Prior to the first EDO mission in June 1992, exhaled carbon dioxide from each of Columbia's crew members was scrubbed from the cabin and Spacelab atmospheres using lithium hydroxide canisters, which had to be changed four times daily. The new RCRS has already been described, but in case of failures a series of 28 lithium hydroxide canisters were kept in reserve, offering five extra days of science-gathering and two 'contingency days' - in case of one or two 'waved-off landing attempts due to bad weather - before the Shuttle would be forced to come home.
Kay Hire had reported hearing a strange noise about the time the device failed. ''It was a noise I did not recognise,'' she told flight controllers, refuting suggestions that it might have been a normal sound from the RCRS' compressor. Already running two hours behind schedule, the crew initially thought the trouble involved one of two electronic controllers; they switched to the backup and restarted the device, but within 10 minutes it shut down again. As a precautionary measure, Mission Control asked them to load two lithium hydroxide canisters, providing ample time to evaluate and recover from the problem.
''The crew was never in any danger,'' insisted NASA spokesman James Hartsfield on the morning of 25 April. ''Carbon dioxide levels remained normal the whole time. A rise in carbon dioxide occurs very slowly [and] the crew was never anywhere near having anything like that occur.'' Meanwhile, as part of troubleshooting efforts, Searfoss and Altman opened the RCRS, removed a hose clamp and used aluminium tape to bypass a suspected faulty check valve, which was apparently allowing cabin pressure to leak into the system and throw off its electronics controllers. The fix worked.
''We have some good news for you,'' said fellow astronaut Mike Gernhardt, on his shift in the Capcom's seat in Mission Control. ''It seems to be working as expected. It looks like we have headed off the possibility of a shortened mission.''
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