Previous Vehicle Flight:

For the review of Endeavour’s previous flight – the STS-126 mission in November 2008 – the OPO identified two issues that gained attention during the STS-127 SSP FRR (Space Shuttle Program Flight Readiness Review) last month. The first issue pertained to TPS (Thermal Protection System) tile and blanket anomalies.

The OPO presentation, available for download on L2, noted that three gap fillers were found to be protruding from the Left OMS pod during post-launch inspections.

During post-flight analysis, the cause of the gap filler protrusions was noted to be a “torn sleeve or bonding issue” that had been noted on Left OMS Pod #3 during previous flights. Flight rationale for STS-127 was obtained for this issue without much discussion.

All three of the protruding gap fillers were still present post-landing and were removed prior to Endeavour’s ferry flight back to KSC in December. An investigation of the gap fillers indicated minimal RTV application/contact to the bonding surface of the Pod.

The Program Data Requirements Resources Team later identified improvements to the bonded process that will ensure full length bonding of gap fillers on future flights.

During Endeavour’s turnaround flow, all OMS Pod leading edge gap fillers (all 260 of them) were “subjected to detailed post-flight inspections for fraying/protrusion.” In all, 34 suspect gap fillers were removed and replaced using “improved fabrication techniques and a more robust pull test of 10 lbs.”

Additionally, the second STS-126 issue to gain recognition during the SSP FRR process relates to Ku-Band Antenna anomalies: specifically, a lack of “tracking” mode during communications operations in General Purpose Computer Acquisition Mode, Multiplexer/Demultiplexer (MDM) FF3 bypass of Electronics Assembly-1 (EA-1), Forward Link Frame Sync Telemetry Dropouts, and flawed RADAR Data during undocking.

The “tracking” mode error self-corrected on FD-15 (Flight Day 15), the MDM FF3 bypass recovered with Guidance and Navigation Computer Input/Output reset, the Forward Link Frame Sync Telemetry Dropouts was an indication only and did not affect Ku-Band forward link operations, and the Ku-Band flawed RADAR Data during undocking affected range, range rate, and angle rate data displayed on Endeavour’s Flight Deck consoles.

The COMM angle track issue was repeated during flow turnaround and was isolated to the EA-1; the MDM FF3 bypass was also repeated and isolated to EA-1.

Furthermore, the frame sync telemetry and flawed RADAR data could not be repeated during Ku servicing. EA-1 was removed and replaced (R&Red), and a complete retest of Endeavour’s Ku system showed no repeat of any of the four errors seen during the STS-126 mission.

However, should any of these errors re-occur during STS-127, there are several workaround options available to Endeavour’s Flight Crew and Flight Control Team.

“Antenna angle tracking can be switched to GPC designate mode, transient conditions resulting in MDM bypass may be recovered with a GNC I/O reset, and alternate methods can be used during rendezvous to provide data normally provided by the Ku-Band radar such as the trajectory control sensor and hand held laser,” notes the OPO presentation.

The OPO also noted that all three of the orbiter’s GH2 FCV (Gaseous Hydrogen Flow Control Valves) have been approved for flight, after they were installed on Endeavour on May 7 at Launch Pad 39B.

Previous Program Flight:

The first issue from STS-125 (the previous program flight) to carry over to the OPO STS-127 SSP FRR was an erratic MPS (Main Propulsion System) Engine 2 GH2 Outlet Pressure Ducer reading.

“At liftoff, the left Space Shuttle Main Engine (SSME) GH2 Outlet Pressure transducer acted erratic,” notes the OPO presentation, adding the Booster officer in Mission Control declared the measurement failed and the crew was informed to disregard the engine out cues as a result of the toggling transducer.

Furthermore, the OPO presentation notes that “during ascent, the Engine 2 GH2 outlet pressure shifted over 1000 psi low.”

All other GH2 Outlet Pressure ducers on the other two engines and the 2” disconnect pressure functioned normally throughout Atlantis’ ascent. At MECO (Main Engine Cutoff), all GH2 Outlet Pressure readings fell to zero on all engines as expected.

Then, “When LH2 repress was activated on orbit (pressurizes LH2/GH2 systems), the 2” disconnect on Engine 1 and Engine 3 GH2 pressures showed 120 psia increase as expected. Engine 2 remained at zero.”

Adding to the investigation is the prior history of failures for this type of transducer – which is used to measure and verify portions of the LH2 Ullage pressure control post-ascent – during fight.

The measurements do not affect engine function on ascent and are used as cues for main engine shutdown, GO2 (gaseous oxygen) out temperatures, and SSME helium tank pressures.

The OPO has concluded, based on previous flight experience, that the ducer issue on STS-125 is not a constraint for Endeavour’s launch as the flight control teams are trained to identify a true ducer measurement v. a false ducer measurement and act accordingly.

Next up in the OPO report was the TPS tile and blanket anomalies from STS-125.

The OPO presentation states that “imagery analysis noted [that] a dark object appears to release from the Left Hand OMS pod” during first stage flight. A review of all pre-flight baseline images and on-orbit inspection images show no discernable gap filler anomalies.

Furthermore, during flow processing for STS-125, Atlantis’ OMS pod gap fillers were inspected for the same gap filler anomalies identified during STS-126. This inspection led to the R&R of one gap filler on OV-104.

Additionally, SRB video captured a gap filler – which was on its second mission and was not installed with the improved procedures identified after STS-126 – migration and liberation event at Mission Elapsed Time 57-seconds.

This particular OMS Pod gap filler event is bound within the flight support analysis conducted during the STS-117 lifted OMS Pod blanket anomaly in June 2007 and thus is not a concern for STS-127. Protruding gap fillers in the same region have been noted previously on OV-105.

As such, all gap fillers in the area in question on OV-105 have been inspected and/or R&Red via the improved process for this flight.

Finally, the OPO presented information on a low chamber pressure in Atlantis’ R5R vernier thruster, specific to “reduced Chamber pressures observed on all firings beginning with vernier activation on FD-1.”

The chamber pressure readings decreased to 48 psia on FD-2 before recovering slightly over subsequent flight days. However, the chamber pressure never returned to its nominal pressure of around 92 psia.

Analysis of all vehicle rate data indicates that the jet performance of the thruster did degrade, noting the thruster “deselected during sleep periods to avoid potential nuisance alarms for chamber pressures below 36 psia at start-up or 26 psia afterward.”

There was no indication of flight safety issues from this issue, and all of OV-105′s vernier jets were confirmed to be in proper working order during the vehicle’s last flight.

The degraded reading from Atlantis’ R5R vernier thruster confirms that the jet is still viable for flight even if the issue should reappear on STS-127. However, “failure of any vernier removes vernier control capability during ISS mated ops,” notes the OPO presentation.

Other attitude control capabilities exist but with potential loss of mission objectives.

L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. FRR to discuss unique safety requirements for STS-125 and STS-400As preparations continue on Atlantis and Endeavour for their respective...
2. Endeavour and her SCA piggyback ride arrive in Louisiana, via JSC flyoverThe Shuttle Carrier Aircraft (SCA) and Endeavour departed from Edwards...
3. Dual flow ballet for Endeavour and Atlantis – De-stack debatePreliminary milestone schedules have been created for the complex dual...

The pad flow at 39A remains on the timeline, as the vehicle continues to press through the various closeouts and L-15 day (to launch) processes. In tandem, waves of tankers are arriving at the pad to replenish the giant storage tanks with LH2 and LOX, which will be tanked into the External Tank ahead of launch.

“S1287 Orbiter Aft Closeout: Orbiter aft confidence tests are complete less APU (Auxiliary Power Unit), which will be performed today after engineering data review,” noted Wednesday processing information on L2. “Aft Avionics bay and MPS/SSME (Main Propulsion System/Space Shuttle Main Engine) closeouts will be worked today.

“PLBD (Payload Bay Doors) closed for flight last week. Also completed hyperload on Saturday. L-15 water sample is complete. Preps for EMU (EVA Mobility Units) functional are complete; testing is work this morning.

“The LH2 storage tank was replenished yesterday with 3 tankers offloaded. The LOX storage tank will be replenished tomorrow. 4 waves of tankers are planned.”

Wednesday also marks the arrival of the three FCVs from the manufacturer Vacco, several days ahead of the “deadline” to make the February 12 launch date – though the main constraint remains flight rationale.

“GH2 flow control valves are expected to arrive to KSC today. The team is awaiting OPO (Orbiter Project Office) approval to install the vales into the orbiter (expected to start Monday),” added Wednesday processing information.

“Are in position now to pick up with Flow Control Valves (FCVs) once decision is made to install that hardware. Need date for the FCV is nine days prior to launch (February 3); that’s in-hand, installing.”

As previous reported, the issue with the FCVs relates to an incident with one of Endeavour’s valves during STS-126′s ascent last year.

While the shuttle was not in any danger, post flight reviews evaluated the worst case scenario relating to a more severe issue with the valves, which included the “potential” of the failure causing the External Tank to vent beyond limits – deemed a Crit. 1 failure, or a LOV/C (Loss Of Vehicle/Crew) threat.

The role of the three FCV’s relates to the Main Propulsion System (MPS) and the SSMEs (Space Shuttle Main Engines) during thrusting periods. In each SSME, gaseous hydrogen from the low-pressure fuel turbopump is directed through two check valves to two orifices and a flow control valve for each engine.

During the main engine thrusting period, the liquid hydrogen tank’s pressure is maintained between 32 and 34 psia by the orifices and the action of the flow control valve from each SSME. The flow control valve is controlled by one of three liquid hydrogen pressure transducers. When tank pressure decreases below 32 psia, the valve opens; and when tank pressure increases to 33 psia, the valve closes.

If the tank pressure is greater than 35 psia, the pressure is relieved through the liquid hydrogen tank’s vent and relief valve. If the pressure falls below 32 psia, the LH 2 ullage press switch on panel R2 is positioned from auto to open , which will cause all three flow control valves to go to full open and remain in the full-open position.

During STS-126′s second stage flight, engineers noticed an uncommanded drop in SSME #2 hydrogen outlet pressure. The data indicated FCV #2 opened without removal of close command, which was an anomaly. Endeavour’s performance was not compromised thanks to Valves #1 and #3 compensating, and she achieved a nominal MECO (Main Engine Cut Off).

As soon as Endeavour returned back to KSC – following a ferry trip back from her Californian landing – engineers removed the FCVs from the vehicle as a priority processing item, and sent them off to Vacco for examination.

USA Logistics added that the three valves arriving at KSC today – a day ahead of their schedule – will be a mix of three reassembled valves that have come directly from Vacco.

“On the FCVs, Vacco has completed reassembly of three. These are not the three removed from OV-103 (Discovery), but a mix from OV-104 (Atlantis) and OV-105 (Endeavour). Are doing paper review and closeout this week. Which ones they install is still to be worked out by OPO.”

With the FCV issue likely to be removed as the single constraint to launch for STS-119, the Orbiter Project praised the extensive amount of teamwork undertaken by the NASA and contractor teams in working the problem – and gave an indication as to exactly how much work has been involved.

“On FCV, have many activities ongoing. Have been very sensitive to team in terms of workload; tried to give people rest where think may have overtaxed people. Most work now is ongoing at Vacco in terms of getting valves reassembled and with the MSFC (Marshall Space Flight Center) Engineering team in terms of analysis/modal analysis.

“Have also pulled in research centers at Ames and Glenn to help with analysis to try and not overload MSFC team. Have outstanding support from other centers in resolving this. White Sands has worked toward restoring their capability to do FCV testing. Think they may be able to get into a test as early as next week.

“Will take the valves they assembled and downselect based on the analysis later this week. Understand Ground Ops need date to have valves in hand is February 2, to start installing on February 3. Will accelerate that if can without taking undo risk.”

Other pre-launch resolution work taking place includes the completion of modifications to the SRB (Solid Rocket Booster) Holddown Post Debris Containment System (DCS) and work on the T-0 Umbilical Plates in the TSM (Tail Service Mast) on Pad 39A to mitigate ice build up on the vehicle. Articles will follow over the next few days.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

No related posts.

An amazing amount of work has taken place with the tanks that are constructed at Lockheed Martin’s Michoud Assembly Facility (MAF) in New Orleans, successfully rising to the challenge of reducing the threat of debris – mainly in the form of foam – shedding from the tanks during ascent, due to the potential of damaging impacts with the orbiter’s Thermal Protection System (TPS).

ET-129, which flew with Endeavour during STS-126′s launch, was the cleanest tank yet, with only a few areas of minor foam loss.

“(4) observations elevated as Post Flight Assessment Reports (PFARs) and assessed as IFA candidates. No new failure modes identified. No constraints or corrective actions required for STS-119/ET-127. No IFAs recommended for STS-126/ET-129.”

All areas of foam loss were deemed as “understood” and relate to either cryopumping during ascent – a known condition, or small areas of manufacturing damage suffered due to “high traffic” of engineers working in certain areas of the tank. Corrective actions have been noted on latter, via the FRR documentation.

However, STS-126 did suffer one debris threat during early first stage flight.

Although ice is a debris threat from the ET, the STS-126 event originated from Endeavour herself, according to ascent imagery. However, the debris failed to impact the vehicle.

“During STS-126, at approximately 26.7 seconds, debris was observed to liberate between the LH2 T-0 umbilical and port OMS pod,” noted one of 43 FRR presentations, available on L2.

“Imagery analysis concluded that liberated ice measured approximately 11.5” x 2”,” noted the presentation on the size of the ice debris. “Imagery and Debris Team trajectory analysis confirmed no contact with the Orbiter.”

The T-0 umbilicals – located on each side of the orbiter – and mated to the orbiter via retractable plates in the Tail Service Masts (TSMs), which can be seen either side of the orbiter’s aft.

As the name suggests, the T-0 umbilcals are retracted just as the vehicle is lift-offs, and it is thought the ice developed on the carrier plate of the LH2 umbilical during tanking. The ice remained with the orbiter before liberating 26 seconds later.

“KSC led resolution team to determine root cause for STS-126 T-0 ice formation,” noted the FRR presentation. “Decision to perform full analysis to assess risk for future flights over range of masses and release times.”

Engineers studied video taken of the T-0 umbilical area during lift-off, and included historical footage all the way back to STS-51L, and reviewed potential impact threats to several areas of the vehicle. Image left from STS-126′s 330mb engineering launch video on L2 - angle from inside the TSM during LH2 T-0 umbilical retraction.

“Produced impact conditions for Orbiter elements: Side Fuselage, OMS Pods, OMS Nozzle, Body Flap, Upper Wing, Elevon, and SSMEs (Space Shuttle Main Engines, plus RSRB (Reusable Solid Rocket Motors) and ET impacts.”

Work is still taking place on threat analysis, following checks of the pad’s GSE (Ground Support Equipment) on the Mobile Launch Platform (MLP), and on the umbilical connection area on Discovery.

“Purge test on MLP 1 LH2 Tail Service Mast (TSM) Umbilical Helium flow test completed,” noted the status of the investigation. “Inspection of T-0 Umbilical Carrier plate perimeter seal interface on OV-103 (Discovery) T-0 Plate completed.

“Debris Transport Analysis (DTA) of ice/frost release in work to characterize risk. Fault Tree Analysis and Block closure is in work. Assessing Ground Support Equipment hardware and process options to prevent ice/frost or have it liberate at/before T-0.”

Preventative actions for future flights will be the only outcome of the investigation, as opposed to being a threat for STS-119′s launch.

The only threat to launch at present relates to the Flow Control Valve (FCV) changeout, which is taking place over the next week.

While the changeout will be performed in time for launch, flight rationale for the spare valves on Discovery – and the LON (Launch On Need) orbiter Endeavour – is still being built.

This issue remains the one constraint for flight as per the SSP FRR last week.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. SRB Holddown posts undergoing redesign evaluation ahead of STS-119Engineers will meet in the middle of January to push...

The Holddown Post (HDP) #3 Debris Containment System (DCS) failure has already led to an agreed redesign of the system, as reported by this site last week.

However, with STS-119 just five weeks away, the need for the modified solution to containing debris during the release of the four holddown posts (studs) on each booster has gained importance, following the findings of a Debris Risk Assessment study, which was created in late December – with refinements to the findings continuing until the end of this week.

“Objective: Provide assessment of risk to SSV (Space Shuttle Vehicle) from debris liberated by anomaly experienced on HDP#3 on STS-126,” opened the presentation on the assessment’s findings, available on L2.

An integrated team was assembled to carry out the study, which included the MSFC (Marshall Space Flight Center) Lift Off Debris Team, who provided lift off debris expertise and flow field information, along with a team specific to the Reusable Solid Rocket Motors (RSRM).

They were joined by the “USA Graybeards” – engineers that have been involved with Kennedy Space Center systems since the start of the shuttle program and in some cases as far back as the Apollo era. A number of these “graybeards” are currently helping Constellation engineers through their design issues with the Ares vehicles.

“Assignment: Provide a physics based credible and conservative (bounding) debris trajectory analysis that determines if a STS-126 type failed HDP creates debris that threatens the SSV at lift off,” the presentation continued. “Based on the analysis result, provide a quantitative risk assessment.”

Two categories of debris sources were considered, opening with debris from an unseated blast shield cover, and a spring in pieces of different sizes or whole spring – the latter being the largest liberation of debris from STS-126′s event, after it was later found in the north trench at Pad 39A. Plunger pieces of different sizes or whole, and non-metallic shims were also considered in this opening scenario.

The second category referenced debris sources from the RSRB Hold Down Post bore hole, such as plunger pieces and frangible nut pieces, among other items.

Several elements of the opening assessment findings were completed by mid December, such as a “successful TIM (Technical Interchange Meeting) with the Graybeard team, leading to both nominal and failed hold down post system physical characteristics and detailed kinematics explanation being completed, along with the identification of the local geometry near the hold down post.

Other items such as the effect of 2-RSRB plume interaction “needs to be defined to account for possible fluid dynamic mechanism to transport debris toward SSV,” which is set to be completed before the January 13 engineering summit meeting, which will be well ahead of the deadline of January 27 for the installation of the modified DCS on STS-119′s boosters.

The need for a solution to be certified in time for the next launch is made clear by the resulting findings of the assessment study, which shows debris from the holddown posts to be an impact threat on the vehicle.

“Plume driven debris: Debris starts inside the plume with enough initial upwards velocity to impact SSV. Debris is propelled down and out by the plume, impacts the MLP H/W (Hardware), rebounds with enough upwards velocity (no plume) to impact the SSV,” noted the presentation.

“RSRB plume edge impinges on the MLP causing a 90 deg plume flow turn and picking up debris (i.e., spring, non-metallic shim) from the HDP.

“This in turn imparts horizontal delta V to the debris and the plume and debris impact local H/W redirecting these another 90 deg toward the SSV…but now the plume energy diminishes but the debris has picked up enough velocity (approx 40fps) and might reach the SSV.

“RSRB plume excites spring causing it to break, and becomes debris for above scenario. Debris is propelled down and out, does a 180 deg turn via the flow-field, and has adequate upwards velocity (rebound plus plume-fountain effect) to impact SSV. Debris is propelled away from the vehicle downstream of the RSRB flame trench

“Other: Debris starts outside the plume with initial upwards velocity to impact SSV. Debris liberated from RSRB HDP bore hole is entrained into the plume boundary forcing the debris to impact the MLP H/W with enough energy to rebound and travel up to the SSV.”

The physical threat to the vehicle relates to either large pieces of debris – such as the large metal spring found in the north trench after STS-126 – or small sharp fragments of metal – such as tube lock clips – potentially impacting an OMS Pod, a SSME (Space Shuttle Main Engine), an aft Reaction Control System (RSC) “venier” thruster, or part of the vehicle’s TPS (Thermal Protection System).

An impact, such as one referenced at 40 foot per second, might not cause damage to the vehicle, as the vehicle is also racing off the pad.

However, engineers will assess the threat to the greatest detail to ensure a full understanding of the issue, should the certification of the modified DCS fail to be approved in time for STS-119.

That risk is also reduced by flight history, with only one other comparable event with the holddown post DCS occurring over the history of the shuttle program – that being in 1993 with STS-56 – which has no notes of vehicle damage being sustained.

With the full assessment study findings set to be completed – as early as this Friday – ahead of the engineering summit, and the expected certification of the modified DCS, STS-119 should be fully protected from the holddown post debris threat, thanks to expansive process that shuttle engineers carry out on every anomaly recorded on the previous mission.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. SRB Holddown posts undergoing redesign evaluation ahead of STS-119Engineers will meet in the middle of January to push...

The “Holddown Post (HDP) #3 Debris Containment System (DCS) Failure,” received several expansive presentations (available on L2) as part of the Solid Rocket Booster IFA (In Flight Anomaly) review presentation.

Four holddown posts (studs) surround each booster, with each stud 28 inches long and 3.5 inches in diameter.

The stud has a frangible nut at the top end, which contains two NASA Standard Detonators (NSD), which are fired at the time of SRB ignition, breaking the nut and releasing the connection between the vehicle and the post.

Debris from that release is captured in the DCS, which avoids the debris potentially impacting the vehicle.

“SRB Blast Container (BC) Debris Containment System (DCS): Purpose to contain frangible nut debris. Stud travels aft with plunger after frangible nut fractures,” explained the opening remarks of one of several presentations on the anomaly.

“Plunger seats on washer and seals blast container. Stud continues into Mobile Launcher Platform (MLP) HDP.”

However, the DCS suffered a failure during STS-126′s launch, where the post’s plunger, spring and blast container debris liberated, which is unacceptable due to the risk such an event has for the vehicle.

Photography of the liberated debris included a large spring from the holddown post, which was found by engineers in the north flame trench at Pad 39A.

“Initial postflight inspection of MLP hardware and blast container hardware complete for HDP #3: No anomalies with aft skirt holddown post bore location. No evidence of stud hangup,” summarized the findings by ground teams that arrived for inspection of Pad 39A.

“Witness marks on BC lead from NSD contact and on stud from booster cartridge firing confirmed correct assembly. Plunger properly clocked relative to NASA Standard Detonators (NSD)/ Heavy flame erosion noted on forward end of Inconel holddown stud (length reduced by ~0.50 inch).

“Blast container debris assessment determined spring, plunger, frangible nut major web (1 of 4), both NSD and adapters missing. NSD with adapter and portion of spring found during postflight pad walk down inspection. Inspections and material evaluations unable to identify plunger remnants.

“Dimensional analysis shows plunger assembly with one of two shoulders missing contained within blast container. Impact loading with washer not included. Integrated fault tree established. Includes SRB hardware fault, KSC ground processing, and environmental affects. Fault tree blocks assigned and closures in work.”

While on-going work is taking place as to what level of debris threats such liberations may have on the vehicle, engineers have already put forward a redesign option, which is expected to be taken in time for the modification to debut on STS-119′s boosters.

“Modifying DCS to incorporate secondary retention feature. Adding two tapered stop blocks to guide housing 120 degrees apart,” noted the resolution presentation. “Prevents plunger travel following plunger shoulder contact with spherical washer. Only engages in event of total shoulder failure.

“Design minimizes impact to DC components and installation. No changes to plunger. Utilizes existing tapered rib. Allows implementation at guide housing assembly level.”

These stainless steel stop blocks will replace the current anti-rotation device, which would result in the plunger travelling half an inch in into washer bore, if stop block engages due to total plunger failure.

Successful pull tests have already been carried out on the stop blocks, although this is part of an ongoing test plan that will confirm design certification and allow for implementation on STS-119′s boosters.

“Ten drop tests without load carrying contribution from plunger shoulder to verify plunger/spring retention and frangible link fracture by stop blocks,” added the presentation.

“Static pull test to demonstrate ultimate capability. Two full assembly firings to verify no impact to holddown stud release: One flight configuration plunger, One with plunger shoulder removed to ensure secondary retention device activation.”

The effort of testing and certification is all heading towards two decision dates in January – the first relating to an engineering summit on moving forward with the design for STS-119, and the need date relating to the implementation deadline on STS-119′s stack at the pad.

“Hold-Down Post Blast Containment IFA from STS-126: Closed in on a preferred design concept,” noted the 8th Floor News MOD memo on L2.

“It will be discussed at SSP PRCB (Space Shuttle Program, Program Requirements Control Board). The final decision will be made January 13 as to how STS-119 stack will be handled.”

“Currently manufacturing stop blocks for developmental and certification testing at MSFC. Next flight modification planned,” added the resolution presentation.

“Coordinated with Ground Operations (GO) to begin installation on 1-27-09 given successful certification (for STS-119). Creating full assembly mock-up for GO technicians to assess installation.

“Recommendation: Proceed with design and certification as proposed for DCS stop block modification.”

Such incidents with the holddown posts are rare, with the only previous recorded anomaly that mirrors the STS-126 event occurring back in 1993 with STS-56.

“Plunger and spring exited through aft skirt bore but remained attached to stud and intact,” referenced a historical review of STS-56′s incident. “Team determined frangible nut halves contacted plunger assembly before sealing bore of blast container.

“Contact caused plunger shoulder to fail and exit blast container. Evidence of low skew.”

Stud hang ups on the holddown posts was the other issue that was recently addressed, which resulted in the debuting of a modification on STS-126 – initially set to debut on STS-125, before the Hubble mission slipped to May, 2009. It is not referenced as a potential cause of the anomaly with the DCS.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

No related posts.

Ever since the tragedy of STS-107, the main focus on shuttle safety has been concentrated on reducing foam and ice liberation from the External Tanks, primarily during first stage – and early second stage – ascent.

2008 has marked a breakthrough year for MAF, with tank performance improving mission on mission, thanks to a variety of mitigation techniques that have been implemented at the New Orleans facility.

Most of those engineering changes to the TPS (Thermal Protection System) foam has been centred around the removal of as much foam as possible from the tank in areas that could liberate and strike the vehicle – most notably from the Ice/Frost Ramps that run down the side of the tanks.

With the post ET separation photography confirming the least amount of lost TPS on post RTF record, only three minor areas of TPS loss – backed up by an extremely clean orbiter, with no notable TPS damage suffered by Endeavour – ET confidence has been added ahead of the Flight Readiness Review (FRR) season for STS-119.

“Ascent: Nominal performance for all systems – no requirement violations. (3) foam debris events observed during review of imagery assets. (2) from LH2 tank acreage TPS and (1) from Intertank acreage TPS,” added the post flight IFA (In Flight Anomaly) presentation on L2, with a fourth minor area of TPS cosmetic damage also noted.

“Debris size, mass, and time of release were consistent with expectations and within risk assessment mass limits. ET-129 post-flight assessment complete and shows performance consistent with expectations and within requirements.

“(4) observations elevated as Post Flight Assessment Reports (PFARs) and assessed as IFA candidates. No new failure modes identified. No constraints or corrective actions required for STS-119/ET-127. No IFAs recommended for STS-126/ET-129.”

All areas of foam loss are understood, and relate to either cryopumping during ascent – a known condition, or small areas of manufacturing damage suffered due to “high traffic” of engineers working in certain areas of the tank.

Each area of interest gained expansive notes and data in the IFA presentation, before being closed as “known conditions”.

The tanks will always lose a certain amount of foam during ascent, and – as per former shuttle manager Wayne Hale’s comments on one of his many ET presentations – foam loss will never be zero.

However, with a few minor areas of additional modification due to be implemented on downstream tanks, the threat to orbiter safety has been – and will continue to be – greatly reduced, thanks to the fine efforts of the ET engineering community.

“The tank looked phenomenal. ET-129 really performed great,” wrote ET manager Mark Bryant. “Three small foam losses: On Intertank acreage forward of the Liquid Oxygen feedline fairing; on Liquid Hydrogen (LH2) tank acreage just aft of the ‘+Y’ bipod; and adjacent to the Station 1528 Ice Frost Ramp on the LH2 tank – all consistent with previous flight.”

Bryant added that MMT (Mission Management Team) chair LeRoy Cain, said of ET-129 “This is just flat (out) amazing,” when given the overview of the tank’s performance.

“LeRoy asked me to give kudos to our workforce; he was that pleased with the tank’s performance, (and) hence the condition of the Orbiter.”

Bryant also added that in a post-launch performance review one week after lift=off, observers noted that the ET electrical and propulsion systems performed as expected pre-launch and post-launch. The structural and Thermal Protection Systems also performed nominally post-launch.

STS-126 was Bryant’s debut launch as ET manager, which is one of the longest shifts on L-1, due to the early tanking of the ET and the obvious need to monitor the performance of the ECO (Engine Cut Off) sensors during that procedure.

Despite this, Mr Bryant noted he wasn’t nervous – thanks to assistance from Lockheed Martin’s highly regarded ET head Wanda Sigur and Chief Engineer Jeff Pilet – as the countdown proceeded down to the T-9 minute poll.

“Wanda checked in with me often, and actually I wasn’t that nervous. You’ve trained for this. You have great people around you doing their jobs,” he added. “Chief Engineer Jeff Pilet was, as usual, on top of things and kept me apprised of the tank’s condition and the Launch Support team. The Mission Support Room and Huntsville Operations Support Center were also on their game.

“When MMT Chairman LeRoy Cain conducted the roll call before coming out of the 9-minute hold, he called us first and I was able to confidently say, ‘Lockheed Martin (ET) is GO for launch.’”

As per NASA tradition a tie cutting ceremony was performed for Bryant’s first successful launch in his new position.

Other MAF challenges during 2008 related to being able to ship the tanks to Florida in time to support the manifest. At one point, several tanks were over a month down on their required shipping dates, before MAF managers utilized the results of several Technical Interchange Meetings (TIMs), along with additional shifts for the workforce.

Before the delay to STS-125, all the tanks were back on schedule. And while the 2008 manifest remains fluid, 2009 has been relieved of all schedule concerns thanks to the hard work of the past 12 months.

Two tanks are currently in residence at the Kennedy Space Center (KSC) – ET-127, previously set to fly with STS-125, but now flying with Discovery on February’s STS-119 mission, and ET-130 – which recently arrived to take the place as the Hubble Servicing Mission ET, should STS-125 remain on target for a May, 2009 launch.

At MAF, five tanks are undergoing major production, which reaches into the 2010 shuttle schedule. All these tanks are either on or ahead of schedule, which is the first time a set of downstream tanks have had their shipping date pressure removed from the equation since RTF.

“ET-131 (STS-127): The ET is in final assembly flow, with all operations proceeding nominally,” noted the Lockheed Martin/MAF status on ET production, on L2. “Will probably work only a couple of days during holiday outage. Still checking the February 22 date for delivery of tank.

“ET-132 (STS-128): The ET is in final assembly flow, with all operations proceeding nominally. Tank was laid down out of Cell A. Has been moved into Final Assembly 3; allows them to get into some dual tank flow.

“ET-133 (STS-129): Will perform LOX intertank flange closeout spray (which has already begun), no work required over holiday period.

“ET-135 (Currently STS-131) LOX tank was moved into Cell K. After cleaning, exterior of tank has been primed. Doing inspections on that priming now.

“ET-136 (Currently STS-132): Hydrogen tank moved out for proof testing. This will take about five to seven days, and then it will move into post-proof inspections (now completed).”

In a few months time, MAF expect to know the outcome of the Shuttle Extension status, which currently calls for at least five additional External Tanks to be built.

As part of the assessment, MAF managers have worked their funding requirements and floorspace plan, the latter relating to required handover of space to the Constellation program. Their results are understood to be favorable in support of an extension.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

No related posts.

Among the items scrutinized after last month’s STS-126 mission were the twin Reusable Solid Rocket Motors (RSRM), with all information pointing to an In-Flight Anomaly (IFA) free flight for this critical vehicle component.

“All RSRM countdown parameters were within LCC/OMRS limits and within family,” notes the RSRM presentation, available for download on L2. “Performance of both RSRM motors and all ATK BSMs were within family and met all CEI limits.”

However, four squawks have been identified, two on each RSRM, including Scratches in the Dovetail Groove of the 270” OPT and Corrosion on Igniter Chamber of the Left Hand RSRM and Material in BSM CDFI/Igniter Adaptor Port and Abnormal Wash Erosion on Nozzle Nose Cap on the Right Hand RSRM.

The first LH RSRM squawk noted by the Program Requirements Control Board (PRCB) presentation relates to three scratches on the dovetail (secondary) O-ring groove of the 270-degree OPT.

“Scratches were in a diagonal orientation extending from the outboard groove bottom radius but did not cross the entire O-ring footprint area,” notes the presentation.

The scratches were found by using a 5-mil brass shim; however, engineers were unable to characterize the depth of the scratches or determine if raised pieces of metal were present during initial disassembly and inspections at Cape Canaveral.

The presentation goes on to say that the scratches were caused during the assembly of the LH RSRM and were no concern for flight.

The second LH RSRM squawk is corrosion on the igniter chamber. The corrosion was found on 20 of the 36 igniter chamber bolt holes and spot corrosion was found on the chamber face.

The RSRM presentation states that a “review of process suggests that solvent used during cleaning in assembly may have been left behind when joint was mated leading to the corrosion.”

Previous tests by engineers reveal that “wet holes don’t affect bolt torque.” As a result, there is no expected, or observed, effect on RSRM performance.

For the other RSRM, the first squawk noted by the PRCB for the RH SRB is material in the BSM CDFI/Igniter adapter port.

“Foreign material was found in capture feature of the 0” CDFI/Igniter port of a RH forward BSM,” notes the PRCB presentation.

Analysis of the material shows that it consists mainly of magnesium, copper and oxygen with small amounts of carbon, aluminum, silicon, chlorine, and potassium.

A similar substance has been observed previously on static test RSRM in Utah.

“These constituents correlate with the slag/combustion by-product of the CDFI,” notes the presentation.

According to the PRCB, the condition is inherent to the design of the igniter adapter capture feature. Furthermore, the presentation notes that this material build-up is expected on future flights.

The final squawk, and the only one that may be elevated to an IFA after further analysis, is abnormal wash erosion on the nozzle nose cap.

“Abnormal wash erosion was observed on the OD surface of the RH Nose Cap.”

This type of erosion has been seen on previous flights and static tests. A further investigation of this issue will be conducted in Utah during the nozzle disassembly process which will begin after the start of the new year.

Related posts:

1. SRB Holddown posts undergoing redesign evaluation ahead of STS-119Engineers will meet in the middle of January to push...

The latest information on the status of the repair was noted in a recent 8th Floor News internal update.

“Starboard SARJ TBA replacement and grease results: Status briefing on the initial quick look results of the Starboard SARJ rotations and disturbances seen after the ring was lubricated and the TBA’s were changed out,” noted the information on L2.

“The disturbances seen by starboard SARJ motion have greatly decreased based on the two orbits of autotrack that were performed immediately post R&R. The team requested an extended autotrack to obtain more data and determine if the disturbances drop even lower after a long period of operation and distribution of the grease due to rotation.”

These results are vital for the forward plan on ensuring the rotation of the giant Solar Arrays can be carried out without the situation worsening, but also on the required maintenance of the SARJ, which will require lubrication ahead of the current plan to install a replacement race ring called SARJ XL.

However, the results are so positive, SARJ XL may not even be required, as noted via the 8th Floor News information.

“Team is developing a lube rig design that will be used to evaluate the life of a greased ring to determine how long it will be until team is concerned with roller tipping and when the ring should be relubricated,” added the 8th Floor.

“The Board also tasked the SARJ team with identifying a test or series of tests that will identify if the program can live with the existing degraded joint vs having to invest in the SARJ XL modification – which inserts a third race ring into the joint as a replacement for the currently spalled race ring.”

SARJ XL has already been checked over on the ground and is deemed good to fly if required. Should it take a ride to the ISS, it will fly on one of the final missions on the ‘current’ shuttle manifest, in 2010.

Related posts:

1. STS-126: EVA-1 opens major effort to repair SARJ on StationSpacewalkers Heidemarie Stefanyshyn-Piper (EV1), and Stephen Bowen (EV2) have completed...
2. MMT outlines their extension day decision – EVA-4 finalizes SARJ tasksThe Mission Management Team (MMT) has decided to extend STS-126...
3. Cosmonauts complete Russian Spacewalk on ISSTwo Russian Cosmonauts stepped outside the International Space Station (ISS)...

Hearing presentations from the Space Shuttle Program (SSP) Flight Operations and Integration (FO&I) office and the Eastern Range, the all powerful Program Requirements Control Board (PRCB) has approved several forward actions to correct, among other things, Eastern Range Weather Balloon and Meteorological System Computer (MSC) issues and an ROEU (Remotely Operated Electrical Umbilical) motor problem.

Highlighting the excellent work by everyone involved in the launch of a Space Shuttle, the Eastern Range and the 45th Space Wing reported only two issues encountered during the November 14th launch of Space Shuttle Endeavour, of which none were classed as IFAs.

“No STS-126 Eastern Range Anomalies are recommended for an Integrated IFA,” notes the PRCB presentation available for download on L2.

The two anomalies discussed in the presentation pertain to weather systems and radar tracking issues experienced by the range during the final hours of the STS-126 countdown.

“Met-System Computer (MSC) was non-responsive (L-2:15 (2hrs 25mins)) and had to be rebooted (recovered by L-1:50),” notes the presentation.

As discussed in the IFA presentation, all weather balloon data has to pass through the MSC in order to be distributed to the proper locations.

After launch, the cause of the MSC failure was traced to a backlog of weather balloon data. “Wind data edited by hand as it comes in (5k ft segments). Processing slowed due to noisy primary balloon tracks plus decision to process several backup balloon tracks.”

As a result of the MSC reboot, the data from the Jimsphere (JS) balloon was lost and, according to the Eastern Range presentation, the “AMPS HR data was re-transmitted from the AMPS computer and used for DOLILU assessment.”

Furthermore, the data from L-1:10 JS balloon was corrupt and therefore un-useable for the roll maneuver assessment.

The cause of the corruption was later traced to a “junk data file left over from the MSC reboot.”

Nevertheless, data from the L-1:25 AMPS HR balloon was used as a backup, therefore making all the necessary wind data available to Endeavour’s computers for the roll maneuver.

As always, failures or anomalies are planned for via redundancy in the system.

“Several forms of balloon system redundancy (currently),” notes the PRCB presentation. “Two independent balloon systems: Radar-tracked JS and GPS-tracked AMPS.”

In addition to the redundancy in actual balloons, the ground element hardware for the AMPS has a two-sided (A and B) redundancy and there are 6 signal processing channels on each system.

Moreover, the Eastern Range has suggested several forward actions to improve balloon and weather systems operations.

“For STS-119, clarify balloon priorities with Cape, (have) consensus among all weather users, (and) coordinate through DOLILU Working Group,” notes the Eastern Range.

In addition to these changes, the 45th Space Wing has also requested changes to its balloon processing strategies. Included in these changes are only delivering weather balloon data when the operator is ready to process that data and to allow the operators easy access to high priority data by diverting lower priority data “through the system ‘unedited.’”

Also included are two long range suggestions: upgrading the weather PRD for STS-125 and STS-127 and upgrading the MSC altogether at a later date.

The second issue reported by the Eastern Range was interference with the NDR-C1 debris tracking radar.

“NDR-C1 did not support launch due to Eastern Range reported interference,” notes the presentation. “Both NDR X-band radars did support and collected debris data throughout ascent.”

According to the Eastern Range presentation, “When all radars came to the pad at L-9 minutes with sequencers on, ER radar 19.39 reported interference. The interference was verified to come from the NDR wideband waveform, and limited troubleshooting time meant that NDR was asked to inhibit RF during ascent.”

Moreover, the NDR had successfully completed three phasing checks prior to the interference at T-9 minutes. Three phasing checks is usually enough to clear all interference from the radars to enable them to support launch.

With fifteen launches (both Expendable Launch Vehicle and Shuttle) performed under the current NDR phasing checks, the Eastern Range does not believe that the issue experienced during Endeavour’s launch last month is a generic issue.

Furthermore, the NDR phasing check procedures were just updated after minor interference was experienced during the STS-123 launch in March.

“Normal phasing procedure is to ‘tune’ the slot positions,” notes the Eastern Range presentation. “That did not happen on STS-126, yet the checks were passed. It is entirely likely, due to this fact, that NDR was actually one slot removed from its assigned location, but it was too late to change by the time it was observed in the late minutes of the count.”

As part of the forward actions for this issue, the Eastern Range is recommending that the phasing check procedures be reviewed – and updated where necessary – to ensure that “greater insight is provided from these checks.”

Also, a comprehensive troubleshooting plan will be developed prior to STS-119 in case this interference is experienced again.

Like the Eastern Range, the SSP Flight Operations and Integration (FO&I) office reported a relatively clean and issue free flight of Endeavour from a program standpoint.

In charge of tracking issues in the payload hardware and software, cargo integration hardware, payload-to-Orbiter interfaces, and Orbiter-to-ISS interfaces, the SSP FO&I identified only five issues during STS-126, of which only one was recommended for further action.

SSP Flight Operations & Integration recommends that one STS-126 issue be tracked as a new STS-126 FO&I IFA,” notes the FO&I presentation available for download on L2.

This issue relates to the ROEU mate procedure to the MPLM.

“On Flight Day 13 (FD-13), during the mate, latch, relax sequence operation which is part of the ROEU mate procedure to MPLM, phase C of the ROEU AC arm drive motor associated with system 2 (AC2) did not draw the expected current,” notes the PRCB presentation. “Plots showed that the arm drive motor AC 2 phase C had a current draw of ~0.08 amps instead of the expected current of 0.24 amps.”

According to the FO&I, the low amp draw of arm drive motor AC 2 phase C was compensated for by phase A & B of the same motor. When compared with the demate and stow operations performed on FD-4, the FO&I discovered that the signatures were identical.

The problem was not an issue for the remainder of the Endeavour’s mission as the ROEU was properly mated to the MPLM and in a good configuration for landing. All power and data lines were correctly connected to the MPLM and all necessary information for the crew about the MPLM was confirmed through a pressure check of the MPLM later in the mission.

Nevertheless, since the cause of the ROEU failure is unknown, “testing and evaluations of wiring and motor will be necessary to determine cause of failure and any fixes,” notes the FO&I.

In addition to this issue, the FO&I identified four other problems during STS-126. These included the Hardline Communication failure between Shuttle and ISS, the OI-33 software inability to load Orbiter Interface Unit format, the CWC #4 leakage, and GAP #7 ISS payload activation problem.

For the hardline communications failure, “After docking, the hardline communication (big loop and ICOM-A) were tested and failed as seen on previous missions,” notes the presentation. This issue was expected and the crew used UHF communications as a workaround for the hardline communication failure.

For the OI-33 software issue, “Environmental check of the MPLM could not be performed due to an Orbiter Interface Unit telemetry format issue,” notes the FO&I presentation. The cause was traced to a software change that “added a data item in the middle of a common data area.” This unintentionally caused a data shift which is being tracked by the SSP System Engineering and Integration office as an IFA.

For the CWC #4 leakage, “CWC #4 (SN 1076) was reported leaking after it was filled. Water was processed on ISS and crew reported 3-4 L of residual.” The bag was then sealed in a zip lock bag and returned to Endeavour for return to Earth.

All of these issues are not constraints for STS-119 or STS-125. The only possible constraint is to the next flight of the ROEU on STS-127 in May or June 2009.

No related posts.

Among the various reviews conducted, the PRCB heard reports from the Kennedy Space Center (KSC) on countdown and post-launch anomalies, as well as presentations from Systems Engineering & Integration (SE&I) and Pratt and Whitney Rocketdyne on Endeavour’s performance during ascent.

KSC:

As part of the complete pre-launch and post-launch activities at KSC, a total of 42 items met the criteria for classification as In-Flight Anomalies (IFAs) for STS-126. Of these 42 items, only two were presented in-depth to the PRCB, the Orbiter Access Arm (OAA) White Room side hatch clearance door issue and the LOX (Liquid Oxygen) Tail Service Mast (TSM) door issue.

As noted by the KSC IFA presentation, available for download on L2, “During launch countdown the Orbiter Access Arm White Room side hatch clearance door was left unsecured.”

While the Launch Team was able to determine that a handrail inside the White Room would prevent the door from contacting Endeavour in the event that the OAA had to be extended back into place near Endeavour’s side hatch later in the countdown, “White Room safety railing on the door was found bent post launch.”

As always, an extensive review was conducted in order to identify areas of improvement for White Room closeout procedures.

“Several areas for improvement identified and will be incorporated for STS-119 including reorganizing the S0007 procedure into sequential steps centered on work areas,” notes the KSC IFA review.

Other areas for improvement include real time use of buy copy of White Room securing paper, providing additional time for a final closeout walk down of the White Room, and emphasizing the responsibilities of each Closeout Crew member as part of a check and balance system.

The second KSC IFA presented to the PRCB related to the LOX TSM door on the Mobile Launch Platform (MLP). Engineering cameras on the MLP captured the service door swinging open at T+4.5 seconds.

The presentation states that “During post launch inspections the door roller chain sprocket was found misaligned and loose and the upper hinge was found bent due to plume impingement.”

As such, two forward actions have been assigned to improve door latching procedures for STS-119 in February. The first procedural change relates to the call out of the tool being used to close the door.

“Enhance procedure to call out specific tool to be used during door dogging and verification that door does not move after dogging.”

Additionally, “Enhance procedure to call out specific number of revolutions of tool to ensure that door dogs are properly engaged,” notes the KSC presentation.

Moreover, the KSC IFA presentation lists the remaining 40 items identified during the post-launch walk down of the launch pad. Among the items noted include a wooden bristle brush found underneath the west flame deflector and several large pieces of rust found on various levels of the Fixed Service Structure.

Also noted in the KSC IFA presentation were 12 Ground Support Equipment (GSE) IFAs. Of these, three require forward action prior to STS-119.

The first GSE IFA pertains to camera 060 on the Sound Suppression Water Tower. “During launch countdown camera 060 on the Sound Suppression Water Tower could not focus clearly when zoomed all the way in,” notes the KSC presentation.

The camera view was still adequate to perform the standard Gaseous Oxygen vent arm post-retraction External Tank TPS evaluations.

The second GSE IFA is the failed RF verification of the Space Shuttle Main Engines (SSMEs). “During launch countdown column parity errors where seen on all three Main Engine FEPS during RF verification.” The RF verification was re-run without issue prior to launch.

During post-launch evaluations, the RF verification failure was traced to a MILA (Merritt Island Launch Annex) reconfiguration issue. Enhanced KSC procedures will be adopted prior to STS-119 to ensure that this problem does not reoccur.

The third and final GSE item requiring action before STS-119 is the Inertial Reference Alignment Management System (IRAMS) software. During the STS-126 countdown, the IRAMS software did not perform after GMT clock rollover to the following day. “Software sensitivity between application and SDC during GMT rollover has been identified and will be corrected before STS-119,” adds the IFA review document.

Launch:

In addition to the KSC IFA presentation, the PRCB also heard presentations regarding Endeavour’s ascent from Systems Engineering and Integration (SE&I) and from Pratt & Whitney Rocketdyne, the company in charge of maintaining the SSMEs.

A failure of the System Management General Purpose Computer was the first IFA presented by SE&I. “System Management (SM) General Purpose Computer (GPC) failed to send Ground Command Interface Logic (GCIL) commands,” notes the SE&I presentation, available for download on L2.

The failure has been traced to an unrelated change in the OI-33 software which debuted on Endeavour/STS-126. The failure to send GCIL commands resulted in an “inadvertent data shift affecting Payload Signal Processor port moding… and Ku automatic handover commanding,” notes the presentation.

Despite the fact that this failure was not a problem for Endeavour and her crew, SE&I made a point of mentioning in their IFA presentation that certain flight software generic problems have the ability to cause loss of command and control of the vehicle.

In addition to this IFA, two issues with the Solid Rocket Booster (SRB) Hold Down Posts (HDPs) were discussed by the PRCB at the IFA review meeting.

The first issue relates to the presence of multiple pieces of debris shortly after the detonation of the NASA Standard Initiators (NSI) on the SRB hold down bolts.

“Debris ejected from the area of the Debris Containment System (DCS) of HDPs #1,2,5,6,&7 during NSI firing,” the PRCB presentation notes.

The second HDP issue discussed in the presentation is the DCS on HDP#3 for the SRB aft skirt.

“Hold Down Post M3 plunger and spring extended through DCS bore hole during liftoff,” notes the IFA presentation. “Plunger and spring released from SRB aft skirt and remained on the ground.”

These two types of debris are not covered by the current risk assessment baseline. As such, they are presently classed as potential ascent debris risks to the Space Shuttle; however, assessments are underway to determine if this debris source does indeed represent a debris threat to the Space Shuttle during the first few seconds of liftoff.

Also of note for SE&I was the ice debris liberation from the area around Endeavour’s LH2 (Liquid Hydrogen) T-0 umbilical plate 26.6 seconds after liftoff.

“Ice was observed to liberate from the (left hand) side of the Orbiter aft fuselage TPS (Thermal Protection System) at T+27 seconds,” notes the SE&I presentation. “Imagery taken inside the LH2 TSM after T-0 but prior to bonnet closure indicated ice on the Orbiter TPS between the Orbiter LH2 T-0 Carrier Plate and the (left hand) OMS Pod.”

Ice buildup has not been observed in this area of the vehicle before, nor was it expected by the Orbiter Project Office (OPO). Furthermore, this area is not visible by ground cameras prior to liftoff.

As such, ice buildup and liberation from this area of the vehicle is not currently accounted for in the risk assessment for launch debris.

Finally, the last items presented to the PRCB by SE&I were the anomalies of the Main Propulsion System (MPS).

During the 2nd stage of ascent – after SRB separation – a gaseous hydrogen pressure Flow Control Valve (FCV) opened without being commanded to do so.

“During 2nd stage, there was an uncommanded drop in SSME #2 hydrogen outlet pressure,” adds the SE&I presentation. “Data indicates FCV #2 opened without removal of close command. Valves #1 & 3 compensated.”

Furthermore, “During ascent and after the thrust bucket, the E2 GH2 outlet pressure had a 200 psi step down without a corresponding ullage pressure signal conditioner command change,” notes the Orbiter and GFE IFA review presentation available on L2. “The delta outlet pressure for this FCV position was 260 psi during previous command changes before the thrust bucket.”

While the anomaly did not have an impact on ascent performance, simply resulting in an improper MPS configuration during SSME operation, it is a constraint to STS-119 as engineers will have to determine whether the anomaly was the result of the FCV itself, or, more seriously, the result of a fault with Endeavour’s wiring.

As noted by the extensive IFA review, any failure of the GH2 FCV is a 1R/2 condition. Now that Endeavour is back in her Orbiter Processing Facility a radio graphical analysis, as well as x-ray and visual analyses, will be performed prior to SSME removal to try to isolate the problem to either the FCV or Endeavour’s wiring.

Additionally, the Mission Evaluation Room (MER) identified two further MPS issues during Endeavour’s flight that are still under evaluation and, as of now, not classed as part of the Integrated IFA list.

These two issues include an unexpected helium pneumatic pressure decay and the loss of a “closed” indication from LH2 pre-valve valve#1.

“During ascent, MPS helium pneumatic bottle (drives MPS valves) had pressure decay of 140psi,” notes the presentation. “This is greater than expected thermal effects of 20-60psi.”

The pressure readings stabilized after Endeavour was transitioned for on-orbit operations and the decay was later traced to a leak in the internal helium system.

Additionally, the LH2 pre-valve issue relates to the loss of the “closed” indication on valve#1. “Shortly after Main Engine Cutoff, closed indication for the center hydrogen pre-valve was lost. Should have shown closed.”

Nevertheless, the valve does appear to have functioned properly and the anomaly did not impact that remainder of Endeavour’s mission.

All the same, all three of Endeavour’s SSMEs functioned properly, with Pratt & Whitney Rocketdyne reported no IFAs.

“All SSME observations are encompassed by previous flight and/or test experience and identified as no impact,” notes the SSME presentation available for download on L2.

Additionally, all three engines performed as predicted with the modified Control Mixture Ratio (CMR) of 6.048mru. The previous CMR had been 6.032mru.

As first reported by this site in October, the change to the CMR comes after a noticeable drop in the Over Board Mixture Ratio (OBMR) since Return to Flight in 2005 – with the most noticeable drops occurring during Endeavour’s two post Return to Flight missions.

A fleet-wide mitigation plan for the decreasing OBMR will debut on STS-119 next year.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. Thruster issue requires clean up operations on Endeavour’s TPSEngineers are working on a plan to clean up around...
2. Endeavour rollaround moved forward to Thursday – FRR concludesThe unique transfer of Endeavour and the STS-126 stack from...
3. Dual flow ballet for Endeavour and Atlantis – De-stack debatePreliminary milestone schedules have been created for the complex dual...