STS-115’s launch date could slip, should NASA fail to find a solution to the continuing problems with ET-118, which is having processing issues at the Michoud Assembly Facility (MAF) in New Orleans.
A series of high level teleconferences took place over the weekend, as concerns grow over the evaporation of contingency days for the second launch of 2006, set to see Shuttle Atlantis re-start International Space Station (ISS) assembly missions.
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Sources indicate that the delay noted at Thursday’s PRCB (Program Requirements Control Board) meeting left engineers with just ‘a handful’ of contingency days in STS-115’s flow for the STS-300 (Launch On Need) requirement, with further delays due to unknown closeout problems – noted the following day – now threatening the planned launch date for Atlantis’ primary mission.
At present, Discovery’s second test flight mission STS-121 is not believed to be threatened, due to a fluid CSCS (Contingency Shuttle Crew Support) date which has consistently expanded on recent manifests – in the highly unlikely event the crew of STS-121 require rescuing from their ‘Safe Haven’ of the ISS by Atlantis.
Already, NASA is working on reducing the delays incurred by ET-118’s completion, as they focus on getting the tank over to Florida.
One possibility that has been discussed consists of shipping the tank before its ECO (Engine Cut Off) sensors have been replaced. This now appears to be set and may allow for the shipping of the tank this week, as re-planned via Thursday’s PRCB, minus ECO sensor R&R and various closeout work.
This would also involve the R&R work being speeded up, faster than the process seen with ET-119’s ECO sensor R&R – which involved moving the tank from the vertical, to the horizontal for the R&R work involving closeout of the TPS (Thermal Protection System) foam around the manhole access hatch at the aft of the tank, and back to the vertical for transfer to its mating with the twin solid rocket boosters.
‘After ECO Sensor R&R, the ET is required to be lifted out of the ET cell and placed on the transporter to perform AFT closeouts (Horizontal) KSC requested the closeouts be performed while the tank is still in the ET cell (Vertical),’ noted a United Space Alliance document, dated June 1, and presented to the PRCB meeting of that date. ‘Process saves one ET lift.
‘Schedules have been refined to optimize the work in the ET cell prior to placing the ET on the transporter. Closeouts performed in the ET cell save two days to the schedule, these are the days required to lift and place the ET on the transporter. Risk assessment was performed for ET-119 ECO R&R. The ET-118 horizontal closeout will be the same, and previous risk assessment applies. Vertical and horizontal TPS closeout risk assessments are green.’
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Lockheed/MAF technicians would need to travel to the Kennedy Space Center, as they did for ET-119’s ECO sensor R&R. While special scaffolding constructed for worker access inside the Vehicle Assembly Building (VAB) won’t be required for vertical work, the special tent and platforms will be required to keep a clean room environment. NASA is confident this can be done, as they recommended:
‘KSC can support closeout (both) in the ET cell (vertical) or in the transfer aisle (horizontal). We would prefer vertical to save the extra ET move and 2 day schedule impact, but understand the challenges MAF has to validate a vertical closeout.’
MAF (Michoud Assembly Facility) are understood to have approved this ‘vertical closeout’ procedure over the weekend, especially in light of their consistent objection to an alternative option on saving processing time with the tank, omitting the ECO sensor replacement. MAF fear that would add fuel to the debate on whether to revert to a 3 out of 4 LCC (Launch Commit Criteria) on the ECO sensors – something that has already been rejected by Shuttle managers for STS-121.
Acquired documents note that around 30 days will be required by technicians to replace the LH2 ECO Sensors on ET-118 in the VAB – with one document noting the process (as of Thursday) would be completed on July 10. That date is understood to have slipped yet further.
Another reason noted for the ECO sensor R&R work to be moved to KSC is the growing issue of STS-115’s supporting LON mission, currently tagged STS-301 with Discovery – ahead of her primary mission at the end of the year with STS-116. STS-301 will revert to STS-300 once Discovery’s STS-121 mission has stood down the rescue requirement whilst in orbit.
STS-301 will use ET-123, and concerns with that tank’s processing have been voiced by MAF for some weeks. ‘All hands’ were moved to deal with ET-118’s processing delays, to the detriment of ET-123. Contingency plans are being drawn up by ET managers, with large amounts of work yet to be started on that tank.