In anticipation of the kind of research that the crew would perform during their 16 days aloft, at 3:28 pm, a mere one-and-a-half hours into their mission, the crew opened Columbia's payload bay doors, positioning the port-side one at a 62-degrees-open position, instead of fully open. During STS-73, the Shuttle would operate in a 'gravity gradient' attitude - tail-to-Earth and left-wing-facing-forward - to provide a stable microgravity platform for the sensitive USML-2 experiments. Consequently, the part-open port door helped to minimise the chance of micrometeorites or other orbital debris hitting its delicate radiator panels.
Later, on the afternoon of 25 October, Bowersox briefly opened the port-side door fully for about an hour to enable a waste-water dump from Spacelab's condensate tank to take place. Such dumps had to be performed every few days to get rid of water from the module's dehumidifiers. The payload bay door had to be fully opened during the dump to provide sufficient clearance for the waste water, which was ejected through a nozzle on top of the module's forward endcone. After the completion of the dump, Bowersox returned the door to its 62-degrees-open position.
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