Repaired ET-120 ready for mating – Discovery prepped for rollover

by Chris Bergin

STS-120’s processing timeline is picking up the pace again, following the successful completion of repairs to ET-120 – the tank that will fly with Discovery on STS-120 next month.

The tank is being moved from its checkout cell inside the Vehicle Assembly Building (VAB) ahead of mating with the twin Solid Rocket Boosters (SRB). At the same time, Discovery is undergoing final rollover preparations, ready to join the stack on September 19.

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STS-120 build up of documentation in action on L2 – including major baseline presentations on orbiter and ET-120. Presentations and memos on the ET-120 repair status also available.

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The mating of ET-120 will mark a major milestone of what has been a troublesome piece of hardware over its lifetime, ranging from ECO (Engine Cut Off) sensors and Return To Flight processing challenges. Now, the tank is finally set to carry out its mission of feeding Discovery’s engines for the eight and a half minute ride to orbit, before bidding farewell during its burn-up after separation.

The latest issue with the tank related to four of its five LO2 feedline brackets, found to have cracks embedded into the foam, following X-ray tests – tests which were called after a foam liberation event on the previous mission, STS-118.

Those observed anomalies in ET-120 handed NASA with an easy decision, to replace all four of the bracket’s surrounding foam, removing the foundation of the Super Lightweight Ablative (SLA) in the bracket – thus removing the denser debris hazard, should there be another liberation event.

Work on the brackets – carried out by a special team from the Michoud Assembly Facility (MAF) – was completed over the weekend, with the tank handed back over to United Space Alliance engineers, for final walkdown inspections.

These have also been completed, allowing the scaffolding that surrounds the tank to be removed, ahead of being lifted out of the checkout cell for mating with the nearby SRBs.

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‘ET/SRB Mate Preps are complete. SRB pre-tensioning was completed on 3rd shift, Monday night. B-Platform Retraction will be in work today,’ noted processing information on Tuesday.

‘LO2 Feedline Bracket Inspections/Rework: MAF completed their activities on Sunday and released scaffolding to USA. Shakedown Inspections were completed on Sunday. Scaffolding Removal was completed on Sunday night. ET Pre-Move Inspections and Platform Operations were completed yesterday.

‘ET FWD Sling Preps will be in work today. Fire/Safety Pre-Move Walk-downs and Inspections will be in work today. S0003 ET/SRB Mate is scheduled for tomorrow, with ‘Hook-down’ scheduled for 0800 hrs (local time).’

STS-120, commanded by US Air Force Colonel Pam Melroy, will deliver launch package 10A to the International Space Station, which consists of the US Node 2 (with four DC-to-DC Converter Unit (DDCU) racks and three Zero-g Stowage Racks (ZSR) installed), a Power and Data Grapple Fixture (PDGF) for the station’s robot arm, and a Shuttle Power Distribution Unit (SPDU).

The mission remains on schedule for the first launch attempt to take place on October 23 – the third of (currently) four missions pencilled in for 2007 – with no major issues in work on the current processing flow.

That flow has already seen the recent delivery of the first wave of tanker loads of LH2 (liquid hydrogen) being offloaded at Pad 39A.

Discovery is almost ready for rollout of her OPF-3 (Orbiter Processing Facility) for the short trip to the VAB, ahead of mating on September 19. Rollout to the pad as a full stack is scheduled for September 27.

‘Final Roll preps and Aft Closeouts continue. Final Payload Bay Door Closure was completed last Friday,’ noted Tuesday’s processing information, which noted a few issues – all of which are expected to be resolved ahead of rollover.

‘PRSD (Power Reactant Storage and Distributation) hydrogen tank 5 supply line overtorque resolution may require reentry into the payload bay. Engineering resolution is expected early this week. Strongback removal will be constrained.

‘Soft Window Cover Removal/Hard Cover installation was completed. Small dark particles found in the APU water system last Friday are being analyzed. Engineering determination of the source of the contamination is expected early this week.’

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.


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