ET-94: Fate unknown for the last remaining External Tank at MAF

by Chris Bergin

The last External Tank, known as ET-94, has been moved into Building 103 – known as the “thru aisle” – at the Michoud Assembly Facility (MAF), with its ultimate fate hanging in the balance. The tank – which was previous in storage inside MAF’s Vehicle Assembly Building (VAB) – played a key role in the Return To Flight efforts following the Columbia disaster.

The Last Of The External Tanks:

While ET-94 will never have the opportunity to launch as part of the shuttle stack for the eight and a half minute ride uphill, its role in the Space Shuttle Program (SSP) was hugely important.

As a Light Weight Tank (LWT), its role in the upmass-hungry latter stages of the program was always highly unlikely, with Super Light Weight Tanks (SLWTs) – weighing 58,500 pounds, a 7,500-pound weight saving from the LWT version – aiding missions tasked with carry modules into orbit, for the assembly of the International Space Station (ISS).

However, due to it being the sister production tank of ET-93 – the tank that shed the chunk of Thermal Protection System foam from its bipod ramp, ultimately causing the Columbia disaster – it provided vital data into both the understanding of surprisingly complex phenomenon of foam loss and the highly successful modifications that led to vastly improved safety for the final run of shuttle missions.

While ET-94 sat around the New Orleans facility, watching brand new tanks take shape, prior to riding on the Pegasus Barge to the Kennedy Space Center, the numerous efforts to extend the Space Shuttle Program past STS-135 did – albeit slightly – raise the tank’s hopes of flying.

The discussions evaluated the timescale involved with providing ETs for STS-136 and beyond, with a tradeoff between opening with ET-94, or “simply” restarting construction of the tanks at MAF.

It was deemed that ET-94 would require a huge amount of modifications to bring it up to the post-RTF (Return To Flight) level of requirements, while the mission would also lose a large amount of payload capability when compared to a mission with a SLWT.

With parts of three new SLWTs already on site at MAF – namely ET-139, ET-140 and ET-141 – the extension studies decided on utilizing those tanks, prior to the final drive to save the Shuttle program ending last year.

All options relating to the production of additional ETs suffered heavily from the shutdown of suppliers and the loss of skilled workers over the latter years of the program, resulting in estimates that it would take a full two years, from the point of an extension being approved, before a new tank would be available at KSC for a mission.

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While ET-139 provided a test bed for work surrounding the Stringer crack issue suffered by STS-133’s ET-137 near to the end of the program, the part-built spare tanks at MAF have since been sent for scrap.

Pictures of ET-139’s parts, acquired by L2 (LINK) – show the tank had almost all of the required hardware on site, as much as it was yet to be welded together.

With those tank parts now scrapped, the giant facility is left with just a few pieces of tank hardware – mainly being used to refine measurements on new tooling – and ET-94, a tank that is yet to find out its fate.

However, on September 15, the Manufacturing Support and Facility Operations Contract team at the facility performed what was classed as the final critical lift of the Space Shuttle’s External Tank Program, as ET-94 was moved from its storage cell at the VAB to Building 103, translating it from its the vertical position, and prior to gently placing it horizontally into its wheeled carrier.

Michoud’s VAB stands 210 feet high and has served both the Apollo and Shuttle Programs. The removal of ET-94 allows for construction crews to begin modifying the VAB to install new tools for manufacture of the core stage booster of the Space Launch System (SLS). This work will begin immediately.

“It’s a historic moment and the lift team performed flawlessly,” said Robert Champion, NASA deputy director of Michoud. “This is the last external tank to leave our VAB, and while it marks the final critical lift of external tanks at the facility, it clears the way for the facility modifications needed to build the Space Launch System rocket.”

There is some hope ET-94 won’t suffer the fate of ET-139-141, with MAF noting the tank is being kept in a climate-controlled environment and “monitored to preserve it for future testing or display.”

Technically, the tank could find a role with the SLS program, previously associated with the Sidemount SD HLV option, but now potentially as part of a Main Propulsion Test Article (MPTA) during ground testing in the coming years. However, no decision has been taken on an official level.

Sources note (See L2 Link) the tank is in somewhat of a sorry state, after its umbilicals and feedlines were removed, along with large amounts of foam missing due to dissection activities.

A lot of the tank’s cable trays have been removed, and it is not clear if ET-94’s LO2 and LH2 tanks were kept pressurized during recent years, when storage requirements during the Shuttle program required both tanks to be pressurized to 6.0 PSIG, with nitrogen to keep the tanks dry internally. This may impact its ability to become a test article.

The tank now belongs to Jacobs Technology, who hold the Manufacturing Support and Facility Operations Contract at MAF, under the management of the Marshall Space Flight Center (MSFC).

Images: Via L2 content and MAF.)

(L2 is – as it has been for the past several years – providing full exclusive transition to SLS coverage, available no where else on the internet. To join L2, click here:

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