CAPE CANAVERAL, Fla. - The countdown
is on once again for the launch of the space shuttle Discovery, NASA's first
shuttle flight since the Columbia tragedy.
The clock began ticking down toward
Discovery's July 26 launch, currently set for 10:39 a.m. EDT (1439 GMT), exactly at noon Saturday as engineers, astronauts and
mission managers prepare for their second launch attempt in almost two weeks.
Discovery's STS-114 flight has been
delayed since July 13, when launch controllers scrubbed the attempted space
shot after a liquid hydrogen engine cut-off (ECO)sensor
in the external tank failed a standard countdown test. A subsequent engineering
investigation found that wiring grounding issues that have since been repaired,
NASA officials said.
"Discovery is in excellent shape,"
said NASA test director Pete Nickolenko during a
pre-launch status briefing here at Kennedy Space Center (KSC). "We are all very confident that all
of the engine cut-off sensors will work as they're designed to in this next
launch attempt."
Shuttle weather officer Kathy
Winters said there is only a 43 percent chance that rain and thunderstorms
could prevent Discovery's Tuesday launch attempt. While forecasters continue to
watch Tropical Storm Franklin, it should not be an issue for the planned space
shot, she added.
During Discovery's July 13 launch
attempt, the No. 2 liquid hydrogen ECO sensor failed to comply with a standard
test launch controllers run to make sure it and three other sensors are working
properly. All four sensors are required to function properly under current
shuttle flight rules, and serve as an engine cut-off back up to make sure
Discovery's three main engines shut down before the external tank runs dry.
Should the engines continue to fire without fuel, they could rip apart.
Orbiter engineers suspected that the
grounding issue, as well as electromagnetic interference from other hardware on
Discovery's launch stack, could lead to the sensor glitch that scrubbed the
July 13 launch attempt. Tests to check eight potential sources of that
interference, which included new heaters and cameras installed as safety
measures after the Columbia accident, all turned up nominal, Nickolenko said.
Shuttle workers are now buttoning up
Discovery's aft compartment, home to a sensor electronics box that commanded
much attention during the engineering investigation, and are preparing to load
the cryogenic reactants that power the orbiter's fuel cells on Sunday.
Other than standard system
confidence checks, no additional troubleshooting measures are expected, Nickolenko said.
"It makes us feel good that we can
go into another launch attempt," he added.
In addition to fine-tuning three
suspect wire grounds, which failed shuttle specifications by just the slightest
degree, pad engineers also switched wiring connections between the No. 2 and
No. 4 liquid hydrogen ECO sensor to better understand the glitch.
"We think they have a great plan
that they're going forward with," STS-114 mission commander Eileen Collins said
of the troubleshooting efforts Friday. "We have a lot of confidence in what
they're doing."
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