Open atmosphere and illumination cycle

Established environmental architecture; quantitative climate model remains open.

The inhabited rim is not roofed.

The current Station model uses an open atmosphere retained against the rotating inner surface by artificial gravity. The approximately 60 km vertical figure used in scale studies is an engineering and visual envelope rather than a membrane or hard ceiling. Gas density decreases with altitude; terrain, towers and vehicles therefore pass continuously into thinner atmosphere rather than approaching a roof.

This distinguishes the Station from a sealed cylindrical habitat. Environmental containment is a global dynamical property of the rotating structure, not a transparent enclosure over the landscape.

Altitude is an environmental limit before it is a geometric one.

Large artificial mountains and tall polarward structures are permitted by the geometry, but increasing altitude brings lower pressure and stronger exposure to atmospheric motion. Earlier design discussion therefore treated very tall terrain as climate- and wind-limited as well as structurally limited. High ground can become progressively hostile without requiring an arbitrary architectural ceiling.

The exact maximum useful mountain height remains open. Figures in the rough 10–20 km range have been explored as plausible landscape-scale extremes, not adopted as universal limits.

Daylight is broad, copper-red and unlike terrestrial sunlight.

The central low-temperature star is treated in the current visual model at roughly 2,075 K with an apparent disc around nine degrees and a provisional visible illumination target around 15 klux. Much of its output lies in infrared. The large apparent disc produces weak-edged shadows, while the visible environment reads copper-red rather than as ordinary white sunlight with a colour filter.

These photometric values remain provisional and are shared dependencies with 600.20:10:01; this record preserves their environmental consequence rather than asserting an independent stellar solution.

Night is engineered by occlusion, not produced by planetary rotation.

Because the inhabited surface continually faces inward toward the central star, ordinary rotation cannot create a terrestrial day/night terminator. The developed model therefore introduces a largely static occluding structure above the equatorial region. As the inhabited rim rotates beneath it, locations pass through the occluded region and experience an artificial night interval.

A working night duration of roughly eighteen hours has been used in design discussion. The value is not yet supported by a final occluder drawing or latitude model and should remain provisional.

The system creates geography as well as weather.

Atmospheric depth, terrain height, illumination and occlusion couple directly to settlement patterns. Low inner-rim regions can support ordinary open habitation while high terrain and increasingly polarward or structurally elevated zones become progressively exposed. This supports the broader habitation gradient from natural central landscapes toward more engineered, enclosed and low-gravity environments without requiring a single sharp environmental boundary.

Environmental faults need not resemble hull breaches.

With no roof membrane, local structural damage does not automatically vent the complete habitat. More credible environmental failures arise through loss or alteration of rotation, large-scale atmospheric circulation, heating, occluder operation, terrain/support failure or pathways that allow atmosphere to migrate into unintended Station volumes. Local landscape collapse may also change drainage and airflow without destroying global atmospheric retention.

The rate at which atmosphere would redistribute following major rotational or structural failure has not been modelled and remains explicitly open.

The environment is inseparable from other Station systems.

Atmospheric retention depends on rotation and gravity (600.20:20); topography and subsidence couple it to geological support (600.20:40); stellar input and artificial night couple it to energy and thermal management (600.20:60); and altitude/exposure shape habitation and transport (600.20:70, 600.20:80). Ecology can eventually become part of environmental regulation and structural persistence, but those biological mechanisms require their own recovered record rather than being treated as solved here.

This is the current environmental model, not its entire design history.

The discussions that produced the open-atmosphere choice, scale-height reasoning, mountain limits and occluder proposal belong in 400 Development Records. Real atmospheric, rotating-habitat and stellar references belong in 700 Factual References. Fictional habitat comparisons belong in 750. Any Tribunal specification, environmental bulletin or occluder drawing represented as an in-universe object belongs in 100 Universe Records.