The reusable laboratory module that first flew in the shuttle payload bay on STS-9 was Spacelab.
STS-9, launched aboard Columbia on November 28, 1983, carried the first Spacelab mission. Developed primarily by the European Space Agency with NASA participation, Spacelab turned the shuttle’s cargo bay into an orbital research facility. Its pressurized module gave astronauts a shirt-sleeve workspace, while an external pallet could hold instruments exposed directly to space.
The six-person crew conducted 72 experiments during the mission, covering fields such as astronomy, atmospheric physics, solar physics, materials science, and Earth observation. The crew worked in two teams, allowing experiments to continue around the clock. Spacelab subsequently flew on many shuttle missions between 1983 and 1997.
A common mix-up is treating Spacelab as another spacecraft orbiter. It was instead a removable payload and laboratory carried inside the shuttle. Spacehab, one of the wrong options, was a later commercial laboratory module; Unity and Raffaello were unrelated station or cargo hardware.