Which company built the Space Shuttle orbiters in Palmdale, California?

Rockwell International built and assembled the Space Shuttle orbiters in Palmdale, California.

Rockwell served as the orbiter’s prime contractor under NASA’s Space Transportation System program. Its facilities and subcontractors produced major sections in several locations, including the forward and aft fuselage, crew cabin, thermal-protection components, and payload-bay doors. Final assembly and testing took place at Air Force Plant 42 near Palmdale.

The word “built” can cause confusion because Rockwell did not manufacture every component itself. Grumman produced the wings, Fairchild supplied the vertical stabilizer, and other companies built the mid-fuselage, propulsion hardware, and maneuvering-system components. Rockwell coordinated these contributions and brought the completed orbiters together.

North American Aviation was the original orbiter contractor, and its space division later became part of North American Rockwell and then Rockwell International. That corporate history explains why older references may use North American or North American Rockwell instead of the name in this answer.