CAPE CANAVERAL, Fla. -- NASA is investigating a problem with the explosive nuts that release the space shuttle upon launch after a backup system failed during Atlantis' lift-off last week.
At T-minus zero in the countdown, eight pyrotechnics nuts on hold-down posts, one on the external tank vent line and one on a lanyard explode, releasing bolts so the shuttle can lift off. Immediately afterward, the solid rocket boosters fire.
Each nut has two pyrotechnics in it, NASA spokesman James Hartsfield said. Only one set of pyrotechnics fired, the 10 nuts exploded, and Atlantis lifted off safely.
Until Atlantis lands at Kennedy Space Center on Friday, however, investigators won't be able to determine exactly what went wrong. The shuttle's on-board computer sent the command to fire the nuts that release the bolts.
"The investigation needs the orbiter back to proceed to its full extent," Hartsfield said.
He doesn't expect the problem to delay Endeavour's scheduled Nov. 10 launch, he said, but NASA has to address the problem.
"We won't fly Endeavour until we are confident that this won't happen again on Endeavour," Hartsfield said. "Honestly, this one was safe, but we want all of our primary and backup systems all working."
The system that sends signals to the pyrotechnics is always tested before launch, he said. Today, there's a countdown test at Kennedy Space Center for Endeavour and its crew, but the test usually cuts off a few seconds before the point in the sequence when the nuts explode. At T minus 9 minutes in the shuttle countdown, the ground launch sequencer computer begins to control all countdown functions automatically. At 31 seconds before launch, the shuttle's on-board computers begin their terminal launch sequence.
At 10 seconds before launch, the ground launch sequencer gives a go for main engine start. The main engines ignite about 6 seconds before launch.
The ground launch sequencer can stop the engines until just before the solid rocket boosters are ignited at the zero-point in the countdown.
Spokesmen from NASA on Tuesday weren't able to say what would happen if the pyrotechnics in the nuts didn't fire at T minus zero, just before solid-rocket booster ignition and lift-off.
The investigation isn't limited to Atlantis' computer. "They're taking a look at all aspects of the pad, boosters, the orbiter, all sides of it, to take a look to see if they can determine what happened," said Kari Fluegel, spokeswoman for shuttle contractor United Space Alliance.
At this point, Hartsfield said, "they haven't pinpointed the cause of the problem yet."
In a post-launch news conference, launch director Mike Leinbach speculated the problem was related to a failed circuit card called a hardware interface module. Also on launch day, the ground launch sequencer looked for two signals that the shuttle had lifted off and didn't find them, he said, so launch controllers had to put the liquid hydrogen and liquid oxygen systems into a safe configuration manually.
"We would have gotten through an on-pad abort just as safely as we got through the safing that we did," Leinbach said at the time. "We practice it so often that it's almost second nature to us."
Endeavour is scheduled to leave for the International Space Station sometime between 10:30 p.m. Nov. 9 and 2:30 a.m. Nov. 10. The exact launch time will be announced 24 hours in advance.
Published under license from FLORIDA TODAY. Copyright © 2002 FLORIDA TODAY. No portion of this material may be reproduced in any way without the written consent of FLORIDA TODAY.
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