m. c. de marco: To invent new life and new civilizations...

BDO of the Day: Hex

The Big Dumb Object (BDO) of the Day comes from yesterday’s long post: the Hex is a BDO invented by Allen Steele in the eponymous Coyote universe novel. It’s quite similar to a Bucky Habitat, a skeletal Dyson sphere formed of O'Neill colonies, but instead of the segments spinning individually, the entire sphere rotates to generate gravity like a Ringworld.

The Hex is a hexagon-tessellated, hollow, non-solid sphere of radius 1AU, with a sun at its center. (No mention is made of the twelve pentagons required to hexagon-tessellate a sphere.) The sphere also surrounds the decayed orbit of the homeworld of the species that constructed the Hex.

Cylindrical biopods are laid out in pairs on the sides of the hexes. The hexagons formed by the biopods are mostly empty space, but are strung across with cables supporting small, movable solar sails to collect energy and correct for any orbital perturbations of the sphere. Biopods are linked by separate structures, nodes, at the vertices of the hexagons, which house docking bays for spaceships. The biopods are numbered for navigation, and automatic tramways run along the biopods and through the nodes, connecting all of the biopods.

Each biopod is 1000 miles long by 100 miles in diameter—about the size of Colorado, but more like two Tennessees laid out the long and skinny way. The novel claims a total of 6 trillion hexes with 36 trillion biopods for a total of 3.6 quintillion square miles (the equivalent of 18 billion Earths at 200 million square miles per Earth). But according to my calculations there would only be about a quarter-trillion hexes, so one and a half trillion biopods and only 150 quadrillion square miles (750 million Earths). Needless to say, either number qualifies the Hex as a BDO, although the size of an individual biopod may not be adequate to maintain a biosphere without outside help. (One out of every six biopods is not an actual biopod but some sort of recycling center used to maintain the others, and to which the builders do not permit access; the square mileage numbers have not been adjusted for that.)

The sphere’s rotation gives a gravity range of 0g to 2g, depending on latitude. Individual biopods have a self-healing transparent sky surface facing the sun which darkens to black to simulate the diurnal cycle of whatever planetary environment is being reproduced. Various landforms fill the lower half of the cylinder; they generally seem to feature a river valley, fed from one end of the biopod, rising to more mountainous terrain along the walls and requiring an escalator to reach the valley floor from the point where the trams let out.

At least one hexagon full of biopods and cabling has been removed from the Hex, and others are reportedly unfinished. The BDO is not abandoned (as they so frequently are) but is still inhabited and regulated by its creators, apparently as an interstellar nature preserve in which weapons and warfare are forbidden. Several extinct and unknown (except to the creators) species can be found here, if you’re willing to look (peacefully) through the trillions of biopods for them.

Commentary

It’s not clear to me that the structure of the hex in any way solves the stress issues of rotating a megastructure to produce gravity. According to my new favorite tool, SpinCalc, the sphere’s tangential acceleration would be about 4 million miles an hour, whipping around the sun in less than a week. The author doesn’t mention the stresses involved or the magical materials usually required to build such a BDO; his aliens seem more concerned that their recycling secrets will be discovered, not that their BDO will be mined for its unobtanium. So I think he would have been better off with a traditional Bucky Habitat and rotating O'Neill cylinders.

Personally, if I were making such a BDO I would cut down the number of biopods and make each one bigger in the McKendree cylinder style, say 10,000 miles long by 1,000 miles diameter (10 million square miles, the equivalent of a good-sized continent like North America). This would yield about 420 million hexagons, and because I’m not doubling them up, only one and a quarter trillion habitats. Their area would be 12 quadrillion square miles (63 million Earths).

If that seemed insufficient, I could make the BDO in the other Bucky Habitat style, geodesic, which would add a star of six more habitats in the center of each of my hexagons (and five in the few pentagons), for an approximate total of 3.75 trillion habitats, 38 quadrillion square miles, and 189 million Earths. Approximately.