STS-133: Tanking Test plan outlined – Rollback to allow for additional ET scans

by Chris Bergin

With unacceptable weather at KSC restricting preparations for STS-133’s Tanking Test, managers decided to delay the test until at least Friday. With the Program Requirements Control Board (PRCB) approving the plan to collect data from ET-137’s stringers, a decision was also taken to roll the stack back to the Vehicle Assembly Building (VAB) next week – allowing for further inspections of the tank.

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Cold weather and high winds interrupted what was always a tight schedule to be in a position for Call To Stations (CTS) on Monday, which would have resulted in the Tanking Test taking place on Wednesday. The weather also affected the numerous offloading operations, which now relate to the official call to rollback the vehicle to the VAB just prior to Christmas.

“S0072 HPU (Hydraulic Power Unit) Offload is scheduled to be performed this week pending ET instrumentation/tanking test progress and acceptable weather conditions. The offload requires a Pad clear. The HPU servicing carts were lifted on to the MLP (Mobile Launch Platform) on Friday,” noted the NASA Test Director flow report (L2) on Monday.

The offloading operation was scheduled to take place as early as Sunday. However, the cold weather added a number of constraints to the immediate plans for the flow – not least that of keeping elements of the vehicle within the required temperature range.

“Due to the potential for continued cold weather the RCS (Reaction Control System) heaters and SRB (Solid Rocket Booster) aft skirt purge remain configured for use as needed,” added the NTD. “Contingency engineering support also remains available.”

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Although the weather is expected to improve later this week, it is not yet certain the Tanking Test will be carried out on Friday. A review will take place ahead of CTS on Wednesday to assess the status of work to install nearly 100 sensors into two locations on ET-137’s stringers.

Preparations – ranging from simulations of the Tanking Test, through to foam removal and the opening installation work of the strain gauge and thermocouples – continued until high winds prevented engineers from being on the associated scaffolding.

The reapplication of BX foam over the instrumentation, along with a cure time, is yet to take place, with the initial task of curing the instrumentation on to the two stringer locations still in work. A purge of warm air may be pumped into the intertank to help cure the instrumentation on to the tank.

“OV-103 / SRB BI-144 / RSRM 112 / ET-137 (Pad-A): S0037 ET Tanking Test: A tanking test model run was successfully completed in the Control Room last week. The final tanking test requirements and LCCs (Launch Commit Criteria) were presented to the PRCB (Program Requirements Control Board),” added the NTD reports.

“+Y and -Y foam removal is complete. Surface preparations and mapping for instrumentation installation are complete. Alternative heating techniques and bonding systems are being considered to enable sensor installation in the cooler temperatures which are being experienced and forecast for KSC.

“Strain gauge installation, wire routing, and channelization was completed over the weekend. Thermocouple installation continued Monday morning. Scaffolding was erected on the intertank access arm to allow access to panel 6 on the -Z side of the tank for photogrammetry. High winds are predicted to prohibit personnel from working on the scaffolding until later on Monday.”

As mentioned, the PRCB meeting on Friday overviewed documentation relating to the upcoming Tanking Test, outlining procedures which will benefit from the experience gained during the most recent Tanking Tests – such as those carried out for STS-122’s Engine Cut Off (ECO) sensor issues, and STS-127’s Ground Umbilical Carrier Plate (GUCP) leaks.

“STS-133 Tanking Test per S0037 Requirements Review: Same approach taken for the STS-122 ECO Sensor trouble shooting Tanking Test and the STS-127 GUCP GH2 leak Tanking Test. The request to perform this Tanking Test is not unique in that the team has performed taking tests via S0037 in recent history,” outlined one of the PRCB presentations (L2).

“The vehicle configuration and LCCs were built from this collective experience. STS-114 (Return to flight , 4/14/2005 and 5/20/2005). STS-122 (ECO trouble shooting, 12/18/2007). STS-127 (GUCP trouble shooting, 7/1/2009).”

While the Tanking Test is solely related to the ongoing work towards the root cause of the stringer cracks during the November scrub, the actual cause of the scrub – an unacceptable hydrogen leak from the GUCP during tanking – will gain a ‘free’ test, with the PRCB noting an observation plan for the GUCP during the upcoming Tanking Test (another article will follow on the specifics).

The plan for gaining data from the stringers was the main focus of the PRCB meeting, with a plan outlined and approved at the meeting.

“ET Instrumentation powered up prior to WX (Weather) tanking meeting to monitor/verify performance of sensors. ET tanking data team will be located in LCC Ground Measurement Room allowing real time view of raw instrumentation data. Presently only available location to see data real time,” added the documentation.

“Verify Design Center specified minimum required instrumentation available to begin tanking. Launch Team and Design Center will make recommendation to Launch Director and Launch Integration Manager on whether to proceed with Tanking Test at WX tanking meeting. Once Launch Integration Manager gives go for tanking controllers will specify Temp (start) and begin recording data.”

Providing the Tanking is green-lighted, the usual process of loading the tank will be conducted, taking the tank through to “topping” (stable replenish) and through a pressure cycle, which also conducting a check of the GUCP. With the tank loaded, and a pressurization of the tank confirmed, the Final Inspection Team (FIT) will take a close look at the stringers to check for any defects.

“One Pressure cycle on LH2 tank has been taken before LO2 introduced into tank. LH2 transition from fast fill to topping for GUCP evaluation remains a goal of this tanking test. NDE (Non Destructive Evaluation) of stringers post pressurization remains a goal of this tanking test. Team recommendation is to continue full load and prepress even without tank instrumentation available,” the presentation continued.

“At Stable Replenish: Four hours minimum for LO2 stable replenish. FIT will perform standard inspections and reporting. Will utilize enhanced IR (Infra Red) camera equipment. In hold at T-9 minutes Integration will poll controllers to ensure all goals have been satisfied.”

The Tanking Test will continue through T-31 seconds in a nominal countdown situation, prior to holding for five minutes, before calling for a Ground Launch Sequencer (GLS) abort and a nominal drain of the tank.

“Once given a GO the launch team will execute remainder of count down. Data recording will be terminated at point when overall skin temperature is approximately Temp (start) or configuration is released by Design Center and KSC Chief Engineers,” added the overview.

“Once we have satisfied Tanking Test data gathering requirements. Vehicle and ground will count down and hold at T-31 seconds for the ET GO2 pressurized generic certification time of 5 minutes. After 5 minutes GLS will give cutoff followed by standard vehicle and ground safing and recycle. LH2 and LO2 will transition to nominal drain.”

As expected, and now official, the plan would be to inert the tank and prepare for a rollback to the VAB, four or five days after the Tanking Test. This will allow for backscatter and X-Ray scans on the areas of the tank which are currently inaccessible at the pad.

With the payload still inside Discovery’s Payload Bay (PLB), the schedule would allow for rollover back to the pad sometime around the first week of January, in order to make the current February 3 launch date target.

(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: Larry Sullivan, MaxQ Entertainment/ Within the article: via L2 acquired PRCB presentations and NASA KSC).

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