re: After 1986
Perhaps keeping the Shuttle program after Challenger was a mistake, and then conceiving the space station around the Shuttle, so long after 1986. And leaving no room to build a new shuttle.
The Mir space station had a certain size relative to the vehicles it depended on to go on working (the Soyuz and the Progress). That must be the case for all space stations, I believe.
And if the space station is built around a vehicle the size of the Shuttle, and there's no more shuttle, it has a serious impact on the station!