The all-powerful Program Requirements Control Board (PRCB) met on Thursday to discuss the status of ET-137’s stringer crack root cause, as part of their effort to gain flight rationale for STS-133. Forward options range from conducting a Tanking Test, through to the contingency of rolling back and destacking the vehicle – in order to carry out modifications to ET-137’s stringers. UPDATE: Launch date NET slips to Feb 3, 2011 – decision taken on Friday.
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For now, Discovery remains powered down at Pad 39A, with only minor processing work – relating to changing out batteries in the stored EMU suits and preparations for a few days of expected cold weather at the Kennedy Space Center (KSC).
“Flight EMU batteries were removed on Wednesday. A functional check and airlock closeout will be scheduled based on decisions by the PRCB later regarding launch date,” noted the NASA Test Director (NTD) report (L2).
“Due to expected cold weather over the next few days the RCS (Reaction Control System) heaters and SRB (Solid Rocket Booster) aft skirt purge have been configured for use as needed. Contingency engineering support has been scheduled and is available.
While all the repairs have been completed on the Ground Umbilical Carrier Plate (GUCP), engineers have been waiting for good weather to install reference dots on the GUCP to monitor for movement during tanking. That effort is expected to take place today.
Also continuing to taking place at the pad are scans of the lower LH2 flange on ET-137, via the use of Backscatter imaging, although the flight rationale effort continues to focus on the flange between the LOX/Intertank region – which suffered from the four cracks on two stringers.
Although those two stringers (S6 and S7) have been repaired via the use of two doublers, along with the reapplication of BX-265 Thermal Protection System (TPS) foam, STS-133 won’t be allowed to fly until managers have completed their investigation into the root cause of the cracks, assurances foam won’t liberate from the region during ascent, thus creating the required flight rationale.
“The ET structures engineering community is continuing to develop the plan to analyse, test, and determine a flight rationale for the ET stringer cracks,” the NTD continued on Thursday. “The test team is working toward a launch window NET (No Earlier Than) Dec 17; however no formal launch date has been selected. The option to perform a tanking test is still under discussion.”
A preliminary plan has already listed an instrumented Tanking Test, which may allow for additional data to be gained on how the tank – with its newly installed doublers – behaves during the cryo cycle of propellant loading, whilst providing a “bonus” check of the GUCP.
Meetings have been taking place all week on the forward plan within – and including outside – the Space Shuttle Program (SSP), with daily tag up meetings leading into Thursday’s PRCB meeting at the Johnson Space Center (JSC).
“SSP has initiated daily tagups beginning today to discuss the ET stringer crack investigation status. The purpose is to focus on the forward plan, schedule, key decision points, etc. The technical results of the analyses and tests are expected to be discussed at the program level on a weekly basis at the PRCB,” notes (L2) from the latest – pre-PRCB – tag up noted. “The ET Project is also conducting daily telecons to review status.”
That latest tag ups outlined numerous options that are under discussion within the Agency, ranging from a continued effort to make the December 17-20 window, through to a rollback, destack and modifications to the tank.
“Most of this meeting focused on reviewing the schedule of activities supporting the root cause investigation and development of flight rationale as well as an assessment schedule for making modifications to the tank to strengthen the stringers,” added the tag-up notes.
“The schedule for the investigation/flight rationale still reflects a December 15th completion date for the analysis and testing identified at last week’s PRCB. They have included a placeholder for other testing that may be required, which extends into January, but since these activities are dependent on results of other activities, it’s a placeholder that hasn’t yet been well-defined.”
Modifications to the stringers would involve the installation of additional doublers or “clips” – adding strength to that area of the tank – which would be conducted inside the Vehicle Assembly Building (VAB). Depending on how many doublers would be installed will determine when the modifications would be completed.
“They also reviewed a preliminary schedule for modifying the stringers. The decision on whether to mod the tank and what that mod would entail has not been made but (SSP Manager John) Shannon wants to ensure he understands the schedule enough to know when we are coming up on a key decision date.
“So they down selected to a repair option that involves installing “Z” doublers for the purposes of building an assessment schedule. This assessment schedule assumed rollback and demate and showed a completion date of 1/9 or 1/15 depending on whether the +Z or both the +Z and -Z sides were modified.
STS-133 Specific – Includes all GUCP and ET Stringer Issue – Articles: http://www.nasaspaceflight.com/tag/sts-133/
“KSC is integrating this into their overall schedule to show when STS-133 could be back out at the pad and ready to support launch.”
A decision to conduct an instrumented Tanking Test does not appear to support the December window, although a non-instrumented test would still allow some small hope for Discovery to conduct a Christmas mission. Regardless, a Tanking Test is likely to be approved in order to confirm the doublers on Stringers S6 and S7 have provided the required integrity to that region of the flange.
“We talked both a noninstrumented tanking test and an instrumented tanking test. The non-instrumented test can be done and support the 12/17 window. The instrumented tanking test precludes the December window,” added the notes.
“(Mr) Shannon wants to make a decision at the PRCB as to whether to proceed with the tanking test. He feels a tanking test is required to verify the repair that has been done on stringer 6 and 7.”
Engineers are set to present to the PRCB on the pros and cons on both an instrumented and non-instrumented Tanking Test, with an instrumented test likely to be the outcome, although some sources claim this will be preceded by a non-instrumented Tanking Test – simply focusing on the two new doublers.
For an instrumented Tanking Test, TPS foam would be removed from the LOX and LH2 flange areas, followed by the installation of the instrumentation, reapplication of TPS, perform the tanking test, remove the TPS, remove the instrumentation, and then reapply the TPS. Discussions at the PRCB will relate to potential ascent liberation threats of further work on the TPS.
For a non-instrumented test, a preliminary plan would allow for tanking to take place on December 6, technically preserving the option to launch on December 17, pending root cause and flight rationale success. This plan would be to tank, pressurize, and stay in that config for some amount of time.
The Final Inspection Team (FIT) would then perform inspections, prior to Non Destructive Evaluations on the areas that have been previously scanned , in order to check for any new defects.
UPDATE: The PRCB members were presented with an update on the root cause investigation, noting they are still evaluating several paths.
“Summary: Root cause remains indeterminate. Working scenarios emerging based on process assessment investigation,” noted one PRCB presentation from Thursday’s meeting (L2).
Favorable notes for conducting a Tanking Test were also listed in the summary findings, with KSC noting they are currently preparing for the test late next Wednesday (3rd shift). Although the PRCB decided a Tanking Test will be conducted before STS-133 launches, the type of Tanking Test and an official date are yet to be decided.
The option to rollback and conduct modifications to the tank continues to undergo planning, but also remains as a contingency at this time, with the launch date continuing to track the December 17-20 window at this time.
“Dual-path approach continuing: Analysis supported by tests in work for flight rationale. Tanking test provides additional confidence hardware configuration,” continued the presentation. “Contingency repair plans in work.”
UPDATE 2: Prelim plan for a non-instrumented Tanking Test NET Wednesday, 12/8. The plan is to go down to T-31 seconds and secure. Opted against – will aim for an instrumented tanking test sometime in December.
UPDATE 3: NET slips to Feb 3, 2011 – decision taken on Friday. New article later today.
(Further updates and articles will follow. Refer to live coverage threads linked above. L2 members refer to STS-133 live coverage sections for internal coverage, presentations, images and and updates from engineers and managers. Images used, Lead: NASA.gov. Within the article: via L2 acquired PRCB presentations).