Engineers find issue with Atlantis’ radiator retract hose

by Chris Bergin

Atlantis had her payload bay doors opened Tuesday, though the operation was halted due to a flexed starboard aft radiator retract flex hose.

Engineers were checking the hoses after the same problem was noted on Discovery – the first time such an issue had arose. Meetings are taking place on a forward plan, as the issue is a constraint to closing the payload bay doors in the vertical.

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‘During Stbd PLB door opening, observers noted a kink/bend in the stbd aft radiator retract hose. Door motion was halted,’ noted information on L2.

‘Near-Term Plan: perform borescope inspections of hose, retract box assy, Close FCL2 rad isol vlv to mitigate any potential freon leakage, then take photos. Operation to take PLB door to full open is on hold.

‘Constraint to closing of PLBD in vertical.’

New article will follow soon.

Pre Inspections (Tuesday morning):

Engineers will carry out boroscope inspections – due to the possibility of finding a cracked hose, which may cause a Freon leak on orbit – to check on Atlantis’ hoses, though it is unlikely they will find a problem, due to the issue found on Discovery being the first of its kind.

The need to check Atlantis hoses relates to a number of concerns such an issue can hold for the orbiter once in orbit, though mitigation processes can be utilized in such an eventuality.

Flex hose distortion could result in: Freon coolant loop flow rate restriction. FCL leakage. Omega bend increases risk of leakage due to reverse bending,’ noted Flight Readiness Review (FRR) documentation. ‘Distorted flex hose could protrude into payload envelope. Distorted hose may have put unacceptable loads into door drive mechanism.’

Adding to confidence that the issue is a one-off with Discovery, and unlikely to be found on Atlantis, are inspections relating to Discovery’s STS-116 and STS-120 missions, which showed a progression of changes to the shape of the hose, possibly as a precursor to the current observations.

‘Evaluation of photos from STS-116 and STS-120 pad flow show change in flex hose geometry in the door open position – may be a precursor to distortion,’ added the documentation, which also noted no issues have been found on Endeavour.

The forward plan is focusing on root cause, mainly via additional testing by Boeing, while flight rationale is built for all potential scenarios relating to Atlantis, including on orbit.

‘Discovery: Testing at Boeing, Huntington Beach. Flex hose X-ray evaluation and internal wall borescope inspection to baseline as-received condition. Map performance parameters for two flex hoses installed in the removed OV-103 aft starboard radiator retract container assembly using a test fixture that simulates the payload bay doors. Testing may yield data to determine root cause.’

‘Atlantis: Operational work-around/risk mitigation technique to be utilized for door closure: Ascent and Post Insertion payload bay door opening operations will occur per nominal procedures. Deorbit Prep (D/O Prep) payload bay door operations to be modified:

‘Radiators will be pre-emptively isolated prior to payload bay door closing: Crew will perform visual inspections after closure. Ground (MCC) will verify no leaks. If no leaks, crew will return radiators to the nominal bypass config (unisolate). If a bend is observed in a radiator hose, that radiator will be isolated prior to the deorbit burn and remain isolated through entry.

‘The coldsoak from the radiator may be used during post landing. For wave-off scenarios, the affected radiator will be isolated prior to door opening. Post opening, assuming no leaks, the radiator will be returned to a nominal on-orbit config.

‘Accept risk of freeze up and associated blockage in radiator while in isolate config. Possibility of freezing due to water within freon freezing and blocking radiator outlet filters. Minimize time in isolate until thermal analysis assess potential for freezing.’

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Even if such a problem was observed on orbit, there wouldn’t be a safety issue, due to alternative paths of cooling the orbiter when the payload bay doors are closed for deorbit and re-entry.

‘Small to moderate radiator retract flex hose leaks mitigated by auto radiator isolation capability,’ added the FRR presentation. ‘Orbiter cooling provided primarily by the FES during deorbit/entry. Loss of cooling capacity for cold-soaked radiator can be compensated by early ammonia boiler activation.

‘Acceptable for STS-122 Flight: Prelaunch verification limits the distortion risk to the end of mission payload bay door closure. Radiator isolation prior to payload bay door closure mitigates loss of Freon loop if hose distorts and leaks.

‘Precludes complete loss of FCL (in case of large leaks) and is least impact to crew activity. Radiators nominally in bypass prior to door closure. If a large leak develops, no time-critical actions required to preserve loop. ATCS can support safe return with radiators isolated.

‘Crew can visually monitor radiator retract flex hose condition for on-orbit door closure. Return to nominal configuration after verification of no distortion. Power and water management procedures in-place to manage vehicle operations for weather wave-off.’

Meanwhile, STS-122 is continuing to prepare for S0007 Launch Countdown, with the pad undergoing several levels of returning to a launch posture. Yesterday the flame deflectors were returned to their launch configurations, while the water bags under the Solid Rocket Boosters will be installed on Tuesday.

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