The EDO system, meanwhile, was performing admirably on its first outing and began supplying cryogenic reactants about 24 hours after launch. Four additional tanks were mounted underneath Columbia's payload bay floor, as well as the four attached to the EDO pallet, and on 26 June mission controllers detected a slight leak in one of them. The quantity of oxygen escaping from the tank was too small to present any problem to the success of the mission, but it was decided to use the leaking tank first to minimise wastage. This procedure was completed on 27 June.
Problems also occurred with the RCRS, which had been switched on shortly after Columbia reached orbit and operated successfully for the first 25 hours of the mission. Then, beginning at 8:26 pm on 26 June, it suffered a series of six failures, forcing the crew to shut it down 90 minutes later. Fresh lithium hydroxide canisters -which absorbed carbon dioxide and were replaced when they became saturated -were installed in the cabin and the Spacelab module. It was found that faulty sensors showing the positions of internal valves caused the unit to prematurely switch itself off. A maintenance procedure to revive the RCRS was devised and rehearsed on the ground, before being transmitted to Columbia's teleprinter for Richards and Bowersox to perform on the afternoon of 30 June.
The 32-step procedure took the two men almost five hours to complete. First, they pulled out four middeck lockers to gain access to the Shuttle's lower deck, under which the RCRS was situated. Next, Bowersox unscrewed its top cover, unplugged one electronic wire connector and spliced two sets of wires together to bypass the faulty sensors. Finally, the system was reactivated at 5:00 pm and performed normally for the rest of the mission. ''As it recovers, it's belching and wheezing,'' Richards told Mission Control as the repair drew to a successful conclusion.
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