An operation aimed at mating the external tank and solid rocket boosters for the upcoming launch of shuttle Discovery is on hold while NASA examines x-rays that show indications of hairline cracks in foam covering propellant line brackets on the bullet-shaped fuel reservoir.A decision on a go-forward plan is expected late today after tank engineers brief shuttle program manager Wayne Hale on options during a meeting at Michoud Assembly Facility in New Orleans.
A chunk of foam the size of a baseball broke free from one of five aluminum brackets that held the liquid oxygen feedline to the tank used during Endeavour's Aug. 8 launch on an International Space Station assembly mission. The foam ricocheted off a metal strut attaching the tank to Endeavour, damaging fragile heat shield tiles on the underside of the orbiter.
NASA ordered up x-ray inspections of the brackets on the tank being readied for the planned Oct. 23 launch of Discovery. The 15-story tank now is located in the checkout cell on the northwest side of the Kennedy Space Center Vehicle Assembly Building.
The x-rays showed evidence of small hairline cracks in four of the five foam-and-cork covers that keep ice from building up on them.
Two different types of foam and cork laced with an epoxy bonding material are used to form the bracket covers, which are about three inches wide, five inches long and 2.5 inches thick.
Technicians early today shaved foam down to the apparent crack in one of the covers so that engineers could examine it. Any modifications to three of the four foam covers would have to be done in the checkout cell, where work platforms would provide access. The fourth bracket could be modified in High Bay 1, which now houses the mobile launcher platform and twin boosters for the October flight.
NASA already had been considering five options aimed at minimizing ice build-up on the brackets while reducing the amount of foam on them.
The leading option: Sanding or shaving the foam covers to the minimum dimensions allowed under manufacturing specifications. The covers now comprise more foam than specified to add safety margin.
The covers also could be removed and then replaced with ones fashioned only from foam. The higher-density cork would be left out of the mix, and the replacement covers would be contoured to the current shape or smaller dimensions allowed under manufacturing specifications.
Another alternative: adding foam chevron diverters to keep moisture and water away from the brackets. The fifth option would involve spraying the covers with an "ice-adhesion inhibator" -- a material designed to keep ice from sticking to foam.
Hale will outline the go-forward plan during a media teleconference scheduled to begin at 4 p.m. today. We'll post an update after it concludes.
IMAGE NOTE: Click to enlarge the NASA photo of the ET-120 being lifted into a checkout cell at the Kennedy Space Center Vehicle Assembly Building. Photo credit: NASA/George Shelton.
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