CAPE CANAVERAL, Fla. Shuttle Endeavours five astronauts were one failure away from a potential catastrophe during their thundering Nov. 30 launch to the International Space Station (ISS).
The was the word Friday after NASA discovered that a key detonator used to separate a strut holding Endeavours left-hand solid-fuel rocket booster to the shuttles 15-story fuel tank failed to fire in flight.
A back-up detonator, however, did fire, and the 149-foot (45-meter) booster separated cleanly from the external fuel tank. But an ongoing investigation could trigger a delay in plans to move shuttle Atlantis to its oceanside launch pad Monday.
"Engineers are evaluating the cause of the misfire, and that evaluation will continue through the weekend," said Kennedy Space Center spokesman Joel Wells.
A decision on whether to move Atlantis to its pad for the planned Jan. 18 launch of the stations first science lab the bus-sized U.S. Destiny module -- is expected early Monday.
NASA space shuttles employ two solid-fueled rocket boosters and three liquid-fueled main engines to make an 8.5-minute climb into space.
Attached to the shuttles tank by heavy-duty metal struts, the boosters fire for the first two minutes of flight before explosive charges are detonated to separate the solid-fueled rockets from the ships external tank.
The segmented rockets then fall into the Atlantic Ocean, where they are recovered for refurbishment and reuse on future flights.
During post-flight inspections late Thursday, technicians noticed that an explosive charge associated with Endeavours left-hand solid rocket booster failed to fire. Known as a NASA Standard Initiator, the detonator was one of two located on either end of a strut that connected the booster to the bottom of the tank.
The firing of either detonator results in the separation of the booster and the tank.
"The way I understand it and I dont have all the details yet is that one initiator didnt fire and the other one did the job," said NASA flight director Bill Reeves.
Had both detonators failed, though, the booster and the tank would not have separated cleanly. The likely result would have been the loss of the vehicle and its crew.
The booster problem was news to the Endeavour astronauts, who joined the first full-time crew of the international station aboard the outpost Friday.
Asked about the glitch during a space-to-ground news conference, shuttle skipper Brent Jett said Mission Control had yet to tell the crew about the malfunction.
"We havent been told any of that, so its difficult for me to comment on that without seeing all the data," Jett told SPACE.com.
But, he added: "Obviously we have redundancy in critical systems for a reason, and this is one of the times we relied on that redundancy -- if the report is correct."
Reeves said Mission Control didnt receive a report on the problem until just before the news conference. Consequently, NASA hadnt had time to transmit the report up to the crew.
The same NASA Standard Initiators have been in use since the Gemini program in the mid 1960s, and the devices have been very reliable since then, Reeves said.
"For sure I can tell you weve had no catastrophic failures as a result of these things," he added.
Engineers, meanwhile, are not certain what caused the explosive charge to fail. Among possible culprits: Flaws in electrical circuitry that routes computer commands that initiate booster separation during flight.
"There will be a thorough examinationto determine why the one [charge] didnt fire," Reeves said. "But the redundant system did perform its job."
Endeavour and its crew are due to land at Kennedy Space Center Monday.
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