CAPE CANAVERAL, Fla. - The countdownis on once again for the launch of the space shuttle Discovery, NASA's firstshuttle flight since the Columbia tragedy.
The clock began ticking down towardDiscovery's July 26 launch, currently set for 10:39 a.m. EDT (1439 GMT), exactly at noon Saturday as engineers, astronauts andmission managers prepare for their second launch attempt in almost two weeks.
Discovery's STS-114 flight has beendelayed since July 13, when launch controllers scrubbed the attempted spaceshot after a liquid hydrogen engine cut-off (ECO)sensorin the external tank failed a standard countdown test. A subsequent engineeringinvestigation 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 apre-launch status briefing here at Kennedy Space Center (KSC). "We are all very confident that allof the engine cut-off sensors will work as they're designed to in this nextlaunch attempt."
Shuttle weather officer KathyWinters said there is only a 43 percent chance that rain and thunderstormscould prevent Discovery's Tuesday launch attempt. While forecasters continue towatch Tropical Storm Franklin, it should not be an issue for the planned spaceshot, she added.
During Discovery's July 13 launchattempt, the No. 2 liquid hydrogen ECO sensor failed to comply with a standardtest launch controllers run to make sure it and three other sensors are workingproperly. All four sensors are required to function properly under currentshuttle flight rules, and serve as an engine cut-off back up to make sureDiscovery'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 thegrounding issue, as well as electromagnetic interference from other hardware onDiscovery's launch stack, could lead to the sensor glitch that scrubbed theJuly 13 launch attempt. Tests to check eight potential sources of thatinterference, which included new heaters and cameras installed as safetymeasures after the Columbia accident, all turned up nominal, Nickolenko said.
Shuttle workers are now buttoning upDiscovery's aft compartment, home to a sensor electronics box that commandedmuch attention during the engineering investigation, and are preparing to loadthe cryogenic reactants that power the orbiter's fuel cells on Sunday.
Other than standard systemconfidence checks, no additional troubleshooting measures are expected, Nickolenko said.
"It makes us feel good that we cango into another launch attempt," he added.
In addition to fine-tuning threesuspect wire grounds, which failed shuttle specifications by just the slightestdegree, pad engineers also switched wiring connections between the No. 2 andNo. 4 liquid hydrogen ECO sensor to better understand the glitch.
"We think they have a great planthat they're going forward with," STS-114 mission commander Eileen Collins saidof the troubleshooting efforts Friday. "We have a lot of confidence in whatthey're doing."
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