The Space Shuttle programme was conceived as a plan to design a spacecraft that could work as a reusable ‘space truck’. It would be used as a workhorse to provide cheap access to low Earth orbit for the US and associated partners. The main goal of the Space Shuttle was the planned construction of a United States space station in the early-Nineties. After completion of this station, the Shuttle would then be retired and replaced with a new vehicle.
Despite flying 135 missions, the Shuttle never really fully achieved its original plans, with nine flights being the most in a single year (1985) compared to the planned 50 per year. It also didn’t make spaceflight much cheaper. This, of course, was compounded by the fact that the US space station soon became an international endeavour and grew in complexity. In order to complete the International Space Station the Shuttle programme had to be extended 15 years past its scheduled lifetime.
The continuing operation of the Shuttle programme diverted funds from developing new spacecraft. So it was decided that with the support of private companies like SpaceX the programme could be discontinued, allowing NASA to concentrate on research for future deep space exploration.