Engineers have successfully retracted the starboard aft radiator retract flex hose and have closed the payload bay doors – required ahead of the S0007 Launch Countdown.
The retraction – completed by 10pm local time on Sunday evening – was aided by an engineer guiding the hose back into its box via a special tool on the end of a long pole. The retraction went very smoothly, adding confidence it may not even be a problem on orbit.
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Sunday afternoon: Process to start at 8pm Eastern on Sunday. Remote Manipulator System (RMS) and OBSS (Orbiter Boom Sensor System) to be stowed a few hours ahead of the operation.
Sunday evening: SUCCESS!!! Hose retracted, payload bay doors closed for flight (10pm Eastern). STS-122 is GO for proceed to S0007!
Only eight door closure cycles were required, with the special tool on the end of the pole used on six of those cycles, as the doors were closed. The hose did not appear to show any problems during the closure, and may not have actually needed the tool.
This means the hose may retract without issue ahead of re-entry, adding to the good news.
Atlantis is now is a good posture to continue with the move to the start of the S0004 launch countdown later on Monday.
Engineers found the problem with the hose via boroscope inspections, called after a similar problem was found on sister ship Discovery – the first time such an issue had been observed.
The concern with such a kink in the hose relates to the possibility of the hose cracking under the stresses of the Omega bend, which may cause a Freon leak on orbit.
‘OV-104 (Atlantis) starboard aft radiator retract flex hose found to be distorted during PLB (Payload Bay) door open at the pad. OV-103 (Discovery) starboard aft radiator retract flex hose found to be distorted after OPF PLB door closure in mid December 2007,’ opened a large PRCB (Program Requirements Control Board) overview presentation – available on L2.
‘Both flex hoses have an omega bend with the starboard payload bay door closed (other three hoses nominal).
‘Concerns: Flex hose in an uncertified configuration for flight. Flex hose distortion could result in FCL leakage. Distortion increases risk of leakage due to reverse bending.’
While a root cause is unknown, engineers checked images of Discovery’s previous two pre-flight processing flows and noticed the bend on her hose – one of four which carry the freon cooling liquid to the orbiter’s radiators – may have worsened over a number of flights.
‘Evaluation of photos from STS-116 and STS-120 pad flow show change in flex hose geometry in the door open position which may indicate hose had already experienced omega bend,’ noted the presentation.
‘Four open/close cycles done at Huntington Beach (Boeing) while measuring torque on hose. No leakage noted.
‘Torque required was larger than normal, but an order of magnitude less than door mechanism capability. X-rays show flattened convolutes. Evaluation of observed braid damage indicates that it may have been induced by one or more flights.’
Opening findings on Discovery’s now removed hose shows damage appears to be related to ascent vibration contact with upper roller in the omega bend configuration. Meanwhile, Endeavour has also been checked, and is found to have no issues with her freon loop hoses.
Crucially, Atlantis’ hose does not appear to have suffered anything more than small cosmetic damage, following last week’s X-Ray and visual inspections – and is deemed to be in a better condition than the hose on Discovery.
‘Verified no flow (of freon) restriction due to bend. Verified no leakage (via) 10 minute, system pressure test. Hands on inspection showed no evidence of significant damage to the flex hose
‘Two broken strands approximately 8” from the collar (acceptable). Some disturbed braids approximately 2” from the flex hose collar, but no damage consistent with a crease. X-rays show little or no change from nominal configuration.
‘While X-rays do not have the capability to detect micro-cracks, hose from OV-104 has experienced significantly less plastic deformation than that from OV-103.’
Side view X-rays of the hoses at the collar on both Atlantis and Discovery noted a ‘series of deformed, or flattened, convolutes on the OV-103 hose at the ID of the bend radius basically covering the entire view. On the OV-104 hose, there may or may not be a single deformed convolute (the second convolute out from the collar).
‘Side view of hoses at center of bend: A few (around five) deformed, or flattened, convolutes on the OV-103 hose at the ID of the bend radius. Possibly one or two deformed convolutes on the OV-104 hose.’
‘Side view of hoses looking under the collar. A few deformed, convolutes on the 103 hose. On the 104 hose it all looks good. Permanent deformation is evident on OV-103’s hose both pressurized and unpressurized.
On Friday, shuttle managers concluded that a successful retraction of the hose back into its box is the preferred option, with no safety risk associated with the orbiter, due to the ability to automatically isolate the freon loop on the hose, should it show signs of leakage during the payload bay door closure on orbit ahead of re-entry.
‘Path to Flight Rationale: Fly as-is. Preferred option is to assist hose retraction into the container. Returns hose to certified ascent configuration save for condition induced by omega bend. Stress and loads engineering judgment deems this configuration to be less stressful than the out-of-the box omega bend condition.
‘Risk of leakage during flight is a mission success risk only, not safety-of-flight. Flying with hose in omega bend condition requires more engineering assessment and would be a more significant risk of mission success.’
‘Risk Assessment: Distorted flex hose could result in leak/loss of FCL (Freon Coolant Loop) or restricted flow during flight. Evaluated radiator isolation and determined that system risks for two-phase fluid dynamics outweigh potential for hose failure.
‘Small to moderate radiator retract flex hose leaks mitigated by auto radiator isolation capability in Ops 2. Loss of cooling capacity for cold-soaked radiator can be compensated by early ammonia boiler activation. Orbiter cooling provided primarily by the FES (Flash Evaporation System) during de-orbit/entry.
‘Catastrophic failure of flex hose would result in complete loss of FCL before radiators could be isolated. Low risk, since distorted hoses did not leak during 12 cycles on vehicle or at HB (Huntington Beach).’
Confirming the hose is acceptable to fly as-is for flight, is based both on the condition of the hose, and the mitigation processes that are built in – should there be a leak – and the abundance of flight history.
‘Acceptable for STS-122 Flight: X-rays of OV-104 shows hose is in an acceptable condition. Condition of OV-103 hose envelopes OV-104 hose. OV-103 hose did not leak after multiple ground and test cycles. Braid damage analysis indicates that OV-103 hose may have flown multiple times in omega bend condition.
‘No visible evidence to suggest the OV-104 hose has flown in omega bend condition. Qualtest experience of 39 mission duty cycles x scatter factor of 4 (0-180 degrees travel plus vibration and pressure) showed no leakage. Limited omega flexures this flow and no flight environments since
‘Testing demonstrated that hose can successfully be returned to an in-the-box configuration. In-the-box configuration is as close to nominal ascent conditions as possible. Distorted hose condition is only a mission success risk, not safety-of-flight.’
Retraction of the hose via special tool:
The process, which will be carried out by a United Space Alliance technician, calls for a large element of skill, as he helps guide the hose back into its box via a special tool at the end of a long pole.
The technician has already practised the technique at Boeing’s Huntington Beach facility, which proved to be successful on the three occasions the retraction was performed. He has since been flown back to KSC to assit with the retraction.
‘Overall plan for ‘assisting’ hose back into box for launch: Proof of concept testing has been completed at Huntington Beach. Hose ‘manipulation’ was successful and repeatable at 130 psia. Hose was successfully ‘guided’ into the container 3 times.
‘Tool concept was also verified during Huntington Beach testing. Some minor modifications may be made to the tygon saddle of the KSC tool based on the configuration tested at Huntington Beach.’
The closure of the payload bar doors will be stepped, allowing the engineer to carry out the manipulation of the hose at various points of the retraction process.
‘Current plan: Nominal closure of port payload bay door with final inspection of forward and aft retract hoses. Stepped closure of starboard door (approximately 10 degree increments).
‘At each stop point, access will be established and the ‘tool’ will be used to position/guide hose to allow for normal retraction into box. Access for first 2-4 increments (or as long as clearances allow) will be from a ladder placed as close to the hinge line as possible and using the tool (or by hand) to position the hose.
‘Once clearances no longer allow for close up operations, tool will be attached to extension rod and directed from centerline of vehicle and in between payload and OBSS (Orbiter Boom Sensor System).
‘Last increment where access will be available is approximately 20 degrees open. Huntington Beach testing showed that 20 degrees open is past the last point where adjustment/guidance is required to ensure normal retraction into the container during the last 20 degrees of door movement.’
If retraction is unsuccessful:
The alternative options – ones which would come into play should there be a problem with the retraction of the hose at the pad – would led to one to two months worth of delays to STS-122.
‘R&R at OPF or pad: OPF R&R would delay launch approximately two months. R&R at pad probably feasible, but with significant technical risk. Results in an unknown launch delay, at least one month.’
Timelines and processes have already been drawn up for both R&R at the pad, and R&R back in Atlantis’ Orbiter Processing Facility (OPF) – with the latter the most likely, due to the challenges of completing the task at the pad.
‘Radiator Retract Assembly replacement has never been performed at KSC. Access for rework is intrusive and non-standard for vertical operations. Freon deservicing timeline unknown due to vehicle orientation
‘Radiator retract assembly installation procedure is still undefined. Rigging procedure and functional retests are also undefined.’
Hopefully, neither will be required, due to the confidence with both the safety assessments and the retraction process.
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