With the STS-122 astronauts in attendance at the Kennedy Space Center (KSC) for the Terminal Demonstration Countdown Test (TDCT), engineers have taken the opportunity to present Atlantis’ engineering flow overview to the crew that will fly onboard her in just over two weeks’ time.
The TDCT was completed on Tuesday, but not before the crew were given a full run down of Atlantis’ processing flow and modifications since her last flight – STS-117.
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Classed as part of the TDCT, the crew were presented an overview of significant issues that have been encountered by KSC Engineering during ground processing and testing of Atlantis, ahead of what will be her 29th flight.
STS-122 was set to be her last flight to the International Space Station (ISS), though managers will soon make the official announcement that she’ll gain two additional missions, following her trip to service the Hubble Space Telescope this summer on STS-125.
Shuttle crews have always taken an interest in the processing flows of the orbiters they are scheduled to fly on, which includes special trips from their home base in Houston to visit the orbiters and their engineers inside the Orbiter Processing Facilities (OPFs).
However, given the rigorous training (crew loading) schedule the astronauts undergo in preparation for their mission, NASA and the United Space Alliance (USA) compile an overview, for presentation at their TDCT, allowing them to review the flow’s highlights.
‘Because of the amount of work accomplished during an Orbiter flow, only those items which are thought to be of interest to the crew are included herein,’ noted the 34 page presentation (available on L2).
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The presentation outlined each system with significant issues or modifications during the post flight STS-117 and pre flight STS-122 flow, including IFAs (In Flight Anomalies) from the last shuttle mission (STS-120) that have implications for the STS-122 mission.
It also contains major system problems that occurred during Atlantis’ turnaround testing, significant system modifications that have been implemented on Atlantis during this flow, and a brief description of any Unexplained Anomalies (UAs) that have been documented.
While the various Flight Readiness Reviews (FRR) concentrate on the finest detail of the hardware, the flow overview is a fast track review of processing notes, along with various waivers that were produced throughout the flow.
‘Problem: The APU (Auxiliary Power Unit) 1 exhaust duct was inadvertently overpressurized during ground testing; duct is not supposed to be pressurized above 30 psia, but duct was subjected to an estimated 32 psia,’ noted one example.
‘Resolution: Exhaust duct subsequently leak checked at correct pressure and leakage rate found to be within specification. Waiver approved to accept the over-pressurization condition. Impact to this flight: None.’
‘The Gas Generator Valve Module (GGVM) Heater modification was implemented on all three of Atlantis’ APUs this flow. This mod was implemented to replace the function of the original, internal A/B GGVM heater assembly (the B heater could short out and quit working),’ noted another example, classed as a significant modification.
‘Internal heater still present but no longer powered. Mod was installed without removing the APUs from the vehicle. Retest of the modification was successfully completed. Former flight restriction to use ‘A’ heaters only being lifted.’
The rationale for producing a flow overview for the crew is in evidence via reported issues, with the information providing the astronauts with a solution, should – in the unlikely event – the issue relate to a problem on orbit.
The O2 System 1 relief valve poppet does not fully seat at the OMRS (Operational Maintenance Requirements and Specifications) specified pressure of 205 psig resulting in out-of-spec leakage of 14 SCCMs (10 SCCMs allowable),’ noted the presentation, accompanied by a schematic overview of the area in question.
The Relief valve design utilizes a helical/Belleville spring and an elastomer valve seat. Deformation of the poppet, seat or spring or the possible contamination could result in the poppet not sealing fully at OMRS-specified pressure.
Condition accepted ‘as-is’ for flight based on the following: Normal system operating pressure is 100 +/- 10 psig. The leakage only occurs after RV has been subjected to its cracking pressure (approximately 235 psig) after which the valve fully seats with zero leakage at approximately 194 psig.
‘Impact to flight:
None anticipated. Operation of N2/O2 revitalization system is unaffected. If leakage were to worsen dramatically (was stable throughout troubleshooting), have option to isolate the O2 System 1 leg. Even with leakage, system could still be utilized if required as there would be no loss of O2 consumables because the valve relieves into the cabin.’
Replacements for certain hardware on Atlantis is also noted, as seen with the changeout of two Master Event Controller (MEC) elements, due to the concern, noted last year, with ‘tin whiskers’ – which are small slices of metal which can fall off on to the circuit boards, which could cause shorts in the orbiter’s electrical components.
‘Atlantis will be fly a mixed configuration of MECs this flight. STS-117 flew with EMECs in both locations, but both were replaced with AMECs early in the STS-122 flow due to EMEC tin whisker concerns,’ noted the presentation.
‘Subsequently, the new MEC 2 was replaced again with a screened EMEC due to concerns over AMEC card retention and possible voltage spikes on command lines that has been observed on some units. A special test was successfully performed on the installed AMEC (MEC 1) to verify functionality and acceptability for flight.’
As noted in processing information since Atlantis arrived in the Vehicle Assembly Building (VAB) – and after rollout to Pad 39A – the ET Digital Sep Camera, which includes a new ET Umbilical Camera Flash (Sync Cable and Flash) modification for improved imagery of the expended External Tank (ET) after separation on orbit, has been troublesome.
‘During OPF troubleshooting of the in-flight problem, were initially unable to establish any communication between the CM PGSC laptop and the digital camera. Although communication was eventually re-established, no definitive cause of the initial failure was determined and this problem was closed as an Unexplained Anomaly (UA).
‘Since going vertical, picked up another problem: are unable to consistently and reliably download all pictures/data from camera. Unknown, suspect intermittent problem with PGSC fire wire card or Kodak Camera Manager software initialization. Troubleshooting involved a variety of PGSC/cable/converter combinations in an attempt to isolate the problem.’
As explained to the crew, this issue is still undergoing evaluation by engineers at the Johnson Space Center (JSC), although it is not a constraint to flight.
Unknown issues, found with the Ku-band antenna during STS-115 and STS-117 (both with Atlantis) are also noted by the presentation. Though it has no mission impact, the crew were informed that Mission Operations Directorate (MOD) will create work-around steps, should it reoccur during STS-122.
‘During the STS-115 and 117 missions, Ku-band angle tracking dropped lock and returned to designated angles before reacquiring TDRS (Tracking and Data Relay Satellite) – required for live video on orbit. Cause is unknown. Ground testing has not isolated any failures within the hardware; MOD cannot correlate the events to blockage.
‘Performance will be monitored throughout the mission. No mission impact is expected. Frequency of events decreased from STS-115 to STS-117. Should angle-tracking errors occur during flight, work-around steps will be invoked by MOD.’
The best known issue from STS-117 – which required a level of OPF processing – related to the protruding piece of blanket on Atlantis’ port OMS (Orbital Maneuvering System) Pod.
This required an EVA repair, one that proved highly successful in protecting the underlying structure from any issues during re-entry, and from any extended repairs back in the OPF.
During Atlantis’ processing flow, new replacement tiles and blankets were installed over the pod, reducing the chances the same problem will reoccur during STS-122.
During STS-117 ascent the forward edge of a LOMS pod thermal blanket came loose.
‘Cause: Height difference between blanket and adjacent leading tile,’ noted the presentation.
: For STS-117, an EVA was performed: the blanket edge was tamped down by hand and pinned to adjacent tile. After flight, blankets/tile were removed and new ones installed using new criteria to lessen chance of similar occurrences in the future.
‘All new installation FIB were bonded to the adjacent tile to prevent a peeling/lifting effect that would cause the FIB to become debonded.’
Next up for Atlantis is the Agency level (SOMD) Flight Readiness Review at the end of the month, which will confirm the launch date for STS-122.
Should stage work on the ISS continue at the current pace – with EVA-11 completed today, and EVA-12 to come – shuttle managers are likely to give a green light for December 6, in a launch window that only extends to December 13.
This will be a major achievement, following the eventful second half of the STS-120 mission, which challenged the ISS timeline in preparation to receive the Columbus module from Atlantis’ flight – the fourth shuttle mission of 2007.
L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.
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