Tag: shuttle

NASA engineers think they might have found the root cause of the cracks that have been appearing on the shuttle external tank. The cracks appear on structural units called stringers. Key quote:

“Some material used for the stringers was found to be ‘mottled,’ with a different surface appearance than the standard material. Testing revealed this mottled material had lower fracture toughness than the nominal material and exhibited unstable crack growth. All of the cracks found during tanking as well as cracks fixed during manufacturing were located on stringers made with this mottled material.”

NASA engineers are considering giving Discovery’s external tank the equivalent of a girdle in order to keep it from developing more cracks during launch. Key quote:

If that decision is made, it is unlikely NASA could complete the work, repair the tank’s foam insulation and get Discovery back out to the launch pad in time to support a launch attempt during the next available window, which opens Feb. 3 and closes Feb. 10. Work to beef up all 108 stringers at the top of the intertank almost certainly would delay Discovery’s launch on a space station resupply mission to the next available window, which opens Feb. 27 and closes in early March.

The repairs to the cracks on Discovery’s external tank continue, with the hope for a February 3 launch.

The initial results from the tank test performed today on the shuttle external tank are as yet inconclusive.

It’s official: The launch of Discovery is delayed until February.

Bad news for the space shuttle: The root cause of the cracks on Discovery’s external tank is still not identified.

NASA engineers continue to struggle to analyze the cause of the cracks in Discovery’s external tank. Key quote:

Forty-three tanks have been constructed with the lighter alloy, requiring just more than 4,600 stringers. So far, 31 cracks have been found, including those on Discovery.

“All of those have been known assembly issues,” Shannon said of the previous cracks, which were traced to misalignments of the stringers as they were fastened to the tank or to mishandling in which the fragile stringers struck or were struck by other hardware. Discovery’s cracks were the first found and repaired at the launch pad using techniques previously employed only at the production plant.

The ongoing detective work is immune to schedule and budget pressure, according to Bill Gerstenmaier, NASA’s associate administrator for space operations.

Discovery’s launch delayed until December 17 at the earliest. Key quote:

Shannon said that one of the concerns was that another major crack might liberate a piece of insulating foam large enough to damage Discovery, as happened during the January 2003 liftoff of Columbia. A suitcase-sized chunk of foam punched a hole in Columbia’s wing, dooming the ship and her crew of seven astronauts when they reentered the atmosphere.

Shannon said that teams were also examining the possibility that the tanks have been flying with undetected cracks for years.

Cracks became more common after the 1998 debut of “super-lightweight” tanks built with a more brittle aluminum-lithium alloy. Since then, 29 cracks in stringers making up the ribbed “intertank” section that separates liquid hydrogen and oxygen tanks have been found and repaired in 18 tanks, including Discovery’s and a tank scheduled for use by the shuttle Atlantis next summer.

NASA management is reviewing the “flight rationale” for Discovery’s next mission, considering the cracks in the external tank. Key quote:

Troubleshooters are assessing the structural integrity of the tank and its foam insulation to develop the necessary flight rationale, or justification, for proceeding with another launch as early as Nov. 30.