Discovery rollover to VAB completed following late tire change

by Chris Bergin

Veteran orbiter Discovery has arrived in the Vehicle Assembly Facility (VAB) ahead of her February launch of STS-119. The short trip was slightly delayed, following a late requirement to changeout a tire on the orbiter.

Discovery will now undergo a week’s worth of operations inside the VAB, which begins with the transition from the transfer aisle to High Bay 3 (HB3) where she will be mated with the waiting ET-127 and twin SRB stack – which was originally set to fly with Atlantis on STS-125.

“Orbiter mate preps complete. Sling build up for Orbiter/ET mate is complete, noted Wednesday morning processing information on L2. “180 degree Operational Pressure Transducer installation complete, safety wire and leak check after Orbiter Mate.”

Discovery’s rollover was only delayed by a number of hours, after MEQ engineers observed a small leak on Discovery’s left main landing gear outboard tire – a leak that was unacceptable for flight.

The orbiter tires are processed over an extended time period and periodically checked prior to being installed on the vehicle. However the final check of the tire pressures on Tuesday appeared to indicate an off nominal leak.

Although the leak was small, and notably the tires do leak a small amount naturally, it is possible this leak was the result of releasing too much pressure when removing the GSE (Ground Support Equipment) during final pressurization, rather than a problem with the tire itself. Due to the rollover schedule, it was decided it would be prudent to change the tire.

“The left main landing gear outboard tire pressure transducer readings were low and out-of-tolerance,” outlined Wednesday morning processing information on L2. “Tire pressure checks indicated the pressure had degraded since pressurization to flight level and tire R&R was necessary prior to rollover.

“Tire R&R and pressurization are now complete and orbiter/OTS operations have resumed. STS-119 rollout to Pad A is planned for next Wednesday 14 Jan.”

Another issue was noted when an inspector noticed what appeared to be an off nominal wire bundle hanging down and potentially crimped in the landing gear mechanism as the gear went up.

However, following an engineering meeting, the wiring was cleared as ok to proceed with the rollover, which picked up in the afternoon, following the passing of poor weather in the local area.

Meanwhile, only a few issues are being discussed during the current stage of flight preparations – notably the run up to the SSP (Space Shuttle Program) FRR (Flight Readiness Review) on January 21-22.

A fleet wide investigation into the health of the orbiter Flow Control Valves (FCVs) has led to a decision to remove and replace the valves on Discovery shortly after she arrives at the pad (full story to follow on the issue), and an engineering summit is due on Friday to discuss the forward plan for the modification of the holddown post Debris Containment System (DCS).

The DCS modification in required, following an anomaly with holddown post number 3 on Endeavour’s right hand booster, which failed to contain pieces of debris – including a large two foot long mental spring – following the separation of the bolts at T-0 during STS-126’s launch.

The modification to the DCS – now known as the “Fail Safe Plunger Retention System” – will protect future launches from such debris potentially impacting the vehicle, after assessment findings noted that threat exists.

“Completed all planned certification testing for new Fail Safe Plunger Retention System over the holidays. Ten drop tests and four full up firings were done, as well as one static pull-test done in Florida,” added the latest Shuttle Stand-up report on L2. “The firings and drop tests were done at MSFC. All of these tests met their pass criteria, and were deemed successful.

“The plan is to present a full story at the (Safety Board). Everything is on schedule to fully support implementation on the next flight. This is a mod that would prevent a plunger ejection as seen on the last flight where SRB took an IFA (In Flight Anomaly).”

With only those two issues currently in work, STS-119 remains on track for February 12.

“Welcome back. It’s clear we’re hitting the ground running. We will support a flight February 12,” added shuttle manager John Shannon on the Stand-up. “There are a few issues on the table, but other than that, overall it looks pretty good. So, thanks a bunch and let’s keep working together.”

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

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