The International System of Units (SI: based on the French term SystÃ¨me International d'UnitÃ©s) is the internationally recognized metric system. Its base units of measure are: meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electrical current, kelvin (K) for thermodynamic temperature, mole (mol) for amount of substance, and candela (cd) for luminous intensity. On the other hand, the system of measurement used in the United States is called the U.S. customary units or English units or standard units. Miles, feet, yards, and inches are all terms used to denote length in the U.S. system.
In actuality, NASA, itself, has primarily used the metric system since 1990. However, many U.S. aerospace companies still use English units when building hardware or developing software. Because of this situation, NASA has experienced problems in the past. For example, it lost its Mars Climate Orbiter in 1999 when a government contractor provided NASA with thruster data in English units (pounds-force) instead of metric units (newtons) that was used by the spacecraft. Shortly after the disaster, Edward Weiler, NASA’s Associate Administrator for Space Science said, “The problem here was not the error, it was the failure of NASA's systems engineering, and the checks and balances in our processes to detect the error. That’s why we lost the spacecraft.” Thus, a benefit for going totally metric is to minimize such costly and embarrassing moments.
The Vision for Space Exploration is the NASA (National Aeronautics and Space Administration) plan to return astronauts to the Moon by the year 2020 and to eventually set up a lunar base on the Moon’s surface. Beginning in April 2006, a series of meetings between representatives of NASA and thirteen other space agencies around the world decided that it would standardize its use of measurements—going completely with the metric system.
The fourteen countries or regions in the world with space programs that participated in these meetings and have interest in exploring the Moon are: Australia, Canada, China, European Space Agency, France, Germany, India, Italy, Japan, Russia, South Korea, Ukraine, United Kingdom, and United States.
Jeff Volosin, strategy development representative for NASA’s Exploration Systems Mission Directorate, stated recently about the decision to convert to the metric system and the interaction between NASA and the other space agencies: “Of course there’s some competitiveness and national pride involved, but we want to find areas where our goals overlap and see if cooperating in certain areas would be best for everyone.”
With the Moon being converted to the metric system, the same situation, unfortunately, still exists on the Earth. The United States, Myanmar, and Liberia still do not use the metric system while every other country does. SI units are still usually denoted alongside English units in the United States and SI units are only sometimes taught in the grade schools. The military, medical, and scientific sectors within the United States are the only ones that regularly use SI units. U.S. companies that have a large international presence are more likely to use the metric system in order to meet international standards and certifications.
Maybe with NASA’s conversion to metric, the United States will be spurred to do likewise.
To learn more about the SI metric system, go to the National Institute of Standards and Technology (NIST) Web site: https://www.physics.nist.gov/cuu/Units/.