Despite the possibilities offered by the large dual-keel station, by 1987-88 it was becoming apparent that the station would be too expensive to construct, both in terms of shuttle missions and spacewalks. Congress balked at the price tag and the station was redesigned to be more affordable and easier to build.
To this end, the second keel was deleted from the design, and the core modules were reduced to “1 Lab, 1 Hab”. Accordingly, the Japanese Experiment Module and ESA Columbus Laboratory were moved into center of the configuration. (Columbus was still a full-sized module.) The PMM now hangs below the central nodes with the airlock on top. The co-orbiting platform for microgravity experiments has been deleted, though the polar orbiting platform was retained. An ACRV (Assured Crew Return Vehicle) was added to the design after the Challenger accident, in case a shuttle was unavailable to return a crew.
Unfortunately, Space Station Freedom was heading into the 90′s in serious trouble and the project came to a head in 1990 when a review found the station overweight, underpowered, and extremely complicated to assemble, requiring up to 3,276 hours of spacewalks to assemble the trusses and other equipment.
It was time to go back to the drawing board and revise the design again…