Atlantis heads back to VAB – ET-127 damaged prior to rollback

by Chris Bergin

With STS-125 delayed until at least mid-February, Atlantis has completed her trek back to the Vehicle Assembly Building (VAB). Once secured inside the historic building, engineers will evaluate damage to her External Tank (ET-127) – which suffered several dings via a falling stainless steel support rod at the weekend.

Atlantis is now expected to avoid a de-stack, following an engineering evaluation into potential requirements that would have favored the orbiter heading back to the home comforts of her OPF (Orbiter Processing Facility).

Those latest evaluations focused on the tire pressures – which naturally decay over time. Data shows the pressures will be acceptable for landing “as far away as April” – making a February launch target within spec.

Engineers will continue to monitor Atlantis’ health during the couple of months she’ll be housed in the VAB, with the option to call for a de-stack if it is deemed to be in her best interests.

Other factors include the possibility Wing Leading Edge (WLE) inspections may be required, Main Landing Gear (MLG) door seal compression measurements, and moisture levels on her Payload Bay Doors.

Most of Atlantis’ hypergolics have been offloaded, should the de-stack option be taken in the coming weeks. This mitigates the undesirable offload of large quantities of the hazardous hypers in the OPF, in the event of a rollover back to her barn.

“Integrated preps for rollback began last week and continued through weekend, following the SCAPE (Self-Contained Atmospheric Protection Ensemble) operation,” noted Monday processing information on L2, relating to the hypergolic propellant offload ahead of rollback.

During the offloading activities, one minor issue was noted with the pressures in the Left Reaction Control System (LRCS) tanks – which was mitigated by increasing the pressure in the associated helium tank.

“LRCS He Tank and LRCS propellant tank equalized. The Delta P should have been greater than 6 PSI for rollback to the VAB per OMRSD (Operational Maintenance Requirements and Specifications Document),” added Monday processing information.

“The He QD (Quick Disconnect) was mated to the vehicle, the manual valve was closed, and the tank was pressurized. S0072 operations then resumed. An OMRSD waiver was required for taking readings with the Heise gages on the panels.”

This action was called to avoid the potential migration of the hypergolic propellant into the pressurization system, which may of caused issues for required locking of the isolation valves.

Meanwhile, following an incident on Saturday, Atlantis’ tank – ET-127 – will also require engineering evaluations, due to what is currently being classed as ‘dings’ on the ET, caused by a liberated stainless steel support rod on Saturday.

Atlantis herself has avoided any serious damage to her TPS (Thermal Protection System) during the 3.5 foot long rod’s fall – which was later found on the floor of the MLP (Mobile Launch Platform).

“On Saturday morning a 3′ 1/2” stainless steel support rod that is used for the R/H FRCS (Right Hand Forward Reaction Control System) spill protection was found on the MLP “0” Level between the Orbiter and ET (Inboard of the Left Hand Solid Rocket Booster),” noted processing information on L2.

“Initial inspections on the dropped tubing found several dings to the External Tank which could be possibly related damage from the tubing.

“Orbiter TPS personnel performed a preliminary inspection of the thermal protection system. The Orbiter was inspected from the 207 level down using binoculars. No Orbiter TPS damage was noted.”

The only remaining issue for STS-125 – relating to a faulty MDM (Multiplexer/Demultiplexer) card – will be mitigated by its replacement later this week inside the VAB.

“Troubleshooting on MDM OA2 was completed last week and indicated that the MDM has a bad port and will need to be replaced,” added processing information. “The plan is to replace the MDM in the VAB following the 1st power up of the vehicle, which is scheduled for Wednesday.”

The now-vacated Pad 39A will undergo preparations to receive Endeavour at the weekend, as she prepares for the November 14 launch of STS-126 to the International Space Station (ISS). Flight Readiness Review (FRR) based mission previews and processing will follow over the coming days.

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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