X-33: The operational challenge

In a cooperative effort with industry, NASA has embarked upon an effort to develop the next generation of reusable space transportation systems. Operational efficiency is the key attribute that will determine the economic viability of any reusable launch vehicle program. This factor not only controls the recurring cost per flight, but also determines the number of flights over which the program’s fixed cost and overhead can be amortized. A single stage to orbit reusable vehicle has the obvious advantage of eliminating expendable hardware and the need for mating stages and interface verification; however, these factors alone are not sufficient to generate the order of magnitude improvement in operational efficiency necessary to justify a new launch system. To achieve these objectives, a clear understanding is needed of the factors that have allowed aircraft to demonstrate operability and reliability levels five orders of magnitude better than launch systems. This understanding must then be reflected in analytical tools which can support detailed design trades. Even with the best of analytical environments, the difficulty in developing an operationally efficient single stage to orbit vehicle should not be underestimated. New technologies and operational concepts must be creatively combined into a design that will initially involve significant development risk. The risk derives not so much from the possibility that the goals cannot be achieved, but from the recognition that any new program with a high investment in new technology is unlikely to succeed without an opportunity to mature these technologies and to correct deficiencies in the basic design. The X‐33 Program represents the first comprehensive testbed developed for the investigation and demonstration of operational technologies and design features prior to final system design and deployment. This paper will focus on the efforts of the Aerospace Corporation to identify the factors controlling operability; develop the analytical tools necessary to quantify their impact on launch responsiveness, reliability, and maintainability; and discuss the verification of operational capabilities through the X‐33 Program.