STS-133 Processing Latest:

Discovery is processing in OPF-3 for her November 1 launch to the International Space Station (ISS). STS-133 was set to be the final mission of the Space Shuttle Program (SSP) until payload problems resulted in a realigned manifest that pushed Discovery’s flight ahead of Endeavour’s heavily-delayed STS-134 mission.

In what is highly likely to be the veteran orbiter’s final processing flow for flight, the milestones of rollover and rollout will likely be marked by ceremonies that will be even more poignant than Atlantis’ STS-132 events – considering many observers were aware Atlantis already had one eye on an additional flight via the proposed STS-135 mission.

With just one more month of her OPF flow remaining, her dedicated engineers are seeing their own final milestones for the old girl, with the final closure of the Payload Bay Doors (PLBDs) upcoming this week – only to be opened one final time at the launch pad when she receives her payload.

“OV-103 (STS-133) Working on preps for PLBD closure, will close the PLBDs next week. Have some TPS (Thermal Protection System) work to do, then will cycle to final closure,” noted Ground Operations on the latest Shuttle Standup/Integration report (L2).

“Working preps for crew module leak checks to be performed tonight. Installing BRI tile on the ET (External Tank) doors. Working the valve position indicator (VPI) indicator on the O2 crossover valve, IPR-35 (Interim Problem Report), and will do some more troubleshooting on that.”

IPR 35 – relating to observations made during data reviews on the O2 system 1 crossover valve – found that the VPI indicated “on” when it should be indicating “off”. This issue remains under review.

“IPR 35 update: O2 system 1 crossover valve cycles (5) were performed.  When (engineering teams working the issue) returned (the) VPI state at power up had changed from the indication prior to orbiter power down. Troubleshooting indicates the valve is physically closed and the issue may reside with the VPI. Engineering evaluation continues,” noted the NASA Test Director (NTD) report (L2).

The NTD also noted other processing work being carried out on Discovery, including TPS operations that have been ongoing through the weekend, along with the closure of one of the early issues in the flow – IPR 5, the problem which was recently highlighted by cable issues.

“OV-103 (OPF Bay 3): Crew Module leak checks were completed and results were nominal. Nose Landing Gear boot repair was completed and RTV is in cure. IPR 5: finished troubleshooting the in-flight anomaly on the S-Band Antenna system. Were not able to duplicate the problem seen on-orbit and expects to close the IPR as an Unexplained Anomaly (UA).”

As per usual, managers will review the status of Discovery’s flow one week ahead of her scheduled rollover to the Vehicle Assembly Building (VAB) – which is currently on track for September 8.

STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-133/

“The Orbiter Rollout Review for STS-133 is September 1,” confirmed the KSC Launch Integration Manager on the Standup report. “On track from rollover to the VAB on September 8.”

There she will link up with External Tank (ET-137) and the twin Solid Rocket Boosters (SRBs) in High Bay 3 (HB-3) for mating operations. Repair work continues to be carried out inside the VAB on a Fairing Support Plate, following problems with the initial TPS work that was conducted over the last few weeks.

“SRB BI-144 / RSRM 112 / ET-137 (VAB HB-3): PR (Problem Report) ET-137: Damaged SLA (foam) on EB-2 Fairing Support Plate; Will Hand Pack both inboard and outboard. New SLA kit has been ordered and will arrive next week,” added the NTD.

“Aft Strut and HDP (Hold Down Post) Firing Line checks are complete. Forward Firing Line checks will be worked after ET Fairing is installed after SLA repair is complete on PR.”

RCS Test Article Failure Update:

The failure suffered by the RCS test article – otherwise known as the “Fleet Leader” – at the White Sands Test Facility (WSTF) remains under investigation, with the latest results scheduled to be reviewed by the Orbiter Project Office (OPO) this coming Wednesday.

Since 1989, the Fleet Leader Program has played a vital role in NASA’s ability to detect, predict, and prevent Orbital Maneuvering Subsystem (OMS) and RCS life-dependent failures and anomalies before they affect the shuttle fleet.

The New Mexico facility’s test article functional tests simulate orbiter flight and maintenance downtime period activities, and special propulsion subsystem tests, using all of the Fleet Leader test articles.

Other special tests have been performed to support the Fleet Leader Program, such as the OMS/RCS Crossfeed Line Gas Sweep Test (Test Stand 301), the Forward Interconnect System Test using FRCS Test Article (Test Stand 328), and Chamber Chiplife.

A problem during testing on the hardware was reported a few weeks ago, relating to a firing of the RCS fleet leader unit experiencing an unplanned controlled shutdown – a result of a large crack in a weld that is between the closeout of a fuel manifold and the injector.

The related hardware is being investigated via both Non Destructive Evaluations (NTE) techniques and more intrusive inspections, in order to understand the root cause.

“On the WSTF RCS test article investigation, the team has completed sectioning of the injector part that has the crack. Half of the part is being used for NDE development, and the other half for detailed destructive evaluation. The crack has been opened, and fractography is beginning,” noted OPO on the Standup report.

“Continuing to inspect the valve sensors, transducers and perform radiography. Also doing a chemical evaluation of what was flushed out of the thruster prior to the cut. There will be an OPO Tech Tagup next Wednesday to discuss all the known data.”

This issue will not impact STS-133′s upcoming Flight Readiness Reviews (FRRs) unless commonality with the fleet’s flight hardware is found.

No related posts.

STS-134 Processing Latest:

Although the youngest orbiter in the fleet is over half a year away from her mission to carry the Alpha Magnetic Spectrometer (AMS-2) and Express Logistics Carrier 3 (ELC-3) to the International Space Station (ISS), Endeavour is enjoying a relatively busy processing flow inside her OPF-2 (Orbiter Processing Facility).

A large element to her recent flow has been related to finalizing Thermal Protection System (TPS) work on the orbiter, following her return from the highly successful STS-130 mission.

“Completed the landing gear functional. The ET (External Tank) door BRI (tile) mod is in work with some prefits. The BLT (Boundary Layer Transition) mod continues,” noted KSC Integration on the Shuttle Standup/Integration report (L2).

“Continuing with the NLG (Nose Landing Gear) TPS evaluations with Mylar pulls. Payload premate testing continues.”

Endeavour and her team have the weekend off, as engineers finalized the installation of the three Flow Control Valves (FCVs)  – which have performed well since the STS-126 incident – into the orbiter’s Main Propulsion System (MPS), ahead of retests next week.

“OV-105 (OPF Bay 2): MPS Flow Control Valve LV58 installation was completed; leak checks worked with electrical retest planned for Monday,” added the NASA Test Director (NTD) processing status (L2).

“Payload pre-mate test was successfully completed. Payload 1553 data bus checkout (complete). Window 7 (ceramic) insert R&R (removal and replacement) has begun. Window 7 installation is scheduled for Tuesday. Weekend Work: None scheduled.”

Endeavour can also look forward to the start of SSME installation operations next week, with Main Engines (MEs) 2059, 2061 and 2057 manifested to aid the orbiter’s ride uphill next year.

It’s been a busy period for the SSMEs, with Discovery’s installation, and subsequent removal – due to an issue with a turbopump on ME-1 – followed by reinstallation, taking place recently, added to the removal of Atlantis’ engines, following her STS-132 mission.

While it is a routine procedure to fully inspect the engines – both before and after removal from the orbiter – engineers will attempt to find the root cause for the hundreds of streaks in Atlantis’ SSME plumes, observed by ground cameras during early first stage flight.

Already, Pratt & Whitney Rocketdyne/KSC (Kennedy Space Center) have confirmed one leak-related observation during initial checks. However, it should be stated that as with the observed streaks, Atlantis’ engines enjoyed no safety or performance issues during powered flight.

“SSME (Pratt & Whitney Rocketdyne/KSC) Last week, removed the engines from OV-104 (Atlantis) post-flight STS-132. Those engines are back in the engine shop, going through nozzle tube leak checks,” added the latest Standup report.

“On Engine 2052, which was in position 1, had some cold wall leaks found after completion of tube leak checks. This explains one of the observations where the film showed a frost area, just above the aft manifold on Engine position 1.”

Over in the Vehicle Assembly Building (VAB), both Endeavour’s External Tank (ET-138) – located in High Bay 2E (HB-2E), and Solid Rocket Boosters (SRBs) – being stacked in High Bay 1 (HB-1), are undergoing the business end of their flows ahead of mating.

ET-138 – the last “new” tank to be shipped from the Michoud Assembly Facility (MAF) – is now undergoing the installation of its Ground Umbilical Carrier Plate (GUCP), which had caused scrubs during both STS-119 and STS-127′s tankings.

Part of the solution involved a new two-piece flight seal being installed into the hardware, which gained a mention for ET-138, as a Problem Report (PR) noted this tank’s GH2 seal is being replaced.

No specifics on what caused the PR to be called have been mentioned in flow documentation, although it appears the issue was spotted during the routine “shakedown” inspections in the VAB’s checkout cell.

“ET-138 (VAB HB-2E): GUCP Installation: PR on seal change out is in work. LO2 & LH2 Preps for checkout are in work,” noted the NTD report, adding status on the early stacking work that has taken place on the boosters. “SRB BI-145 / RSRM 113 (VAB HB-1): Left Aft Center segment stacking is complete. Post Ops & Leak Checks are in work.”

STS-134 Specific Articles: http://www.nasaspaceflight.com/tag/sts-134/

RCS Test Article Failure:

The Orbiter Project at the Johnson Space Center (JSC) are continuing evaluations into a failure of a RCS test article at the White Sands Test Facility (WSTF) in New Mexico.

The test article, also known as the “fleet leader”, is one of multiple elements of orbiter hardware, which undergo a large amount of testing, to the level that wouldn’t be possible in an OPF environment. Only part of the RCS fleet leader remains since its debut in 1989, following the retirement of the Forward Reaction Control System (FRCS) element in 2006.

“In June, there was a firing of the RCS fleet leader unit at WSTF that experienced an unplanned controlled shutdown,” noted the opening Standup report note. “Initial troubleshooting of that fleet leader thruster has been completed, and it was discovered that they were not able to maintain pressure in the injector chamber.

“Borescope inspections revealed an apparent breach behind the injector, possibly at the weld. This event is being looked at closely. History data is being gathered on this thruster, and the (Program) is discussing the events of the test to determine what steps to take next.”

The status of the failure was updated on the latest Standup report, following an Orbiter Project Office (OPO) tag up on Wednesday. During the meeting it was confirmed the test article suffered from a large crack in the aforementioned weld.

“The RCS Community provided a status of the investigation into the unexpected controlled shutdown of an RCS test article that was fired in June. The team has completed their initial evaluation of the test article, which led them to identify a large crack in a weld that is between the closeout of a fuel manifold and the injector,” added the update.

As part of the Space Shuttle Program (SSP) due diligence approach, further investigations will take place on the test article, ahead of any decision to inspect the related hardware on all three orbiters in the fleet. In a few weeks, engineers will complete their findings, and decide if there’s any commonality of failure risk related to the orbiters. Until then, inspections on the fleet will not be required.

“The team has pulled in the larger community to define the next step to evaluate that crack. They have defined a plan that includes CT scans as well as destructive evaluation,” added the latest status report. The team has developed an initial thought tree and will be maturing it over the next few weeks.

“They have been evaluating the history of failures that might be similar, as well as the history of this particular part. They will continue to provide a regular status as they let the data lead them through the evaluation. They will also be evaluating whether this instance is applicable to the fleet or just related to what happened to the test facility.”

No related posts.

STS-131 Processing Latest:

Discovery continues to be processed for an April 5 launch – pending approval at the Agency FRR – with the milestone of final ordnance installation, and preparations for the opening of her Payload Bay Doors (PLBDs) for the installation of the payload being worked.

“Orbiter Mid Body Umbilical Unit mate and leak checks were completed yesterday. Final ordnance installation and connection for flight is complete. Vehicle power up ordnance testing is in work and expected to complete today,” noted NASA Test Director (NTD) processing information on Tuesday (L2).

“Payload bay doors will be opened today in preparation for payload installation into the Orbiter tomorrow. Aft compartment closeout for flight continues with completion planned Friday. Four waves of LOX tankers were offloaded at the LOX storage area yesterday.”

Engineers also noted that a cracked Thermal Protection System (TPS) tile was noticed during the inspection of some of Discovery’s Window Inserts – with a Material Review (MR) being conducted at time of publishing.

“Window ceramic inserts inspection/pull tests are complete and good. MR options are being explored for the cracked tile found during the inspection/pull tests,” added the NTD report.

Three new IPRs (Interim Problem Reports) have been added to Discovery’s flow, although none are deemed to be a problem at this time. Meanwhile, the closure of the PCMMU (Pulse Code Modulator Master Unit) issue on the orbiter is expected this week.

“IPR 0029 Update: Troubleshooting/monitoring continued yesterday with no anomalies noted; instrumentation was removed last night to support ordnance installation. Engineering will recommend launching on PCMMU#2 and not replacing PCMMU#1 to PRCB,” noted the NTD, with the latest Shuttle Standup/Integration report (L2) adding their status via the OPO.

“On the PCMMU work done over the weekend, it still has not repeated again. A bus sniffer has been added onto the bus. Will continue to look as long as there is access. Think there is adequate Flight Rationale even without repeats. Will bring that story forward in a kind of continuation of the PRCB.”

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

Flight rationale is not being classed as a problem for the SRB (Solid Rocket Motor) Rate Gyro Assembles (RGA) – as presented to the Special PRCB today (article will summarize this week), leaving just the one major item of debate outstanding for the FRR.

This came via the Special PRCB’s latest on the RRCS helium isolation valve, which dominated the meeting via an additional five presentations (all 8 Special PRCB presentations are available on L2).

Special PRCB RRCS Debate:

Outlining the issue which was observed during hypergolic loading at the pad, the Special PRCB allowed for a specific debate ahead of the FRR, in order to have a good understanding of progress that has been made ahead of the flight rationale decision.

“There were more issues post-SSP (Space Shuttle Program) FRR, pre-Agency FRR than we have had in awhile,” wrote SSP Manager John Shannon on the Standup report, pre-empting the Special PRCB meeting. “Was a tremendous job by the team on the RCS Helium ISO troubleshooting. Doing all the right testing, and showed that the rest of the system is healthy.

“There are many reviews, but (want) to just get the team together all in one spot and talk about these new issues before going into the Agency FRR. The Special PRCB will be very helpful to us. Otherwise, things seem to be going okay.”

The positive note on the valve troubleshooting was in reference to the weekend test on the redundancy in the RRCS – specifically two regulators on each path. The weekend test put the system through its paces to the equivalent of seven thruster firings, and found no unacceptable decay/leaks from the regulators.

“He iso valve and regulator flow test at 150 SCFM (equiv to 7 thrusters firing) performed (3/20-21/10). System pressurized to ~1800 psi. Each leg flowed to less than regulator lock-up. Target flow rate achieved – no evidence of any flow obstruction,” noted a 36 page review and update presentation to the Special PRCB.

“System repressurized to ~1800 psi. Both legs flowed (together) to primary regulator lock-up. Primary regs monitored for any creep. No creep (leak) detected.”

Problem was known as far back as last year:

Notably, the main presentation also revealed engineers were aware of a problem with the RRCS helium iso valve back in October of last year. Unfortunately, the problem was incorrectly documented, as the issue failed to show a more permanent problem until the vehicle was put through it paces at the pad.

“Review of data collected during STS-131 He System Checkouts in 10/2009 revealed an RRCS fuel A leg He iso valve issue. During helium system blowdown (helium tank vent), after venting 1/2 of the helium tank through the A leg, the A leg helium iso valves were commanded closed,” noted documentation.

“The ox helium iso valve operated nominally, but the fuel helium iso valve did not. The Open VPI (Valve Position Indicator) remained ON and Closed VPI remained OFF. There was also gas flow through the valve. Helium iso valves were cycled three more times with the same results.

“On the fifth attempt to close the valves, the fuel helium iso indicated Closed (Open VPI OFF/Closed VPI ON), but lagged the ox helium iso valve by 2 seconds. The valves were cycled open/closed again with the VPI’s indicating nominal operation (no lag).

“During the subsequent operation the A leg helium iso valves were cycled Open/Closed again with the VPI’s indicating nominal operation. After the first indication of a failure where gas flow through the valve occurred, there was no situation where the valve position was verified other than by VPI indication until the pad (no pressure differential across the valve).

“Likely, the valve stuck in the open position during the tank vent. After a few cycles it moved enough to get nominal VPI operation, but was stuck partially open where it is now. The problem was detected, but mistakenly assumed to be a known and documented problem.”

“VPI problems have occasionally occurred when the iso valves are cycled during tank vents. FRCS Fuel A-Leg He Iso Valve (was also seen to be) slow to show closed during STS-119 post-flight valve test.”

Flight Rationale Debate:

Given it has been known since hypergolic loading that the valve is a problem, and that the mission could still receive the required flight rationale via the redundancy of the regulators, flight rationale should expect approval at the FRR.

“Regulators are healthy, unlikely for dual failure. Operational impacts and management of potential subsequent anomalies in the RRCS helium pressurization system issues to be manageable in flight. All other RCS Helium components (left & right pod) showing nominal, in-spec performance,” noted an outline of OPO’s take on approving flight rationale.

“Nominal regulator performance on RP03 (Endeavour’s hardware) demonstrated in OPF (Orbiter Processing Facility) and past weeks’ testing. Mechanism causing helium isolation valve failure will not likely; propagate into downstream regulator failure during flight, block orifice/regulator filter causing loss of redundancy (leg), result in failed-closed isolation valve.

“Orbiter Project Office recommends fly-as-is for STS-131.”

However, numerous departments are dissenting flight rationale, based on a lack of a root cause for the helium valve’s issues, and what is being classed as a new failure signature. All of the dissenters aren’t listed in the Special PRCB documentation, although both NASA Safety and Boeing Safety are currently heading into the FRR with a recommendation to changing out the valve.

“Some dissenting opinions recommending changing valve prior to flight. Reason for opinion: New failure signature. Root cause not identified. Dissenting opinions held by Boeing Safety, NASA Safety (SAIC) PRT representative and several PRT SSE’s.”

Should the FRR side with such a dissenting opinion, a rollback would be the outcome, as the valve cannot be worked on at the pad.

Moreover, Discovery would have to be demated from the External Tank, returned to her OPF, and the Right OMS Pod removed and sent to the Hypergolic Maintenance Facility (HMF) for around three weeks of work. At the same time, a donated Right OMS Pod from Endeavour would be installed on Discovery, resulting in a total delay to STS-131 of around three months.

However, it is very important to note that dissenting opinion is not unusual even during the FRR meeting itself, where it is debated and evaluated prior to a decision. More often than not, dissenting opinion is based on an overly conservative stance, and as such is welcomed, as those in favor of flight rationale are pushed harder to prove their acceptance – thus aiding the overall confidence in the safety of the vehicle.

This can already be seen via the documented “forward work”, which will provide the FRR with simulated results of the problem becoming more serious while on orbit.

“Helium tank vent model still in work. Simulates time to vent tank in the event both primary and secondary regulators fail-open and vent through relief-valve and overboard vent. Will also provide estimates of thrust forces this will create. Expect thrust to be approximately that of a vernier thruster. NSLD still in work with tests to validate potential failure modes of RCS Helium Isolation Valve,” added one of the presentation.

“Unless results are more severe or different than expected, neither are a constraint to STS-131.”

It should also be stated that the problem holds no risk to the crew – even in the unlikely event of further downstream failures in the system. The worst case scenario – a major leak throughout the valve systems early into the mission – would see the crew being informed to land Discovery at the next available opportunity (nominal landing site).

Further pre-FRR coverage will be published up to – and including – Friday’s decision.

L2 members : Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4500 gbs in size

No related posts.

STS-131 RRCS Issue Latest:

Rollback and a three month delay for STS-131 is still not being ruled out, although it has become far less likely due to the two sets of testing on the RRCS’ regulators. Even prior to the weekend testing, managers were concentrating on “next failure” impacts related to the system during flight – another element of approving flight rationale.

Armed with test data and flight rationale information relating to impacts to the mission should the situation worsen on orbit, managers will conduct a special PRCB (Program Requirements Control Board) meeting on Tuesday to prepare for Friday’s FRR.

“MOD (Mission Operations Directorate) has been looking at Right RCS next failure ops impacts. Will be going over the charts to go forward for the RCS Helium ISO Valve on OV-103 (Discovery),” noted a status update on the latest Shuttle Standup/Integration report (L2).

“The intention is not for this to be the final product, but a health check of where it is at and see if anyone else has any ideas. There is a Special PRCB on Tuesday to talk special topics before FRR.

“All Managers should make sure that your backups are at the reviews, Special PRCBs, and all the presentations that are going on to review the work for STS-131. We have a great team with a lot of depth and talent, so make sure the right people are at the right meetings as we move forward. We have about two weeks before launch, on April 5. We are into the final timeframe.”

The last time a special PRCB meeting discussed a pre-flight issue was during the Flow Control Valve (FCV) issue ahead of STS-119. STS-131′s Special PRCB will discuss both the helium isolation valve and a Solid Rocket Booster (SRB) Rate Gyro Assembly (RGA) issue (article to follow this week).

The issue was first noted during hypergolic loading, when several IPRs (Interim Problem Reports) were charged against the OMS/RCS system. All were cleared bar the IPR-33, which noted: “While performing the Aft RCS fuel tank vents, the RRCS Fuel He tank pressure dropped, indicating a leak through the He Isolation Valves. All attempts to resolve this issue were unsuccessful.”

Engineers immediately pursued pre-written troubleshooting methods, attempting to close the valve and check to see if it was either obstructed from seating, stuck in an open position, or leaking. Five troubleshooting attempts all failed to slow the leak rate.

As far as the root cause, engineers concluded that without inspecting the valve – which can’t be accessed without the OMS Pod being removed – the most likely problem relates to the poppet of the valve.

“The failure appears from the main poppet (not fully seated). With only the pilot stage flowing, the propellant tank pressure does not increase anywhere near the rate that it did during the pre-loading helium tank pressurization,” noted one of eight new presentations from late last week, all available on L2.

“There has to be some main stage flow to account for the relatively fast prop tank pressure response observed during the pre-loading helium tank pressurization.”

Subsequent testing was called for, in order to ensure the two regulator valves – downstream of the faulty helium isolation valve – were in good order. Due to their provision of redundancy, a problem with one or either of these regulators would have caused problems for efforts to approve flight rationale.

Testing during the week and at the weekend found no problems with the regulators, thus aiding the potential the system can fly “as is” – pending PRCB and FRR level approval.

“RRCS fuel helium tank was pressurized to ~2500 psia and the primary regulators were monitored for leakage. Primary regulator leakage indicated in-spec (less than 400 scch). Vehicle ullage transducer has an accuracy of 0.8 psi and test was performed for ~10 hours,” noted an overview presentation outlining the midweek test.

“No adverse trends for the regulators. Regulators function and leakages have been in-spec and consistent.

“Latest testing this flow indicated in-spec secondary regulators at 581 total SCCH (also performed October, 2009). Primary regulators not creep-tested but indicated nominal performance during helium tank vents in the OPF (Orbiter Processing Facility). No reason to expect regulator degradation during the upcoming flight. Assumes no adverse effects from the helium isolation valve failure mechanism.”

The weekend testing also had the benefit of a test panel system, which allowed for closer monitoring of the regulators for the test. During the process, both system legs were flowed through significantly, before the primary regulator was locked for a leak “creep check”.

Mission Management Team (MMT) manager Mike Moses noted on Sunday that it appears the regulator(s) performed well, mirroring the test performed earlier in the week – but this time with a significant flowrate for a significant duration.

“Plan is to perform primary regulator flows with the portable panel to simulate in-flight flow rates to demonstrate system integrity and flowrates. No secondary regulator tests or leak checks,” pre-empted one PRCB presentation on the weekend test.

“Helium isolation valve and regulator flow test at 150 SCFM is planned for March 20/21. Pressurize system to ~1800 psi. ‘A’ Valve Open and ‘B’ Valve Closed. Flow to less than regulator lock-up. Repeat above with ‘A’ Valve closed and ‘B’ Valve open.

“Repressurize system to ~1800 psi. ‘A’ and ‘B’ Valves open. Flow to primary regulator lock-up. Monitor primary regulators for any potential creep to be compared to troubleshooting performed on March 16.

“Goal is to flow through system to potentially remove any contamination on isolation valve and assess possibility of moving any particulate downstream which could cause consequences for regulators or valve orifice. This test may provide additional insight as to which leg and which valve is the problem.

“Previous flow tests were approximately 18 SCFM. Helium tank vent duration and propulsive force analysis. For GNC assessment if vent through overboard dump. Expect propulsive force to be similar to vernier thruster. Assess past-performance of overall health of these regulators from previous flights and flows. Parametric assessment based on plausible failure scenarios that could potentially block helium isolation valve orifice.”

The positive testing leaves managers with a flight rationale discussion, both at the Special PRCB and FRR meetings. This appears likely to be approved, thanks to the performance of the regulators.

“Potential flight rationale encompasses the following: Nominal regulator performance. Mechanism causing the helium isolation valve failure will not likely propagate into downstream regulator failure during flight,” added documentation. “Block orifice/regulator filter causing loss of redundancy (leg). Result in failed-closed isolation valve.”

Also set to become an item of discussion at the meetings is the worst case scenario of the primary and redundant systems failing early in the mission, resulting in what is known as a burst disc. While the crew would not be in any danger, the resulting leakage – or blowdown in the case of both regulators being lost – early in the mission would be the worst outcome, ending the mission early.

“Worst case is early in mission when quantities are high and ullage volume is at a minimum as this minimizes blowdown capability,” added another presentation. “Single pod quantity redline would be violated which results in a NPLS (Next Pass Landing Site).”

“Regulator leak/creep: If both the primary and secondary regulators are leaking in such a way that the downstream tank pressure is rising and the valve won’t close, pressure can be managed by using propellant. It is worth noting, that having one RCS helium press valve open is standard operating config.

“Closing valves to due to leg creep/leak is rare. Have had leaking regs in past for which we have closed both sets of helium press valves (e.g. STS-110).”

Further articles will follow in the run up to the FRR.

L2 members : Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4500 gbs in size

No related posts.

STS-131 Processing and Troubleshooting Latest:

While the RRCS issue is being discussed, engineers will continue with the pad flow for STS-131, pushing forward with the realigned schedule that will see Discovery’s payload arriving at 39A on Friday (delayed again). The Agency level Flight Readiness Review (FRR) remains on track for March 26.

“OV-103 / ET-135 / SRB BI-142 / RSRM 110 (Pad A): S0024 Hypergolic Propellant Servicing was completed less APS (Aft Propulsion System) QD (Quick Disconnect) de-mates (IPR-0033),” noted the NASA Test Director (NTD) on Monday processing information (L2).

IPR (Interim Problem Report) 33 is the latest issue to be charged against Discovery’s OMS/RCS system during hypergolic loading - although all were resolved, bar the decrease (leak) in the helium tank pressure on the RRCS, in unison with the RRCS fuel propellant tank when the tank was vented.

“New IPR 0033 to OMS/RCS: While performing the Aft RCS fuel tank vents, the RRCS Fuel He tank pressure dropped, indicating a leak through the He Isolation Valves. All attempts to resolve this issue were unsuccessful. The test team decision was to continue with hypergolic fuel load with this IPR condition.”

Via an overview presentation provided to the ERB on Monday (and acquired by L2), the real time findings on Friday evening were expanded on – along with the listing of the five troubleshooting attempts that have taken place so far to resolve the leak, all of which were unsuccessful.

“IPR 131V-0033: RRCS Fuel GHe Tank pressure decreased during fuel propellant tank venting (indicating excessive Helium Isolation Valve leakage). Troubleshooting was performed to attempt to establish a measurable leak rate, seat valve(s), and again try to establish a measureable leak rate. Currently the flow through the closed valves has been limited to the controlled vent of the propellant tank (~ 5 million scch),” noted the presentation.

“Troubleshooting Performed to date: 1) Pressurize helium tank and monitor for a pressure increase upstream of the GHe iso – No Joy: Helium tank and propellant tank pressurized at the same rate, pressure subsequently vented. 2) Cycle LV301, GHe Iso ‘B’ valve OPEN then CLOSE. Pressurize helium tank and monitor for a pressure increase upstream of the GHe isolation valves – No Joy: Helium tank and propellant tank pressurized at the same rate.

“3) Cycle LV303, GHe Iso ‘A’ valve OPEN then CLOSE. Pressurize helium tank and monitor for a pressure increase upstream of the GHe isolation valves – No Joy: Helium tank and propellant tank pressurized at the same rate. 4) Pressurize helium tank (and prop tank) to above reg lock up. Vent propellant tank in an attempt to seat the GHe isolation valves – No Joy: Helium tank and propellant tank vent at the same rate.

“5) Pressurize helium tank (and prop tank) to above reg lock up. While venting through propellant tank cycle GHe isolation valve(s) in an attempt to seat the valves: a) Cycle LV303, GHe Iso ‘A’ valve OPEN then CLOSE – performed under flow a total of times, b) Cycle LV301, GHe Iso ‘B’ valve OPEN then CLOSE – performed under flow a total of 3 times – No Joy: Helium tank and propellant tank vent at the same rate.”

Discovery’s Right OMS Pod – and associated hardware such as the RRCS – is known as RP03 (RP=Right Pod). Historical documentation shows this hardware has performed without a major problem since debuting on STS-96.

STS-131 Specific Articles: http://www.nasaspaceflight.com/tag/sts-131/

“RP03 Past Performance: (He Isos) Checked out in OPF at start of flow. Leakage was well in-spec (51 scch). Historically have been good since at least STS-96,” the presentation noted, before showing the historical performance of the associated valves.

“Series regulators: Primary stages. Response testing performed, results in spec. Leak testing was not performed. Since STS-116, one of primary regs creeps after press to flight although did not repeat on STS-128. Secondary stage 252 & 329 scch in the OPF this flow. RV last tested 7/2008, results in spec.”

Options:

Three clear options are available to managers. Firstly, engineers will attempt to troubleshoot the issue at the Pad, with the results passing through to the potential creation of a waiver in the Launch Commit Criteria (LCC) – likely to be discussed for approval at the Agency FRR – to allow Discovery to fly “as-is” via flight rationale. Should those options become unacceptable, a repair would be undertaken.

A repair cannot be carried out at the pad, and would result in rollback to the Vehicle Assembly Building (VAB), demating of Discovery from the External Tank/SRB stack, rollback to her Orbiter Processing Facility (OPF), demate Discovery’s right OMS Pod for repairs in the Hypergolic Maintenance Facility (HMF), whilst Endeavour’s Right OMS is donated to Discovery. An expected three month delay would result in the launch schedule.

“Options: Fly as is – activate system for flight and monitor reg health. Troubleshoot at the pad. Repair – cannot be performed at the pad. Swap pod with OV-105 (Endeavour) RP04 (‘quickest’ option),” the presentation added. “HMF Repair, Three weeks required after pod removal, (donated to Endeavour).”

Additional troubleshooting at the pad is likely to be the first option to be evaluated, with three clear options already outlined – although each path holds no guarantee of success.

“Troubleshooting Ideas: Could cycle valves from cockpit. Each valve cycled nine times via LPS (Launch Processing System) already. No different performance expected, same circuitry used by LPS or cockpit switch,” noted options presented to the ERB.

“Run regulator flow tests. Portable reg panel needs to be reactivated. Panel ready to support – TBD (To Be Determined, around one week). 700 psia inlet pressures (1500 in OPF). Panel designed to test reg response only. Any other test capability, e.g. reg & iso leak rates TBD.

“Try ‘baking’ valve by extended powering of valve Soften Teflon of main seat to improve sealing. May not help if the pilot is leaking. Connection demate in doghouse door required along with subsequent SCAN retest.”

Flight rationale is by no means out of the question, but will be subject to the condition and performance of the related redundancy in the system.

With the current indications pointing to at least one of the two parallel helium isolation valves as leaking, two helium system regulators – a primary and a secondary – will be tested to verify they are functioning correctly.

These two regulators are downstream of the isolation valves, and are used to maintain helium pressure to the fuel tank. If there are problems found with one or both regulators – during testing this week – flight rationale will be very hard to approve.

“Each He iso valve is one of three series valves: He Iso, Primary Reg Stage, Secondary Reg Stage. If all three leak a Burst Disk/Pressure Relief valve protects downstream components from over pressurization,” explained the ERB presentation.

“Depending on leak rate, could use thruster firings to help control tank pressures. Thruster firings limited while docked to ISS (International Space Station).”

Once test equipment has been stationed at the pad, the helium system will be brought to flight pressure and engineers will monitor the panels to ascertain whether the regulators function properly. Even if both regulators are deemed to be in a good condition, a flight rationale debate will still be required.

More information and articles will follow, as information is collated into L2.

L2 members : Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4500 gbs in size

No related posts.

The small thruster (F5R) on the right side of Endeavour’s FRCS (Forward Reaction Control System) came under evaluation during a desiccant inspection that resulted in a “liquid” leaking on to an engineer’s hand.

Due to the dangers of the hazardous substances that power the thrusters, the engineer was evacuated as a precaution. Checks at a medical center confirmed he had not been exposed to any danger.

Orbiters have six Vernier engines or thrusters which are used to make fine adjustments to the attitude or velocity of the vehicle on orbit.

Each vernier RCS engine has one fuel and one oxidizer solenoid-operated poppet valve. The valves are energized open by an electrical thrust-on command. When the thrust-on command is terminated, the valves are de-energized and closed by spring and pressure loads.

Ahead of launch, the openings to the thrusters are monitored by desiccant covers, which provide a visual indication of moisture contamination for the thrusters.

The inspection was called due to the requirement to changeout the VTPA (Vernier Throat Plug Assembly), which was observed to be lodged into the thruster, with part of its desiccant missing – later found on the MLP (Mobile Launch Platform) zero level. It did not cause any damage to shuttle hardware during its liberation.

Under strict safety restrictions, engineers carried out a visual inspection of the truster and nearby TPS (Thermal Protection System). They found liquid to be present on the filler bar bonded to the internal structure shelf surrounding the 28-00 door cavity, and on a number of tiles.

“A thruster Leak (F5R) exposed 15 tiles to liquid dripping that appeared much like syrup; amber in color,” noted processing information on L2. “The (location) tile is where the drop of fluid initially fell before running down the remainder of the tiles.

A drop of fluid was also observed to drip off the hardware during an inspection by engineers and safety officers, which once again called for workers to be moved away from the immediate area. This again was only a pre-caution, with no workers exposed to any dangerous substances.

Efforts proceeded to the sampling of the contaminant, as a forward plan was created to work on a clean up operation – which will be fully evaluated following vapor checks that noted a small trace of MMH (Monomethylhydrazine) in the “ooze”.

“Documenting the resultant contamination of 16 tiles. Engineering is guiding our efforts to clean up this ‘syrup type ooze’ from the TPS and believe that data (toxic vapor checks) has pinpointed the base constituent (MMH),” added processing information on Tuesday.

“Due to the potential presence of hypergols, stringent safeguards will be required to protect personnel from exposure during this work. The disposition that is in draft will be released as a hazardous operation to carefully remove the contaminants and to perform litmus paper checks to verify removal.

“Once these steps are completed, inspections and engineering evaluations will follow to verify no resultant damage and to note the general appearance of the immediate area. Further dispo to follow to address the findings.

“A carboy was installed in the thruster on Friday to control the leaking thruster; Engineering evaluation continues.”

No timescale has been placed on the clean up operation, though Endeavour has a number of days in hand, prior to her move to Pad 39A to take up the roll as the STS-126 shuttle.

“The team continues work supporting a launch date of 11/14 (NET). The STS-126 payload is scheduled to be transferred to the Pad-A PCR (Payload Changeout Room) on 10/23. STS-126 is scheduled to roll around to Pad-A on 10/25,” added Tuesday processing information.

While Endeavour waits for Atlantis to depart Pad 39A for rollback to the Vehicle Assembly Building (VAB), the completion of fuel loading for Endeavour’s systems on Pad 39B has removed several days of pad flow operations after her “rollaround” to the adjacent pad.

In total, the current schedule shows Endeavour has four contingency days for being ready to launch on November 14.

“S0024, prelaunch propellant servicing, was completed this morning. The team drained and refilled the left and right RCS. All S0024 activities are now complete for flight.”

L2 members: All documentation - from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.

Related posts:

1. RSS retracted to reveal Endeavour – ODS issue cleared for flight STS-126′s S0007 launch countdown operations have reached another milestone, with...
2. Endeavour rollaround moved forward to Thursday – FRR concludes The unique transfer of Endeavour and the STS-126 stack from...