Review of the Constellation Programís Request to Discontinue Using the Metric System of Measurement

Status Report From: NASA Office of Inspector General
Posted: Monday, March 29, 2010

image The Office of Inspector General (OIG) examined the Constellation Program's draft request to reverse its 2-year-old decision to implement the metric system (also known as the International System of Units or SI) as its standard system of measurement and instead use the U.S. customary system (e.g., feet, pounds, ounces). Our objective was to assess the basis for the Constellation Program's request to NASA's Chief Engineer for an exception to NASA's policy that requires use of the metric system in Agency programs. In addition to examining this specific request, we considered the possible long-term impact on other NASA projects and the Agency's efforts to expand use of the metric system if the exception was granted, which appears likely. Details of the review's scope and methodology are in Appendix A.


We concluded that the Constellation Program's request for an exception to using the metric system as its standard system of measurement does not clearly meet NASA criteria for granting such an exception. In addition, the request does not adequately consider the long-term impact of the decision on future NASA projects.

Specifically, we found that the Program's draft request for an exception to using the metric system does not meet the criteria for exceptions under NASA Policy Directive (NPD) 8010.2E "Use of the SI (Metric) System of Measurement in NASA Programs," March 4, 2007 (see Appendix B). The request from Constellation Program officials suggests that implementing the metric system is impractical and its use could increase risk and threaten mission success. However, we found conflicting documentation attesting to the practicality of implementing the metric system as the primary system of measurement in the Constellation Program. In addition, other Constellation Program documentation we reviewed refutes the suggestion that implementing the metric system would increase risk in this Program. We also found that neither the Constellation Program nor the NASA Chief Engineer has fully assessed the long-term impact on the Agency of moving away from use of the metric system.

We also found that NASA's written policy directing use of the metric system in Agency programs is deficient in several respects. First, NPD 8010.2E does not define the term "adds unacceptable risk," which leads to differing interpretations of the risks that programs can cite when seeking an exception to using the metric system. Second, the NPD does not provide a mechanism for exceptions to be reevaluated in the event new projects are added to an exempt program or improvements are made in the availability of metric-measured parts. A previous OIG report recommended that approved exceptions should not be "open-ended," but rather reviewed approximately every 5 years to see if conditions underlying the rationale for the exception had changed. Although NASA management agreed with this recommendation and stated that the pertinent NPD would be modified to "require reassessment of opportunities and rejustification of program-wide waivers where still required, at least once every 5 years," the current version of the NPD does not contain this requirement.

During our fieldwork, NASA's Chief Engineer told the OIG that he planned to approve the Constellation Program's request for an exception based on the additional costs required to implement the metric system, which Constellation Program officials estimated at $368 million. These implementation costs arise mainly from the reuse of hardware and software from previous NASA programs, including the Space Shuttle, that did not use the metric system, thus requiring revisions to engineering documents, test plans, test equipment, facilities, training, and operations. According to the Chief Engineer and Constellation Program management, the estimated $368 million for metric system implementation would be better spent on mitigating higher priority Program risks.

We found that because the Department of Defense (DoD) has not fully embraced the metric system as the manufacturing standard in its projects, and because of the size of its contracts, DoD exerts an overriding influence on the U.S. aerospace industry. NASA officials stated that until DoD begins converting its major programs to the metric system, NASA will not be able to easily transition to the metric system due to a lack of aerospace parts designed in metric units.

Full report

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