At the time, only the crew of Skylab 3 had spent six weeks in space. It was unknown what had happened psychologically. NASA carefully worked with crew's requests, reducing their workload for the next six weeks. The incident took NASA into an unknown realm of concern in the selection of astronauts, still a question as humanity considers human missions to Mars or returning to the Moon. Among the complicating factors was the interplay between management and subordinates (see also Apollo 1 fire and "Challenger" disaster). On Skylab 4, one problem was that the crew was pushed even harder as they fell behind on their workload, creating an increasing level of stress. Even though none of the astronauts returned to space, there was only one more NASA spaceflight in the decade and Skylab was the first and last American space station. NASA was planning larger space stations but its budget shrank considerably after the Moon landings, and the Skylab orbital workshop was the only major execution of Apollo Applications projects.