Tin can habitats most often consist of small modules connected either directly to each other or by node modules with common attachment mechanisms. These are bare-bones structures with little more than an exterior debris shield, a pressure shell, minimal radiation protection, plumbing for environmental systems, and wiring for electrical and power systems. Unpressurized sections are connected by an open truss or structural spars that can only be accessed by EVA, robot, or telepresence. Unlike cluster habitat modules, even the most basic functions must be provided by internal racks and attached equipment rather than being built in. This simplicity has its advantages for people who want to live “off the grid,” especially those wary of the modern panopticon.
Many so-called “tin can” habitats are actually inﬂatable structures made of a ﬂexible composite pressure shell and a solid central core to distribute loads and stresses. Held rigid by the internal air pressure, inﬂatables provide more usable volume for the same mass than metal structures and offer superior radiation protection. When radiation hits metal, backscatter radiation can be generated such that there is actually higher exposure on the inside of the pressure vessel than outside. The high hydrogen content of the composites allows an inﬂatable module to absorb or deflect more radiation without creating backscatter. By lining the interior wall with the station’s water tanks, the only significant threat over the long term comes from galactic cosmic ray exposure.
Repairing an inflatable module is much more difficult without nanomachines than damage to a metallic hull. Multiple layers interlock on an inﬂatable to provide structural strength, debris protection, atmospheric containment, and moisture protection. Breaches must be repaired by weaving in the permanent patch from the innermost layer out, as opposed to the relatively simple welding of alloys. Much as submarines have an inner pressure shell and an outer hydrodynamic skin, many tin can habitats—especially those controlled by military or security interests—will have a depressurized outer armor made of replaceable segments or blocks that does not carry any structural loads. Its only purpose is to protect the pressure shell beneath from debris or attack.
Though tin can habitats free-ﬂoating in space are entirely in microgravity, some can actually generate artiﬁcial gravity by spinning one or more modules on a tether or structural ring. This is cheaper and quicker than building a torus habitat, though not as efficient over the long term. The centrifugal force that approximates gravity is felt in the outward radial direction, so internal decks are arranged accordingly. The Jovian Republic has built many a “poor man’s torus” to try to alleviate crowding on the Reagan cylinders. Unless transmitted by egocasting, the only access to a tin can is by airlock or docking with a transfer vehicle. In fact, some tin can habitats are actually a series of crew and cargo transfer vehicles with common adapters permanently docked together and kept on station. Most tin cans are simply far too small to have pressurized landing and cargo bays.