Spin Habitats (IF)

Ubiquitous away from Earth and Venus, habitats with artificial gravity from spin is a must for comfortable and healthy living in space. It has also become a marker of status; bigger is better.

Spin Habitats

Spin habitats are the beating hearts of human life beyond Earth — great rotating cylinders or rings that use centrifugal force to create gravity. After the Fall, they became the default pattern of settlement from Mercury’s orbit to the Belt. Each is a city-state in steel and composite, self-sufficient, insular, and profoundly shaped by spin.

Habitats are rated by Tier, a measure of radius and social comfort. Each doubling of radius roughly doubles population and halves the steepness of the gravity gradient. A Tier-1 drum is a cramped work-cage; a Tier-10 world is a paradise with open skies and a soft, slow spin.

Tier	Radius	Typical Length	Typical Area	Population Density	Typical Population	Rim Speed	Period	Comfort	Floors	Floor Height	Sports	Population /Meter
1	30 m	300 m	0.05 km²	32,000	3,000	15 m/s	12 s	Horrible	2	5	Treadmills	10
2	125 m	1,500 m	1 km²	16,000	30,000	33 m/s	24 s	Tolerable	3	10	Walking	10
3	500 m	10 km	30 km²	8,000	300,000	70 m/s	45 s	Adequate	4	15	Tennis	30
4	2 km	60 km	700 km²	4,000	3 mil	140 m/s	90 s	Comfortable	5	20	Dancing	50
5	8 km	300 km	14,400 km²	2,000	30 mil	300 m/s	3 min	Prestige	6	25	Gliding	100
6	32 km	2,000 km	380,000 km²	1,000	300 mil	600 m/s	6 min	Exemplary	8	30	Golf	150

Tier: The Tier of a typical habitat of this side; small habitats are usually poor. In larger habitats there are several communities and not all have the full Tier.

Radius: The distance between the axis of rotation and the garden ring. Habitat and industrial levels are bellow this.

Typical Length: The length of a typical habitat of this type.

Typical Area: The surface area of the garden ring.

Population Density: Typical population per km² of inner area. Actual habitats is usually on the level below.

Typical Population: Total population of a typical habitat of this type.

Rim Speed: The speed of the outer rim of the habitat, indicating how hard it is to dock. This is not perceptible inside the habitat.

Period: How long a full rotation takes. At 12 seconds you need medicine and acclimatization and still experience some trouble. Airflow bends with Coriolis; fans, toilets, and plumbing must be engineered for curved motion. Sounds can Doppler-shift oddly as you move. At 24 seconds Light vertigo, manageable with meds/training. Noticeable Coriolis when moving head, but daily activity possible. Typical range for small habitats. At 40 seconds and more there are no acute medical issues, but comfort and safety still increases with radius. garden ring.

Comfort: A general description of conditions of living.

Floors: The number of floors below the garden ring. The garden itself is not counted.

Floor Height: The height of each of these floors. Greater height naturally creates room for larger installations; higher houses, shopping malls, sport centers, and industrial installations.

Sports: Sports practiced for exercise and amusement.

Population/Meter: Not all habitats have the standard length. A habitat holds this many people per meter of length, tough almost nothing is under 10 meters. On a ship population is usually at least twice as high as this.

I used to list gravity but all were in the 0.8 to 1.2 g range and thus not very interesting.

Habitat Structure

Every spin habitat shares the same basic anatomy:

Central Core — A microgravity transit and industrial hub along the rotation axis. Cargo, data, and power systems converge here; long-term workers adapt to low-G.
Open Air — The broad space between the core and the hull. Here gravity rises sharply with distance. In smaller habs, it is a lethal void of high angular speed a dropped tool here can scythe across the habitat with deadly force. Large habs make it a playground of light and motion: skimmers race the horizon while children learn to glide on polymer wings.
Garden Ring — Facing the open air, this is usually left as a park for relaxation. A few houses, perhaps some pastoral farming. More indulgent habitats have true wild areas with wild animals, usually following an ecological pattern from Earth.
Residential Ring — The main living band, where gravity stabilizes near Earth standard. Housing, workplaces, markets, and schools cluster here. High-status residents claim upper terraces near the light tube; lower decks shade into the factories.
Industrial Ring — The lowest level of the pressurized interior, heavy with machinery, refineries, and storage. Gravity here is higher and the air is warm and noisy. Workers call it “the ground” or “the under.” Slums often cling to the upper vaults of this zone.
Shielding and Reserves — An outer layer of water, rock, and slag bags that soaks up radiation and micrometeors. It also serves as an emergency resource stockpile — ice can be tapped for life support, metals for repairs.

From the zero-G core to the heavy underdecks, a well-designed habitat is a vertical world: sky above, soil below, all curved around its own horizon.

Gravity and Comfort

Spin gravity grows with radius. Smaller stations must rotate faster, creating steep gravity gradients between decks and disorienting Coriolis effects. In the smallest habs, you can feel gravity change between floors; in the largest, a ball dropped from head height falls straight. This makes small habs strict and utilitarian; they must be. Space, air, and gravity are precious. Every cubic meter is planned. Crowding and vertigo breed zealotry, discipline, or madness.

Large habs allow leisure and diversity. When the horizon curves gently, politics replace fanaticism. Power correlates with Tier: higher tiers have slower spin, better shielding, richer trade, and more autonomy.

Low-Tier (1–2): harsh, crowded, and loud. Gravity gradients exceed 10% per deck. Constant vertigo and spin sickness for newcomers. Survival depends on discipline or faith.
Mid-Tier (3-4): comfortable city-scale habitats with stable gravity across most levels. Recreation, flight sports, and small parks. Populations stable and self-governing.
High-Tier (5-6): vast, slow-spinning worlds with gentle gradients and curated ecosystems. Architecture imitates nature: valleys, lakes, clouds, and weather cycles.

Microgravity Core

The central core is the habitat’s nervous system. It houses docks, data centers, power conduits, and small workshops that rely on freefall. Cargo and personnel move by shuttle or elevator along the spin axis. Here gravity is negligible; items drift, tethered to rails and webbing. Core crews work in short shifts to avoid Degrav, returning to the rings for sleep and recovery. Communication hubs and control arrays live here, shielded from hull vibrations and population noise. Here we also have the light of the habitat, either powered or led in by mirrors.

In luxury habitats the core hosts a leisure park or sculpture hall — a weightless cathedral of art and light. In poor ones it is a stinking warren of coolant lines, drone racks, and storage tanks.

Industrial Levels

Below the main residential band lies the true engine of the station. Heavy industries cluster here: fusion stacks, recyclers, and fabricators. Gravity exceeds 1 g, making labor exhausting and accidents severe. Slums often develop in the upper galleries where rent is cheapest but air and heat rise from the factories. Civic managers claim it’s all automated. Workers know better.

Shielding Layer

The outer hull holds hundreds of meters of water, rock, or slag sealed in cellular tanks. These absorb radiation, capture stray impacts, and act as a strategic reserve. The temperature here is cool and constant; maintenance crews walk among pipes and valves under twice Earth gravity. In a crisis the layer can vent water inward for firefighting or hull balance, or outward as propellant.

On-World Rings

Spin habitats are not limited to free space. On moons and planets, vertical-axis rings are dug into regolith to blend centrifugal and local gravity. Inside, “down” is the vector sum of both forces; the floor tilts slightly outward. Each ring forms a district a few hundred meters wide, holding Earth-standard gravity even on small worlds. When more room is needed, new rings are added side by side rather than widened. Common to Luna, Ganymede, and Callisto, these rings anchor whole cities — surface by day, spin by night.

Ship Habitats

Spacecraft in long transit are temporary habitats. A cruiser or freighter is a Tier-1 or Tier-2 world: fast spin, dense air, high population per cubic meter. The crew tolerates crowding because voyages are measured in weeks, not years. Comfort zones are narrow: a brief walk toward the axis moves you from 1 g to floating. Every object is secured, every deck labeled with its spin offset. The culture of long-haul crews descends directly from the smallest permanent habitats — endurance, ritual, and dark humor.

Cultural Notes

Flight and sport — gliders and jet wings are prized hobbies in high-Tier habs. In smaller ones, it’s an expensive way to die.
Sky illusion — upper mirrors and light tubes simulate dawn, dusk, and weather cycles; the wealthy buy custom skies.
Underdeck cults — religions and unions rooted in the industrial levels, worshipping labor, silence, or heat.
Slum gravity — low-Tier habs sometimes boast “two-gee bars,” where heavy spin and cheap drink keep outsiders away.
Festival of the Axis — weightless dances and contests held in the microgravity core at solstice or founding day.

Spin habitats are humanity’s second home — cities that never touch the ground, yet grow soil and weather of their own.