STS-133: Several troubleshooting reviews highlight a busy flow for Discovery

by Chris Bergin

As Discovery closes in on rollover to the Vehicle Assembly Building (VAB) in just over three week’s time, engineers are working through a number of minor issues on the veteran orbiter, ranging from an O2 system Valve Position Indicator (VPI), a troublesome KU-band system, and a dent in one of her Payload Bay Doors (PLBDs) – which also requires a new Power Drive Unit (PDU).

STS-133 Processing Latest:

Discovery is still tracking a November 1 launch date target, as the complex ballet of operations focus in on the orbiter’s departure from her Orbiter Processing Facility (OPF-3) on what is currently scheduled to be September 8.

Several issues have been at the center of processing evaluations on the orbiter of late, none of which hold any major impact to her milestones during what is very likely to be her final lap of OPF processing for flight, with STS-133 scheduled to be her final mission.

“OV-103 (STS-133): Continued processing in OPF HB-3 (VAB High Bay 3). All the troubleshooting is complete on IPR (Interim Processing Report) #35 on the O2 crossover valve on the MO10W panel. This is in for final engineering review,” summarized KSC Ground Operations on the latest Shuttle Standup/Integration report (L2).

“On IPR #37 on the Ku-Band, troubleshooting wrapped up and it is in review. Looks like an EA1 (Electronics Assembly) or EA2 issue. Closed the PLBDs on Monday to facilitate the TPS (Thermal Protection System) blanket R&R (Removal and Replacement) and to do the positive pressure testing for the midbody. Completed the positive pressure tests.

“On the structures PR (Problem Report) on the door, the blanket was removed last night to perform the R&R. Small damage on the door was seen. This is being evaluated by Engineering. During door closure, there was a deferred PR on the PDU (Power Drive Unit) centerline latch, right-hand side 1-4. This ran longer than expected, so the actuator (will) be R&R’d.”

With the closure of the IPRs in work, nominal processing has continued on Discovery, via the scheduled closeouts and leak checks.

“OV-103 (OPF Bay 3): Airlock closeout for rollover was completed. The Forward structural leakage test was successfully completed,” added the NASA Test Director (NTD) processing updates (L2). “Final OPF flight controls cycling, SSME (Space Shuttle Main Engine) TVC (Thrust Vector Control) and ET (External Tank) actuator checkouts and aero-surface positioning were completed.”

STS-133 Specific Articles:

On the specifics of the IPRs, an Engineering Review Board (ERB) was in the process of discussing the O2 cross-over valve issue, thus the Orbiter hydraulic system was configured with the issue in mind to allow the aforementioned flight control final OPF cycling, SSME TVC and ET actuator checkouts and aero-surface positioning to take place.

At present, it appears the problem with the misbehaving Valve Position Indicator (VPI) on the O2 system may be closed, after it was noted it would not hold an impact to the functionality of the Atmospheric Revitalization & Pressure Control System (ARPCS).

“Valve Position Indicator (VPI) transitioned from Closed to Open when pressure was applied to the inlet of the valve and the DSC was power cycled. With no pressure on the valve, DSC cycles had no response. The valve was left pressurized and the VPI was monitored for a change in state to Open. The VPI remained Closed,” noted the NTD.

“Performed a delta pressure test and a GN2 qualitative flow test with nominal results. A deferral is being discussed since the failure would not affect the ARPCS form or function.”

Notably, it was only recently that the orbiter fleet was given the ability to sense the mechanical state of the two O2 crossover valves, via the output of the VPI. Although the valves have always had VPIs fitted, its is only since STS-128 that they have been wired into the orbiter systems – as noted in at least two expansive Program Requirements Control Board (PRCB) processing baseline presentations (L2)

Prior to this modification it was only known whether or not voltage was being applied to the solenoid actuation coils, rather than the actual mechanical position of valve internals. The resulting wiring modifications gave the ground engineers – as opposed to the crew – insight into the valve states. Changes were also made to the Launch Commit Criteria (LCC) as a result of the modifications.

Given the valve itself appears to be working properly, with only the VPI talkback no longer reliable, the situation is still slightly improved on the pre-STS-128 configuration, as the state of the other crossover valve can still be verified.

On IPR 37, Discovery’s Ku-Band troubleshooting – related to the system failing the angle rate/pitch rate portion of the self test – is coming to a close, following its constraint to final stowing of the Ku-Band antenna during PLBD closure for rollover.

“A self test was re-performed to determine if powering down the system might have reset the problem however the same error signature was seen,” noted the NTD’s summary reports. “A breakout-box was installed and another self-test was performed. Three more self tests with same results as previously. Initial data suggests failures isolated to self test mode.”

As noted by KSC Ground Operations, one of the system’s Electronics Assemblies is believed to be the root cause, with engineering reviews are in work – which includes powering Discovery up over the weekend to aid the review into the Ku-band system.

Discovery’s PLBDs were already closed – but not for rollover – earlier in the week, to allow for final TPS work and pressure checks to take place on the orbiter. Two issues arose during this operation, one of which related to a stalled PDU as the doors were being closed and latched.

“During the PLBD closure for TPS on, C/L (Centerline) latch 1-4 Power Drive Unit (PDU) stalled going latched. This was similar to the previous times this has occurred,” noted the NTD. “However, this time it occurred during a dual motor operation indicating recent degradation.

“(Program) was uncomfortable accepting this condition for another flight, and is requesting the PDU be replaced. A spare PDU is available that was recently refurbished at the NSLD (NASA Shuttle Logistics Depot). Replacement is expected to take 3 or 4 days. Deployment of the RH radiator is required for access.”

The other issue related to an observation of a dent on a Fibrous Insulation Blanket (FIB) on the Right Hand (RH) PLBD, which is undergoing replacement. Prior to the damaged blanket’s removal, engineers took mold impressions to try and find out the root cause.

“PR: A depression was discovered in the FIB of RH PLBD 1. A 4”x4” section of the FIB was removed. Mold impression indicated a graphite epoxy dent with dimensions (in inches) of: length = 1.004, width = 0.9891, and depth = 0.0406. PR is under evaluation,” added the NTD, prior to providing an update.

“Ultrasound Inspection performed on the dented area of the PLBD. A small (0.125”), localized area of delamination was noted in the bottom of the dent and is contained within the defect area. Planned repair involves face-sheet removal, probable potting, and bonding of a doubler. No thermography is required, and no constraint to PLBD opening for further processing.”

Over in the VAB, the long-running repair on a Fairing Support Plate has come to a close, following the use of a recently arrived “new” SLA (Super Lightweight Ablative) kit.

“SRB BI-144 / RSRM 112 / ET-137 (VAB HB-3): PR: Damaged SLA on EB-2 Fairing Support Plate: Will Hand Pack both inboard and outboard. New SLA kit has been ordered (and arrived),” noted a series of NTD reports. “SLA removed, found missing primer. Preps to apply primer in work.”

EB-2 is a reference to the ET/SRB upper attach point on the right-hand side of the stack, which contains a 62lb bolt that is separated when the boosters depart from the stack after just over two minutes of powered flight (Booster Separation).

“Primer application complete. SLA application next,” continues the NTD reports over the period of around a week. “SLA hand pack is in cure (midweek). SLA repair complete (Friday).”

The completion of work on the Fairing Support Plate will allow for the checks to take place on the Forward Firing Line, as the stack prepares to welcome the arrival of Discovery for mating next month.

“Aft strut and HDP (Hold Down Posts) Firing Line checks complete. Forward Firing Line checks holding for completion of PR SLA application. Left and Right GEI/Igniter heater snap hot ready to work. Left & right forward crossover installation complete. Forward firing line check complete.”

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