STS-124: Discovery preparing to enter S0007 following ELSA meeting

by Chris Bergin

Shuttle managers met on Tuesday to finalize clearance for Discovery to enter the launch countdown (S0007) on Wednesday, via a Program Requirements Control Board (PRCB) meeting.

Items that were discussed included an update on how an Emergency Life Support Apparatus (ELSA) unit was accidentally left inside Discovery’s aft – though no damage was caused.

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ELSA Investigation:

The ELSA unit fell a short distance to a location behind Avionics Bay 6 during mating operations inside the Vehicle Assembly Building (VAB). This occurred when Discovery was rotated from the horizontal to a vertical position ahead of mating with the External Tank.

ELSA units – which are emergency air supply apparatuses used by engineers when working in confined spaces inside the orbiters – are installed in the aft of the vehicles during OPF (Orbiter Processing Facility) flows.

A presentation – available on L2 – was shown to the PRCB members on Tuesday to show the unit – which should have been removed before Discovery left OPF-3 – failed to cause any damage to critical items during it fall.

Interestingly, the unit was spotted by coincidence during aft closeouts at the pad, when an eagle-eyed engineer noticed a strap that belonged to the ELSA protruding from behind the Avionics Bay. The technician was initially searching for a lost screw.

‘Emergency Life Support Apparatus (ELSA) unit detected during inspection associated with a Lost and Found Work Authorizing Document (WAD) issued for a missing screw,’ noted the presentation.

‘Technician vacuuming behind avionics bay 6 encountered the strap of an ELSA unit. Technician notified his Lead and the appropriate documentation was generated to record the finding.’

Initially it was thought that the unit had caused tears that were observed in Thermal Control System (TCS) blankets – silver and goal mylar material that provides passive thermal control in various areas of the vehicle – in the aft when the ELSA unit was removed. However, this continues to be classed as unrelated.

‘Thorough search of the aft compartment was conducted. Close out inspections were completed. Aft confidence check were completed successfully. All ELSA units deployed to OV-103/104/105 (OPF, VAB, Pad) have been physically verified. Engineering is confident no damage was caused by the ELSA unit.

‘No fluid lines, wire bundles, or ducts located in area where ELSA unit was located. No damage to structure found. Borescope inspections found only minor TCS blanket damage – not attributed to ELSA unit.

‘With no access to the bottom side of Avionics Bay 6, two small tears in the TCS blanket cover will be accepted as-is for one flight. All signatures have been obtained.’

The lack of damage is related to the original location of the unit and where it was found, a position that stopped it from falling into the plumbing of the MPS (Main Propulsion System) and related hardware for the three Space Shuttle Main Engines (SSMEs).

‘ELSA unit was found positioned upright between structural stringers under Av Bay 6. Movement restricted to around six inches within the cavity,’ added the presentation, which was accompanied by an array of images taken from inside Discovery’s aft.

‘Prevented ELSA unit from traveling aft to engines, MPS lines, etc. during transition from horizontal to vertical – slow transition prevents sudden impacts. Monitoring personnel did not report any noise.’

Though the presentation makes no assumptions on what may have happened had the unit of fallen past Avionics Bay 6 during mating operations – or dislodged during ascent – it is important to note that the aft hardware is built to withstand some abuse.

This was exemplified in October, 1990, when a nine foot long support beam audibly fell inside Atlantis’s aft compartment during her mating operations in the VAB. That incident only caused damage to a small portion of a manifold relief line and minor abrasions to the surface coating of a strut and scuff marks on freon lines.

Regardless, the United Space Alliance (USA) are immediately taking action to ensure such an incident does not take place in future processing flows, with an accident investigation board tasked with ensuring the prevention of an occurrence.

‘Standing Accident Investigation Board (SAIB) Team Activated May 21, 2008. Board Objective: Gather facts, determine causes, and make recommendations to prevent future occurrences,’ added the presentation.

‘Actions to date: Reviewed scene for investigation data. Performed documentation review: Logs. OPF ELSA Installation and Removal processes. Review of witness statements.

‘Interviews of relevant personnel involved in deployment, installation, and removal of ELSA units for OPF-3. Release of 48-hour quick-look. Directed an inventory of all ELSA units deployed for OV-103. Board Deliverables: Root Cause Analysis. Process Improvement/Corrective Action.

‘At conclusion of the SAIB investigation, a presentation of findings/recommendations will be made to the daily PRCB: Approximately 2-3 weeks.’

STS-124 Pad Flow Update:

Discovery’s flow towards launch continues to be extremely smooth, and remains as the lowest amount of IPRs (Interim Problem Reports) recorded during a processing of an orbiter.

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Whilst most of her engineers enjoyed up to four days off over the long Memorial Day weekend, Discovery remained issue free as she sat patiently on the pad.

‘Preparations for Launch Countdown continue. S0007.200 Call to Stations is planned for 14:30 EDT Wednesday,’ noted the latest processing information on L2. ‘On Friday, the crew escape pole was lifted into position. The Front End Processors (FEP) were base lined Friday morning.

‘(Fuel Systems) and MPS pressurization for flight (S0071) picked up Tuesday morning with Call to Stations at 00:01 EDT. Pad cleared of personnel at 01:50 EDT for Stage I pressurization. OMS/RCS helium regulator lock-up complete. Drag Chute Door checkout complete.’

One issue was noted, namely with the Forward Reaction Control System pressurization, though this is not deemed as a constraint to enter the launch countdown.

‘IPR: During FRCS regulator lockup, oxidizer ‘B’ leg locked up at 268.9 psi should be no more than 268 psi,’ added the processing report. ‘Engineering will seek a waiver.’

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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