L-1 – Endeavour ready to be revealed by RSS retract

by Chris Bergin

A couple of minor processing issues have been cleared with Endeavour, as she continues to move ever closer to Wednesday evening’s opening launch attempt at 18:36 local time.

STS-118’s S0007 launch countdown procedures have continued with smooth flow towards launch, catching up on the schedule to allow an on time retract of the Rotating Service Structure (RSS) this evening (21:00 local).

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Behind by two hours on the schedule earlier in the day, engineers have caught up to be on time for the key event of RSS retract, following a day of preparations that included the loading of the PRSD (Power Reactant Storage and Distributation) subsystem. The PRSD stores the LH2/LO2 reactants that supply the three fuel cell power plants, which generate all the electrical power for the vehicle.

The PRSD event was surrounded by the bulk of the minor issues – mainly relating to the support equipment, as opposed to the shuttle – which were noted in processing information. All have been resolved and there are no constraints to launch.

‘During pre-ops for LH2 PRSD loading Haz Gas reported that their system B vac turbo pump RPM was fluctuating around 300 RPM. Normally this vac turbo pump fluctuates near or below 100 RPM,’ noted one processing report.

‘Haz Gas system engineer stated that this higher fluctuation in the RPM is indicative of a pending vac turbo pump failure. IPR (Interim Problem Report) was taken to document problem and to allow Haz Gas folks to prepare to R&R (Remove and Replace) the vac turbo pump as soon as they can regain access to the MLP compartment where it resides. There is no concern with proceeding with LH2 PRSD loading.’

Another reported issue – again showing how minor the problems being worked in the pad flow are – related to a loose nut, that simply required tightening to allow PRSD loading to proceed. This process has now been completed.

‘During initial PRSD LH2 Load, a leak was detected at the LH2 sample panel on A Line B-Nut,’ noted the report. ‘During engineering walkdown of the LH2 PRSD loading system during initial LH2 flow a small leak was detected on the 155 foot level near the LH2 Low Press Skid.

‘Terminated LH2 fill and safed the system to inspect and troubleshoot the leak. The leak was coming from a loose B-nut fitting (found to be only hand tight). The B-nut was torqued and flow was temporarily resumed to check if the leak was fixed. LH2 PRSD load has resumed.’

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Other issues noted during the preparations for RSS retract included the removal of a Tyvek cover on thruster F1D, which had debonded. Also, a fastener on the Waste Collection panel was classed as missing.

The return to being on schedule was yet another fine effort from the United Space Alliance engineers, after coming out of the successful leak checks on the crew cabin pressure.

That issue was explained as debris in the affected Positive Pressure cabin Relief Valve (PPRV B). How debris managed to get into the valve will be investigated.

‘Removed pressure relief valve from vehicle and sent (away to) investigate why leaking,’ noted integration information. ‘Found contamination on valve seat about the size of a grain of rice. Will analyze to determine what it is. Must investigate how contamination got there. Valve was tight in OPF and not on pad.’

More will follow…

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