Alderson Disk

An Alderson disk (named after Dan Alderson, its originator) is an hypothetical artificial astronomical megastructure, like Niven's Ringworld, or a Dyson sphere. The disk is a giant platter with a thickness of several thousand miles. The sun rests in the hole at the center of the disk. The outer radius of an Alderson disk would be roughly equivalent to the orbit of Mars or Jupiter. According to the proposal, a sufficiently massive disk would have a larger mass than its sun.

Close to its surface, the gravity of the disk would closely approximate that of an infinite flat plate, for which gravity is perpendicular to the surface. Near the inner and outer edges of the plate, edge effects would become significant.

The mechanical stresses within the disc would be far beyond what any known material can stand, thus relegating such a structure to the realm of exploratory engineering until materials and construction science become sufficiently advanced. Building a megastructure of this magnitude would require an amount of material that far surpasses the amount of material found in all of the solar system we are located in. Another option in the way of heliocentric habitats is the Dyson Sphere proposed by Freeman Dyson, it could be scaled up to use roughly the same amount of usable material in the solar system if the sphere were 8-20 cm thick and had a radius of 1 AU to keep the edge of the habitat in the habitable zone.

Life could exist on either side of the disk, though close to the sun the heat would make life impossible without protection. Conversely, further away from the sun living beings would freeze. Therefore, for the entirety of such a structure to be made habitable, it would have to include a vast number of life support systems.

Because the sun remains stationary, there is no day/night cycle, only a perpetual twilight. This could be solved by forcing the sun to bob up and down within the disk, lighting first one side then the other.