STS-133: Pad work progressing for next week’s instrumented Tanking Test

by Chris Bergin

Engineers are pressing forward with work relating to next week’s instrumented Tanking Test – a key milestone in gaining data towards the root cause of the cracks found two of ET-137’s stringers – with Thermal Protection System (TPS) foam already removed from the tank, allowing for the installation of strain gages and thermocouples into two stringer locations.

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It could be forgiven if Discovery was feeling rather miserable of late, with her launch date slipping, along with a large amount of space flight interest switching to the Falcon 9/Dragon launch, all whilst shivering out at Pad 39A as temperatures dropped during the week.

As a contingency to warm up the veteran of the fleet, Reaction Control System (RCS) heaters and Solid Rocket Booster (SRB) aft skirt purge remained configured over recent days, for use as needed – with contingency engineering support available should Discovery’s systems require assistance.

Depressurization tasks have also been completed on Discovery’s Orbital Maneuvering System (OMS) Composite Overwrap Pressure Vessels (COPV), with only one Interim Problem Report (IPR-77) noted by the NASA Test Director (NTD), relating to a Quick Disconnect on the Ground Support Equipment (GSE). Troubleshooting proved to be successful.

With SpaceX’s Falcon 9 launching on Wednesday, the pad – closed due to safety requirements when another vehicle is launching nearby – reopened later in the day, allowing for additional pad flow tasks to be completed.

“The remaining S5009 ordnance disconnects (SRB Forward Skirts) were completed yesterday following the Falcon 9 launch,” noted the NTD report on Thursday (L2). “SRB Range Safety battery connects and test code loads were completed yesterday. MPS (Main Propulsion System) Aft Confidence Test Thursday, which re-completed aft closeout.”

STS-133 Specific – Including ET Stringer Issue – Articles:

The main focus for STS-133 continues on the preparations to conduct an instrumented Tanking Test next week. Known as S0037 operations, the current schedule points towards a Call To Stations (CTS) on Monday evening, ahead of the Wednesday test.

“S0037 ET Tanking Test: The team is working towards a tentative tanking test date of December 15. Call to Stations is planned for 2030 EST on Monday, December 13,” noted the NTD, referencing the decision taken by managers at a Noon Board meeting this week – which approved a plan laid out by the Engineering Review Board (ERB).

The ERB decided on the prime locations for the installation of instrumentation into two areas of the tank, which will provide vital data towards the root cause – and ultimately flight rationale – for ET-137, following the observation of cracks in two stringers during the tanking of the scrubbed launch attempt last month.
“An ERB was held to discuss the instrumented tanking test plans and a detailed map of the instrumentation locations was finalized. The team is going forward with the recommendation of installing strain gages and thermocouples on panel 2 at and near the site of the S6/S7 repairs,” the NTD continued.

“Stringer S11 on panel 3 will also have strain gages and thermocouples installed to provide the Analysis Team with corroborating data from an alternate site on the ET I/T (Intertank) structure.”

The reconstruction of an environmental tent – last seen during the BX foam repairs to the S6/S7 stringer location – has been completed, as engineers began foam removal tasks.

“Once the instrumentation has been installed, foam will once again be reapplied to the tank, followed by a period of curing, bringing the tank back into a nominal configuration ahead of the Tanking Test.

“The +Y ET access platform was repositioned to the same location as the -Y platform. Environmental enclosure build-up is complete on the +Y and is in work on the -Y to support the installation of the required instrumentation and foam work for the Tanking Test,” the NTD added.

“Environmental enclosure build-up on the -Y ET access platform is complete less the door panel. A temporary has been installed to allow foam work and surface preps to proceed. Foam removal and surface preps on the +Y side (Panel 3 Stringer 12) and the -Y side (Panel 2 Stringers S7 and S8) began Wednesday night. Strain gauge and thermocouple instrumentation installation and cable routing will follow.”

With the launch date slipping to February 3, managers believe all the required work can be completed in time, including the contingency of rolling the STS-133 stack back into the Vehicle Assembly Building (VAB) for the purpose of additional scans in areas which can’t be accessed out at the pad.

“An instrumented tanking test on the STS-133 ET is scheduled for 12/15 which protect the option to roll back to the VAB for access to do NDE (Non Destructive Evaluations) or other work and still meet a 2/3 launch date,” noted on memo circulating through the teams (L2), which also provided some positive fault tolerance comments in the event of finding additional issues on some of the other stringers.

“ET reported on structural fault tolerance analysis that shows having 2 adjacent bad stringers is acceptable as long as there are two good stringers on each side of the two bad stringers (e.g. 2 good, 2 bad, 2 good around the circumference of the tank is acceptable).

“Similarly, a pattern of 1 good, 1 bad, 1 good around the tank is acceptable. However, 1 good, 2 bad, 1 good around the tank is not acceptable. More work is required to perform non-linear finite element analysis to look at more complex scenarios.”

So far, the use of backscatter and X ray scans on the accessible areas of the tank – including the lower flange area between the intertank and the LH2 tank – have found all the stringers to be in a good condition, with no defects noted. “Review of the backscatter x-rays of the stringer bottoms at the LH2 flange on the -Y side of ET-137 did not identify any anomalies in the stringers,” the NTD recently noted.

Plans will continue to be refined leading up to the Tanking Test, with the main goals outlined by managers at JSC, as they work on several paths to gain the required data – both at the pad with ET-137 and out at the Marshall Space Flight Center (MSFC) test rigs.

“The goals of the tanking test is to assess any structural issue in the tank and assist in correlating some of their models of the tank. This test will also verify the stringer repairs so far,” noted another memo to shuttle teams (L2). “A combination of strain gauges and thermocouples along with camera assessments will make up the test.

“There are some limitations on this testing scheme due to access of the locations of interest. Some of the primer is also being sanded down to install the instruments. Both sides of the tank are being instrumented to provide comparison data.”

Also part of the plan is to place the tank under flight pressure, allowing for additional confidence in the stringers and likely meaning ET-137 enjoying a full countdown scenario as previously pre-empted.

“The order of operations will be to remove the foam, instrument the tank, reapply the foam, perform the test, remove the foam and the wires off of the sensors, reapply the foam, and then be ready for flight. The tanks will be pressurized as part of this test,” added the memo.

“This will cause additional deflection beyond just filling the tank without the pressurization of the tank. The cost is an additional cycling of the LO2 tank which can only be cycled 13 times. Success criteria has not been determined for the tanking test.”

It was also noted that a potential forward plan for both ET-122 (STS-134) and ET-138 (STS-135) will be to conduct a nominal – uninstrumented – Tanking Test prior to their launches, although this plan remains only as an option.

“There may be taking tests on the rest of the shuttle flights with the other ETs, but no talk of instrumenting them,” the memo noted.

(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: Within the article: via L2 acquired PRCB presentations).

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