NASAengineers have found another crack ? the fourth so far ? in the metal skin ofthe external fuel tank attached to the space shuttle Discovery.
Thenew crack is similarto three others spotted on aluminum ribs near the midpoint of Discovery's15-story external fuel tank. The cracks and a hydrogen gas leak on the tankhave prevented Discovery from launching on its final spaceflight this monthfrom its seaside pad at NASA's Kennedy Space Center in Florida.
NASAspokesman Allard Beutel told SPACE.com today (Nov. 15) that an analysis isunder way on Discovery's fuel tank and engineers are discussing plans toinspect other nearby ribs for cracks as well. The cracks and gas leak onDiscovery's tank must be repaired before the shuttle can launch on its lastspace voyage, he added.
Inspectorsinitially spotted a long crack in the insulating foam on the shuttle fuel tank.
Whileinvestigating that crack, engineers found two smaller cracks in one of the 108ribs that girdle the external tank's midpoint between its liquid hydrogen andliquid oxygen tanks. A third crack was discovered last week, only to befollowed by this latest, fourth crack over the weekend.
Beutelsaid that NASA has repaired cracks similar to those on Discovery's fuel tankmany times in the history of the agency's nearly 30-year shuttle program.However, this is the first time the cracks have been detected on a tank alreadyat the launch pad, awaiting blastoff, he added.
"Thekey thing is this work that we've never done before on the pad," Beutelsaid.
Thecracks are on ribs that provide extra structural support to the shuttle fueltank's so-called "intertank" region ? a transition spot between thetwo fuel tanks. [GRAPHIC:NASA's Space Shuttle ? From Top to Bottom]
"It'swhere we keep the electronics and wiring for the tank," Beutel said."It's mostly just empty space."
Tofix the cracks, engineers typically cut off the cracked portions and replacethem with thicker aluminum ribs that are then bolted into place. The foaminsulation is then reapplied.
Beutelsaid NASA is still aiming to try and complete repairs on Discovery's fuel tankin time for the next window to launch the shuttle on its mission to theInternational Space Station. That window opens Nov. 30 and closes around Dec.6, he added.
The nextpossible time that Discoverycan attempt a liftoff is Nov. 30 at 4:02 a.m. EST (0902 GMT). Discovery isscheduled for an 11-day supply mission to the space station to deliver ahumanoid robot helper for the station crew and a new storage room for theorbiting lab.
The STS-133mission will be Discovery's grand finale in space beforebeing retired in 2011 along with the rest of NASA's shuttle fleet.
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