the port that is along the long axis of the Tianhe core module. Which means that if there is a second core module later added to the station, the "bottom" port of the first core module will become unusable at some point. It would temporarily be used as a docking port for a Shenzhou spacecraft that was moved there prior to the second core module being attached, but then once that spacecraft returns to the surface with a crew, that specific port will become inaccessible.The only way around this is if that Shenzhou is just left there as a long term emergency escape spacecraft, and CNSA instead sends up an empty Shenzhou to return the current crew to earth.
