Also, the arrangement solved some early assembly problems for space station freedom, the beginning of the construction and its first module had never been precisely specified and was still open to be completed for a CDR. Also the resupply of vital goods with the Space Shuttle was not really reliable and carrying fuel to the station even essentially ruled out. With the Russian DOS modules, it was possible to be ready for permanent habitation after a few launches and had a pretty reliable Progress vessel for carrying the critical goods and fuel to the station.