>>12892518The gold standard is always going to be some sort of flexible docking tube such as was already available by the time of Skylab. The stresses on a rigid tube are generally too high unless one vehicle has much greater mass, and in any case a rigid structure means that the vehicle with higher thrust can push the other against its will. Any advantages of a rigid tube can be replicated by adding a rigid coupling to the end of a flexible docking tube.
