# Units of Measurement

#### Roberto

Can someone describe to me whether all calculations be it distances, forces, movements, pressures and densities etc. in the SpaceX design and development facilities are performed in the Imperial or Metric format. My initial training up to University levels were all carried out using Imperial measurements until 1970 when Australia decided to switch to the Metric system. Since that year all my calculations involving architectural and engineering tasks have been using the Metric system and I wonder still at the amazing simplicity of it all and why we ever used the archaic Imperial system? If I am correct was there a Mars probe some years ago that failed to reach its destination because of inaccurate translation between the two systems?
Roberto

#### IG2007

##### "Don't criticize what you can't understand..."
Well, the metric system is more recent than the old imperial system. The SI system of units came in 1960s although there have been many talks before it about making an international system of units that might reduce irregularities between different units.

Catastrophe

#### Catastrophe

##### "There never was a good war, or a bad peace."
Well, we just decided long ago that
16 oz to the lb
14 lb to the st
112 lb in a cwt
20 cwt in a ton (old)
was just more interesting than boring old 10 for everything.

IG2007

#### Helio

It was around 1972 when the U.S. tried to switch to metric. I think the cost of re-tooling and other costs caused industry to oppose it. But I was just a student who happened to notice only a little of the effort. Having to add and multiply fractions, convert lbs. mass to lbs. force, etc. made me root for the metric system. Metric, for some reason, just sounds like it has more merit for some reason.

#### Lasso a train

I too remember when we were forced to abandon what we had already been taught and start over using a new language. It may had been no big deal to students that did not have FTS Syndrome
( failure too succeed syndrome)
And a drag for those kids struggling to just sit still for an hour or more at a time. The reason i believe was not so much that it was a superior system but because it allowed us too do buissness on a planet scale with those other countries with global economies.
In return these other countries took up the task of learning English as a second language for the same reason. And they did a wonderful job .you can go any where in the world almost and others speak some english .even in Russia they speak english very well. And now in the U.S we go through twice as much paper and ink printing everything twice. Once in English and again in Spanish. Dont figure.

IG2007

#### PaulZussman

Yeah, metric system had changed around 1972-1973

IG2007

#### Catastrophe

##### "There never was a good war, or a bad peace."
If you go back to the question,

"Can someone describe to me whether all calculations be it distances, forces, movements, pressures and densities etc. in the SpaceX design and development facilities are performed in the Imperial or Metric format."

Should it not be in one OR the other, or is the suggestion that both are used in parallel?

IG2007

#### Roberto

Hello Catastrophe,
I was just wondering in the factories and laboratories developed under Elon Musk's enterprise, there would be hundreds of researchers, scientists and workers developing these new machines, gadgets, steel sheeting, pipes etc etc. In what form measurements would they be using considering the States is one of three countries in the world still operating under the Imperial system? Going back 50 years to my Architecture course we had for a while use both systems of distances and heights for example brick courses and heights. As you know the standard brick was 9x41/2x3 inches with the mortar joint either in 1/2 or 3/8 inches. Yes of course we had tables to make it easier but it was painful! Not to mention my early primary school education for year 5,6 and 7 where we had to learn a myriad of weights and measures and perform weekly tests classed as Arithmetic in those days. In retrospect that time would have been better spent on basic science, biology or learning other languages. I ma happy to say that is happening now in the Australian education system
Roberto

IG2007

#### Catastrophe

##### "There never was a good war, or a bad peace."
I am in England, so I cannot speak for other countries, except to say that, as far as I am aware, all science is conducted in metric.

#### Helio

If I am correct was there a Mars probe some years ago that failed to reach its destination because of inaccurate translation between the two systems?
Yep. Here is one article on that failure.
Space.com article said:
Investigations into the orbiter's crash found that it occurred because of a mix-up between the metric and imperial measurement systems that caused the orbiter to drift off course during its voyage and enter into a much lower orbit around Mars than was planned.
And for fun, here is a great video of some of those events as seen from Mars,.... Spring on Mars

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#### Roberto

Helio, loved the video!
Roberto

#### Catastrophe

##### "There never was a good war, or a bad peace."
In answer to the original question, which was:

"Can someone describe to me whether all calculations be it distances, forces, movements, pressures and densities etc. in the SpaceX design and development facilities are performed in the Imperial or Metric format."

I hope it is now obvious why we must settle on one system only, and that the only logical choice is metric.

That is why god gave us 10 fingers

#### lemmy

In answer to the original question, which was:

"Can someone describe to me whether all calculations be it distances, forces, movements, pressures and densities etc. in the SpaceX design and development facilities are performed in the Imperial or Metric format."

I hope it is now obvious why we must settle on one system only, and that the only logical choice is metric.

That is why god gave us 10 fingers
I have worked as a mechanical systems engineer in the US aerospace industry for almost 30 years. Imperial units (inch/pounds/etc) are still the primary standard used for most US aerospace/defense programs. But metric unit equivalents are commonly provided everywhere for reference. I've never had a problem working with either system. Only seems to be a problem for people unable to perform the basic math calcs required to convert between units, or those who fail to pay attention to the specific details contained in design requirement specs.

#### Roberto

Good for you Catastrophe! but I am so thankful that God did not give us 12 fingers, otherwise we would have been saddled with the Imperial system?

#### ChrisA

Can someone describe to me whether all calculations be it distances, forces, movements, pressures and densities etc. in the SpaceX design and development facilities are performed in the Imperial or Metric format. My initial training up to University levels were all carried out using Imperial measurements until 1970 when Australia decided to switch to the Metric system. Since that year all my calculations involving architectural and engineering tasks have been using the Metric system and I wonder still at the amazing simplicity of it all and why we ever used the archaic Imperial system? If I am correct was there a Mars probe some years ago that failed to reach its destination because of inaccurate translation between the two systems?
Roberto
As you say, people studying engineering have been trained using the metric system for the last 5 decades. You would have to be close to retirement age to have been brought up using Imperial units.

Almost all the engineers at SpaceX or younger than "close to retirement age".

#### Helio

As you say, people studying engineering have been trained using the metric system for the last 5 decades. You would have to be close to retirement age to have been brought up using Imperial units.
So have engineering schools abandoned the Imperial units, or are they included with metric?

#### ChrisA

So have engineering schools abandoned the Imperial units, or are they included with metric?
I have not been in school for decades (except briefly as a teacher after retiring from engineering) And what I saw was that students are given a brief lecture of how the imperial system works just so that they know that pound is force and "slugs" are mass but they are not taught in that system. Just made to do a few homework problems in Imperial. This was how it went in my high school in the 70s and university in the 80s and later when I taught high school science in the 2000s we never used imperial at all. It is not in the California science textbooks.

#### Helio

Thanks ChrisA. In the early 70s, engineering was more Imperial than metric, but we all recognized that metric was the future. We didn't use slugs hardly ever but pounds-mass instead, which was tricky in knowing when to divide by g to go from weight to mass.

Catastrophe

#### fsFoster

##### Amateur-amateur scientist
This is “on topic” relative to the string’s title, but “off topic” relative to SpaceX.

One way to think about units of measure is to pit imperial versus metric.

Another way to think about units of measure is to imagine how they will change in the future.

Let’s suppose that among the 10 septillion—one followed by 25 zeroes—planets estimated to exist in the observable universe there are a few intelligent species that have been around longer than we have. [medium.com/starts-with-a-bang/how-many-planets-in-the-universe-9153a05bd0d5 cited for planet count .] How would those species measure, for example, distance?

Let’s suppose that there are more than one of these species that are either in contact with other species already or are intending to connect with other species. How can those species best support interstellar conversations?

One of their tools is the simplification of the elements of conversation. One of the elements of conversation is measurement. Measurement requires units of measurement. Units of measurement can be like those used on Earth, like the imperial and metric systems which are Earth-centric and unguessable beyond Earth. Both systems are based on the anachronistic division of the distance from the north pole to the equator. In metric the original distance was redefined relative to light speed to enhance its accuracy, but the underlying measure remains a fraction of an Earth distance.

Units of measure developed beyond Earth won’t relate to Earth’s circumference, but all imaginable forms of intelligent life will have units of measure. Going back to our interstellar communications, what have those lifeforms that are more mature than Humans are, used as a basis for their units?

Suggestion: they have based units such as distances in space and time on features of the universe that are constant to all intelligent life. For instance, spatial distance will be based on the distance from the nucleus of a hydrogen atom to its electron. (I’m ignoring the more accurate rendition of an atom posited by quantum physics and going with the classical Rutherford model.) This distance can be considered one or even one-trillionth of a daily-use unit, but the measurement will be universally available.
Staying with hydrogen, a not unreasonable assumption, then the measure of duration could be the time it takes for a beam of light to travel from hydrogen’s nucleus to its electron. Or time could be based on (what I’m guessing is) the most common naturally occurring radioactive element, uranium-238. Like us, they know its decay rate and can do a progression of half-lifes to a unit that is practical in daily use. And so on.

BTW, Humanity has already started thinking in absolute, universal terms. We measure temperature in Celsius and Fahrenheit, two not unreasonable scales based on water’s most common phase-transition points, but we also measure temperature relative to absolute zero, in units Kelvin. Kelvin isn’t universal in its use of the temperature increase defining one degree, but it is in its setting zero equal to absolute zero. A great first step.

Humans who believe that we will remain Earth-centric forever can be comfortable in their provincial view of the future, but those of us who believe that we will someday interact with other species, likely more intelligent than us, can begin our what-if analysis. Why would we not? In seeking best-case universal options, isn't it likely that we will discover currently unperceivable knowledge? We can begin to consider the natural world and its constants as the basis of measure that our children’s children’s children will be comfortable with. None of those measures will use Earth as a source of definition.

What is the most-natural unit for expressing Coulomb's law? Gravity? Weight? Certainly we're not using any of those units.

Although I first proposed hydrogen as a reasonable focus of defining units of space and time, would other species consider it more reasonable to extract measures from the nature of light? If so, then we can also start populating our notions of what zero means, as in when did the universe begin? We currently use the big bang as our zero, as our starting point, but I suspect the first 100,000 years or so are due for drastic changes in how we understand the period. However, the universe as we understand it has what might be a better beginning date; the moment when matter and energy expanded sufficiently to create light. In the beginning, God said “let there be light.”

How finely can we hone universal time’s zero? For a first attempt, can we define day-one, minute-one, second-one as the moment precisely 300,000 years after the big bang? No, but we can make an educated guess and refine it as we focus on the problem. Our first approximation won’t hold forever, but isn't it better than our current time map that begins 2020 years ago, with it's bizarre plus-and-minus data points?
And what will we discover to replace those silly Babylonian seconds, minutes and hours ? What does nature tell us to use as our divisions of time?

Will the general public accept so outrageous a shift in perceptions as I’m proposing? Of course not, but they don’t need to. Rather, scientists, philosophers and other thinkers must.

How can we begin to simplify our conversations with beings from other stars? Our first effort was beautiful, but the beauty of the Pioneer recordings was conceptual, not practical. Aliens won’t depend on nor expect other forms of life to have ten fingers, so won’t assume base-ten units. Thus, much of the data we sent to them will be initially indecipherable, but the underlying units are binary, and they will certainly understand binary. (They’ll also get a chuckle out of discovering that there are aliens that use something so complicated as is base ten.)

No, we don’t need to think in terms of natural units of measure. Not yet. But remember the reason we lost the probe that we sent to Mars: a couple of highly intelligent, highly competent engineers didn’t make the conversion from metric to imperial.

What will future communication failures cost us?

#### Helio

I would assume the use of a given atomic frequency would work nicely. No measurement (wavelengh) is needed only the use of their numbering system and their time units. It would be easy for them to reveal their choice of atom and the base of their number system, we would then know their unit of time.

We now use time to know distance thanks to the constancy of the speed of light.