SpaceX is rapidly changing what is possible in space. Instead of taking 40 launches over a decade to build the 400-ton space station, we could have 1000 launches in a year from ten fully reusable SpaceX BFRs that would place 150,000 tons into space. The 1000 SpaceX BFR launches would cost $10 billion versus $40 billion for the space shuttle launches of the International space station.
We will be getting 1000 times the capability in space.
The most technically challenging aspect of designing a growth-capable space habitat is growing the pressure hull. One method of growing a torus-shaped pressure hull is illustrated in the animation shown here. In this method a new folded pressure hull is constructed inside the existing pressure hull. When the new hull has been pressure tested, the existing hull is removed and the material recycled. The new pressure hull is then expanded by a controlled release of the restraining cables. The animation shows one way of folding the new pressure hull to enable proportional growth where every facet of the torus grows by the same proportion, resulting in a uniformly scaled expansion.