Manufacturers lack an adequate method to balance performance, reliability, and affordability. The reliability-asan-independent-variable methodology is the solution proposed by expressing quantitatively the reliability trade space as ranges of a number of hardware sets and a number of hot-fire tests necessary to develop and qualify/certify a liquid rocket engine against a stated reliability requirement. Therefore, reliability-as-an-independent-variable becomes one of the key decision parameters in early tradeoff studies for liquid rocket engines because the reliability trade space directly influences the performance requirements and, as a result, the affordability. The overall solution strategy of reliability-as-an-independent-variable is based on the Bayesian statistical framework using either the planned or actual number of hot-fire tests. The planned hot-fire test results may include test failures to simulate the typical design-fail-fix-test cycles present in liquid rocket engine development programs in order to provide the schedule and cost risk impacts for early tradeoff studies. The reliability-as-an-independent-variable methodology is exemplarily applied to the actual hot-fire test history of the F-1, the space shuttle main engine, and the RS-68 liquid rocket engine, showing adequate agreement between computed results and actual flight engine reliability.

No abstract

No abstract

No abstract

Rocket propulsion systems belong to the most critical subsystems of a space launch vehicle, being illustrated in this paper by comparing different types of transportation systems. The aspect of reusability is firstly discussed for the space shuttle main engine, the only rocket engine in the world that has demonstrated multiple reuses. Initial projections are contrasted against final reusability achievements summarizing three decades of operating the space shuttle main engine. The discussion is then extended to engines employed on expendable launch vehicles with an operational life requirement typically specifying structural integrities up to 20 cycles (start-ups) and an accumulated burning time of about 6,000 s (Vulcain engine family). Today, this life potential substantially exceeds the duty cycle of an expendable engine. It is actually exploited only during the development and qualification phase of an engine when system reliability is demonstrated on ground test facilities with a reduced number of hardware sets that are subjected to an extended number of test cycles and operation time. The paper will finally evaluate the logic and effort necessary to qualify a reusable engine for a required reliability and put this result in context of possible cost savings realized from reuse operations over a time span of 25 years.