notes.husk.org/likes images.

     Project Habu recently had the honor of touring behind the scenes at NASA Michoud Assembly Facility in New Orleans, Louisiana. All of the Space Shuttle External Fuel Tanks were manufactured at this site, including this tank, ET-94, the last remaining fully assembled External Tank.

     During launch, the external tank contains liquid oxygen and liquid hydrogen propellants, which are stored at −182.8 °C and −252.8 °C respectively. One of the systems in place to maintain this cryogenic temperature is the thermal protection system surrounding the tank; the orange foam that gives the tank it’s distinctive look.

     You may ask, why didn’t ET-94 fly? Some light may be shed on the subject when you learn that the tank made before this one, ET-93, flew on STS-107; the final, disastrous flight of Columbia.

     Through the whole 8.5 minute duration of launch, this external tank feeds its cryogenic propellants to the orbiter’s three main engines. Then, it drops away from the orbiter to disintegrate in the atmosphere. During that 8.5 minute ride uphill, the tank is subject to extreme vibration and aerodynamic loads. On the launch of STS-107, a 1.7lb piece of insulative foam shed from ET-93, and struck the leading edge of the orbiter’s wing, putting a basketball sized hole in a reinforced carbon-carbon panel. Days later, during reentry, superheated plasma was allowed to enter the structure of the wing, impinging upon key systems and structural elements of the orbiter, causing the vehicle to break up. This resulted in the loss of the Space Shuttle Columbia Orbiter and her crew.

     During the accident, ET-94 was at Kennedy Space Center, in the vertical assembly building, being readied for its mission. ET-94 was shipped back to Michoud, then dissected and studied during the columbia accident investigation. ET-94 never flew, but she played an extremely important role in enabling a safer return to flight and closeout of the Shuttle Program.