Bernal Sphere – —designs ranged from two miles to 10 miles in diameter—was meant to be hollow and filled with air, along with 30,000 people that presumably didn’t have outstanding debts on Earth. The sphere would be attached at its two “poles” to massive motors that would rotate the thing like a rotisserie.
O’Neill Cylinders – would each be two miles in diameter and 20 miles long. They would be side-by-side but not directly touching, and would be connected at their ends via rods. Each cylinder would spin to provide internal gravity via centrifugal force, and they would spin in opposite directions.
Stanford Torus – provides its gravity by rotating around its hub, and at a suggested 1.8 kilometers (1.1 miles) in diameter could theoretically support some 10,000 people inside. Sunlight would be bounced from mirrors in the hub into the living space, providing the effect of “overhead” sunlight.