STS-123: Booster concern cleared – Endeavour on track for launch

by Chris Bergin

Engineers have cleared the remaining issues associated with pressing towards the STS-123 launch countdown (S0007), which takes another step closer with the Hyper/MPS (Main Propulsion System) pressurization and closeouts on Thursday.

Literally a fallout from STS-122, one issue had to be cleared ahead of Endeavour’s flight, namely a suspect SRB (Solid Rocket Booster) factory joint debond issue, caused by the observation of missing weathershield “plug/cap ply” material on one of Atlantis’ now-returned boosters.

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 **LIVE news updates on Endeavour STS-123 PAD FLOW**

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STS-123 Pad Processing Latest:

Processing at the pad is on track for the March 11 launch target. Key events in the pre-countdown flow included the successful installation of the final ordnance on Monday.

‘S0007 – Launch countdown preps continue. S0071, Hyper/MPS pressurization and closeouts call to stations is scheduled for Tuesday 2nd shift. 1st stage pressurization will occur on Thursday 3rd shift, with final pressurization on Friday 3rd shift,’ noted Tuesday processing information.

‘APU (Auxiliary Power Unit) cart lowering is scheduled for Tuesday afternoon. The LH (Left Hand) and RH (Right Hand) SRB forward skirt doors are installed for flight. Five waves of LOX tankers were offloaded Monday for tank replenishment and two waves of LH2 tankers are scheduled for Tuesday.’

The two of the main issues that were being worked at the weekend involved the SRB debond issue, and the required changeout of Endeavour’s UHF radio – the latter will be re-tested later this week.

‘On vehicle at pad, completed hyperload activities Friday. Ran hydraulic circ pumps over weekend, and that issue is behind us. Changed out UHF radio, completed ordnance connections, and are into power up PIC test,’ added the latest Stand-up report. ‘This week, will continue with orbiter aft closeouts and closeout of SRB aft skirts.’

SRB Clearance:

The observation of missing weathershield ‘plug/cap’ material wasn’t mentioned in the STS-122 IFA (In Flight Anomaly) reports, given the boosters only recently returned to the mainland.

Once they had undergone inspections, a small piece of SFEPDM weatherseal (3.24 in. X 2.14 in. X 0.060 in.) was noticed to be missing from the top third of the right hand booster.

The problem related to whether this rubber ply material had come loose during ascent, which would prove to be a debris hazard for the orbiter. This was the only related concern, given any liberation would not be detrimental to the actual performance of the boosters.

‘Issue: Potential for unacceptable debris liberation during ascent,’ noted the STS-123 Flight Readiness Review (FRR) presentation for the RSRM (Reusable Solid Rocket Motors). ‘No motor issues – weatherseal performance is not affected by potential missing cap ply.’

However, the belief is the material actually came loose after their ride uphill, liberating from the booster during its splashdown in the Atlantic ocean, and/or possibly debonding during the heating period the boosters undergo not long after separation.

Regardless, confidence in STS-123’s boosters was still required, given NASA does not take any chances.

Engineers subsequently evaluated the need for thermography inspections on the STS-123 boosters – which would have been time consuming in the pad flow – to checking flight history and manufacturing records at ATK, along with further checks on the returned STS-122 boosters.

The eventual plan was a mix of all the available options, with thermography inspections carried out on STS-122’s boosters, which found all the other plugs to be in good shape.

Cross referencing paperwork at ATK found the plugs were installed correctly, leading to the belief this was a one-off incidence that related to the adhesive/poly film that bonds the material in place.

‘Very high confidence that any previous occurrences of missing material would have been detected in post-flight inspection and assessment. 7 cap plies per factory joint x 7 factory joints per motor x 2 motors per flight = 98 cap plies per flight x 96 flights = 9408 cap plies flown,’ added the FRR presentation.

‘Design and process of weatherseal unchanged over RSRM production history – no change in process, planning, personnel.’

Flight rationale was placed on standby by the FRR, which backed up the eventual findings that this was an isolated incidence, and the likelihood of it occurring again is not expected, especially during ascent.

‘Flight Rationale: No motor performance concerns. First time occurrence of liberated cap ply material (9408 flown). Low likelihood of having a cap ply with poly film on STS-123 – recurrence of cap ply liberation is unexpected,’ noted the RSRM FRR presentation.

‘Debris liberation during ascent not predicted. Based on demonstrated reliability – 1 in 470 chance of having cap ply with poly film at a critical location on STS-123. STS-123 is safe to fly.’

Incidentally, the FRR presentation also added that the modifications that debuted on STS-122’s boosters – which included the redesigned nozzle-to-case joint, and the ATK manufactured Booster Separation Motors (BSMs) – all performed as advertised.

In fact, the fast turnaround from STS-122 post flight, to the preparations for the launch of Endeavour have gone extremely smoothly, as was observed at last week’s FRR, which was summarized on Monday by Flight Director Cathy Koerner.

‘The STS-123 Combined SSP (Space Shuttle Program) and Joint Shuttle/Station FRR took place at KSC last Thursday and Friday (2/28-29). The two day review covered all project and program elements’ readiness and concluded with Headquarters giving a GO to proceed with a 3/11 launch,’ Koerner noted on the NASA 8th Floor News.

‘A few items generated additional discussion, including Virtual Spacecraft (VS) configuration and TDRS scheduling, Sidewall Payload Accommodation (SPA) Beam Bolts, ascent debris due to cryo ingestion, and contamination due to a filter failure in a vehicle purge circuit.

‘The flight rationale presented for the SPA Beam Bolts and filter contamination were accepted as well as MOD’s plan for utilization of VS. The ascent debris item did not have a conclusion nor is it a constraint to launch, but it will be further analyzed in an effort to better quantify its risk.

‘Two open items, WLES criteria to drive a late focused inspection and clearance of a bogan bracket baseplate location, will be closed at the L-2 MMT (Mission Management Team) meeting.’

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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