Why the X-33 Venturestar Gave SSTO a Bad Name

Abstract

The X-33/Venturestar program was initiated by NASA in 1995 to develop a technology maturity demonstrator that would give future entrepreneurs the confidence that the technologies required for a commercially-developed Single Stage To Orbit (SSTO) vehicle were sufficiently matured to permit successful development to start by about 2000. The X-33 prototype was to demonstrate these maturities through a brief series of flight demonstrations. The Lockheed X-33/Venturestar concept was selected to fulfill this role. Taking note that the “Prime Directive” for designing an SSTO vehicle is to “keep the weight out,” the resulting X33 design that consisted of side-by-side tanks (2 hydrogen and 2 oxygen) plus an aeroshell to form the external shape clearly violated this rule. The failure of this design approach has had the residual effect that SSTO concepts are not viable. How did this happen? We have to go back to the beginning to the mid-1960s and a prophetic conversation by the author with a Lockheed person in the early 1990s. Lockheed had embarked on a continuing series of studies featuring side-by-side and nestled tanks that were reported periodically during that same period. This design path evolved to the X-33/VentureStar vehicle concept with the inherent design deficiencies. Thus, the X-33/Venturestar concept was doomed to failure as an SSTO at the outset. The eventual tank manufacturing problems only rang the final bell.