A risk-informed manufacturing influenced design framework for affordable launch vehicles
Milner, Tyler Reid
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Launch vehicle development programs have experienced significant difficulties in achieving first flight. Optimism during the initiation of these complex programs, coupled with the innovative nature of the technologies they employ, has resulted in a long list of programs unable to remain within the national means. A recent example of this challenge is the Constellation program which was canceled in 2011 due to excessive cost overruns and schedule slippage. The budgetary constraints currently placed on NASA's Space Launch System (SLS) highlights the need for a greater emphasis on affordability. Where affordability is defined in this research as the ability to remain under the mandated funding curve for all points in a system's life cycle while simultaneously meeting schedule goals given that performance requirements are met. The proposed research aims to address the gap between current practices and an affordability-centric design approach by capturing manufacturing technology effects on the affordability of the baseline vehicle concept. Historically, cost overruns and schedule slippages escalate once production begins and are only truly realized at the first launch of a system. These trends, based upon systems which leveraged traditional materials and processes, suggest a shortcoming in the ability of current practices to assess manufacturing implications during the early design phases. The advent of advanced materials and the new process required to fabricate parts from them, further challenges these practices, and threaten to exacerbate the already excessive overruns experience once production begins. Manufacturing technologies, such as composite materials, automated fabrication processes, and the use of stiffener concepts, can no longer be considered independently. This observation leads to the conclusion that improvements in vehicle affordability can only be realized by bringing manufacturing information forward into the Conceptual Design phase. The goal of this research is to support the development of affordable launch vehicles by quantitatively capturing the effects of manufacturing technology selection during Conceptual Design. A manufacturing influenced design methodology is combined with established techniques of time-phasing and risk propagation to evaluate the expected affordability of a launch vehicle baseline concept. The method is benchmarked against expected performance and affordability trends established in literature. The experiments used to build this methodology provide interesting insight into the excess risk typically carried into Preliminary Design due to a lack of the temporal nature of cost. Fundamental implications include the notion that the most expensive candidate (i.e. the highest total cost) does not correspond to the candidate with the highest annual cost insurance. Furthermore, the assessment of risk — within the traditional total cost domain — by overlaying vertical constraints onto uncertainty distributions results in the inclusion of many unaffordable candidates. The final chapter of this thesis applies the method to a relevant launch vehicle, the Exploration Upper Stage (EUS) of the SLS Block IB, which is currently in its Conceptual Design phase. This chapter compares two viable candidate manufacturing technologies based on affordability criteria established herein. The application of this methodology provides the decision maker with a significant amount of information previously unavailable and affords her additional degrees of freedom regarding appropriate Design, Development, Testing, Evaluation, and Production (DDTE&P) planning. This will ultimately enable the selection of an affordable vehicle baseline which will be robust to uncertainty in congress-appropriated funding and thus circumvent risks associated with government program cancellation.