Just look at this beautiful shuttle External Tank! It’s the Super Lightweight Tank that was used by the Space Shuttles from 1998 on. Weighing 58,500 pounds empty, this tank is 7,500 pounds lighter than its predecessor, the Lightweight tank, and 17,500 pounds lighter than the original Shuttle External Tank.
The Super Lightweight External Tank weights 1.6 million pounds when filled with the liquid hydrogen and oxygen propellants required to power the Shuttle into space. It was built to withstand 7 million pounds of thrust exerted at launch.
NASA started using the lighter tanks in 1998 in preparation for the heavy payloads the Shuttles would be carrying during the construction of the International Space Station. Every pound taken away from the tank meant an extra pound of cargo that could be taken into space. The lighter weight also meant that the Shuttle could climb to higher orbits.
The shuttle External Tank was the only part of the spacecraft that couldn’t be reused.