Rationale and Procedures for Development of a NASA Primary Metrology Lab. for Large Optics
Theodore V. Vorburger, Christopher J. Evans, William T. Estler
Traceable optics metrology is not an expensive overhead. Rather it can improve NASA's procurement process and eliminate costly Hubble-like mistakes. Improved procurement? In deciding if a part meets specification, ISO Standard 14253, Part 1 states that the vendor must subtract the measurement uncertainty from the tolerance, ensuring that the customer always gets a good part. This process is not common in the US optics industry; indeed, we have heard of optics companies who subtract the uncertainty from the difference between the measured value and the specified value of a part rather than from the tolerance, arguing that the actual value of a parameter of a specified part must be better than the measured value. The more rigorous approach in line with the ISO standard increases the probability of shipping a part that meets or beats specification. Elimination of mistakes? Two measurements were made of the Hubble primary mirror.u^ If those measurements had been accompanied by rigorous uncertainty analyses, it would have been clear that the measured values disagreed by more than the estimated uncertainty in each measurement - automatically launching an investigation (rather than launching a flawed mirror). It is therefore in NASA's best interests to develop traceable large optics metrology capabilities and with them the culture of rigorous statement of measurement results with associated uncertainty. This report provides a preliminary roadmap toward that end.
, Evans, C.
and Estler, W.
Rationale and Procedures for Development of a NASA Primary Metrology Lab. for Large Optics, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD
(Accessed February 26, 2024)