Sunday, February 12, 2017

Did you know that NASA only recently went metric?

I am currently reading a science fiction series by an American author, the Paradox series by Rachel Bach, and it occurred to me that, centuries into the future, the characters were still using Imperial units: feet, miles, pounds, etc. Which prompted me to look into what units NASA use today, and what I found surprised and shocked me somewhat.
It turns out that, when the Americans landed a man on the moon, they managed to do so using an almost random combination of metric and Imperial units. Which is, frankly, astounding.
In fact, it was only in 2007 that NASA officially switched to metric, precipitated by a bunch of accidents including the loss of an expensive Mars Climate Orbiter robotic probe in 1999 (when a contractor provided thruster firing data in Imperial, while NASA was using metric units). It seems that, although NASA has ostensibly been using the metric system since about 1990, some missions still use Standard Imperial (SI) units, and some (including, amazingly, the International Space Station) use both!
What I had also not appreciated is that international aviation and air traffic control also still uses Imperial units (feet for altitude, nautical miles for distances, etc). Or at least most do, but not all: China, North Korea and Russia, for example, use the metric system for altitude and for wind speeds; and only North America and Japan use inches of mercury for pressure, while everyone else uses the metric millibars or hectopascals; nautical miles are pretty standard worldwide for distances, although North America uses Standard Miles; and some runways are measure in metres and some in feet. What a mess! Apparently, pilots use little conversion cards to do on-the-fly calculations, which seems like a quaintly low-tech solution to a potential problem that affects the lives of millions of flyers every year. It's amazing there have not been more accidents.
NASA's decision to switch to metric came after a meeting in 2007 between NASA and 13 other space agencies, all of which use metric, and it ended decades of American intransigence on the issue. In an era when space exploration is becoming more and more international in nature, it only makes sense.
And who knows, maybe the USA will also change their national measuring systems across the board, in a spirit of consistency and international cooperation. But don't hold your breath on that one, particularly during the next four years of Donald Trump control.

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