Busy weekend as Endeavour undergoes minor troubleshooting

by Chris Bergin

A few issues are being worked on the STS-123 stack, as Endeavour edges ever closer to her opening launch attempt on March 11.

The main focus of attention relates to troubleshooting a problem with the orbiter’s UHF radio, along with evaluations regarding the possible requirement of thermography inspections on a suspect Solid Rocket Booster (SRB) factory joint debond issue.

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As expected, the Flight Readiness Review (FRR) approved continuation towards the March 11 launch attempt, in a meeting that lasted little over a day – a sign of the absence of any major issues with the pad flow for STS-123.

At Launch Pad 39A, Endeavour has been put through S0024 (pre-launch propellant servicing) procedures, which has included the completion of FRCS (Forward Reaction Control System), RCS and OMS propellant loading.

‘FRCS oxidizer propellant tank load complete,’ noted Friday processing information. ‘Left and Right OMS oxidizer propellant tank load complete. Left and Right RCS oxidizer propellant tank load complete.

‘Aft Propulsion System oxidizer crossfeed valve is configured. Fuel flow to RSS (Rotating Service Structure) complete. FRCS fuel propellant tank load, system purge and QD leak check complete. ROMS/LOMS fuel propellant tank load complete. Right RCS fuel propellant tank load is complete. Left RCS is in-work.’

As per normal for a pad flow, several IPRs (Interim Problem Reports) have been documented for STS-123, most of which have been corrected, or are in the process of being corrected.

‘New IPR: During Right OMS oxidizer propellant fill; following flow initiation, flowmeter F3 was reading 9.49 gpm. Downstream F1 and F2 flowmeters showed 5.34 gpm indicating valve B7 was not completely closed,’ added the processing information. ‘During trouble shooting, valve B7 was manually closed and skid checked for leaks. Flow was reinitiated with nominal results.

‘New IPR: During Left RCS oxidizer low pressure loading, a false low pressure spill indication came on indicating tank was full, when it was not. a few gallons of oxidizer were removed to reduce the tank pressure. Low pressure fill to spill was successfully re-performed. This IPR will be closed.

‘New IPR: Pressure transducer leak – two drops/minute at body joint. Drip pan was installed. Will remove/replace post S0024. TVCs (Thrust Vector Controls) will be checked and area controlled accordingly once the pump is secured. Constraint is S0007.200, Step 15-3.’

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Still under review, but not deemed a major concern, is the SRB factory joint debond issue. The insulatator material – a heavy rubber material that is vulcanized into the joints on the booster – is under focus, after a piece liberated at some stage during the booster’s transit on STS-122. This was observed after the boosters arrived back in port following recovery operations downrange.

‘Suspect PR on SRB factory joint debond issue: Awaiting program decision to ‘fly-as-is’ or perform thermography inspections at Pad A,’ noted processing information on Friday.

While it is likely this was a one-off event, evaluations are checking the material has been correctly cured into the hardware. This may require thermography inspections of the joint – if the conservative option is taken – though the concern is currently believed to be minimal, given the likelihood is the liberation event during STS-122 occurred when the booster hit the ocean.

Should managers call for thermography inspections, access to the joints – and some 49 locations on each booster – could prove to be labor intensive.

A decision on carrying this out appears to be moving back and forth with regards to carrying out thermography inspections, following Thursday processing information which noted inspections wouldn’t be carried out, only to then retract the note and add that the decision had not yet been taken.

‘SRB factory joint unbond issue: Program decision was to NOT perform the Thermography inspections. Disposition to the suspect PR is in-work. (This note was added as an addendum: The Program has not yet made a final decision on the SRB factory joint unbond issue regarding any potential inspections to be done.)’

Meanwhile, another issue relates to the UHF radio on Endeavour, which may require a donation from sister ship Atlantis. While the specific issue was not noted, the fault did not repeat during initial troubleshooting.

‘Orbiter UHF radio transmits on both 259.7 AND 243 (GUARD) MHz simultaneously with 259.7 MHz selected. Troubleshooting was nominal and the failure could not be repeated. As a result, the UHF mode switch and/or transceiver may be removed and replaced, then re-tested.’

Troubleshooting on the UHF radio will continue over the weekend, along with evaluations on an earlier IPR relating to a hydraulics flex hose – that was detected to be leaking at a greater than allowable rate. The hose in question was earlier re-torqued, but was still leaking.

The weekend will also see the opening aft closeouts, ordnance installation preps, and launch countdown preparations (S0007). S1287 aft compartment closeouts are scheduled to begin 1st shift Saturday, with S0007 preps also scheduled to begin 1st shift.

S5009 Ordnance installation is schedule to pick up Sunday 2nd shift and will continue into 3rd shift Monday.

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