ET-124 heads into critical flow

by Chris Bergin

The next External Tank (ET) due to be shipped to the Kennedy Space Center (KSC) has headed into its critical processing flow at the Michoud Assembly Facility (MAF).

The tank (ET-124) is behind schedule, and is required at KSC within a timeline to support LON (Launch On Need) requirements to support Shuttle Discovery’s launch, currently NET (No Earlier Than) December 7.

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ET-124 isn’t flying with Discovery, that task goes to ET-123, which is already at KSC and will be soon mated with the twin Solid Rocket Boosters (SRBs), ahead of the arrival of Discovery in the VAB (Vehicle Assembly Building) – to make up the STS-116 stack.

ET-124’s primary mission will be on the NET February 22 mission with Atlantis on STS-117. However, due to rescue mission support of her sister, Atlantis has to be on schedule for a LON date of February 9 – the current NET date for STS-317.

The tank is expected on dock at KSC by December 17, although that is currently MAF’s ET complete date, which doesn’t include the days it takes to ship the tank from New Orleans to Florida.

The smooth processing of the tank is important, especially after flexibility in the timeline is not being helped by the on-going problems with the consumables – namely the O2 supplies – on the International Space Station, which is one of the defining factors that determine the deadline for Atlantis to be ready to launch in support of STS-116 in the event of a ‘safe haven’ situation being called.

However, ET-124’s processing is progressing without any major hiccups, as MAF/Lockheed workers head into the critical flow with the final work on the tank in Building 420, Cell 2 – the final home for tanks at Michoud before departing for the space coast.

Currently, the tank has had its PAL (Protuberance Airloads) ramp removed – as per Return to Flight requirements – and work is under way to remove and replace the gaseous oxide diffuser, with preparations continuing for longeron BX265 foam spray activity, plus final primer review and application.

Fixtures and base foam on the Liquid Oxygen Tank and Liquid Hydrogen Tank is down to one inch of base foam, with the next phase to slowly remove the remaining inch of foam and conathane line.

The Intertank access kit has been installed and mechanical technicians are drilling holes to mount the camera harness installation inside the Intertank. Technicians will soon start drip lip trims. After final foam and conathane are removed, the ‘footprint’ area can be assessed for acceptability of application of Ice Frost Ramp (IFR) extensions.

The decision on the final redesign of the IFRs continues to be pushed back. Originally, NASA were expected to have the rationale on whether to leave the ramps ‘as is’ or make further design modifications last week.

However, due to a number of issues, including a fault at one of the wind tunnels where verification work has been taking place, the CDR – which will result in data being presented to Shuttle managers – has not yet taken place. November 1 is being mentioned as the new date for the CDR. 

The final outcome – according to sources – is expected to recommend that the ramps are left ‘as is’ – following the lack of foam liberation that has been observed during ascent on recent flights. However, there are rumours of a plan being in place for redesign of LH2 cable tray brackets to eliminate ice-frost ramps on in-line tanks.

The lack of foam shedding during the ride uphill has given increased confidence that NASA finally has a design that works, which aided the process of approving a return to night launches.

However, evaluations will continue, given the way foam reacts during the aerodynamic pressures of ascent is not an exact science. Only the hard data from further flights will be the defining factor, although NASA has come a long way from the worrying dissenting opinion that was seen before STS-121, where MSFC (Marshall Space Flight Center) led the protests of flying without further modifications being made to the IFRs.

The current status of the IFR redesign evaluations were noted last week on a NASA memo, which stated: ‘Still working on CDR dates for redesigned ice/frost ramp. Hope to pick dates (within days). No new data. Group from MSFC went to MAF (this past week) for discussions on MAF facility and process of controlling and granting access to personnel who want space at MAF.’

MSFC are believed to be pushing for a redesign, witha huge amount of pre-CRD documentation from the last PRCB (Program Requirements Control Board) meeting a few days ago now acquired by this site’s L2 section. An article will follow once that documentation has been evaluated.

ET-123, which will fly with Discovery on STS-116, and ET-124 are also the first tanks that have had their ECO (Engine Cut Off) sensors removed and replaced at MAF, as opposed to KSC as with the previous two tanks. ET-117 will be the next tank to head into the final processing flow at the end of the year.

Image Credit: Lockheed’s internal MS Bulletin: Technician Verna Freeman kneels to work on ET-124’s manhole cover.

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