![]() ![]() Three days previously, in the first launch attempt, the launch was stopped at T−7 seconds, just prior to the SSMEs' ignition sequence, due to a senior console operator manually triggering a cutoff in the countdown. This incident brought on a maintenance practice change that required damaged oxidizer posts to be removed and replaced as opposed to being intentionally plugged, as was the practice beforehand. Though the premature shutdown resulted in a velocity 15 ft/s (4.6 m/s) lower than targeted, the vehicle safely achieved its intended orbit and completed the mission as planned. The increased oxidizer consumption during ascent resulted in a premature shutdown of all three engines near the end of the projected burn due to low liquid-oxygen level sensed in the External Tank. The hydrogen leak and increased oxidizer consumption resulted in the right engine deviating from the desired oxygen/hydrogen mixing ratio of 6.03 and running hotter than normal. To bring the engine back up to the commanded thrust level, the controller opened the oxidizer valves a bit more than normal. This wiring issue led to a program-wide inspection of the wiring in all orbiters.īecause of the leak in the right engine, its controller sensed a decrease in power or thrust-measured indirectly as main combustion chamber pressure-since the leaking hydrogen was not being burned in the SSME's two pre-burners or the main combustion chamber. The electrical short was later discovered to have been caused by poorly routed wiring, which had rubbed on an exposed screw head. The redundant set of DCUs in each engine controller saved Columbia and her crew from potential catastrophe, as shutdown of two engines at that point in the flight would have resulted in a very risky contingency abort with no guarantee of success. The center and right engines continued to operate on their remaining DCUs for the rest of powered flight to orbit. However, approximately 5 seconds after liftoff, an electrical short disabled the center engine's primary digital control unit, DCU-A, and the right engine's backup unit, DCU-B. ![]() This anomalous event and the automatic response to the leak by the right engine's controller did not violate any launch commit criteria and liftoff proceeded normally. These ruptures resulted in a leak upstream of the main combustion chamber. Problems during ascent STS-93 SSME hydrogen coolant nozzle leak at liftoffĭuring the main engine ignition sequence, a gold pin used to plug an oxidizer post in the Space Shuttle's number three (right) engine came loose and was violently ejected, striking the engine nozzle's inner surface and tearing open three cooling tubes containing hydrogen. The payload was also the heaviest payload ever carried by the Space Shuttle system, at over 22.7 tonnes (25 tons). The successful launch of the flight occurred 3 days later. The launch was originally scheduled for 20 July but the launch was aborted at T−7 seconds. During the interim, Columbia would be out of service for upgrading, and would not fly again until STS-109. It would also be the last mission of Columbia until March 2002. Its primary payload was the Chandra X-ray Observatory. ![]() Eileen Collins became the first female shuttle Commander on this flight. STS-93 in 1999 marked the 95th launch of the Space Shuttle, the 26th launch of Columbia, and the 21st night launch of a Space Shuttle. ![]()
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