consumables for an additional day-and-a-half of research work. ''We looked at the mission extension and it was tempting,'' said science manager Lele Newkirk, ''but because we have Sunday [3 May] and Monday [4 May] to land at Kennedy, obviously we chose to land on Sunday. The KSC landing is important primarily to the animal projects, that's where we want to receive all the animals and they do all the post-flight data collection down there.''
Although weather in Florida was expected to remain acceptable on 4 May, it was not as good, which prompted Newkirk to opt for an on-time landing, rather than risking a wave-off to land at Edwards Air Force Base in California. Moreover, the KSC weather was anticipated to become more doubtful late on the 4th. ''There is a front that we expect to start to affect the Cape on Monday [4th],'' said Entry Flight Director John Shannon. ''It will bring rain showers and low cloud ceilings.'' Summing up, he felt that the decision to come home on time was correct.
In the meantime, as his crew readied their ship for its return to Earth, Searfoss successfully transferred more than 30 kg of waste water into a rubber contingency bag on 2 May. This provided enough volume in the tank to accommodate the seven astronauts' needs even if bad weather kept them in orbit longer than planned. The procedure was successful and Searfoss reported no unpleasant odours from the bag or the tank, joking ''We'd like to join the plumbers' union!'' to mission controllers. A day later, with pinpoint precision, Columbia swept smoothly and perfectly onto Runway 33 at KSC.
Sixteen days in the closed microgravity environment on board Columbia did not, Searfoss later told an interviewer, induce a claustrophobic reaction among any of the seven astronauts. ''The Shuttle appears to be pretty small for seven people to live in for a couple of weeks, but when you go to space, it seems like you have a lot more room,'' he said. ''Try this thought experiment: on Earth, all the people in a room have their bodies at approximately the same level, sharing the same area. In space, those people would utilise all of the room's volume!
''They'd be hanging out up around the ceiling and drifting freely. In space, you don't get any feeling of claustrophobia. It's a great experience to be up there and work in that kind of environment.''
Even before Columbia lifted off, there was a possibility that their great experience would be repeated. At a press conference on 15 April, Shuttle manager Tommy Holloway told journalists that engineers were looking at the feasibility of flying Neurolab again in the late summer of 1998. The reason: more International Space Station delays had opened up a three-month gap in the Shuttle launch schedule. ''There are two or three things we need to think about,'' Holloway explained. ''First of all, the value of Neurolab and what we can learn from it. Secondly, the overall workload across the system, in terms of what [NASA] wants to do.'' Ultimately, partly to protect an anticipated early September launch of the first station components on the already-long-delayed STS-88, the decision was taken not to refly Neurolab, but the results from STS-90 proved more than enough to keep neuroscientists and biologists busy for several years to come.
''For the most part,'' said Mary Anne Frey, NASA's chief scientist for the mission, ''our scientists received more data than they anticipated.'' When the inaugural results were published in April 1999, they offered promising insights into the neurological mechanisms responsible for Alzheimer's disease and epilepsy and the astronauts' cognitive work with the spring-loaded ball could ultimately lead to new diagnostic and rehabilitation tools for sufferers of brain injuries. Neurolab's sleep studies, too, could find Earth-bound applications to aid shift workers, the elderly, jetlag sufferers and insomniacs.
Summing up the scientific accomplishments of their mission, the payload crew members were both philosophical - and jocular. ''If we don't figure out how to stem nerve-muscle degeneration,'' said Linnehan, ''we're not going to be able to travel to other planets or live in space stations. We would face the risk of fractures when returning to Earth.'' On the other hand, said Buckey, who later returned to his previous job as a professor of medicine at Dartmouth Medical School, at least in space ''you can put your pants on both legs at the same time!''
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