A BACK-UP system saved the day for the space shuttle Endeavour on its recent
mission to the International Space Station, NASA has revealed.
On 30 November, for the first time in 100 launches, one of the explosive
charges that jettison the shuttle鈥檚 two solid rocket boosters failed to
detonate. Fortunately, only one of the two charges on each booster needs to
fire. The back-up detonated properly and the spent booster fell into the
Atlantic, where it was rescued for use in a future launch.
No one noticed the glitch until technicians examining the booster found the
charge intact. Last week they traced the problem back to an electrical connector
which transmits the command that triggers detonation. The contact 鈥渟howed signs
of standard wear and tear over time鈥� [but] not severe damage鈥�, according to a
NASA spokesman. A second set of cables carried a separate detonation signal to
the back-up charge.
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The cables are part of the solid rocket booster assembly, which is overhauled
and reused after recovery from the ocean. NASA said that after being used on
several flights, 鈥渢he integrity of the connector became compromised,鈥� so it
failed to conduct the signal. Last week, NASA checked for similar defects in the
shuttle Atlantis, which is being prepared for a launch on 18 January. Atlantis
will deliver the Destiny laboratory module to the space station.
NASA also announced a two-week delay in the following mission, in which the
shuttle Discovery will bring the first space station crew back to Earth. The
agency needs to replace 10 of Discovery鈥檚 34 thrusters, which it uses to adjust
its orbit. They are normally replaced after four or five launches, but
inspections showed that four had failed prematurely. The mission is now due for
launch on 1 March.