ISLAND
THREE

An O'Neill cylinder — 8 km across, 32 km long,
spinning once every 127 seconds for Earth gravity.

PRIMARY MIRRORS3 × 30 km, hinged — fold sunlight into the windows

AGRICULTURAL TORUSindependent climate, feeds ~1M residents

RADIATOR ARRAYrejects habitat waste heat to space

DOCKING HUBzero-g port & industry, on the spin axis

AXIAL APPROACH — matching habitat rotation · 0.47 rpm · relative spin nulled

01 STRUCTURE

The pressure hull is steel and aluminium smelted from lunar regolith, flung to L5 by mass driver. Three land strips alternate with three window strips, each 32 km long — about 800 km² of inner surface.

LENGTH 32 kmDIAMETER 8 kmSHELL Al / steel + slag shield

02 SPIN GRAVITY

Centripetal acceleration a = ω²r stands in for gravity: 1.00 g at the rim, fading linearly to zero on the axis — where you can strap on wings and fly. At 0.47 rpm the Coriolis forces stay below what most inner ears can feel.

PERIOD 127 sω 0.0495 rad/sAXIS 0 g

03 ATMOSPHERE

Half of sea-level pressure, with full sea-level oxygen. Four kilometres of air scatter sunlight blue and haze out the far side of the valley hanging 8 km overhead. Weather is engineered — clouds condense near the 1,000 m level.

PRESSURE ~51 kPapO₂ 21 kPaCLOUD DECK ~1 km

04 SUNLIGHT & SEASONS

No lamps — three planar mirrors ride alongside the hull and fold raw sunlight in through the windows. Their hinge angle sets the sun's apparent height; swinging them away brings night. A 24-hour cycle, and seasons on demand.

MIRRORS 3 × 30 kmDAY 24 h, tunableNIGHT mirrors feathered

05 LAND & PEOPLE

Each strip is a valley 4.2 km wide and 32 km long — some 400 km² of towns, forest, parkland and streams for a population in the millions. Farming is exiled to the external torus, tuned to its own perpetual growing season.

LAND ~400 km²POP up to 10 M designVALLEYS 3

“The surface of a planet is not really the right place for an expanding technological civilization.”

— Gerard K. O'Neill, The High Frontier, 1976