It may not look like much more than a strangely shaped hunk of metal, but this contraption was a key part in paving the way for NASA’s Space Shuttle program. It’s one of only three listed Space Shuttle test articles today.

The Main Propulsion Test Article 098 (MPTA-098) was a testbed for the United States shuttle program. It was built with a complete Space Shuttle Main Engine (SSME) assembly and used in combination with the Main Propulsion Test Article External Tank (MPTA-ET).

Having overcome two major failures, the MPTA-098 went on to have a number of successes. What is perhaps its biggest moment of glory took place with just three months to go before the big launch of Space Transportation System-1 (NASA’s Space Shuttle program’s first orbital spaceflight). On January 17, 1981, MPTA-098 fired for 625 seconds, doing everything needed to get the SSME cleared to fly. This amazing achievement cleared the way for the first space shuttle launch on April 12, 1981.

Yet despite this accomplishment, the MPTA-098 went unused again until 1988. Late into 1988, it was revived to help develop the then-proposed Shuttle-C Vehicle. However, the body became disassembled in 1990 after the Shuttle-C program was cancelled.

Now on display (though without a sign so you have to know what to look for) at the U.S. Space and Rocket Center, it can be seen without truss work, near the MPTA-ET and one of the other three Space Shuttle test articles, the Space Shuttle Pathfinder.