The case for the evolution of the Shuttle system

Examining the expendable and reusable space transportation systems currently in use, it appears that the service life of a launch system, with periodic upgrades, can be 30 to 40 years. It is also evident that both reliability and performance increase with flight experience. With a life expectancy of at least 30 years, the Shuttle system is today only in the first third of its potential service life. This paper addresses the issues of why Shuttle evolution is warranted, how the evolutionary process is managed, and how that process can improve system performance and reduce costs. Specific examples of enhancements currently under consideration are presented and discussed in terms of their relationship to the achievement of greater inherent reliability in the Shuttle system.