STS-133: Discovery to undergo unique leak repair to avoid rollback
Discovery’s IPR-47 (Interim Problem Report) has become a potential schedule concern, after the replacement of a flight cap failed to stop a vapor leak in the orbiter’s aft. The leak is now believed to be in the crossfeed flange area, with the forward plan requiring the draining of the left and right Orbiter Maneuvering System (OMS) tanks and a unique in-situ repair at the pad. If repairs fail, rollback to the VAB is a threat.
(Scroll down for Tuesday mini-update).
Discovery is continuing her pad flow for the interim, with calibrations, closeouts and checkouts all taking place, ahead of the midweek effort to begin repairs on the orbiter’s troublesome leak.
“OV-103 / SRB BI-144 / RSRM 112 / ET-137 (Pad-A): S0017 Terminal Countdown Demonstration Test (TCDT) was successfully completed Friday. IMU (Inertial Measurement Unit) calibration was completed Friday night following S0017,” noted the NASA Test Director Processing report (L2) on Monday.
“S1287 orbiter aft closeouts continue. S08133 Payload Closeouts: Payload closeout operations and Payload bay door closure for flight were completed on Saturday. S1005/S1006 LOX/LH2 Dew Point Conditioning are scheduled for today. S5009 Final Ordnance Connection/Installation is scheduled for tonight. EMU (EVA Suits) checkout is scheduled for tomorrow.”
As reported by this site last week, IPR-47 was first thought to be related to a Quick Disconnect (QD) or Flight Cap, when engineers “smelt” a whiff of vapor (a fishy smell – indicating fuel vapor) coming from the aft of Discovery last Tuesday.
The suspected QD/Cap, located in the area of the crossfeed system between the two OMS Pods, was accessed by engineers via the 59-64 door – a triangular door located on the aft bulkhead of the orbiter – ahead of a weekend effort to remove and replace the flight cap and clean the AHC.
This effort was successful, with Discovery now sporting a new cap and a cleaned AHC. However, toxic vapor checks still showed signs of a leak.
With the cap and AHC ruled out as the cause, engineers pinpointed the issue to be with the crossfeed flange area, likely to be a problem with an associated seal.
“IPR-0047 update: The flight cap was removed after TCDT. The AHC was cleaned to flight requirement and a new flight cap was installed for flight. Once completed, toxic vapor checks still indicated a leak; the location of the leak has been narrowed to the crossfeed flange,” noted the NTD report on Monday.
“Engineering performed additional troubleshooting Saturday to help identify the root cause of the leakage. Based on the results, SCAPE (Self-Contained Atmospheric Protection Ensemble (suits used while performing task such as hydrazine loading)) operations will be required to drain the left and right Orbiter Maneuvering System (OMS) tanks and decontaminate the crossfeed in an effort to address any discrepancies to the internal crossfeed flange seals.”
Draining the tanks on Discovery’s OMS should not be a problem from a schedule standpoint, with around four days of contingency still remaining in the flow. However, the plan to disconnect the flange – and indeed reconnecting the flange – has never been carried out at the pad before. Such work is normally carried out when the orbiter is in the horizontal position, such as when she’s in her OPF.
Ahead of the OMS tank drain, engineers will attempt one final torque check of the flange, as noted in late processing information on Monday:
“IPR-47 work tonight includes torque check of flange, and leak checks if movement detected,” noted the update. ”Further work is in engineering review.”
Tuesday Update: However, overnight information from the NTD (L2) reported no movement was observed in the bolts (which were torqued at the “high end”, showing this is not the problem. Further Engineering Review Board (ERB) meetings will take place again on Tuesday to outline for forward plan – which will likely call for the draining of the OMS tanks ahead of the replacement of the seals on the flange.
However, notes from around 7am local point to engineers claiming the leak has vanished, after what appears to be a 100 psid increase in the crossfeed line. The verdict is this may have actually seated the primary seal. Questions remain on the status of the secondary seal, but it appears Discovery no longer has a leak.
Meetings on Tuesday call for further testing and the replacement of the primary and secondary seals - new article pending.
STS-133 Specific Articles: http://www.nasaspaceflight.com/tag/sts-133/
Should the flange repair effort fail, Discovery would – according to sources – be at risk of requiring a rollback to the Vehicle Assembly Building (VAB), ahead of undergoing demating operations from the stack, and prior to a rollback to her Orbiter Processing Facility (OPF) for repairs.
The current plan as of midday Monday is to proceed with an attempt to disconnect the flange later this week, allowing engineers to check and replace the seal, prior to attempting a reconnection, reservicing the OMS tanks and further leak checks. The leak – which is only vapor not liquid – is currently being contained by an aspirator.
“SCAPE operations will begin no earlier than Wednesday. An aspirator is in-place and will be activated to collect any vapor at the leak-site allowing work to continue in other locations around the aft of the ship,” added the NTD. “Previously scheduled work will continue through Tuesday while the test team develops procedures.”
Discovery needs to be ready to launch in the first week of November, prior to to a Beta Angle Cutout on November 8.
This is followed by a traffic jam of visiting vehicles to the International Space Station (ISS), with Dual Docked Operations (DDO) constrains from a Russian Soyuz, Europe’s ATV and Japan’s HTV – with a Year End Roll Over (YERO) constraint sandwiched inbetween.
Potential solutions to DDO constraints continue to be worked, while a mitigation plan may be available for the YERO constraint. However, failing to launch in early November would likely result in Discovery’s launch date slipping to late February, 2011 – in turn bumping Endeavour’s STS-134 mission to the summer, and the notional STS-135 flight of Atlantis to around the Fall.
“Available Shuttle Launch Window: 1-7 Nov – maximum of four opportunities. Beta angle constraints from 8-23 Nov. Dual Docked Ops (DDO) constraint from 20-30 Nov. Possible window 1-5 Dec (3 man ISS crew – substantial loss of science ops) – Not currently an option,” noted the STS-133 Space Shuttle Program (SSP) Flight Readiness Review (FRR) documentation (L2).
“Other constraints starting 6 Dec (DDO, ATV DDO, YERO, 3-angle, Node 2 nadir conflict) through 26 Feb – (the Node 2 nadir conflict is due to the docked HTV2 vehicle).”
Such a slip would be a worst case scenario, with the hugely experienced engineering teams being no strangers to challenging issues – with successful mitigation usually the outcome.
(Updates will be posted into the live coverage thread and updated into this article. Images via L2 and L2 documentation).