Space colonization will be a process with multiple stages, on this site we usually discuss the latter stages of this process. However, it is important also to discuss the earlier stages. These earlier stages will be characterized by small human presence in space and extensive use of robotics and teleoperation.
As space colonization will develop, the number of humans is space will grow. Hence we distinguish between different generations of space settlements. The first generation of space habitats are dumbbells and similar designs. The second generation consists of Bernal spheres and toroidial designs. And the third generation consists of O’Neill cylinders.
The second and third generation of space habitats, as defined above, are large structures designed for large populations. The reason why these designs are large, is because they use centrifugation to replace gravity. The centrifugal force depends on the product of the radius and the angular velocity. A larger radius requires a lower angular velocity, which is preferred by most humans.
Both the Bernal sphere and the Stanford torus have a radius in the order of a few hundred meters, which implies about one revolution per minute. Their designs require a lot of material resources, however. On the other hand, these designs also provide living space for tens of thousand people.
First generation space habitats will also use centrifugation to replace gravity, but use a simpler design which would require less material. But consequently provide room for fewer people. Though this is not really an issue in the early stage of space colonization.
The dumbbell habitat design consists of two modules, with an equal mass, which are connected with each other with a tether. The structure rotates around its midpoint, halfway the tether, and hence generating a centrifugal force.
The tether can be of any desired length, while there no special size requirements for the two modules. Even if the tether is a few hundred meters long, the material requirements will be modest. The modules themselves are similar to those of the international space station, though we could also opt for the inflatable modules of Bigelow Aerospace.
A similar design is the bola space habitat.
Dumbbell habitats will serve as a first base for asteroid mining and the construction of next generation habitats. Depending on the size of the modules a few dozen people will stay at the habitat.