Atlantis’ ET arrives ahead of STS-117

by Chris Bergin

The External Tank for the next shuttle mission has arrived at the Kennedy Space Center (KSC), ready to fly with Atlantis on STS-117, which is currently set to launch in March. 2007.

ET-124 has now been secured in the Checkout Cell in the giant Vehicle Assembly Building (VAB), as NASA and the United Space Alliance build towards the busiest launch schedule for the shuttle since 2002.

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STS-117 will follow along a similar path to Atlantis’ previous mission, STS-115, installing a pair of giant solar arrays and the starboard integrated truss segment, making up the elements of the S3/S4 truss assembly. STS-115 installed the twin P3/P4 truss assembly back in September.

Once again, workers at the Michoud Assembly Facility (MAF) in New Orleans managed to turnaround a tight processing flow to ship the tank within a few days of schedule, in time for what would have been LON (Launch On Need) requirements on LON-317. That rescue mission requirement was stood down, following the hugely successful conclusion to STS-116 with Discovery this month.

Just prior to departure from MAF, a NASA memo noted that the ET would not be immediately unloaded from its barge, due to the Christmas holidays, but with all element of STS-117’s processing in a smooth flow, this holds no issues for the continued drive forward to the first mission of 2007.

‘On ET-124 transport, the barge and tug are at MAF,’ noted the final Shuttle Stand-up/Integration report of the year. ‘The tug company does not work on Christmas, which would put the tug in the turn basin on December 27th.’ The tank made it into the VAB on Saturday.

Atlantis’ tank was set to be the first to have up to four of its Ice Frost Ramps (IFRs) modified in order to reduce the risk of foam liberation during ascent. However, the November Critical Design Review (CDR) concluded that the performance of the tanks on recent missions – added to some inconsistent wind tunnel results on the redesigned IFR – allows for the current design to remain in place for the interim.

However, it is expected that NASA will still go ahead with a redesign of the ramps, but such efforts will now be targeted for the launch prior to the flagship mission to service the Hubble Space Telescope on STS-125.

‘We’re looking at it pretty closely, but I think we’d like to make some changes,’ said Associate Administrator for Space Operations, Bill Gerstenmaier. ‘We’d really like to get some foam off the tank, because you then don’t have to worry about it.’

The insulating foam on the outside of the tanks has been one of the major challenges for NASA since the loss of Columbia in 2003. While the agency has made huge strides towards reducing foam shedding during ascent, eliminating certain areas of foam from the tank in the first place has proved to be the best solution, as has been the case since the removal of the Protuberance Air Loads (PAL) ramps, post STS-114.

‘Foam is a very difficult material to control, so the way you apply it on the tank is very dependant on the conditions it gets sprayed on,’ added Gerstenmaier. ‘So we’d really like to get rid of some foam – and we’re looking to making another change to the Ice Frost Ramps which will remove 17lbs or so of foam.’

The CDR decision to push back the redesign of the IFRs has also aided the processing flow at MAF, which recently decided to place ET-120 back into the tank manifest to allow the facility to remain on track with the current shuttle manifest.

This delay to the redesign will allow MAF to work on being prepared to hit the ground running with the modified ramps, currently targeted for ET-128 onwards.

‘We want to continue with that redesign. Our goal is to get that in place for ET-128, which is one tank in front of the Hubble mission, so that we get to see the design perform before we then take that tank on the Hubble mission,’ said Gerstenmaier.

‘We think that is the right thing to do. We’ve focused our efforts to go do that and get the foam off the tank as the right overall design decision. But we’ll continue to let the data drive us (on decisions).’

Meanwhile Michoud are continuing to work on the next two External Tanks that are due to be shipped to KSC in 2007, namely ET-117 – for Endeavour’s STS-118, her first flight since coming out of a major modification period, and ET-125 – the second mission of 2007 for Atlantis on STS-120

‘ET-117 (next tank) processing is on schedule. Primary efforts are TPS removal and readying the tank for RTF mod,’ added the Stand-up/Integration report. ‘ET-125 (next tank after ET-117) was loaded into Cell A (vertical assembly building) last week (mid December). Should be moving forward on flange modification.’

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