ECO change-out – no easy process

by Chris Bergin

More information has come to light on the intriguing process that will be undertaken by Lockheed and United Space Alliance techinicans on ET-119.

Workers will have to build a climate controlled tent around the aft dome section of the tank, as they change-out faulty ECO (Engine Cut Off) sensors, a process that recieved NASA management approval today, delaying STS-121 to July, as exclusively revealed by this site.

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Currently a 17 day process – as per work schedule if all goes to plan – technicians will begin work on the tank with a ‘foam dig’ – where insulation foam surrounding the aft dome access door is removed from the tank.

Before entering the tank, a climate control tent will surround the whole aft section of the tank, with the aim in creating a ‘particulate free environment’ – a process made more difficult by work currently being carried out on the Vehicle Assembly Building (VAB) roof and doors. It’s not clear if that work will be halted during this process.

Lockheed specialists will then work on replacing the ECO sensors, likely to be all of the LH2 sensors. Certification work will be carried out on the new sensors before the more complicated process of foam re-application begins.

It is vital that the clean room environment is adhered to around the tank, with the risk of contamination damage to the inner workings of the tank being avoided at all costs.

Once satisfied the ECO sensor problem has been fixed, workers will carefully lift the tank – still with large areas of its aft dome missing insulation foam – on to the transporter it arrived in the VAB with, using a VAB crane and lanyards.

This process will also be critical, following an incident with ET-121, which was cosmetically damaged by a loose lanyard last year.

One safely removed from the checkout cell into the VAB transfer aisle, the tank – now horizontal – will undergo closeouts and foam re-application. This transfer has to take place as Lockheed don’t have a process of foam application for the aft dome of the ET in the vertical position.

Once work is completed, the tank will once again be moved into the vertical, placed back in the checkout cell, and will undergo the same testing that initially confirmed a phase shift with an LH2 ECO sensor. 



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