Launch vehicle reliability growth

This paper addresses the importance of considering the initial reliability and reliability growth as opposed to only the mature risk estimate when making relative comparisons among developmental launch vehicle (LV) alternatives and introduces the current model used to perform this type of analysis. Probabilistic risk assessments (PRA) often focus on modeling the mature state of a system under consideration; however, in the aerospace field of LV design such an assessment can be dangerously misleading. Due to the low flight rate, a given LV may never reach maturity prior to retirement and will fly mostly in an immature state. The historical record of early LV flights suggests a risk posture well above the mature estimate predicted through the standard PRA approach. Thus, any decision based upon the mature estimates may be significantly different than a decision based upon the predicted risk during the bulk of its useful life while it is still maturing. In order to make an informed decision about the relative merits of competing LV architectures, decision makers must consider not only the mature system risk, but also the reliability growth for the system along the path to maturity. The current model described in this paper uses a reliability growth methodology, which has expanded the scope of risk influencing factors and has been able to provided Loss of Mission (LOM) and Loss of Crew (LOC) risk estimates for over 20 LVs in a period of less than two months. The advantage of employing such a methodology to conceptual LV de signs is that it enables a more realistic estimate of campaign success during early flights without the need for detailed de sign information. This model captures the reality that element heritage and maturity are more important to early flight success than first order component reliability calculations while yielding valuable insights for designers of future vehicles.