later Shuttle missions. Discovery rockets into orbit, seen here just after Solid Rocket Booster (SRB) separation Five space-worthy orbiters were built: Columbia (OV-102), Challenger (OV-099), Discovery (OV-103), Atlantis (OV-104), and Endeavour (OV-105). A mock-up, Inspiration (OV-100), currently stands at the entrance to the Astronaut Hall of Fame. An additional craft, Enterprise