Instead of 3 parts, the space station could also be partitioned into only 2 entities by combining the habitat wheel and the machine room. Basically, this would be possible because the orientation in outer space for these two units is determined only by the direction of the sun's rays; more specifically, it is determined in the same manner.
If the mirror of the machine room is to be exempted from participating in the (for its size) relatively rapid rotation of the habitat wheel, then, for example, the habitat wheel and machine room (including its mirror) could both be rotated around a common axis of rotation- but in a reverse sense. Or the habitat wheel and machine room could be completely integrated into one structure, and the large mirror of the machine room alone could be rotated around its axis of rotation, also in an opposite direction. Other methods could also be employed.
The advantages of a two-component space station would be as follows:
Movement within the space station is simplified.
The provisions necessary in a separated partitioning to compensate for the mutual attraction between habitat wheel and machine room are no longer needed.
The rotational motion of the habitat wheel can now be produced, changed and stopped through motor power instead of thrusters without any expenditure of propellants because now the entire machine room and/or its large mirror are available as a "counter mass" for this purpose (consequently, the reverse rotational direction of the mirror).
These advantages are countered by the disadvantage that significant design problems result, but these are solvable. We want to refrain from examining any further this partitioning of the space station in more detail here in order not to complicate the picture obtained of it up to this point.