July 14, 2010
External Tank #138 Arrives at KSC
 
External Tank-138 (ET-138), designated as the ‘last tank scheduled to fly’, may, indeed be the very last tank to fly. NASA officials are currently discussing the advantages of swapping the missions currently assigned to ET-138 and ET-122. At present, ET-138 is scheduled for the STS-134 mission with ET-122, the Katrina-damaged tank that has been re-certified for flight, to be the LON (STS-335) for the STS-134 mission. Should Congress authorize the STS-135 mission, then ET-122 would fly on that mission.

That all might change. Discussions among the managers should reach a conclusion at the end of the month and if the new assignments are approved, ET-122 will fly on STS-134 with ET-138 as the LON tank. With only a very small chance of needing the LON mission, the tank, in all liklihood, would be assigned the STS-135 mission.

The reasoning for the ET swap is that should a LON mission be required it would be prudent to use the latest and very best tank design on such a program-ending mission.

The question could be asked, then, about the quality of ET-122. Nothing about the tank, say officials, is below the current flight criteria for External Tanks. There is full confidence in the flightworthiness of ET-122.

But when you consider the experience accrued by the team at NASA’s Michoud Assembly Facility between the manufacture of ET-122 and ET-138 it is easy to see the truth to the team’s slogan, ‘The Last One will be the Best One’. On that reasoning, if a LON mission was required, NASA would want the best of the best for that critical mission. Lacking that mission, we have ET-138 as the ‘final tank to fly’ on an increasingly likely STS-135 mission.