‘Unknown’ incident noted with ET-121

by Chris Bergin

Two United Space Alliance sources have noted an incident that occurred with the External Tank that will fly with Shuttle Discovery on STS-114.

The incident – with no word on the seriousness, and/or affect on the already-tight Return to Flight timeline – happened in the Vehicle Assembly Building on Thursday.

Both sources have confirmed that the unknown incident happened prior to “sling hook up” – and caused concern among workers preparing for the stacking to its two Solid Rocket Boosters.

The incident was said to have caused a “small ding” on the ET and the decision was to go ahead with stacking and then have a look at “damage”.

ET-121 was set to feed Atlantis’ three main engines on her mission (STS-121) – but will now provide the propellant for her sistership Discovery following the decision to de-mate the STS-114 stack.

The ET that Discovery is currently mated with will be sent back to its manufactures –  NASA’s Michoud Assembly Facility in New Orleans – for heater modifications and check-out on potential issues that arose during the first Tanking Test last month.

Insight into those issues may be more forthcoming on Friday, when a second Tanking Test will occurring – starting at 8am UK time and lasting for around 12 hours.

Following the test, Discovery will be rolled back into the VAB, de-stacked from her SRBs and ET-120, raised and stacked with ET-121 and its set of SRBs, with the process hopefully completed within the next two weeks. 

Discovery’s three auxiliary power units (APUs) will be tested on May 23 before the Shuttle is rolled-back to the VAB the following day. June 14 is targetted for when Discovery will once again roll back to pad 39B. However, today’s incident involving ET-121 may affect that timeline.

It had already been noted that even with USA engineers working everyday on Return to Flight, the soonest Discovery could feasibly launch would be July 18. STS-114 has until the end of July to launch, or see her mission delayed until the next available window – in September.

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