The Space Architecture Failure Evaluation (SAFE) tool enables probabilistic risk assessment (PRA) of mission, vehicle, and crew risk for space transportation vehicles. A Technology Development Risk Assessment (TDRA) tool is currently being developed to estimate the risks associated with technology maturation projects.
NASA Ames Research Center has addressed the need for conceptual-level risk assessments of exploration systems by creating software tools in multiple areas and adding new risk assessment capabilities for the competitive portfolio selection process.
Software tools have been, or are being, developed at Ames Research Center to facilitate the inclusion of probabilistic risk assessments (PRA) early enough in the program lifecycle to impact the final outcome. The elements of the software focus on physical risk and technology development risk.
Caption: Figure 1. SAFE execution overview.
The Space Architecture Failure Evaluation (SAFE) tool is a PRA tool which addresses the physical risk of the space transportation system. SAFE performs Monte Carlo simulations of a system through its operational phases. The system is represented by its risk driving components and a schedule of the state of the system. These components, along with a failure database developed as part of the tool, (Figure 1) enable calculation of mean failure probabilities, uncertainty estimates, identification of the relative risk contribution of the systems, and generation of risk intensity plots. The results allow designers to quickly identify high-impact areas for re-design or possible mitigation. Because the architecture is represented by its risk drivers, it is possible to perform high-level trades before all of the design details are finalized, impacting the design early enough to make changes if needed.
SAFE has been used to compare the risk impact of engine technologies for the Space Launch Initiative (SLI) Program. It has also been applied to guide the high-fidelity simulations in the Computing, Information and Communications Technology (CICT) Abort Grand Challenge Project.
Figure 2 shows the results of a SLI engine technology risk assessment. First, the overall system risk was computed, then the primary risk drivers were decomposed far enough to enable differentiation of technology development efforts. The figure shows the relative risk reduction of six engine technologies. These results are then rolled back up to determine an overall system risk impact.
SAFE-R (reduced) is a desktop version of SAFE complete with a graphical user interface. SAFE-R performs mean risk calculations from a small set of user inputs. It is very useful for rapid, high-level trades.
The Technology Development Risk Assessment (TDRA) tool is currently being built to estimate the likelihood that a technology development project successfully meets its milestones. TDRA represents technology maturity using the Technology Readiness Level (TRL) scale. The probability that a technology will evolve up the TRL scale is calculated as a function of time and budget for each technology sector.
Caption: SAFE sample results (left) and TDRA process overview (right).
The calculations are performed using a Markov-Chain Monte Carlo model. The model derives baseline TRL transition probabilities from heritage data of similar systems and supplemented by a formal expert opinion solicitation process. The baseline probabilities are modified to reflect funding levels, specific technical difficulties, and management philosophy. An overview of the TDRA process is shown in Figure 3.
The tool will be used to add a development risk metric to the overall assessment of a technology project. TDRA is currently under development.Background
Historically, the determination of a technology development portfolio was driven by technologies which promised increased performance of a system. Recently, risk has been added to the metrics which determine the overall value of a technology to a program.
Risk has several aspects relating to technology development. First, there is the physical risk which is manifested as a lost mission, vehicle, or crew. The consideration of an increase or reduction of the physical risk is of paramount importance to a successful development effort. Also, the technology development risk is important to determine the feasibility of the promised performance benefits. This metric measures the probability of a technology successfully maturing toward an operational state as a function of time. This relatively new quantitative metric is useful when selecting a technology suite in which to invest.
Teams at NASA Ames Research Center have been addressing the need to include both of these elements of risk analysis early in the system lifecycle. Software tools have been built to predict physical risk and are in the works to estimate the development risk of a technology project.