In 1975 a research group led by Princeton professor Gerard O'Neill conducted a 10 week study of future space colonies. The NASA-sponsored research and the paper born of it was given to artists Rick Guidice and Don Davis, commissioned to illustrate the fantastical and as yet unrealized concepts.
O'Neill's team settled on three potential designs for the future space stations: the Bernal Sphere, the Toroidal Colony (pictured) and the Cylindrical Colony. Potential capacity ranged from 10,000 people to one million, and featured circular designs which rotated to generate artificial gravity.
The Bernal Sphere was first proposed by John Desmond Bernal as far back as 1929, with O'Neill's team adapting the half-century old idea. Shrunk down to 500 meters wide they proposed a highly-curved living surface that featured a "crystal palace" for agriculture and light reflected in via windows near the poles.
O'Neill in a paper presented to NASA uses 1990 as a hypothetical start date for a space colony, with the team drawing up a number of potential costs for construction and transportation -- even the volume of livestock each station would need to ship in.
Rick Guidice's painting of a cutaway of the Bernal Sphere also shows some of the huge solar arrays required to power the station and its rotation.
Despite the futuristic technology required to put such a massive structure in space, all of the artwork from Guidice and Davis shows lush green landscapes -- a far cry from the reality of the International Space Station today.
O'Neill suggests that the compact living area of the Bernal Sphere could be offset with separate agricultural modules, spacious enough for industrial-scale farming.
Don Davis' illustration of a Cylindrical Colony imagines what a solar eclipse would look like from space, featuring two columns of land hidden from the sun altogether experiencing and night time.
Davis depicts a construction crew piecing together a Bernal Sphere complete with houses, grass and rivers, seemingly unscathed by the vacuum of space.
The Cylindrical Colony was never envisaged a solitary structure, instead orbiting with a partner.
A Bernal Sphere with tilted arrays to maximize exposure to the sun.
An exterior view of a Toroidal colony, featuring a giant tilted mirror providing sunlight to the interior surface of the ring.