PRCB: NO tanking test for STS-121

by Chris Bergin

Today’s PRCB (Program Requirements Control Board) meeting has decided against a tanking test – which was provisionally set for June 1 – ahead of STS-121’s launch, following objections across the board, leaving Shuttle manager Wayne Hale with no choice but to call off the tanking test.

Meanwhile, the Michoud Assembly Facility have noted they are pulling out all the stops on ET-118, which is required at the Kennedy Space Center for Atlantis, in time to support STS-300 requirements.

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Updated at 2:27pm Eastern, 4th May.

Shuttle managers heard from KSC’s MK-SIO/J. Draus, and Marshall Space Flight Center’s ED01/R. Champion, while Lockheed Martin’s Wanda Sigur was also present at the meeting to give updates on the status of the External Tanks.

The tanking test requirement – it had been argued – was based on the need to checkout the new ECO (Engine Cut Off) sensors, recently replaced by Lockheed technicians, following the detection of a phase shift in one of the crucial sensors during the checkout of ET-119 in the VAB (Vehicle Assembly Building).

However, engineers feel such a test can be carried out during the launch countdown, as opposed to cryoloading the tank a month prior to launch. Engineers also point to the tests carried out on ET-120 – which determined that the more times a tank is cycled through tanking, the higher the risk microscopic cracks will form, in turn risking foam liberation on ascent.

Following confirmation from sources at MSFC, MAF and KSC, the decision was met with surprise, yet optimism that the Program didn’t overrule their concerns.

Live updates and information resulting from the PRCB are available on L2. Full PRCB Documentation relating to this article will be available on L2 from the weekend.

‘Well, we’ve been against it from the start – because they were going to take the test all the way through prepress,’ said one source, who asked not to be named.

Prepress is short for ‘tank pre-pressurization,’ which occurs at T-154 seconds for LO2 tank, T-104 sec for LH2 tank – and pressurizes each tank with helium to get them at flight levels prior to lift-off. 

‘When you pressurize the tanks that high, you add a ‘pressure cycle’ to the tank – something that is ultimately not good for it. 

‘It’s possible that by doing this, they’d increase the chances that foam cracking could occur.’

Another source noted that very little by way of rationale for the tanking test was put forward at the PRCB – as the meeting failed to mirror the split of opinion that occurred the week previously during the debate on which option of modification the Program would fly with for ET-119.

‘No one spoke up when (Hale) asked for rationale to support the tanking test,’ the source added. ‘He was left with no choice at this meeting. MSFC presented an excellent case against the test.’

Meanwhile, work on ET-118, the second flight tank for 2006, continues to increase as the May 30 delivery date approaches.

The tank, which is in Building 420, Cell 2, now has two critical path activities: installation of Developmental Flight Instrumentation (DFI) and completing modifications to the bipod.

‘Our employees are virtually all over the tank right now,’ says Wanda Sigur, ET Project vice president at Lockheed Martin, in a ‘Mission Success’ announcement to employees. ‘There’s plenty of work to do, and we’re making progress on all fronts.’

Lockheed and MAF note that DFI will provide flight data on how the tank performs without Protuberance Airloads (PAL) ramps, the major modification from ET-121 that flew on the STS-114 mission last summer.

ET-118 will be the second tank to fly without the ramps. Schedule pressure was the apparent reason for ET-119 to go without DFI for STS-121.

‘Currently DFI tube reinstallation has been completed for both the external Liquid Oxygen Tank and Liquid Hydrogen Tank cable trays,’ the ‘Mission Success’ report noted. ‘Technicians have also completed the roughrouting of accelerometers to the filters and harnesses inside the Intertank.

‘Crews continue to work on bipod modifications as well. Completion of the initial Thermal Protection Systems (TPS) work will take place prior to wire bonding and sealing, which will be followed by the final TPS closeout spray.’

The longerons, bellows drip-lip, camera placement and antenna, diffuser and ice frost ramps are also ‘in works’ on the tank.

ET-123 will be the next tank to be worked on, following the shipping of ET-118.


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