Editing Space Shuttle external tank (section)

===Lightweight Tank===
[[Image:Externaltank.jpg|thumb|The [[Space Shuttle]] external tank for [[STS-114]] on its way to the [[Vehicle Assembly Building]]]]
Beginning with the [[STS-6]] mission, a lightweight ET (LWT), was introduced. This tank was used for the majority of the Shuttle flights, and was last used during the launch of the [[Space Shuttle Columbia disaster|ill-fated]] [[STS-107]] mission. Although tanks vary slightly in weight, each weighed approximately {{convert|30000|kg|lb|order=flip}} inert.

The weight reduction from the SWT was accomplished by eliminating portions of stringers (structural stiffeners running the length of the hydrogen tank), using fewer stiffener rings and by modifying major frames in the hydrogen tank. Also, significant portions of the tank were [[milling machine|mill]]ed differently so as to reduce thickness, and the weight of the ET's aft [[Space Shuttle Solid Rocket Booster|solid rocket booster]] attachments was reduced by using a stronger, yet lighter and less expensive [[titanium]] alloy.