Wikipedia
MPTA-ET
The Main Propulsion Test Article External Tank (MPTA-ET) was built by NASA to be used in conjunction with MPTA-098 for structural tests of the Space Shuttle Main Engines prior to construction of flyable craft. It rolled off the assembly line on September 9, 1977 at Michoud Assembly Facility in New Orleans, Louisiana, and was then transported to the National Space Technology Laboratories in southern Mississippi where it was used in the static test firing of the Shuttle's cluster of three main engines.