A 5 km settlement radius corresponds roughly to the sweet design spot where earthlike radiation shielding is produced for free by the required structural mass. The paper is by Pekka Janhunen.
Overall, the settlement concept satisfies the following generic requirements for long-term large-scale settling of the solar system:
1. 1g artificial gravity, earthlike atmosphere, earthlike radiation protection.
2. Large enough size so that internals of the settlement exceed a person’s lifetime-integrated capacity to explore.
3. Standard of living reminiscent to contemporary royal families on Earth, quantified by up to 25,000 m2 of urban living area and 2000 m2 of rural area per inhabitant (290,000 square feet per person).
4. Access to other settlements and Earth by spacecraft docking ports, using safe arrival and departure procedures that do not require impulsive chemical propulsion.
In particular, the proposed lighting geometry enables a long-term reliable architecture, i.e., a design that does not include large moving parts, is free of single failure points and exhibits passively stable rotation.
As a future refinement of the concept, one could consider more general orbits than 1 au circular, and a range of settlement sizes could be analyzed.
This cylindrical space settlement concept has sunlight is concentrated by cylindrical
paraboloid concentrators and reflected by semi-toroidal and conical reflectors and controlled by local blinders to simulate earthlike diurnal and seasonal illumination cycles. The rural wall living cylinder is divided into 20 (for example) z-directed valleys which are in different phases of the light cycles. No moving parts are needed other than numerous and easily accessible local blinders that regulate light input into the valleys. The settlement rotates as a rigid body and the mass distribution is such that the rotation is passively stable.
The geometry has natural spare volume at the equator where one can add multi-storey urban blocks without reducing the rural area. Adjacent to the urban blocks there is natural place where to install a zone of solar panels without reducing the amount of gathered light.
The inhabitant population is limited by the ability of the closed ecosystem of the sunlit rural areas to produce food. The naturally buildable total urban floorspace are
In conclusion, a requirement for settling the solar system in a large scale is that the habitats must be longterm reliable and they should provide a high standard of living compared to Earth. In the light of our analysis, the goals seem possible to reach, without essentially increasing the total mass consumption per inhabitant beyond what is required by radiation protection in any case.
Cylindrical kilometer-scale artificial gravity space settlements were proposed by Gerard O’Neill in the 1970s. The early concept had two oppositely rotating cylinders and moving mirrors to simulate the diurnal cycle. Later, the Kalpana One concept exhibited passively stable rotation and no large moving parts. Here Pekka Janhunen and others propose and analyze a specific light transfer solution for Kalpana One type settlements. Their proposed solution is technically reliable because it avoids large moving parts that could be single failure points. The scheme has an array of cylindrical paraboloid concentrators in the outer wall and semi-toroidal reflectors at the equator which distribute the concentrated sunlight onto the living surface. The living cylinder is divided into a number of ϕ-sections (valleys) that are in different phases of the diurnal and seasonal cycles. To reduce the mass of nitrogen needed, a shallow atmosphere is used which is contained by a pressure-tight transparent roof. The only moving parts needed are local blinders installed below the roof of each valley. they also find that settlements of this class have a natural location at the equator where one can build multi-storey urban blocks. The location is optimal from the mass distribution (rotational stability) point of view. If maximally built, the amount of urban floorspace per person becomes large, up to 25,000 m2 , which is an order of magnitude larger than the food-producing rural biosphere area per person. Large urban floorspace area per person may increase the material standard of living much beyond Earth while increasing the total mass per person relatively little.
The NSS Space Settlement Journal is a peer-reviewed, open access journal which may be found at http://space.nss.org/national-space-society-space-settlement-journal/