Vertiflite May/June 2021

THE VERTICAL FLIGHT SOCIETY Coming to Terms

TRL vs. Readiness By Daniel I. Newman

applicability. Exploration and validation of the rest of the design space is still required, and this long slog to the corners of the operational envelope is expensive and boring. It is referred to as the Valley of Death, into which many promising technologies have fallen. It is typically hard to find sponsorship to cross this Valley, with cost rising exponentially along each TRL step. The Valley is littered with good ideas. But TRL alone is incomplete in assessing the multiple dimensions of technology that affect the ability to successfully transition. It fails to provide insight into the integration between technologies or the maturity of the whole system. To address producibility, the Pentagon developed the Manufacturing Readiness Level (MRL), from 1 “Basic manufacturing implications identified” to 10 “Full-rate production demonstrated and lean production practices in place.” The TRL and MRL are valuable, but still a broad range of metrics that are critical to successful application are not formally addressed, including durability (reliability, environmental vulnerability), supportability (inspectability, maintainability/repairability), user acceptability, sustainability, affordability and — perhaps most significant for the emerging electric vertical takeoff and landing (eVTOL) aircraft market — regulatory approvability. In 2006, Stevens Institute of Technology developed Integration Readiness Levels (IRLs) — from Level 0 “No integration” to 9 “System integration is proven through successful mission-proven operations capabilities” — and System Readiness Levels (SRLs), with SRL 1 “System alternative materiel solutions should have been considered” to 9 “System has achieved initial operational capability and can satisfy mission objectives.” Together, the IRL and SRL indices can be used to determine the readiness of systems with numerous technologies, components and integrations. These additional metrics from the systems engineering community add breadth to the maturity assessment of a technology, but they still do not formally address the “ilities” listed above, so there remains a high risk of late discovery of a critical and perhaps crippling barrier to transition. A common misunderstanding of TRL is that it somehow measures value. Specifically, it is assumed that achieving TRL 6 (“Prototype system demonstrated in a relevant environment”) indicates it will continue to development and then production. In fact, TRL is only one measure of the level of understanding. Maturity does not indicate that the technology or approach is valuable, but only that it is better understood with less uncertainty in benefits and costs. Therefore, a decision must be made whether it should be used. While many technologies fail to transition because there is no sponsor to cross the Valley of Death, often it is because it isn’t as good as originally thought or claimed. This issue specifically applies to new configurations, as well as autonomy, aircraft electrification and more. So, it applies to eVTOL aircraft/advanced air mobility (AAM), Future Vertical Lift (FVL), Clean Sky 2 and most other efforts we, the vertical flight community, are engaged in. Using TRLs to characterize technology maturity is valuable, but must be done with the understanding that it is only one of many critical metrics, and only measures uncertainty and not value.

Technology Readiness Levels (TRLs) were invented in the 1970s by NASA’s Stan Sadin to assist the agency’s space technology development process and to provide a tool to assist in communications between technologists and managers. TRL is a unidimensional scale, originally from Level 1 “Basic Principles Observed and Reported” to Level 7 “System Adequacy Validated in Space.” Over the years, it was refined by NASA’s John Mankins, adding Levels 8 and 9 to carry through mission operations, generalizing beyond space applications and adding a discussion for each level. The US Department of Defense started using TRLs in the early 2000s, and the US Air Force Research Laboratory’s William Nolte developed the TRL Calculator with more rigorous criteria for determining the TRL. The TRL scale characterizes maturation from science and technology (S&T), through research and development (R&D). Any new technology first relies on “science” that discovers the basic physics, rigorously validating and documenting the governing principles and properties. Science is assessed at TRLs 1–2, which ask “Do basic scientific principles support the concept?” Technology, TRLs 2–3, actively leverages these principles toward a specific purpose or performance metric. Technology is performed in isolation, in a controlled environment, to allow a full understanding of the impacts of key parameters (partial derivatives). Research, TRLs 4–6, then seeks to explore the technology in a particular application, characterizing the relevant features and factors in that domain. Research provides the information necessary for potential users to assess the net value of adopting the technology. Development moves a technology beyond TRL 6 and integrates with other maturing technologies to create a specific product or service. Maturing and demonstrating a technology is often done alone, with all other features and factors relying on robust understanding of the science. So, the other system elements in a research effort can be adjusted to accommodate the many needs of the “fragile” emerging technology, to achieve a successful demonstration (e.g. duct tape and putty in a wind tunnel test to get from TRL 4 to 5). Beware trying to mature multiple technologies together, though, as each is only understood within a narrow range; risk of success is amplified exponentially when multiple technologies must accommodate each other. Research is hard enough but maturing two “problem children” at once may prove insurmountable. Each step in the advancement of a technology is costly and takes time, as the breadth of the exploration widens and the number of factors to consider expands, and the requirement for the burden of proof rises exponentially with more sophisticated stakeholders with specific agendas to satisfy. The initial technology demonstration of a single point in the design space is very exciting and noteworthy, but should not be accepted out-of-hand as proof of This series addresses the uses of terminology that threaten to become routine expressions or idioms — or already are — but are misleading or erroneous. Here, we look at the misconception that a high TRL means a technology is ready for production.

May / June 2021

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