STS-121 update, 25-07-2005

Monday, 25-07-2005

While Discovery is on the launch pad, waiting for its launch attempt
tomorrow, Atlantis is in the Vehicle Assembly Building for mating with its
external tank and solid rocket boosters. Atlantis is having some other major
work done, too - replacement of one of its three main engines.

The replacement is deemed necessary because of a problem seen during nozzle
testing at Stennis Space Center. When there are defects in cooling tubes
inside the engine bell, a special material is used to fix the defect, and it
is cured with a bakeout process that hits temperatures around 800 degrees.
On an engine that was being fixed at Stennis, a bakeout caused a
burn-through in a cooling tube, which could cause propellant to leak while
the shuttle hurtles toward orbit.

The hole prompted NASA to look at engines throughout the fleet, to see how
many had been repaired with the same process. Discovery's three engines were
cleared, but Atlantis' engine No. 1 was not. It is being removed and
replaced while the orbiter is in the vertical position in the Vehicle
Assembly Building. Removal is expected Wednesday; the work should be done
Monday, with a rollout to the launch pad scheduled for Aug. 3. Atlantis has
to be available for launch should a rescue mission be deemed necessary after
inspections of Discovery show whether its heat shield is damaged.

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Jacques :-)

www.spacepatches.info