Commentary: Metric Mayhem | Flight Today | Air & Space Magazine

Commentary: Metric Mayhem

Practically the entire world uses the metric system. Is it time for the United States to follow suit?

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Not long ago, I was writing a story for this very magazine about the delicate extraterrestrial dance of a U.S. spacecraft around a potato-shaped asteroid named Eros (see “Hang a Right at Jupiter,” Dec. 2000/Jan. 2001). The simplicity of the spacecraft’s course stood out in a universe that is rarely simple and convenient: The boxy craft would circle 100 kilometers from the asteroid’s cratered surface, then fire its engines to drop into an orbit 50 kilometers above the tumbling space rock.

Finally, I thought, I don’t have to worry about how to round off some impossibly large number such as the speed of light (299,792.458 kilometers per second) or the distance between Earth and the sun (149,597,870 kilometers).

At least that’s what I thought until the editors got hold of the story and reminded me that this magazine does not use metric units. Convert all kilometers to miles, they said, all meters to feet, and all kilograms to pounds.

Why not use metric, I asked. All the scientists working on the spacecraft use metric. All their written materials use metric. Every other country that operates in space uses metric. Their reply: Because we have always done it the other way. It’s what our readers understand. It’s the American Way.

Lengthy investigation suggests that this is about the only explanation for why the United States as a whole evades the metric system while most of the rest of the world embraces it—because we have always done it the other way. We’re like a crotchety old hermit. The rest of the international neighborhood works together and speaks the same language while we huddle in a dark, outdated house at the end of the street (which we share with Liberia and Burma, the only other two nations that have not gone metric), mumbling our own inscrutable tongue of inches, feet, yards, miles, links, rods, furlongs, pecks, bushels, bolts, barrels, fathoms, leagues, acres, ounces, pounds, tons, cups, bales, pints, tablespoons, gallons, hands, chains—most of which have no logical relationship to one another—and all the other aged terms of what is often called the Imperial, or English, system but which metric advocates derisively refer to as FFU (Fred Flintstone Units). So I could have probably said to my editor, “That’s typical FFU.”

But of course I didn’t.

Such lack of backbone may be why the U.S. portion of the International Space Station is built in Imperial Units while the rest of the super-expensive structure has been constructed in metric. About 10 years ago NASA gave serious thought to the idea of building the whole thing in metric, but decided that would drive the cost way up. All the NASA contractors were tooled to build parts in inches and pounds; converting to metric would have required revised designs and new machines. So instead they developed an elaborate and costly computer-modeling and cross-checking procedure to make sure that metric and Imperial parts fit together and work properly.

Of course, an all-out metric conversion would carry costs of its own. No one has ever solidly estimated it, just as no one has estimated the loss of U.S. trade dollars due to the unwillingness of other nations to take shipments in pounds and gallons. Certainly we would need to recalibrate scales, gas pumps, and the like. There’s always a cost to repairing a sinking ship, but the cost of not repairing it may be far greater.

Right now the Russians are controlling the space station, figuring propulsion exclusively in metric units. Once the onboard laboratory (expected to have launched January 18) is up and running, the U.S. will take over control exclusively in Imperial units. When I asked spokesman Kyle Herring of NASA’s Johnson Space Center in Texas what would happen if there were some confusion between the two, if a maneuver supposed to be carried out in pounds of thrust were actually done in kilograms or the other way around, he explained that the station’s propulsion system operates at such low thrust that even a major miscalculation couldn’t send it spiralling into the atmosphere. But it doesn’t always take a major miscalculation to reveal the cost of our old-fashioned tendencies. Remember NASA’s Mars Climate Orbiter? As it headed toward its rendezvous with the Red Planet in the summer of 1999, navigators calculated the effects of subtle maneuvers to adjust its trajectory, based on data from contractor Lockheed Martin. The data was supposed to be in metric units, but it wasn’t, so each maneuver ended up throwing the craft farther out of whack, putting it more than 100 miles off course by the time it arrived at Mars. The $125 million probe probably burned up in the Martian atmosphere.

The problem is that while Lockheed Martin’s space division operates entirely in metric, its manufacturing side and many of its contractors use Imperial Units because rebuilding sophisticated hardware in metric would be wildly expensive, says Edward Euler, the company’s program manager of the ill-fated Mars mission. For similar reasons, NASA requested proposals for its next generation of space shuttles in inches, feet, and pounds even while most of the agency’s own scientists use metric. “You really have two NASAs—one English and one metric,” says Euler, who adds that Lockheed Martin has the same problem. “We can’t buy our nuts and bolts to the metric standard—that’s the place, on the commercial and manufacturing side, where there’s really resistance.”

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