Documents leaked from the US space agency Nasa to a web site suggested that poor air quality or chemicals released by materials used in panels lining the walls of the Russian Zarya module, part of the huge station, could be to blame.
But an investigation by a specially convened team to try to find out the cause concluded "It is virtually impossible to accurately quantify the specific source or cause of the crew's physiological symptoms."
New Scientist magazine today reports that the astronauts described a "definite odour" when they gathered in the "Unity" docking module for a press conference.
The ISS's first components were only launched in December, as part of a $60bn (pounds 35bn) project which will eventually provide permanent living quarters for up to seven astronauts. Its total size, including solar panels, will be 4,000 square feet - as big as two football fields. Assembling it will require a total of 45 assembly flights, and could take three or more years.
According to documents leaked to the Nasa Watch website, the symptoms were noticeable when panels lining the walls of the Russian-built Zarya section of the station were open and astronauts had been working in close proximity for a number of hours. Opening the wall panels would disrupt air flow through Zarya, which might mean that a build-up of exhaled carbon dioxide is to blame. Astronauts and ground controllers are also concerned that the Zarya module uses a large amount of Velcro, whose adhesive backing might be releasing volatile - and nausea-inducing - chemicals into the air.
However, no air samples were taken because none of the astronauts reported the problem at the time. Some had suspected it was simply caused by another syndrome, Space Adaptation Syndrome, which many space travellers suffer in trying to adjust to weightlessness. The problem was thus not reported until two weeks after the team returned to Earth.
Nasa officials now plan to install air-quality monitoring equipment before the first permanent crew arrives on the station next year.Reuse content