The Space Shuttle experience
From a technological perspective, the Space Shuttle system represented a significant advancement in the 1970s and early 1980s. However, reasonable levels of safety and operability, suitable for commercial human spaceflight, were never realized. There were three factors that prevented this.
Design compromise by using a partially-reusable design
The first factor was that the development of the Space Shuttle system was compromised by the political choice of a partially-reusable space access system instead of the technically-preferred fully-reusable, two-stage system such as shown in the accompanying illustration. Without minimizing the significant technical challenges of developing a fully-reusable space access system with 1970s technologies, the partially reusable system brought with it a new series of technical and design challenges to be addressed.
Primary among these was that each flight involved the first flight of new (External Tank) or refurbished (Solid Rocket Boosters—SRB) flight-critical hardware. The consequence was that each mission was, essentially, a flight test of a “new” system—reusable orbiter, new External Tank, and new or refurbished SRBs. In an attempt to minimize the potential for in-flight failure, significant time and resources were used to “process” the system between missions. Mission costs exploded, mission rates never reached any semblance of commercial regularity, and mission safety and operability were significantly compromised.