologies to assist residents in work or to perform habitat maintenance.' This results in oddities such as resident vecs and space-adapted tweaks being required to wear spacesuits when exposed to vacuum, but the volunteer residents accept these amusing conceits much the way Steampunks accept their many self-imposed limitations.

In practice, there are many exceptions to these rules. Pointedly, the restriction on manufacturing techniques and materials has not prevented modern science from being brought to bear on matters like closed-cycle ecologies and heat transfer, and many of the crude, automated environmental control systems were never invented on Earth within the specified era. Advanced personal items not directly applied to habitat expansion and maintenance may be retained so, for example, many residents use DNI implants for regular Known Net access and to simulate and analyze potential habitat improvements before implementing them. Su residents not expected to restrict their intelligence to pre-100 BT human levels, nor restrict their physical speed and mental endurance that allows them to be enormously productive at the many menial tasks required to maintain the habitat. Likewise vec residents may work rapidly and for days on end. All residents and visitors are required to have certain advanced safety equipment: backups and retractable thin suits, or be otherwise able to survive in a vacuum. Genemod plants are acceptable after virtual demonstrations that they could be selectively bred, which significantly eases the habitat's operations - Maha—s night is 150 hours long and plants that can survive this repeating darkness are easier than trying to supply megawatts of electrical lighting in the farms. An entire branch of Wind Cave allows somewhat higher technology, such as a primitive, elegant boiling water fission reactor that runs on Maha—s naturally enriched uranium. (The Cyrus system's young age means that local uranium is 3.1% U235.)



Wind Cave has become an interconnected and sprawling mass of artificial caves and tunnels totaling approximately 5 square kilometers and hosting about 900 occupants at any time. There is order to the geometric confusion: most of the tunnels and small caverns follow single-ended lines extending from major public 'hub' caverns, always ending in another hub cavern. The confusion stems from the fact that the 'branches' are folded and curled in three dimensions. Having the branches start and end at different hubs is done for the straightforward reason of ventilation. Airlock doors (currently made of iron-chrome-nickel alloys resistant to the humid atmosphere of Wind Cave) serve to control air flows and, of course, offer emergency barriers in case of a blow-out.

Architecture & Geography

A number of the hub caverns are styled as "natural" caverns, but they are simply art projects to entertain tourists. For the most part, Wind Cave's tunnels and caverns are hewn from broken regolith unsuited for retaining air, and so the porous ground is meticulously reinforced with rock bolts (if solid enough), lined with grout, and then sealed with panels of interlocking fused basalt produced in solar smelters. Popular sealants and grouts injected to stabilize the regolith include sulfur concrete and tars derived from local carbonaceous deposits. (Maha, being a product of co-formation with Zamin, has a much higher volatile content than an impact-derived moon like Luna.) The basalt panels serve as important fire barriers to the flammable —grouts.— Because the basalt has low tensile strength, most tunnels and caves lined with it are more than 40 meters below Maha's surface where regolith is able to maintain the shells in compression. Higher tunnels shift use metals like the airlock doors.

Many residents spend at least part of their residency expanding the tunnels, which uses a labor-intensive manual shield tunneling technique. There have been periods of Wind Caves' occupancy when much more modern bot- and nanotech tunneling techniques were used for rapid expansion because of occupants' impatience. The lining and air support remain primitive.

Individual residencies and businesses are typically subdivided from tunnels and caves by the use of masonry, rock-derived fabrics like basalt fibers, or even wood from the farms. Residential areas tend to decorate the basalt panels of their walls with murals.

Due to an understandable preoccupation with oxygen supplies, inhabitants have decorated Wind Cave with abundant vines, moss, and potted plants where there is sufficient light. The interior is thus well gardened even outside the farms.

The overall geography of Wind Cave is 4 hub caves (two high, two low) and a couple dozen branches holding the farms, residences, hotels, businesses, and Ice Caves. Underneath their dusting of vines and moss, most of the branch caves are plain, bolted and grouted basalt panels, but the hub caves and farm caves are more lively. The farms have spears and curtains of sunlight piercing the humid air; trickles of water running slow, low-gravity rivulets between ponds performing functions ranging from sewage processing to fish farming and cabbage growing; and terraces of soil and water thick with grains rise to near the ceilings. A couple of branch tunnels (generally, deeper ones) favor brighter, warmer gardens and eruptions of flowers, where visitors must be cautious of the bees that serve critical pollination duties throughout Wind Caves, while some of the higher tunnels are poorly lit and become cool, dry sanctuaries for the cave ecologies of small mammals and reptiles that have escaped the bustle of the lower, warmer caves.

One hub cave is decorated as an open air shopping plaza and town hall, entirely developed with stone and iron buildings that take architectural cues from 100BT European urban developments. The others mix their buildings among artificial stalactites and stalagmites, and lively gardened trees. The low gravity has made it possible for some residents to suspend their light dwellings and businesses from the the cavern roofs, making this an entertaining, three-dimension environment for visitors. Tourists are generally able to find hotels and bed-and-breakfasts throughout the Wind Caves. The "town hub" is popular, but housing is available in almost every tunnel.

Lighting, Heating, Cooling, and Air Circulation

Skylights are used to illuminate the caverns. These use sun-tracking heliostats to minimize the need for large, transparent pressure barriers, which are difficult with available manufacturing techniques and materials. The heliostats use 1-axis fluidic suntracking mechanisms through the day. At Wind Cave's high latitude, there is limited apparent change to Cyrus's declination throughout Maha's year that is addressed with a curve in the heliostats. While the heliostats may be manually diverted to simulate a 25-hour day-night cycle, Wind Caves prefers to leave main skylights lit throughout Maha's 150-hour day to power air circulation.

In addition to the main skylights that provide area illumination in hub caverns, some skylights deliver their concentrated beams to mirror manifolds that then pipe light to other areas. Gradual losses from repeated reflections around corners and at beam splitters limits the range to several hundred meters. The light pipes offer convenient means of simulating a day-night cycle away from the hub caverns - the ports on the pipes may be closed. Similarly, many of the rooms in branches may close doors to block 'external' illumination from public areas. Some concentrated sunlight beams are used in hub caverns for water heating and restaurants' solar ovens.

Wind Cave depends on Maha's daily temperature swing for temperature control, tolerating a gradual temperature climb during the day and exploiting the long night to chill thermal masses. This is done for lack of other low technology cooling systems. The soil temperature of Maha—s poles is low (-20C), but so is its thermal conductivity. Some branch tunnels on the perimeter of Wind Cave are frosty due to heat loss into the surrounding regolith, but regions near well-lit hub caverns or toward the physical center of the habitat temperatures may grow uncomfortably warm during the day. At all times, warm, rising air is directed to surface radiators placed in shaded trenches. However, some radiators are inevitably in sunlight during the day at some point in the year (and manual valves isolate these to avoid carrying extra heat into the habitat). At night, no radiators are sunlit and the megawatts of sunlight input to the habitat cease. The deeply chilled air from radiators at night is used to refrigerate water reservoirs in upper caves, the Ice Caves. Radiator return air flows through the Ice Caves before spilling to deeper, warmer caverns. When daytime radiator cooling is inadequate, the ice becomes a key thermal reservoir. Air is the primary coolant and the habitat is arranged with its most-lit, warmest sections are located deepest so that warm air can rise to the radiators and chilled return air easily sinks. Though heat is viewed as undesirable during the day, the warmed caverns - especially the huge thermal masses of the water-rich farms - continue to heat air into the night to provide useful air circulation. The constant flow of air through the caverns also helps battle bad air pockets and gives the habitat its name: Wind Caves.


Wind Cave does have some electrical power, primarily applied to some industrial operations like electrolysis and supplying some lighting. It is also used in some communications (telegraphs). Electricity is generated with solar-thermal systems in various forms, from steam piston engines to hydrogen-filled Stirling engines. Power plants change year by year as the residents pursue different goals: more power, higher efficiency, less maintenance in crude vacuum suits, etc. Pneumatic motors (see below) may also spin dynamos as a backup option, and banks of nickel-iron batteries (which use materials commonly produced by Wind Cave) are the primary storage system for nighttime illumination. Crude Nernst and arc lamps are used for electrical lighting.

Pneumatics and Water

Pneumatic systems are used for a lot of mechanical work through Wind Cave, be it pressurizing water systems, powering tools, spinning dynamos, driving fans, or lifting elevators. Though not as efficient for long-range power distribution as electricity, pneumatics are preferred in Wind Cave because of their simplicity and because they can elegantly interface with several life support functions: compressed air can distribute water by the expedient of pressurizing the plumbing; it can deliver spot cooling either by releasing compressed air or by vortex tubes; and, obviously, it is a means of distributing air. As with electricity generation, Wind Cave has gone through several means of generating compressed air. The current popular means is contained in two redundant, isolated caverns: surface heliostats deliver concentrated light to heat engines that mechanically drive compressors, which pressurize reservoirs drawn directly from habitat air. The caverns are isolated because lo tek craftsentities have discovered that manufacturing good, high-pressure air bottles can be tricky and their explosions can be devastating.

Water circulation is primarily handled by gravity, pneumatically-pressurized lines, and condensation. The radiators and Ice Caves condense and collect moisture from the warm lower caves, as do air dryers in the pneumatic systems. From the Ice Cave reservoirs gravity is used to direct irrigation water to the farms. Domestic and industrial water systems use pneumatic pressurization to guarantee circulation, and pneumatic reciprocating pumps may drive water at higher speeds.


Surprisingly for a vacuum habitat, Wind Caves makes use of combustion in numerous low power applications. The habitat is adjacent to a carbonaceous deposit rich in kerogens and other CHON compounds that is relatively easy to process into natural gas and heavier liquid hydrocarbons. There are several needs for combustion. First, electrical cooking and water heating are considered anachronistic by the habitat's technology restrictions, and solar cooking is difficult to arrange in branch tunnels where most residences are located, so gas- and oil cooking are preferred in residences. Second, oil and gas lighting is convenient and sometimes more portable than electrical lighting. Third, plants able to feed a biont with a human-like metabolism in a closed ecology produce about three times as much oxygen as is needed to meet the biont's respiratory needs. The other side of this oxygen glut is a carbon dioxide deficiency, which is met by combustion.

Ecologically-Enhanced Life Support System

Per their charter, Wind Caves attempt to use technology available c100BT to maintain life in a Selenian environment. While not necessarily the easiest means of doing so, the habitat has long-favored biological systems to handle the major roles of a life support system. Biological systems offer a degree of intelligence and responsiveness to variations that are more tedious to accomplish with available mechanical and electrochemical systems. Further, the various charter loopholes have been strained ("like a commgauge wormhole passing The Brobdingnag," according to some authenticist residents) accept genetically engineered plants and animals designed for closed ecological life support systems. However, the system is not closed. Mining and chemical processing activities make up for losses in more than 20 biologically important elements, and various mechanical, thermal, and electrochemical systems must sometimes sequester surpluses. The system is prone to many different feedback cycles that get out of hand more readily than in any more advanced life support system, though a group of Su managers have kept the system avoided the worst collapses of prior decades for a record nine years.

The farms of Wind Caves are a cluster of caves with various food production systems that are intertwined with the rest of the habitat's life support. Aquaponic pools clean sewer and other waste water streams while generating a diverse range of plant and animal products, from algae to mollusks to fish and berries, and producing abundant amounts of oxygen. Soil trays and terraces grow plants unsuited for aquaponics. Together, they clean the habitat's air. Some caves raise populations of animals suited for the closed habitat: fowl, rabbits, and sheep. While the farming caves are seemingly a 3D jumble, they are arranged intelligently to exploit natural convection and gravity, minimizing the need for mechanical pumps. The farms are the largest user of electricity in the habitat for night time illumination, keeping vulnerable plants healthy against the long Mahaian night.

The farms are plural for a reason: they are several partly-connected ecosystems following different combinations of algae, plants, animals, fungi, and environments. After past collapses of more monolithic, integrated farms, the Wind Caves currently favor some diversity despite the complications in control. The farms are also very oversized and tolerant of shutdowns among their redundant pools, terraces, and tunnels. The farms could support a resident with a few tens of square meters of pools and terraces, but upwards of 1000 square meters are budgeted per resident (not counting the decorative biota elsewhere). In addition to being overly productive and redundant, this allows the farms to be designed in a more relaxed, labor friendly manner than the densest possible trays and tanks seen in 0AT and 100AT closed ecological life support systems.

Extensive manual labor is required not just for common farming activities, but also to monitor the numerous primitive chemical sensors that track the health of the farms' waters, soils, and air. Near the farms are numerous workshops (from crafts to life support chemical processing) that produce far more than foodstuffs. Textiles, clothing, paper products, oils, alcohol, polymers, soap, and innumerable other products used by a 100BT community come from these workshops.

Major life support functions are backed up by assorted non-biological systems, sometimes multiple systems. Solar thermal sodium hydroxide scrubbers are a major backup to plant-based carbon dioxide control, while electrolysis of water is the main backup to plant-based oxygen production (the hydrogen is vented as loss). Sodium and potassium hydroxide canisters are used in individual rooms and emergency air masks. At night, CO2 can be also be condensed to dry ice and vented if needed. Large pneumatic reservoirs can replace about 10% of the total air volume, while liquefied gases are a further reserve in case of emergency. The ice caves and hub cave thermal masses are backups to the surface radiators, while the ice caves are less volatile backups to the water reservoirs in the farms. Every life support-critical element is stockpiled in readily usable compounds, and there are several warehouses of preserved food. As of yet, Wind Caves - unlike some imitators - has never had to be completely abandoned.


The residents are fairly blase about catastrophic disasters because they're backed up and must wear skinsuits that deploy automatically during depressurizations. Modern rescue equipment means permanent deaths have never occurred in Wind Cave.

That said, Wind Cave has had no catastrophes that actually threatened the entire community. The branch tunnels and hub caves are all extensively subdivided by pressure doors and bulkheads, which contains any blow outs and leaks. Skylights are likewise made of multiple fused quartz windows and have steel shutters. The doors are generally left open for ease of movement, but the air currents accompanying a large blowout will swing the doors (and skylight shutters) shut by design. With tens of millions of cubic meters of air in Wind Cave, even the blow out of a skylight in a hub cavern is a moderate risk and inconvenience, not an instant catastrophe. However, many water and air lines passing through the bulkheads will need manual closure to halt losses during depressurization.

The two worst depressurization events in Wind Cave's history involved a pneumatic reservoir's explosion and a tourist "Revolt" event. The reservoir's rupture depressurized two full branch tunnels because it also damaged several intervening bulkheads and skylight windows (not to mention all the power and water handling machinery in those tunnels.) The modern skinsuits and medikits saved most workers in those tunnels, but three people were temporarily killed. The other large depressurization event was when some tourists selected an overly energetic means of winning their revolt scenario, which entailed some synthesized charcoal-liquid oxygen explosives in a hub cavern. This not only (temporarily) killed the "corrupt oligarchy" during one of their evening feasts at a hub cavern restaurant, but blew out the cavern's skylights and depressurized five branch tunnels. Revolts are now conducted under tighter restrictions.

Other emergencies tend to be contained by the compartmentalized nature of the habitat. The one most studied by residents is the Great Fire of 10,573AT because of its cascade of failures. A substantial reservoir of stove oil caught fire. The burning oil ran downhill into a hub cavern and started an urban fire. Fire hoses and tunnel sprinklers were insufficient; some sprinklers were damaged by ice-induced ruptures in cold branch tunnels. Fire-driven heating increased air pressure in sealed tunnels, which made access difficult, and ventilation was insufficient to deal with the accumulation of smoke and partly combusted gases, which led to some flashovers. After several hours of failed emergency responses and a refusal to vent the endangered sections to vacuum, the residents voted to activate modern systems of bots and utility fog, which finally suppressed the fire and cleansed the air.

The most common injuries are in vacuum operations. The vacuum suits manufactured with available materials are low-pressure, requiring careful prebreathing, and are prone to high material wear at joints. Flexibility is limited, so operations are clumsy. Chafing, punctures, and tears occur, while crush and thermal injuries in mines or vacuum smelters are fairly common. The current opinion among residents is that baselines actually restricted to 100BT technology would probably have an unsustainable casualty rate.

A common disaster, avoided for most of the past decade, has been collapse of the farms and biological portions of the life support systems. Like depressurization, this has been more of an inconvenience than a habitat-threatening disaster. In the earliest years of Wind Caves, the habitat did have to resort to stored food and air supplies and, finally, ultratech nanites to clean out some parasites. A variety of parasites, diseases, stray nano, and just feedback loops in the ecosystem have caused the farms to partially or completely fail at various times. This has led to both dabbling with somewhat higher technologies (e.g., the boiling water fission reactor) and justified the genetically engineered "decorative" vines in the branch tunnels. So far, the decorative biota's separation from the tightly-knit farm ecologies have spared it from most failures.


The exact rules for Wind Caves' technological restrictions and thus economy vary over the decades owing to the cyberdemocracy practiced by the registered residents.

An interesting element of Wind Caves' population is that quite a few use entirely voluntary, temporary memory and personality alteration to adopt "authentic" identities that fit the narrative of the day. This may be accomplished by several technologies, including rental bodies running forks. Some tourists mistake them for characterbots but that is incorrect. Rather, some residents simply have trouble acting with what they consider sufficient "authenticity" to the technological restrictions and self-imposed culture of Wind Caves. It easier for these residents to block access to some memories or even adopt an entire fictional history. Of course, these experiences are later merged with the original personality. A common fictional history is maintained for consistency between residents.

The residents' de jure cyberdemocracy and interactions with Cyrus' modern, post-scarcity economy are kept behind the scenes from tourists and residents with very immersive memory alteration. For the benefit of these individuals, many of the residents are simulating a small community with a "2nd century BT capitalist monetary economy" and a "hierarchal, pseudo-republican strong-mayoral town government" complete with corruption, entrenched oligarchy of major business and life support owners, and ineffectual democratic elements.

Tourists may acquire metal coins and paper bills to experience manual monetary exchange in the businesses of Wind Caves, or may sign up to participate in various habitat activities like solar smelting of basalt panels, performing several days excavating a few meters of new tunnels, or working in a craft shop. Tourists who sign appropriate waivers and consent clauses will be subjected to the simulated abuses of the backward government and economy, such as being put in a position of begging, mucking sewage ponds, or performing unsavory acts for "air chits."

A particularly popular event held biennially is The Revolt. In this, "disgruntled" residents and tourists have a "revolution" to overthrow the "abusive, entrenched power structures." Depending on the length of the vacation package, tourists may participate in up to a couple of weeks of subversive activities before the grand revolt, and then may participate in the development of the new government afterwards. The community resets to their usual roles about ten days after each Revolt.

A small majority of the residents do not participate in the tourism industry and concentrate on the habitat's lo tek expansion and maintenance activities. Residents are expected to meet the minimal maintenance requirements of the habitat before indulging their own whims. The cyberdemocratic council distributes assignments based on skills and preferences, which may develop into full-time careers if the resident is amiable.

Wind Cave's residents have accomplished a lot within their restrictions and usually adhere to them. Significant social credits are obtained by more authentic use of the limited technology, which reinforces adherence to the restrictions. Other residents are willing to forgo such wealth to use covert modern technology (e.g., genesticks disguised as brass microscopes) to rapidly diagnose problems in the biological portions of the life support systems. There is another monetary advantage to operating within the restrictions: some past Wind Cave residents have become fantastically rich by introducing a new low tech or prim tech solution that caught the attention of the Known Net.


Building and living in lo tek space habitats like the Caverns have become a niche hobby across Terragen space. Though more often simulated in a virch world than reality, there are other lo tek habitats. Those on the planet Batts of New Brooklyn take numerous cues from Wind Caves but have the advantage of being on the terminator of a tidally-locked planet, which simplifies lighting and cooling arrangements.

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Development Notes
Text by Mike Miller
Initially published on 03 September 2015.