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Source: Lectures on Space Habitat Systems Engineering and Design, Prof. Sana Medalie, Titan Tech [Link]
Except for exohabitats open to the local environment, every station and colony is effectively a closed ecosystem designed to keep its inhabitants alive as efficiently as possible. Complex systems are in place to keep the cycle of life going and every detail of their operation must be attended to. In some cases, we’ve found that there just isn’t a substitute for Mother Nature, so we’ve developed bioengineering analogues to do the hard work for us. There are even a few in our profession that eschew mechanical systems entirely in favor of biosystems.
Remember that every habitat must balance the requirements of its owners and operators with the needs, wants, and desires of its inhabitants. These are our homes we’re talking about here. Just as with any city back on Earth or Mars, biomorphs need food, water, shelter against the local environment, sanitation, and communications. Public services like security, fire protection, power, and local transportation are common. Atmospheric generation and processing is perhaps the top priority, though. As habitat engineers, it will be your job to design, build, and sustain the systems that provide all these essentials.
If this sounds like a daunting task, rest assured that it is. We incorporate safety margins where ever we can, but there are simply too many permutations of the interactions of interdependent systems for us to discuss everything that could possibly happen in this class. There are infomorphs that have dedicated their existence to resolving the problem of optimal systems control. You will have to learn how to make the best decisions you can with the information you have available. Intuition and discretion are what separate the good from the great.

(Physical) Access Control

Though some extreme social groups have chosen to isolate themselves since the Fall, effectively locking themselves inside their habitats, most colonies have some method for allowing morphs, bots, and craft to move inside and out. The level of control largely depends on the size of the habitat, its configuration, and local regulations and governance. For example, the airlocks and docking stations on cluster anarchist communities like Locus are controlled by individuals and collectives, while the Jovian Republic’s Reagan cylinders have strict security controls that require both proper identification and authentication for access. Even stations with open access airlocks and ports will almost always have AIs dedicated to monitoring the portal and watching for trouble.

Airlocks

The airlock is the standard system for individuals to conduct extra-vehicular activities while keeping the pressurized volume intact. The simplest airlocks consist of an interior door or hatch, a pressure chamber, and an exterior door or hatch. Internal volume sufficient for two suited individuals is the engineering minimum standard because of the longstanding practice of employing the buddy system for EVAs. Large working airlocks can include a prebreathing and suit donning chamber, heavy suit and equipment racks, capacity for two dozen workers, and multiple exterior doors. Multiple interior doors are uncommon, as a precaution against increasing the number of points of failure in the system.
Standard operating procedure is for the users to don their suits, enter the airlock chamber, close the interior door, depressurize the chamber, and then open the exterior door to space. The procedure is reversed to re-enter the habitat. Pressurizing or depressurizing takes about 12 seconds on average. When not in use, both chamber doors are kept closed to provide two-fault tolerance against a breach to vacuum or the exterior environment.
Some airlocks are also designated as crew transfer points and equipped to capture docking adapters on shuttles and other small spacecraft. Tin can and cluster habitats, where internal volume is at a premium, often have dual-use systems like these to avoid the expense of dedicated spaceport facilities. More simplistic “airlocks” are sometimes used on Mars, Venus, and similar worlds where the habitat exterior has a different non-toxic atmosphere rather than vacuum. These are composed of a simple set of two counterweighted doors and a transition chamber, so that when one door is open the other is pulled shut. These are much quicker to traverse and effective at keeping the habitat’s interior atmosphere intact as long as the doors are not forced open.

Spaceports

Some habitats and all spaceyards are specifically designed to provide dedicated support for space vehicles, including and up to military fleets and heavy transports. Basic spaceport facilities for microgravity habitats usually consist of a dedicated docking module with multiple ports and robot arms for berthing craft with limited in-space maneuvering. While docked, the craft is still in vacuum and is effectively another module of the station. Extendable tunnels can be made available for spacecraft with protrusions that prohibit a direct mate. These tunnels range from simple light fabric and plastic tubes pressurized with air to smart fabric designs or more hardened walkways.
Colony habitats like O’Neill cylinders and other large stations often include protected shuttle and small vehicle bays that allow repair crews to work in a shirt-sleeve environment. These bays are effectively airlocks large enough for shuttlecraft to pass through. If the station has a de-spun section permanently in microgravity, shuttle bays are typically located there. Otherwise, the spaceport must include some kind of capture mechanism that translates the docking craft into the habitat’s spinward motion. This is easiest if the spacecraft can match the habitat’s spin rate and approach along the long axis for capture by a robot arm or landing platform.
Spaceships that are too large for pressurized bays require their own set of procedures and systems. Unpressurized spacedocks provide structural spars for mooring and crew transfer tunnels that mate with the vehicle’s airlocks. Space construction yards are functionally little different, except that they are dedicated to spacecraft manufacturing and assembly. As a result, they tend to be much more utilitarian in design and have less in the way of accommodations for passengers or crew. Many yards are entirely automated and only have emergency shelters for biomorph workers or visitors as a precaution against the occasional solar flare or cosmic ray shower.
Larger or high traffic stations will have dedicated space control systems, typically managed entirely by AIs and infomorphs, to manage and oversee shuttle and spacecraft traffic, docking, flight plans, cargo transfers, and customs declarations.

Entrance and Customs

Once inside the habitat, new arrivals are typically divided into residents and visitors for processing. Residents often have the benefit of an expedited or cursory security screening. The level and implementation of security can vary widely, from physical security check-in points little different to that of airports on pre-Fall Earth to entirely automated systems that require intervention only if contraband or a discrepancy is detected. Examples of such discrepancies can include inconsistent credentials, a measured mass-to-volume ratio above or below established norms, physiological indicators of high stress, and erratic behavior.
Many stations require visitors to report to a kiosk where they can declare their belongings, state the purpose for their visit, and note the planned duration of their stay. These inputs are then checked against the individual’s required declaration of intent that was filed before departure. If there are any inconsistencies in a visitor’s answers that cannot be resolved by the AI, a customs or security official is called to discuss the matter directly and intervene as appropriate.
Only the largest space habitats and surface colonies have on-site immigration facilities dedicated to in-processing new, unanticipated arrivals. Paranoia against external threats and limited resources drive most habitats to require morphs seeking permanent residency or citizenship to pre-register, successfully argue added value to the community by their presence, and obtain at least provisional approval before departure. These individuals are then flagged upon arrival for a more rigorous security protocol and identity confirmation as well as increased surveillance for the duration of their visit.
Almost all mid-sized and larger habitats have radiation detectors and other sensors in place to identify antimatter, nukes, and similar potential weapons of mass destruction.

Administrative

The management of even a small habitat’s various interdependent systems can be an arduous task. Early space stations required as many man-hours for maintenance and repair as, if not more than, their mission operations. Without centralized control on-orbit, large ground teams were required to monitor and control each subsystem—including Communications, Environmental Control & Life Support, Power, Thermal Control, and Avionics, to name a few—and to be alert for cascading effects from changes to the other systems.
Automation and ubiquitous networking now allow support personnel in an on-site control center to conduct multiple tasks in parallel and delegate authority to local subsystems so they can focus on more immediate problems. Software and AIs developed with simple but robust machine learning algorithms assist the control operators by paring down the deluge of data into discernible trends and deviations from control thresholds. Many operators have the data and analysis fed to their personal muse.
Control center positions often include Communications, Data Systems, Environmental & Thermal Control, Power Systems, Mechanical Systems (robotics, linkages, moving parts), Motion Control (station-keeping, attitude control, propulsion systems), and Operations (which can cover EVA and visiting vehicles). Large habitats like O’Neill cylinders may include watch officers for public services—such as fire, security, and transportation—on their control teams. A senior duty officer may serve as the team lead and report ongoing activities or emergency events to the relevant authorities.
Not everyone is comfortable with such a tightly integrated system. Some fear vulnerability to a decapitation strike that would take out the control center or suborn it to another’s will. Others have philosophical objections to such a concentration of power. As a result, some habitats (particularly autonomist stations) have a highly decentralized system that places control in local nodes responsible for subsystems and cross-communication. If a node malfunctions, is destroyed, or becomes compromised, the network can excise that node and divide its responsibilities amongst the remainder.

Communications

Every person in a habitat that uses inserts or an ecto is a part of the internal mesh. Though most habitats have a distributed system of mesh nodes that facilitate data transfer across the various systems and allow varying levels of public access, this basic architecture does not define the topology of the network as it would have in space stations that preceded the nanotech explosion. Instead, the vast majority of habitats have a user-defined mesh topology with nearly countless and overlapping layers of access, range, and intent. The public mesh is a cacophony of local spime data, advertisements, public service announcements, open discussion groups, news broadcasts, and entertainment. Private networks, some of which touch each other and most of which do not, are used for discreet information sharing, whether legitimate or not. Many of the private networks can be seen, but cannot be accessed without proper authentication or an invitation. Others actively try to conceal themselves in the noise of the public nets.
AR visualization software can actually be used to help an individual, usually through a muse, manage their interest in and access to all this data. Though the raw data is the same, two different morphs may have two entirely different perspectives on the mesh topology. Some memetics experts are even beginning to study this phenomenon to better understand the social structures of colonies by examining which visualizations are common and finding sharp divergences in mesh populations.

Long-Range Comms

All of this happens within the immediate vicinity of a given habitat. Long-range communications still tend to be sharply defined by installed hardware because of the vast distances between most habitats. Each habitat itself forms a node in the ad hoc interplanetary communications network. Modular comm arrays are installed on the exterior of the hull and connected to the computers generating the transmission by fiberoptic cable. This prevents tampering and interference from the local mesh.
The comm arrays themselves are arranged to give all-aspect viewing of space, if at all possible. Occultations from planetary objects and debris mean this is an imperfect solution, but managing those fluctuations in the comm links is what good software or an expert is for. A standard integrated array will have a cluster of monochromatic cells for laser beam reception, a tight-beam laser transmitter, a microwave transceiver, and an active electronically scanning radio array. While a small tin can habitat might have as few as four of these clusters arranged in a tetrahedral formation, a massive colony like Extropia will have hundreds.
Some communications hubs, especially those in the outer system, will maintain inflatable antenna loops up to 100 kilometers in diameter to pick up signals traveling from one side of the system to the other. Even a highly collimated tight-band beam will diverge to a width measured in tens (or more) of kilometers over such distances.
Neutrino communications diverge from this standard because they are relatively large, have a significant energy requirement, and solid matter is transparent to the signal. To protect this investment, most habs with neutrino transceivers will locate them near the center-of-mass or behind the power reactor shielding. This allows the operators to use as much physical mass as possible to protect against outside attack with no effect on the transmissions. The most expensive neutrino transceivers have hundreds of multiple tight-beam emitter/receiver pairs arranged in a spherical fashion to permit multiple high-bandwidth links in parallel.
Egocasting relies on the security of the long-range communications system for its integrity. Shielded fiberoptic cable is almost always used to transfer the ego data to the intended transmitter. Quantum encryption is standard. Neutrino farcasters are too easy to intercept, even with encryption, so most egocasting services use line-of-sight laser for moving egos within local clusters of habs and millimeter-wave radio for long distances. If an atmosphere must be penetrated by the signal, centimeter-band radio will be used because of attenuation effects on millimeter-wave signals.

Darknets

In a civilization largely based on panopticism, there will always be people who seek to move their data beyond the watchful eyes of others. There will also always be people who provide those services for a price. Evading network and physical security is not a challenge for the uncommitted. Darknets within the range of the local mesh are often based on portable quantum transceivers that scan for frequencies dominated by local noise and operate in that region. Self-protection software monitors the bands and changes the operating frequency as necessary, sometimes even transmitting on multiple bands in parallel to stay under the signal-to-noise thresholds that would attract attention.
Physical darknets based on shielded fiberoptic lines avoid the problem of attracting attention in the data cloud, but must be installed in such a way as to not be automatically removed from the system by maintenance bots or accidentally create thermal and power signatures that indicate an anomaly. One way of doing this is to have nanomachines embed capillaries in the sheathing of existing lines. Physical darknets also force users to have access points that run the risk of being compromised, unless the cabling itself just serves as a private conduit for mesh users who know how to tap the line.
Darkcasting presents an entirely new level of complexity, given the natural chokepoints in data flow through long-range comms and the unbridled paranoia of legitimate egocasting services. The easiest way to do a clandestine egocast is usually by bribing local officials to look the other way or hiring someone to wipe the records in the wake of your departure. That is still too much of a risk for some egos, however. Some legitimate private organizations maintain their own farcasters with the permission of local authorities, by virtue of whatever vital service they perform. The right combination of cred, contacts, and rep might gain access to this resource. Crime syndicates have also been known to conceal illegal farcasters in the power and data fluctuations of cover businesses, such as orbital manufacturing. The truly desperate can possibly even arrange to sell their body in return for smuggling their cortical stack onto a spacecraft that will then farcast the ego within.

Defense Systems

The vast distance between astronomical objects and most gravitational anchor points where stations and colonies are located means that communities are, by necessity, responsible for their own protection—against both natural threats and those who would do them harm. Isolation is a protective measure in and of itself. Spaceships can be seen coming, as long as they aren’t occulted by something else, and long-range transmissions are quarantined and authenticated before the data is allowed into the habitat’s primary system.
This protection is not absolute, though. Cold asteroids with a low albedo can be difficult to track on optical and thermal sensors. Mercenaries might sneak into close range by using commercial transport as cover. A determined adversary may even forgo subterfuge and attempt the direct assault. All of these possibilities must be considered and mitigated to the extent the resources and governing philosophy allow. Many habitats contract out these functions to private security firms and leave it up to the experts.
External defense is commonly performed by constellations of satellites and/or drones co-orbiting with the habitat. Distributing the sensors and weapons over multiple platforms and away from the main habitat makes it harder to disable the system and safer for the residents. Most civilians don’t want to live near directed energy cannon and high explosives. On the other hand, external platforms can be hijacked and used against the habitat. The advantage of a weapons emplacement on the side of a station is that it can’t be used to target the station. Each strategy has its risks.
Kinetic attacks inflict damage proportional to the square of the impact velocity. Thus, incoming projectiles must be deflected or vaporized to effectively stop the threat. Only doing enough damage to break up the projectile into smaller chunks just makes for multiple, smaller incoming targets. Directed energy weapons are the method of choice for kinetic defense because they will turn small objects into carbon compounds and inert gases and burn off mass from larger projectiles to redirect them. Conversely, directed energy attacks can be mitigated by clouds of dust or surface coatings that break up the beam.
Defense against incoming spacecraft isn’t as simple as in pre-Fall Hollywood and Bollywood vids. Taking out the propulsion system just means the vehicle will continue on its last trajectory indefinitely. It won’t miraculously come to a halt. Instead, the interlopers are attacked in such a way as to cause more pain to continue to press their assault than it is worth. Beam cannons are employed to ablate any armor and weaken the hull from far away. If that doesn’t send the message, the radiators are pelted with clouds of pellets to breach the ship’s vital cooling loop.
After attempts to get the enemy to divert from an intercept course fail, the next course is to eliminate the threat completely. Anti-ship missiles with shaped-charge armor penetrators can open up pressurized volumes to space. Teller mines detonate tactical nuclear weapons to form powerful X-ray lasers that will both ablate the hull through thermal erosion and cause lethal exposure to neutron radiation from secondary effects. Smart dust can be employed to both physically and electronically attack weapons batteries, airlock doors, communications and sensor arrays, and other vital systems.
Fixed satellites only require propulsion for station-keeping, so they are typically used for mounting heavy long-range beam weapons, deploying large sensor arrays, and serving as depots for attack drones. Attack drones have the advantage of mobility, so most are little more than a fusion jet with a sensor package, missiles, and a beam cannon or railgun strapped on. They are intended to close the distance quickly, perform high-acceleration maneuvers that would kill a biomorph, and conduct precision strikes on key targets. Of course, the enemy spacecraft can carry drones of their own. The outcome of a battle often depends on the superiority of drone hardware and combat management software and can be decided by the survival of a single drone from that clash.
Secure communication in a defense network is invaluable. As a result, quantum farcasting is ubiquitous in defense systems that require wireless comms. Tight-beam optical communications are typical for line-of-sight transmissions, while encrypted millimeter-wave radio is the standard over long ranges. The Jovian Republic is suspected of using quantum-encrypted neutrino transceivers to coordinate their fleet of dreadnoughts, taking the mass penalty in return for omnidirectional fleet networking. The expense of quantum-entangled communications tends to limit their use to highly sensitive covert operations that may require instantaneous, if limited, information exchange.
Detecting the enemy is always the first part of interception. At distances such as those between planets, the easiest tracking is done by watching the thermal signature move across the near-absolute-zero background of space. This only tells a habitat that someone is coming and gives a rough estimate of the contact’s trajectory. Radar is the most common method of pinpointing a contact’s size and mass and determining an accurate course and estimated time of arrival. Spectroscopy—separating out the light into its component spectra—can be used to determine the vehicle’s exhaust characteristics and thus likely propulsion system. At tactical ranges, lidar and tight-beam radar are used to construct a high-definition 3D map of the contact, correlated with IR imaging of major heat sources. When all else fails, many habitats still have their own defensive batteries to deal with drones, missiles, or other spacecraft that penetrate the outer screens. Beam weapons are often preferred because they can respond rapidly to many threats without creating additional debris. Lasers and railguns are often employed as point-defense weapons, while plasma cannon are favored for attacking armor. Missile launchers are almost always mounted as external modules with integral ordnance bays. Shaped plating inside the bays is designed to deflect an accidental detonation away from the primary hull.

Emergency Systems

Whether by accident, deliberate action, or the ravages of time and space, the protective cocoon of a habitat will almost inevitably be breached. The measure of good habitat design is in its emergency response functions. Fire, decompression, and catastrophic structural failure are the top three issues every habitat must be prepared for.

Fire

Fire will consume breathing gas, destroy critical systems, and weaken structural integrity. If the blaze continues uncontrolled, the increase in pressure can seal hatches and exceed a module’s burst strength. Just as on the seagoing ships of old, fire is a morph’s worst enemy in space. In modular habitats or those that can be partitioned internally, the section that hosts the fire is typically sealed while appropriate fire suppression techniques are applied. To avoid electrical fires, most automated fire suppression systems are based on flooding the affected area with an inert gas or non-conductive foam. If this fails, an emergency purge to vacuum may be required to stop the fire before it spreads. In extreme cases, entire modules can and have been jettisoned to save the rest of the station. Aerogel is particularly good at resisting fires and so aerogel barriers are used as firewalls. Metallic foam can also be constructed with fire-retardent gases that are released when melted. Diamond, on the other hand, burns.

Depressurization

Unplanned depressurization events are actually not terribly common. Because the hostile environments outside most habitats are an ever-present threat, great care is taken in design and construction to mitigate the risks of a hull or dome breach. The infrequency of such incidents does not lessen the abject terror that happens when they occur, though. It is standard practice in most tin cans and cluster habs to include an emergency hull repair kit in every module.
Once a leak or puncture is detected, the user sprays a self-sealing, self-hardening foam into the internal volume that can plug a hole up to five centimeters in diameter. This is to address the immediate danger of the decreasing internal pressure. The kit also includes composite fabric patches and a self-setting adhesive to complete the seal. Many kits incorporate spimes in the patches that report pressure and temperature and structural strain levels in the vicinity to ensure emergency responders have time to act if the patch is going to fail.
Larger breaches almost always require the affected areas be sealed until venting is complete and rescue crews arrive on-site. If not killed or critically wounded by flying debris, unprotected biomorphs have a very narrow survival window during rapid decompression. Habitats with massive internal volumes enjoy longer recovery windows and can withstand larger breaches without fundamental structural integrity being compromised. Even so, hazard stations often carry emergency face masks that seal around the ears and provide a few minutes of oxygen. This is a relatively cheap and surprisingly effective way of tipping the odds a little more towards survival.

Catastrophic Damage

In the event of catastrophic damage and/or a cascading core systems failure, the call to evacuate will be sent out over whatever means remain—mesh, audio/visual displays, and personal contact. Inhabitants are directed to don suits, pack only what they can carry, and go to their assigned lifeboat boarding stations. If enough power and time are available, egocasting can be done to expedite the evacuation process. If not, ego backups can be transmitted or shunted to cold storage for later retrieval.
Lifeboats are typically sized for up to 100 people and carry enough consumables for eight days. Four zero-g toilets are standard. Solid-fuel jettison motors clear the lifeboat away from the station and gyroscopic stabilizers prevent the lifeboat from tumbling. Docked shuttles and spacecraft are also used to ferry evacuees and tug ejected lifeboats to another station or rally point where a rescue ship can take on survivors.
On larger stations, it is quite likely that there will not be enough lifeboats for the entire population. In this case, priority is always given to biomorphs. Children are given first access, but beyond that each habitat has their own procedures. High status figures may be berthed first, whereas others seats are given to the first people to claim them. In more managed evacuations, lotteries may be held. Synthmorphs and pods are evacuated last, though they are sometimes carried externally on lifeboats or tugged in open-vacuum pods. The worst-case scenario is that the station is dying quickly, there are no more lifeboats, there are no more shuttles, and there is not enough power to egocast out of Dodge. Individuals may still have a chance in this situation by donning a suit, taking possession of resupply tanks and an emergency beacon from a hazard station, and evacuating through an airlock. Remember to turn the beacon on. If a group evacuates in this manner, they should tether themselves together to make an easier target for rescue services to see.
Escape still may not be feasible, though, especially without an emergency farcaster. In that case, a biomorph’s last resort is to protect its cortical stack as best as possible. If a spacesuit is available, don it and set the oxygen to the minimum safe level for the morph type. Though physiological death is inevitable if rescue does not come before the air runs out, the morph will already be unconscious at the time (minimizing pain and suffering) and the brain kept in the best possible condition for the longest amount of time.

Environmental and Life Support Systems

From the smallest tin can to the largest cylinder colony, every habitat must provide a breathable atmosphere, waste management, and thermal control. Fresh oxygen must be supplied and carbon dioxide must be removed from the air. To grow plants, an artificial nitrogen cycle must be maintained. Fresh water must be available and waste water reclaimed. Whether through mechanical or biological means, each habitat is its own miniature ecosystem.

Breathable Atmosphere

Though the first space explorers operated in a pure oxygen environment, such practices are rare anymore because of the extreme fire hazard. Most habitats keep their internal gas pressure and mixture of nitrogen and oxygen comparable to pre-Fall Earth normal to ensure a minimum safe level for biomorph survival. The most common oxygen generators use electrolysis to split water into hydrogen and oxygen. O2 is vented to the inhabitable volume, while the hydrogen can be collected as fuel or dumped to vacuum. Reclaimed greywater is the usual source for these generators, as living inhabitants take first priority for fresh water.
Solid-fuel oxygen generators—often called “oxygen candles”—work on the exothermic reaction of an oxygen-releasing compound, such as lithium perchlorate, ignited by a mechanical firing pin or a burning fuse. The oxygen gas is cooled and filtered for particulates before being released. Oxygen candles have a nearly indefinite shelf life, but malfunctioning insulation or fuel contamination can lead to catastrophic fire hazards. As a result, they are more popular as emergency generators.
Habitats with enough interior surface area to support large green spaces can actually provide integrated oxygen production and carbon dioxide scrubbing through plant life, be it grass, trees, or, even, algae. However, most “green” habitats still require electrolytic oxygen generators. Only a few habitats are actually large enough to sustain the number of plants and trees required to match the daily oxygen consumption and CO2 generation of baseline humanoids. Even then, genetic engineering is required to increase the plant respiration rates to high enough levels.
Carbon dioxide is toxic to biomorphs as it accumulates. Headache, dizziness, shortness of breath, and confusion set in above 5% concentration by volume. Muscle tremors, decreased vision, and unconsciousness occur at exposure to 8% concentration by volume for several minutes. This can happen fairly quickly in microgravity, as there is no buoyancy effect to separate gases by density. Constant airflow is necessary to prevent dangerous “pockets” from forming. Early explorers depended on lithium hydroxide canisters to scrub CO2 via chemical reaction, with water as a byproduct.
Most carbon dioxide removal is done with swingbed systems that require little power and are self-regenerative. CO2-enriched air is drawn into an adsorbing bed of amine. Upon exposure to vacuum, the amine releases the carbon dioxide and is effectively recharged. By using alternating adsorption beds, the air can be continuously scrubbed. With additional filters, water and oxygen can be captured and recycled before the beds are vented to space. These systems are efficient enough that their only real limitation is the air flow rate.

Nitrogen Cycle

Atmospheric nitrogen is non-reactive and typically serves on spacecraft and habitats to maintain a comfortable gas pressure without elevating the oxygen content above that required for habitation. However, plants require fixed nitrogen for healthy growth. In microgravity, nitrogen fertilizers produced industrially are infused in the plant growth chamber’s feed stock. This can be an expensive process, though, and is avoided on the large habitats with artificial gravity and more natural growing areas.
Bacteria in the soil or in the nodules of nitrogenfixing plants, like legumes, converts nitrogen in the air into ammonia, which is released when either the bacteria dies or the plants are composted. Through crop rotation, colonists can sustain a local nitrogen cycle of absorption and release virtually indefinitely. Industrial nitrogen fixation synthesizes ammonia from the catalyzed reaction of nitrogen and hydrogen gas with a magnetite catalyst at high temperature and pressure. Because the gases can be recycled, the completed process is as much as 98% efficient and was responsible for a majority of all agricultural fertilization before the Fall. This is the primary method of producing ammonia and other nitrogen compounds when they are not available naturally or are required on short time scales.

Water

The water cycle in a habitat is one of its most essential functions because water is the universal currency in the solar system. Even infomorphs have a hard time getting on without a key base material in industrial processes. It is no coincidence that the major population centers tend to have local water resources.
Only Mars and the subsurface oceans of some moons have accessible liquid water, so it arrives at most habitats in the form of ice. The first step in the process is using vapor-compression distillers with a dual evaporator-compressor system to eliminate contaminants both lighter and heavier than water vapor, leaving only pure water at ambient temperature to flow out. From there, the potable water is pumped throughout the habitat for a variety of uses. Many microgravity stations also treat the purified water with anti-microbial nanobots.
Water transport must be done at pressure or through capillary action in microgravity habitats because there is no intrinsic force to assist. As a result, proper wetting of soil, for example, becomes problematic. Capillary “nets” that spread water distribution from the input in a plant growth chamber and draw out any excess water flow to the chamber output can help with this. Waste water, including from biomorph activities, must be removed by suction.
Habitats with artificial or local gravity have the advantage of a natural flow direction for plumbing. Some larger colonies even provide a pseudo-random rain system designed to maintain ideal moisture levels while simultaneously providing the psychological benefits of changing weather. At the designated times, water droplets at elevated temperature are vented into the atmosphere for condensation. This can be easily done in a dome structure on a planetary surface, while a rotating habitat requires some sort of “overhead” irrigation that avoids trapping the water near the axis of rotation.
Waste water is usually sorted into two categories: sewage or “blackwater” contaminated with urine, feces, or industrial waste and “greywater” from washing, bathing, atmospheric processing, and other activities that do not introduce toxic materials. Sewage is routed to vapor compression distillers for purification, while greywater can be recycled for such things as plant irrigation and oxygen generation. Spimes monitor water quality throughout the process and immediately identify the responsible authorities if a leak is detected or a contaminant is introduced to the fresh water supply.

Ecosystems

Green space is considered by some to be the crowning achievement of space settlement. With greenhouses, gardens, grass fields, and (in habitats large enough) forests, transhumanity can grow food, provide psychological comfort, scrub wastes, and provide oxygen. Next to the terraformation of Mars, cylindrical and torus habitats are the closest facsimiles of old Earth and often the easiest for infugees inhabiting new bodies to adapt to. Selective breeding, genetic mods, and hybridization exchange programs across habitats have allowed post-Fall horticulture to thrive and prevent evolutionary dead ends from destroying entire biospheres.
Succulents, such as aloe, agave, and cacti, are extremely popular for personal and decorative use because they are tolerant of temperature fluctuations, require little water, and come in a variety of shapes, sizes, colors, and leaf forms. Food gardens and farms tend to focus on producing the most nutritional content in the smallest area possible and are typically managed by professional agriculturalists who monitor soil conditions and plant health constantly. As a result, superfoods that could never have arisen naturally dominate. Owners of commercial operations protect their intellectual property—the genetic code of their product—fiercely.
Grass fields, parks, and forests tend to be common areas primarily intended for personal relaxation and air cleaning. Though O2 and CO2 respiration rates are not high enough to sustain large populations on their own, these green spaces are actually quite effective at removing other contaminants and improving general air quality. Areca palms, pothos ivy, spider plants, and ficus plants and trees are common ancestors of spaceborne plants for this reason.
Runoff water from green spaces and artificial rain is almost always reclaimed as greywater, unless it is over-concentrated with fertilizers or other chemicals. In that case, the runoff is captured as normal sewage and treated accordingly. Even the wealthiest habitats get every possible use out of every last drop of water.

Heat Controls

Even though people often think of space as being cold, heat rejection is actually one of a habitat’s most serious issues. Colonies in either an atmosphere or hydrosphere can reject excess heat from power generation, biological activity, and other station operations to the local environment. Natural convection does the rest. In microgravity and vacuum, though, there is no buoyancy to drive convection. There is no external fluid to carry away the heat by conduction, either. Thermal radiation is the only natural process.
This is a problem because the vast majority of space habitats generate more excess heat than can be removed by ambient heat radiation through the hull. The most common solution is an active thermal control system. Greywater is pumped past coldplates and heat exchangers inside the habitat walls and is heated in the process. Before continuing on for purification or reclamation, the greywater passes heat exchangers with a closed ammonia loop that carries the heat to external radiators. In some cases, the surface area required for external radiators is infeasible. Heat evaporators that actually vent the hot liquid to space are an option for those circumstances. Many soft spacesuit designs incorporate semi-permeable membranes that wick sweat from the body and evaporate it to space. Bioengineered analogues of this technology can be used for heat exchange to space on organic habitats.

Infrastructure

The outer hull of any station or colony is akin to a suit of armor. Whether manufactured from advanced nanopolymers, high-strength metallic alloys, inflatable composite materials, fused rock, or ice, the exterior shell must contain the internal volume, protect against kinetic impacts, mitigate radiation transmission, and account for unique local threats to the habitat.
In microgravity, most loads come from propulsion or mechanical forces from objects of significant mass in motion. Internal atmospheric pressure can be easily distributed over structures designed to withstand micrometeoroid impacts and the vibrational loads from internal machinery or crew activity. Thus, the hull itself in a tin can, cluster, or cylindrical habitat also serves as the primary structure for the habitable volume. Environments where the external pressure is higher, such as under the Europan ocean, require significant structural adaptations internally that are intended to keep the habitat from being crushed.

Windows

Windows serve a number of functions, from helping reduce the stress of confinement to providing line-of-sight for external operations for someone monitoring an activity in space from within the pressurized volume. They can be as small as portholes and as large as the immense window “stripes” on O’Neill cylinders. Windows are almost always multi-layered to prevent both a hull breach and contamination of the optical pane. The presence of orbital debris and the transparency of most optical materials to cosmic rays mean that many windows have exterior shutters that can be opened and closed from the inside, as needed. Quantum dot and other technologies allow for windows that can be changed from transparent to opaque or to an active display with simple commands.
Observation bubbles and cupolas with segmented windows are used to provide a wider field-of-view than is possible with porthole windows. They are often sized so that a morph can float or climb inside without obstructing traffic in the main volume. However, this is effectively a larger hole in the main hull and the supporting structure must be proportionally larger. To avoid this problem, it is not uncommon for tin can and cluster habs to build separate observation modules that attach at the nodes and limit the size of windows in the primary modules.
From a distance, the window stripes on O’Neill cylinders and their kin appear to be single-piece structures. This is an artifact of scale. These enormous windows are comprised of many small sections on a lattice frame that carries the structural load from the internal atmospheric pressure. Each pane consists of three transparent layers—a thin outer layer of aluminum oxynitride ceramic for projectile impact protection, a middle optical layer of sintered alumina nanomaterial, and an inner polymer layer to prevent shattering if the outer layers are breached. Two to three panes per section provide redundancy. This arrangement mitigates the spread of window damage in an emergency and allows for relatively quick, standardized repair.

Internal Architecture

The internal architecture of a habitat is as flexible as the designers and the pressurized volume allow. Tin cans and cluster modules in microgravity are usually cylindrical shapes intended to maximize efficiency. Equipment racks and even crew quarters are thus designed to fit in semi-cylinders flush with the pressure shell. This leaves the core internal volume open for people to do work and move between modules. Curtains and retractable polymer sheets provide only a modicum of privacy. Hatches between modules are similar, if not identical, to airlock hatches and the only real means of sealing off from the rest of the station.
As the size of the habitat increases, so do the options. At the most basic, recyclable walls can be extruded from plastic, arranged as the inhabitants desire, and broken down as needed. This is not uncommon in spin habitats without large, contiguous volumes. Otherwise, the internal volume is divided up much like submarines and spaceships, with pressure bulkheads that can be sealed in the event of an emergency and the internal spaces defined by their function.
On the scale of a torus station or larger, freestanding structures can be built on the floor or soil level no different than any on Mars or old Earth. The style and form depends entirely on the cultural and regulatory norms of the residents. If the spin gravity is less than 1 g, taller, lighter structures are possible. Gliders and motive-powered flight are an available mode of transportation in such habitats with a dense enough atmosphere to generate lift.
The most common building materials in large spin habitats tend to be light, cheap, local, or some combination of those properties. Bamboo is very popular because it can be relatively easily grown and maintained and pressed into an engineered hardwood for construction material. Excess metal from the fabrication of a colony’s primary structure is easily recyclable for internal uses.
Habitats with a soil layer tend heavily towards adobe walls because they are durable, excellent thermal reservoirs through a day/night cycle, recyclable, and almost infinitely customizable. Though maintenance and upkeep is often performed by robots that extrude adobe plaster as needed, many of the people who live in such habitats prefer to actually build the structures themselves. Making adobe bricks and assembling the structures are strong community-building exercises and create a tangible sense of connection between the residents and their homes.

Monitoring, Maintenance, and Repair

Information overload is extremely easy to come by when monitoring a colony with tens of thousands of residents, all relying on the successful parallel and interdependent operation of hundreds of systems and subsystems to stay alive. There is simply too much data for any one ego to watch everything. Most infrastructure maintenance is completely automated and handled by AIs with little direct transhuman oversight. Though spimes are widely used to provide instantaneous information as needed, most sustaining operations are automatically processed and handed off to robots for regular maintenance. Even structural repairs that bring the system back within design tolerances are often handled immediately and simply noted in the system log.
Transhuman oversight is only brought in when a trend exceeds control limits—such as a progressively failing structural member—or when a severe anomaly such as a deliberate attempt to circumvent the system is detected. At that point, the control authority can access local spimes keeping track of pressure, temperature, structural stresses, power availability, and atmospheric composition. Distributed multispectral optics provide real-time video in, at least, the visual and infrared bands. Connectivity monitors can even inform the operator when parts of the communication network (sensors, mesh, cabling, etc) fail, adding another layer of information.
For example, a breach in the hull that opened the internal volume to vacuum could be detected by pressure sensors reading the local ambient drop and the suction, the breaks in communication between connected spimes or any severed system conduits, and pattern recognition software noting the visible damage. A water tube ruptured by the breach would report the drop in fluid pressure on the other side of the tear and the flow rate into the void, while a damaged power cable would be signaled by the break in the local circuit. All of this sort of information would inform anyone with access to the system about the severity of the problem.
Emergency repair is primarily concerned with stopping whatever danger or anomaly has presented itself until a permanent solution is found. Some habitats actually have an automatic patching system filled with a liquid polymer that expands and self-hardens in vacuum. Like coagulants in blood plugging an open wound, this polymer will fill any hull breach small enough that the escaping air volume does not overwhelm the patch. Affected systems can then be rerouted or shut down, as necessary. Inflatable scaffolding is usually installed over the inside of the breach to provide a seal while the polymer is removed and permanent repair work begins, whether by robots, synthmorphs, or “old school” welders in space suits. Standard maintenance is a more methodical and controlled process. For habitats that cannot afford sustaining nanomachines, standardized robots with interchangeable tools are common. Often resembling crabs or other small arthropods, the bots have multiple legs with grapple fixtures, onboard sensors, mesh inserts, and reservoirs for carrying stock materials. Thus, the same bots could be used for fixing repair welds on the exterior structure, assembling parts for a work crew, removing grime and debris, or extruding adobe mortar for patching a decorative piece on someone’s home. Some can even reprocess waste materials on the spot for recycling with internal microfurnaces.
An alternative to robotic maintenance is the smart animal. Smart rats or mice can be implanted with mesh inserts and neural monitors to effectively allow the control system to direct their behavior. Surviving off the detritus from the habitat, the smart rodents can remove waste products, deposit their own in a pre-determined location, control the population of unwanted insects and other invasive species, and serve as mobile eyes, ears, and noses. Thanks to the behavior control algorithms, their reproduction rate can be limited to population maintenance levels and modified as needed.
Some habitats also employ smart monkeys because of their strength, responsiveness to commands, and ability to learn new tasks. They will also perform menial, repetitive tasks that many fully sapient egos would consider boring or beneath them. This can be problematic, though, in colonies with high pressure to provide physical bodies for infomorphs, as the partially uplifted simians are considered competition for work. Habitats geared towards agriculture or acting as a nature preserve will also often engineer biocompatible spimes to constantly monitor the health and status of their animal population. While an individual animal may not be any more intelligent than its predecessor on Earth, the behavior of the group can be tracked to watch for emerging patterns or trends that indicate the health of the entire habitat—the “canary in a coal mine” principle.

Mesh Systems

A habitat’s mesh is its nervous system. Except for the smallest tin can habs, there are simply too many components, services, and factors and too much information for any single intelligence to oversee. A station’s mesh is almost always broken down into decentralized subsystems, each monitored by dedicated AIs and infomorphs. Most subsystems are individual VPNs, often secured with encryption given the importance of their functioning for habitat safety. Particularly sensitive systems may be hardwired rather than wireless for increased security.

Subsystems

Though a single rack of quantum computers has enough power to run all of the basic functions of most habitats, it is standard practice to subdivide mesh infrastructure for safety and security. This prevents a single point of failure from taking out all habitat systems. Particular regions of larger habitats and specific habitat functions will almost always have their own dedicated subsystems. Certain processor-intensive tasks, such as running AGIs and simulspaces, will have dedicated subsystems as well. This is normally true even on smaller habs where there might otherwise be only one master control system running everything. Subsystems are almost always slaved to whatever system is in the hierarchy above them. This means that an authenticated user on a master system will usually have access privileges to the subsystems underneath it. Particularly secure systems may require an extra layer of authentication when accessing each subsystem, but this is often impractical for day-to-day operations. A more standard practice is to only apply extra security to critically sensitive devices and functions.
On habitats with a centralized authority (meaning most inner system, hypercorp, and Jovian habitats), there is likely to be a master control network that oversees all habitat subsystems. Depending on their security set-up, this control system may simply have monitoring privileges or the subsystems may be slaved and controlled. There are sometimes complications with these arrangements, particularly given that many inner system stations privatize certain aspects of habitat operations, turning them over to hypercorps. It is not uncommon, for example, for egocasting/farcasting and defense/security operations to be under the private control of a specific company and thus separate from the habitat’s master control. In these situations, the overall authority of the hab usually maintains monitoring privileges, but accessing the privately run subsystems requires authorization from that privatized authority. In some cases, even habitat authorities may be forbidden to access certain subsystems.
Elsewhere, a habitat’s mesh systems may be far more decentralized and independent. For example, anarchist cluster habitats often have communal reactors, power grids, makers, and harvesters. Many other systems, like recycling, life support, and hull repair are the province of individual modules. Customs, defense, and security, where they exist, are frequently run by specific collectives, syndicates, or worker’s councils—or sometimes even flash mobs. By custom, actions taken and information collected by such groups are logged as a matter of public record, available to anyone with a public mesh connection.
On other habitats, control of certain systems is factional. Kronos Cluster in Rhea’s orbit has several distinct power grids, split between anarchist and guanxi neighborhoods. There is effectively no security, but the ultimates in control of the spaceport have sole control over customs, defense, and spaceport operations.
Redundancy and backup systems are a common feature. If a specific subsystem fails, there is quite often another one that can be invoked to take its place in whole or part—particularly if the system is critical to habitat function or biomorph survival.

AIs and Infomorphs

AIs, AGIs, and disembodied egos are common in habitat mesh subsystems, keeping a continual virtual eye on important functions. AIs are typically used for routine and non-critical functions, each a specialist in their particular field. AGIs and infomorphs are reserved for more important functions, especially those that require more sapient qualities of discernment, evaluation, and adaptability. These software entities are usually programmed/instructed to alert habitat officials when specific situations, problems, or security breaches arise. Habitats with populations that are more distrustful of AIs and AGIs will lower this threshold and employ embodied personnel to oversee system controls. Critical systems like life support, space control, and defense will almost always have security AIs that provide overwatch against intrusion and subversion.

Habitat Sleeving and Jamming

Many habitat systems are automated and/or feature robotic components, so they can be operated through the mesh via remote telepresence. By the same measure, a habtech may jump into and “jam” such automated habitat systems. This is a common procedure for operations that require fine control or the finesse of an ego. Some stations go even further, hooking up habitat systems to specially designed cyberbrains, enabling an ego to sleeve into the habitat or subsystem as if it were a morph. The sensory input received from a habitat is much different than standard humanoid morphs so this job is unnerving to some, especially those that do not take well to non-standard morphs.
Sleeving a habitat as a morph does not make the ego omniscient or all-perceiving, any more than being in a transhuman morph would make one aware of all of the blood corpuscles, bacteria, and food particles moving through one’s body. It does however confer a sense of proprioception: the perception of “body” awareness and where all of the parts of a body are in relation to one another at any given time. This means that the inhabiting ego is aware of the macro-scale state of the habitat, including such things as hull integrity, atmospheric pressure (interior and exterior, if any), the functional status of the power grid and energy intake and consumption, orbital position and velocity, and the position and functionality of major external “appendages” such as axial space docks or the mirrors and windows on an O’Neill cylinder.

VR Simulspaces

Given the high bandwidth consumed by virtual reality simulspaces, many habitats feature hardwired connections for simulspace functions, which also tends to ensure a more stable connection. The particular simulspaces offered vary with each habitat, but a wide array of resort, recreational, and roleplaying sims are usually provided.

Mining and Harvesting

Though recycling is a way of life for virtually every habitat, the laws of physics mean that no system is entirely perfect. Water stores must be replenished. Exterior damage from cosmic radiation and debris must be repaired. Broken equipment must be rebuilt or replaced. Reactors must be refueled. Local mining and harvesting is always the first choice to provide these inputs, if at all possible.
Habitats in orbit around the gas giants—Jupiter, Saturn, Uranus, and Neptune—operate craft specifically designed to fill their tanks with atmospheric gases, like hydrogen and helium, and rocket back to the habitat for offloading. This is the primary method for collecting helium-3 for fusion reactors. Atmospheric mining craft—skimmers—must be adapted for their particular environment to safely operate. For example, Jovian skimmers require larger engines to overcome the planet’s gravity well and heavier shielding for electronics. Even virtual crew operating the skimmer require some protection for their digital systems. Saturn skimmers must deploy retractable stabilizers to maintain control in the high winds. Nuclear thermal rockets are common amongst all skimmers because of their high thrust-to-weight ratio and ability to use the ambient atmosphere as reaction mass.
Microgravity harvesting bays are employed by most habitats to bring in outside materials, such as rock and ice, for processing into useful materials. Dense fields like Saturn’s rings or debris clumps are relatively easy to mine because there are so many particles and chunks of material that can literally be grabbed with a drone’s robot arms and propelled back to the station. These capture drones are disc-shaped to give a 360-degree reach from the main body and allow the plasma thruster in the center to be pointed through the center-of-gravity of any object. Most are no larger than 1.5 meters in diameter, with six to eight articulated appendages that can reach another four meters each.
The mining of objects too big to be brought into the harvesting bay requires a more methodical approach, as there is no point in paying the reaction mass to bring back mining slag. While large ice blocks can be broken up into smaller pieces for delivery, captured asteroids and comets are often covered with swarms of microbots that locate veins of useful material, burrow into the object, and extrude it to the surface for capture drones to carry to the station. Thoroughly blended objects will be encased, much like a Cole bubble at its initial stages, and broken up into their constituents with heat and gaseous reactants. All of this is necessary to maximize the natural resources obtained without adding orbital debris to the system.

Public Services

Not all habitats provide public services, but they are common on larger stations as well as autonomist colonies and populations with dominant memes that include social welfare.

Medical Care

With widespread genetic engineering eliminating most common diseases and defects, much of the medical care on a habitat is geared towards emergency response, research, biomorph cloning, and resleeving. Provisions in a tin can habitat can be as sparse as a single medical rack outfitted with first aid kits and an auto-doc that can perform simple diagnostics, wound treatment, and fluid infusions, while torus habs, cylinders, and Cole bubbles with large populations may have a full trauma center with a hypobaric chamber for decompression sickness and “healing vats” that stabilize the patient while high-quality medichines go to work.
Most people actually turn to their personal muse to resolve everyday problems and temporary maladies, such as an allergic response to a pollutant in the environment. The muse can identify the problem, determine the appropriate response by cross-referencing data on the mesh with their user’s medical history, order whatever is required, and have it nanofabbed or delivered to their user with little to no conscious input. Except for residents in communities without access to modern technology, no one really goes to see the doctor anymore unless the problem is beyond “off-the-shelf” solutions.

Body Banks and Resleeving

Resleeving is both big business and a part of everyday life in most colonies. While areas controlled by the hypercorps almost exclusively operate commercial facilities that require direct payment for their services, some autonomist and cooperative habitats actually have public resleeving facilities that provide access to basic, unmodified morphs. Highly specialized morphs, of course, require more individual resources, some kind of barter arrangement, and/or access to privately owned facilities, but this ensures a minimum standard of living for everyone in the community.
Public resleeving is almost always restricted to citizens to mitigate a mass influx of infugees and prevent the transient population from putting a strain on the system, though wait times have a strong inverse correlation with an individual’s standing in the rep economy. Such facilities provide the standard-of-care in terms of maintaining cleanliness, only using certified ego bridges and providing untampered bodies. However, there are no frills. Once an ego integrates with its new body and finishes acclimating, the individual is free to go. On-site psychosurgery facilities are available in the event of the rare emergency, but the public centers do not take responsibility for any non-critical complications.
Gravity is essential to the tissue-development process involved with growing new biomorph clones, which can be a strongly limiting factor on the morphs available on tin can, beehive, and cluster habs. Morph availability on habitats with spin or natural gravity is only constrained by the resources and volume available for the growth chambers or assembly lines.

Nanofabrication

Public nanofabricators run off the trash and other wastes generated by a habitat. Anything on the blueprint list that can be made from the recycled materials and does not violate contraband restrictions, such as weapons or volatile chemicals, is available on-demand. For example, many people will change clothes by selecting their new attire from the list and discarding what they have on into the recyclers to cover the cost. Hazardous materials can only be recycled at designated drop points to prevent cross-contamination. Some public fabbers do have the option of expanding the available blueprint list for a nominal fee or the input of additional material by the user.
Access is usually first-come, first-served, though larger jobs that require more system time are automatically scheduled during off-peak hours. The fabber will send the user a notification over the mesh when the project is complete, if it cannot be assembled immediately. Individuals who overuse the public system can find themselves facing fees, based on either the frequency or the scale of their requests, to cover the additional cost of maintenance and upkeep. For most habitats, this serves as an effective deterrent against the free-rider problem.
Nanofabrication of larger items, heavier construction materials, or goods that require exotic or rare elements may not be an option, but most larger habitats have ample robofactories. These robofacs are capable of handling custom design orders, often with a quick turnaround time. Similarly, many nanofabbers are not capable of disassembling large items that can’t be broken down or particularly dense objects, so these must be taken to larger disassembly centers for recycling.

Power

A wide variety of options are available to provide power for habitats, from generators that draw energy from the local environment to immense fusion reactors. However, the selection of a power source is not just about generating current. Factors such as population safety, refueling, structural limitations, environmental limitations, and cost all play significant roles in determining what keeps the lights and life support on.

Solar

Solar power remains common in the inner system because the only costs are fabrication and maintenance. Far from the bulky, finicky, and toxic photovoltaics of the early Space Age, panels are now printed in sheets on a composite substrate with integrated micro-scale concentrators that focus up to 90% of the sun’s light on each cell. This reduces the size and mass required to generate electricity dramatically. Arrays that were once the size of a playing field are now no bigger than a person. Excess heat rejection is accomplished with capillary tubes circulating coolant from the thermal control system.

Electrodynamic Tethers

Habitats that move through planetary or solar magnetic fields can generate power by extending electrodynamic tethers but require reboosting as they exchange kinetic for electrical energy. Electric potential builds up along the cable as it moves in its orbit through the magnetic field. Skyhooks and rotovators can reduce this process to generate thrust, but stationary space elevators are motionless with respect to the local magnetic field. However, this system requires enough proximity to a local plasma source for electron exchange. In the case of Jupiter, such regions are also home to dangerous radiation belts. Vibrational modes from pendular motion and unexpected surges or discharges from variations in the local field can also make an electrodynamic tether unstable.

Thermal Generators

Thermal generators typically are based on the Stirling engine. A heat source such as a solar mirror or radioactive pellets warms a working fluid, which drives a piston in a linear alternator. The piston, in turn, drives the generator to produce electricity. The remaining heat is rejected to space. Though thermal generators are limited in output by the efficiency of the Stirling engine, they are very robust, provide constant, low levels of power, and can operate for decades. Some pre-Fall probes in the Kuiper Belt are still functioning on these systems with a minimal loss from the steady decay of their radioactive fuel pellets. Thermal generators are also popular with processor loci and as emergency backups. Nuclear batteries are a special variant of the thermal generator and directly convert the heat from radioactive decay into electricity by thermocouples. This is less efficient because of conversion limitations, but more easily miniaturized because there are no moving parts.
Nuclear batteries are a special variant of the thermal generator that converts the products of radioactive decay into electric power. The oldest and least efficient generate power from heat via thermocouples, while modern optoelectric batteries use either photocells tuned to capture IR or betavoltaics that convert captured beta radiation with minimal thermal losses. Some work has been done with converting higher-energy emissions, such as gamma rays, but the risk of backscatter radiation is much higher and requires heavy shielding.

Nuclear Fission

Nuclear fission remains an option on planetary habitats in the inner system, where most radionuclides are concentrated. The most widely used design is the fission fragment reactor. Nanoparticles of fuel are electrostatically suspended in the core, while a magnetic mirror focuses the ionized byproducts of fission into a beam. The surface area of the “dusty plasma” is high enough that radiative cooling is effective on its own. Deceleration of the ion beam provides direct collection of electricity at up to 90% efficiency. During the fuel cycle, the majority of the highly toxic fission byproducts are consumed, such that the final waste only emits alpha particles. These are blocked by biomorph skin, though workers must take care not to inhale or ingest any of the fuel during loading and maintenance.

Nuclear Fusion

Fusion generators reside at the top of the chain because no other system can match their balance of high output, high efficiency, and storable fuel. Deuterium-tritium reactors are both widespread and the oldest generation of the technology because they are the easiest to ignite. The problem with D-T fusion is that the neutron flux is relatively high and power must still be generated by transmitting heat to a working fluid. Over time, the containment vessel will become irradiated and the moving parts in the generator will break down.
Habitats in the outer system solved this problem by mining helium-3 from the atmospheres of the gas giants. Though He-3 fusion has a higher ignition temperature and lower reaction efficiency, the neutron flux is reduced by as much as two-thirds and the average emission is much less energetic. Helium-3 fusion also produces electrons for direct transmission, eliminating a separate generator. As a result, He-3 reactors are smaller and lighter for the same production capacity, though they require a special fuel.
The Planetary Consortium refuses to be dependent on shipments from the Titan Commonwealth, though. The dense plasma focus reactor was originally developed on Titan for researching exotic, low-neutron fuels, but scientists and engineers in the Consortium have perfected it for the deuterium-deuterium reaction. Cycles of electromagnetic acceleration and compression generate plasma that is “pinched” into a state where fusion occurs. As with helium fusion, DPF directly converts the fusion energy into electricity, but at much higher efficiency and with fuel from any source of hydrogen.

Power Transmission

Most power transmission is over low-loss carbon nanotube filaments or fiberoptic cable, unless particular environmental conditions favor metal wire. This allows a habitat to provide power without high voltage lines that present both an electrification and thermal hazard. Fiberoptic lines require the electricity be converted into a laser for transmission. Power can also be transmitted wirelessly by electrodynamic induction or beaming. The induction method is useful at short range for universal charging pads, RFID patches, smartcards, and portable devices. While it is possible for a habitat to install induction coils throughout the volume for constant recharging, this is inefficient unless absolutely required.
Long-distance wireless power transmission, such as from powersats, is done by laser or microwave. The microwave method has efficiencies on the order of 95%, but requires large transmission and receiving antennas. A 750-megawatt system would require a 1-kilometer diameter transmitter and a 10-kilometer rectenna, for example. Laser transmission can be miniaturized, even to the level of nanosatellites, but loses some efficiency in the conversion process. The receiver is simply a monochromatic solar cell optimized for the laser frequency.

Security

Except for tin can hovels on the edge of the system, widespread surveillance is a fact of life thanks to the nearly uncountable number of small data-gathering devices. Even anarchist and autonomist habitats have the same surveillance and security systems as the hypercorps, Consortium, and the Junta; the difference is in the philosophy and control schemes that govern them.
Spimes are useful because they provide data at nearly any level of granularity a person desires. Though the majority of individuals prefer to filter out data at the conscious level that isn’t directly relevant to their interests, most muse software includes automatic subroutines that access local spime data and status updates from Habitat Control to immediately inform the user if a threat presents itself. This is a much faster and more efficient method for getting residents out of harm’s way than a centralized alert system. It also gives individual morphs a greater chance of evading harm until the proper authorities respond to the threat, be it a criminal, an environmental hazard, or a structural issue. If carbon dioxide levels are getting dangerously high in a certain area, for example, the local mesh will provide the muse with a constant update of the conditions, allowing a muse to guide its user to safety. If someone is being chased in an alley, their muse can access the mesh to tell authorities which local spimes can view the threat, plot multiple courses to safe areas, and even put a public alert out to draw attention.
Like other habitat systems, many colonies rely on sentry bots and similar AI-piloted robotic guardians to handle routine security measures. Bots are favored over personnel because they follow orders without question and avoid putting an actual ego in danger. Microgravity habitats, especially tin cans, very often rely on drone security because the machines do not impose on their life support margins or create organic waste to be dealt with. Quite often these bots are overseen by infomorph security personnel, who can evaluate if an incident requires more discretion, tact, or overwhelming force than the security bot is applying. These operators can also teleoperate or jam the bot directly, putting themselves in control of the situation.
Aside from standard sentry bots, many habitats employ automech, dwarf, and similar utility robots to handle security threats because they can be used for other tasks when not responding to alerts. Hypercorp habitats are well-known for using this method to save costs in non-essential areas. These bots can also be equipped with standardized packages that vary with the assignment. A “pacification loadout” typically consists of a vortex ring gun or shock baton, a grenade launcher with concussion or overload rounds, and a freezer spray weapon or microwave agonizer. The “assault loadout” trends more towards seeker rifles, explosive mini-grenades, and submachine guns with zero bullets or laser-guidance. Bots can also use whatever tools or equipment they have on hand, though the results can vary. Just the presence of a dwarf bot with mining bores spinning might be enough to scare off a would-be attacker. It might also incite unruly protestors to cry, “Oppression!”
Morph guards are used in habitats where the authorities give the security forces more discretion, a private company provides the services, or drones are distrusted. Olympians and novacrabs are common biomorphs in security, as well as arachnoid and slitheroid synth-shells. These are sometimes equipped with heavier armaments, military armor, or exoskeletons in situations that call for force multipliers. Mil-spec reapers and similar combat morphs are kept on stand-by in case of serious disturbances, dangerous outbreaks, or military assaults. The Jovians are particularly reliant on biomorphs for physical security because they don’t trust computers to do all the work and they have a deep disdain for police baboons that “put good men out of work.” The average Jovian enforcer is likely to have a shock baton and a pistol with flex or zap bullets. Only higher-ranking officers, corporate security, and military police have the authority to use fully lethal firearms, though most of the Junta’s leadership looks the other way if a dissident is outright beaten to death.
Habitats that lack the compunctions of the bioconservatives have also been known to include smart animals in their security apparatus, from smart dogs upgraded with defensive bioware and cybernetics to the dangerous but effective police baboon. Smart rats and mice can also serve as an unobtrusive network of monitors.

Sensor Systems

All of the functional systems that make up a habitat rely on either embedded or parallel sensors to function smoothly. Pressure and strain gauge spimes on mechanical systems provide that data that lets the control system know when a pump or seal is going to fail. Infrasound detectors can quickly communicate the presence and intensity of systemic disturbances that may take out local electronic sensors, such as the detonation of an EMP device.
Electromagnetic field meters and magnetometers built into the external structure of the habitat are used to monitor solar weather. They can also be used to detect if an approaching spacecraft isn’t everything it seems. For example, there could be a problem if lidar and t-ray scans show a bulk cargo freighter, but the reactor power and EM field are more consistent with heavy directed energy weapons.
Chemical sniffers can be optimized to trigger upon the introduction of a compound that should not be there, such as explosive materials or the exhalations of biomorphs in restricted areas. Rare element scanners are more expensive and specialized, but virtually impossible to beat without enclosing the contraband in an entirely closed-loop environmental system and cleaning the exterior of the container thoroughly to match ambient conditions. Such an apparatus will itself require a strong cover story or masking of its own to get past customs and security.

External Sensors

External sensors such as lidar scanners, radar arrays, passive T-ray detectors, and IR cameras are often mounted on modular pallets that can be repaired and replaced without requiring a massive overhaul of the habitat structure. These sensor pallets can also be easily distributed over the hull to increase the effective size of an array without necessarily making a bigger target. Large sensor arrays and antenna are only used for very specific purposes, such as wide field detection of galactic gamma ray bursts and military electromagnetic warfare operations (jammers). Smaller sensors arranged into interferometers and partnered with powerful data processing software typically are more than sufficient.

Transit Systems

Fully enclosed habitats with little open space often rely on elevators and internal rail cars to move people around. In the case of microgravity habitats, there is little difference between the two in function. Elevators tend to be thought of more for moving people inside buildings and discrete structures, while a tram or train is used for transit across the entire habitat. In habitats with artificial gravity, elevators are associated with moving “vertically” in the direction of the gravity gradient.
Floatways are the lifelines between modules in tin cans and cluster habs. Entirely in microgravity, the walls are designed to carry power connections, fluid transfer tubes, gas hoses, and various other infrastructure lines without blocking personal traffic, internal airflow, or emergency hatches. Automatic linkages at each connection point have valves that simultaneously cut off the flow through the wall lines if the emergency hatches are closed. This ensures that fires, hull breaches, and other hazards can be quickly contained. Early space stations often passed internal lines and hoses through the open hatches, which meant there was not enough time to close the hatch in an emergency because the astronauts had to clear the volume first.
Grab-loop conveyors in floatways and within large hab modules themselves allow morphs in microgravity to quickly get from place to place without expending a lot of energy or risking bumping into people, which often has a cascading effect of bodies ricocheting off each other in a crowded volume. The conveyors follow predetermined routes and entoptics are tuned to the system to provide directions and notification if a transfer to another line is necessary. Within a floatway, grab-loops are self-contained and do not cross the seal at the connection point, so most riders let go at the end and coast to the next line. Monorail lines can be installed both within the pressurized volume and on the exterior of the hull for rapid transit across the habitat. Many Bernal spheres, Cole Bubbles, and O’Neill cylinders have monorail lines that traverse the rotational axis and along the surface of the habitable area. The trains that transition between the low gravity at the poles and the spun gravity on the interior surface typically have grab loops all over the interior walls and gel couches that a morph can press into to hold still during the change in gravity. Some habitats forgo trains in favor of personal travel pods that run back and forth across the lines. This allows each traveler to adjust the interior to their personal level of comfort and select a route and travel speed of choice.
Many habs with rotational gravity maintain a public bicycle system in the habitable area. Bikes for rent tend to be more common in the inner system, while free bicycle networks are typical in the outer colonies because they are so easily produced by nanofabrication. In either case, bicycles are cheap, provide good exercise, don’t pollute the internal environment, and take up little space—especially if a folding bike or urbanized design is used. More people know how to ride a bike than drive a ground vehicle, after the Fall.

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