22.214.171.124 Results, Sensitivities, and Uncertainty Ranges
Sensitivities of vehicle cost to assumed design heritage and engineering management are shown in Figure 4.3. Clearly, DDT&E costs are significantly reduced as a result of the RBD effort, which results in a higher confidence in the RBS vehicle design as the program enters full-scale development. Potential variations in the RBS assumptions used for the NAFCOM inputs covering design heritage (design levels 1-8) and engineering management (management levels 1-5) appear to show a potential for RBS DDT&E estimates to increase by 50-100 percent, although the assumptions used for the baseline cost appear reasonable.
The engine estimates cover DDT&E and production. For the RBD, a NK-33 engine is used with Castor 30 and Star 63D solid motors in the second stage. The RBS uses five AJ-26 engines in the reusable first stage and an RS-25E engine for the expendable second stage. The reusable AJ-26 engines are assumed to be refurbished every 10 flights and replaced every 20 flights.
The models and methodologies used to generate cost estimates for the engines are contractor-proprietary. These models are generally accurate when based on similar applications, although they rely on assumptions about reusability requirements, which carry some uncertainty.
FIGURE 4.3 Sensitivities to NASA/Air Force Cost Model inputs normalized to the baseline RBS design, DDT&E program. Sensitivity of cost to the design maturity (e.g., whether or not requalification of an existing design, Requal, is needed) and Engineering Management Level needed for program execution. NOTE: DDT&E, development, test, and evaluation; RBD, reusable booster demonstrator; RBS, reusable booster system. SOURCE: Air Force Space and Missile Systems Center, SMC Developmental Planning, “Reusable Booster System Costing,” presentation to the committee, February 15, 2012. Approved for Public Release.