Space Shuttle Enterprise

The real shuttle Enterprise, which flew, just not into space.

The Space Shuttle Enterprise (NASA Orbiter Vehicle Designation: OV-101) was the first Space Shuttle built for NASA. It was constructed without engines or a functional heat shield, and was therefore not capable of space operations; its purpose was to perform test flights in the atmosphere.

Originally, Enterprise had been intended to be refitted for orbital flight, which would have made it the second space shuttle to fly after Columbia. However, during the construction of Columbia, details of the final design changed, particularly with regard to the weight of the fuselage and wings. Refitting Enterprise for flight would have involved dismantling the orbiter and returning the sections to subcontractors across the country. As this was an expensive proposition, it was determined to be less costly to build Challenger around a body frame (STA-099) that had been created as a test article. Similarly, Enterprise was considered for refit to replace Challenger after the latter was destroyed, but Endeavour was built from structural spares instead.

Source: Wikipedia