 The idea of a “common” mechanism for both docking and berthing appears to have been discarded, and major mechanisms specific to each of those distinct operations were identified.The concept of a “common” module pressure shell with a range of Radial Port configurations, still being studied by NASA at least as late as 1991, was discarded in favor of dedicated “Resource Nodes” having four Radial Ports near one end of a cylindrical pressure shell.Closure of the “module pattern” was deferred from the initial system-level design by 1992, eliminating the bellows-based variant of the PCBM.