McKendree Cylinder

Rotating cylindrical habitats up to 10,000 km long

McKendree Cylinder Axis
Image from Arik
Looking along the length of a McKendree cylinder, The axial lighting array can be seen, as well as intra-habitat structures reaching up to the hub.

Cylinder World - video by Darren Ryding

Closed, rotating cylindrical habitats have been built since the Interplanetary age; at first these were no more than a hundred metres or so in radius, the smallest possible radius that could give Earth-like internal centrifugal gravity while avoiding excessive coriolis effects. But over time the habitats became larger, until they reached the maximum possible size for habitats constructed with non-exotic materials.

A McKendree Cylinder is designed much like an O'Neill Cylinder but built with the carbon buckytube technology used in Bishop Rings. As such McKendree Cylinders with an interior gravity of one standard gee can have a radius of 1,000 km and a length of 10,000 km. This radius and length will give a single McKendree Cylinder more than 62,857,000 km2 of living area or about 12% of the surface area found on a Gaian type planet. [Please note: first century hu are reported to have lived on only 10% of the surface of eir home world (Earth) due to inconvenient surface features - oceans, mountains, deserts, icecaps, etc. On the other hand these hu did draw on the planet's whole biosphere for life support.]

McKendree Cylinder
Image from Steve Bowers
A double, nested McKendree Cylinder ten thousand kilometers in length (note: the second, counter-rotating cylinder is inside the first)

However McKendree Cylinders can also be linked into counter-rotating pairs which may be side-by-side like the original O'Neill colony design or nested with a counter-rotating inner cylinder (or several). If a counter-rotating cylinder is included inside the outermost shell, the two layers must be separated by at least 50 kilometres of vacuum above the top of the atmosphere to eliminate atmospheric drag effects. Doubling the cylinder in this way increases the living area and counters gyroscopic effects so that the cylinders can be oriented in any chosen direction. (For example with their axis pointed towards the local star for easier direct lighting.)

When multiple levels or floors are added to the design a McKendree colony can quickly equal a Gaian type planet in total surface area. 'Ceiling height' in a multi-floor colony is generally determined by its psychological effects on the inhabitants but in the counter-rotating nested designs an inner cylinder must clear the rimwalls and upper atmosphere of the cylinder below it. This requires more than fifty kilometers between levels in a standard gee habitat; habitats with lower values of gravity can be larger, but the separation between the levels must be greater, as the scale height of the atmosphere is greater in low gravity conditions.

Savard cylinder 2
Image from Steve Bowers
Stadener Habitat, an early McKendree cylinder 1000 km in length with extensive light collection facilities at each end, opened by Ruby Marine in 2764 AT

A full-sized McKendree habitat can be constructed from a large asteroid or dwarf planet, or from a number of smaller objects. A typical dwarf planet of 1000 kilometres diameter can contain enough material to build 12 Mckendree cylinders, with a potential population of hundreds of billions of sophonts.

The interior of a McKendree cylinder may contain landscape features such as seas, lakes, hills, and even mountains; but these items add mass to the habitat and therefore increase the load on the buckytube fibres holding the cylinders together. To cut down on the additional load, the landscape is constructed with internal voids and arches, to make the hills and mountains as hollow as possible; these internal voids can be useful for storage.

The McKendree habitat was named after a 1st century AT human baseline, Tom McKendree, who first outlined the concept.

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Development Notes
Text by AI Vin with additions by Steve Bowers

Initially published on 09 October 2006.

see Tom McKendree's original paper here:

Implications of Molecular Nanotechnology Technical Performance Parameters on Previously Defined Space System Architectures

Fiction that includes a McKendree Cylinder

Dirty Hands