SCRUB: Second STS-128 launch attempt scrubbed due to valve issue
Discovery was undergoing S0007 Launch Countdown Scrub Turnaround procedures, with the goal to launch on Wednesday morning at 1:10am local time. However, during tanking, the PV12 (pneumatic valve) failed ‘stuck’ on the fill and drain system on Discovery, causing the scrub for “at least” 48 hours.
STS-128 Attemp 2 (pre-scrub):
The local Florida weather – notoriously hard to forecast – closed in on Discovery, resulting the vehicle receiving a soaking from a downpour during the T-9 minute hold. With the RED weather constraints failing to clear in time for the launch window, the decision was made to place STS-128 into a 24 hour scrub turnaround stance.
“Orbiter: OV-103 / ET-132 / BI-139/ RSRM 107 (Pad A): S0007 Launch Countdown. Launch was scrubbed last night at 0125 EDT due to weather violations. The team is working 24 hour Scrub Turnaround operations for a Launch attempt at 0105 EDT tomorrow morning,” outlined the Mission Management Team (MMT) via morning processing in L2.
“Scrub Turnaround operations are proceeding well. Critical vehicle safing was completed at 0147 EDT. LOX drain was completed at 0346 EDT. LH2 drain was completed at 0505 EDT. LH2 boil-off is in work.
“Pad A safing and inspections are in work. Pad A should be reopened for controlled work by 0700 EDT. LO2/LH2 Tanking is scheduled to begin at 1545 EDT.”
“Probability of KSC weather prohibiting launch – 30 percent. An upper level trough is located in the Eastern US and a surface boundary is located over Central Florida,” added weather information.
“The boundary will migrate slowly northward as the upper level trough gradually weakens. There is still a possibility thunderstorms may affect the area near tanking time as the boundary moves north.
“By launch time, the boundary will be northwest of KSC. There is a chance of showers near the area at launch time. Our primary concerns for launch are cumulus clouds within 10NM of the launch pad and showers within 20NM of the Shuttle Landing Facility (SLF).”
Fuel Cell activation procedures have already been worked during the scrub turnaround, with no anomalies in work.
The three power generating Fuel Cells are located under the payload bay area in the forward portion of the orbiter’s midfuselage, and operate as independent electrical power sources, each supplying its own isolated, simultaneously operating 28-volt dc bus.
“Fuel cell 1, s/n 109, has 354 hours on the stack, 698 hours on the regulator, and 2 flights. The regulator contains the new elastomer material, AFLAS/EPDM. The cells were made by the drip-fill method. It has PEEK Insulator Plates,” noted FRR materials on Fuel Cells that will ride with Discovery.
“Fuel cell 2, s/n 107, has 1552 hours on the stack and 1544 hours on the regulator after 4 flights. Fuel cell 3, s/n 115, has 0 hours on the stack and regulator and no flights.”
“The cells, Unitized Electrode Assemblies (UEA), are Long Life Alkaline Fuel Cell (LLAFC) type and were made by the drip-fill method. It has a PEEK Insulator Plate on the accessory end. Fuel Cell 1 and 2 Diagnostics Tests were performed on 04/13/09 at KSC; Fuel Cell 3 Diagnostics Tests were performed on 11/20/08 at the UTC, the vendor; no issues with the results.”
The PV 12 pneumatic valve – on the fill and drain system – stuck during cycling. This was a Launch Commit Criteria (LCC) breach, leading to loading of LH2 loading stopped, drainback being called, and a scrub for the day. This will be at least a 48 hour scrub turnaround.
The valve in question was set to be replaced ahead of Discovery’s next flight – STS-131, according to PRCB documentation – specifically the 89 page STS-131 Program Freeze Point presentation.
Further notes will follow, along with a full article on the troubleshooting on Wednesday.
Good GUCP (pre-scrub content):
Tuesday morning’s opening STS-128 scrub did provide some additional confidence for the work that has been undertaken on the mitigation of leaks from the Ground Umbilical Carrier Plate (GUCP) – with Discovery’s tank (ET-132) undergoing its debut loading without issue.
No leak detectors were tripped, as the modifications to the hardware – and the continued inclusion of a new two-part flight seal – performed as planned during fuel loading and stable replenish.
This success is thanks to the engineering teams that were tasked with checking historical issues with the hardware, in order to attempt a root cause analysis of not only ET-131’s leak during STS-127’s opening two countdowns, and the leak on the opening launch attempt of STS-119 with ET-127.
Following an extensive review, engineers confirmed that a misalignment of the plate was to blame. However, the previous one part flight seal – noted to have slight damage observed on its surface – may have also contributed.
“Root cause: plate misalignment resulted in gapping at flight seal/bellows probe interface. Contributors: As-built flight hardware misalignment ETCA & hinge pin brackets. Insufficient controls during assembly to account for off-nominal ET geometry,” noted an investigation presentation to the Program Requirements Control Board (PRCB) on L2.
“Measurements, Alignment pins, Flight/ground plate relative motion (lateral) during assembly. Reduced capability to accommodate motion at interface during operations due to stiffer Inconel bellows.
“Unexplained Anomaly, possible contributors include: Flight seal defects and/or damage during assembly. Potential plate misalignment.”
The mitigation – involving both the installation of the two-part flight seal, and work on the “feet” of the GUCP, specifically “tighter tolerance alignment pins (0.515”). Tailored GUCP feet (0.180” & 0.230” offset). analysis shows adequate strength. Hinge pin washers restrain GUCP lateral motion,” – has now shown to have stopped the leaks on both ET-131 and now ET-132.
Another successful tanking was on track today – with no leaks noted – prior to the valve issue causing the second scrub. On the GUCP mitigation, yet again it showed how successful the engineering teams are in providing capable forms of mitigation on issues associated with such highly complex hardware.
For all 19 NASASpaceflight.com articles on the GUCP, click here: https://www.nasaspaceflight.com/tag/gucp/
Shuttle manager John Shannon also asked his workforce to concentrate on the launch in hand, and avoid distractions from the ongoing debate into the future of the Human Space Flight program by the Augustine Commission.
“There is no new information from the Augustine Committee. Everyone is awaiting the release of the final report. The briefing to Congress will be in mid-September,” noted Mr Shannon on the latest Shuttle Standup/Integration report (L2).
“Let’s go fly STS-128 and keep the focus that has been displayed the last few weeks. The pace has been rapid, but we need to keep it up just a little longer.
“After STS-128 lands, the next launch is not planned until November, so we’ll have some down time. Everyone needs to stay focused and keep looking for ways we can support the Ops Teams at KSC and JSC. We are all looking forward to a good launch!”
Lead Image was taken by Ben Cooper/NASA.
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.