NASA Will Go Metric On the Moon

An anonymous reader writes "Space.com is reporting that NASA has decided to use the metric system for its new lunar missions. NASA hopes that metrication will allow easier international participation and safer missions. The loss of the Mars Climate Orbiter was blamed on an error converting between English units and metric units. 'When we made the announcement at the meeting, the reps for the other space agencies all gave a little cheer,' said a NASA official."

Yay!!!

[Spritzer]

Now if only American car companies will budge that extra 17/32" and finish going metric rather than forcing me to have 2 sets of tools for one car. Then I can "Compare Prices on Physics and Engineering" here at /.

Why are we still using the US system?

[octavian755]

I was under the impression that most scientific agencies used metric as a standard (Guess US educational system failed me there). My father is a builder and I grew up seeing how contractors can be so loose with measurements. It amazes me that NASA got this far using a very inaccurate system (at times) for such precise operations.

The irony of calling it the "English" system.....

[Stormthirst]

... is that in the UK we've been using the metric system for at least 20 years!

Re:Why are we still using the US system?

[Average_Joe_Sixpack]

It's still being used because there is a massive infrastructure of machine tools and instruments amongst the contractors. The move to digital instrumentation and CNC is facilitating the transition.

It amazes me that NASA got this far using a very inaccurate system (at times) for such precise operations.

It's actually quite precise, just more complicated to use.

Necessary but difficult

[carambola5]

This is a necessary, but difficult transition. Yes, difficult. Maybe it's pretty easy for the programmers, but for the mechanical guys out there (like myself), this introduces a huge relearning phase. Say, for example, I need some sheet metal to function as a structural piece. I can be pretty confident that my initial guess will be pretty close to the final thickness value if specified in imperial units. I also know what's typically readily available from suppliers (eg: 1/4" is far more common than 15/64"). Not only must I do a conversion from my ingrained inch units into "foreign" metric, but I must also look up which sizes are common.

With time, I would be just as good with metric as with imperial units. And I want to change to metric for its obvious advantages. It's just that my design confidence and productivity would falter through the transition. I'm quite sure I'm not alone on this.

Re:Why are we still using the US system?

[porcupine8]

There's nothing inherently inaccurate about the measurement system itself. You can measure down to the millionth of an inch if you want. If a contractor is going to be loose with their measurements, they could just as easily say "Eh, that's about two meters" as "Eh, that's about seven feet". You can't make people measure down the the millimeter just because it's available on their measuring tape.

Re:Yay!!!

[illegalcortex]

I'm not sure why Americans feel the need to stick to imperial

Because using a crappy system 95% of the time is better than using a good system 50% of the time and a crappy system 50% of the time?

I wish everyone in the US had switched to metric before I was born. But if they were only going to do it half-assed (0.196850394-assed for metric folks), I'd just as soon stick with the crappy system. If you're going to do something poorly, at least by consistent.

Re:Good start

[Dunbal]

recruited a 2.1336 meter guy

      You use 3 significant figures in the imperial system when you say 7'11". Why do you feel you have to use 5 significant figures in the metric system? 2.13 m is good enough. It's not that hard really.

Re:American metric system

[tie_guy_matt]

You say it amuses you that Americans like to keep the imperial system but then go on to show that the one system is linked to the other. In other words you just showed yourself that it really doesn't matter.

We all know that God himself came down and defined a meter to be exactly so big.

Personally I don't think it is bad that we still use inches sometimes because it just goes to show that all units are just made up. It starts to get you used to switching between different units which you even have to do if everything is metric. How many electron volts in a joule? Both metric units for energy and switching between them is more fun than going from meters to yards. Since they are all made up anyway you should just use what unit is convenient and understand the limitations of any unit.

about time

[smash]

All the standard scientific units are metric. It's an international standard. Metric "just works" nicely in conversions/calculations. Fair enough if the US wants to keep it's general populace crippled with the imperial units - but science really is better off with metric.

Note that you don't see any movements to "bring back the imperial system" elswhere in the world, because metric *works*.

Re:Yay!!!

[Spritzer]

My Ford Ranger was assembled in the U.S. with a German-built engine, a Japanese transmission, and a mostly American body. It's a frigg'n Craftsman/Snap-On conspiracy as far as I'm concerned.

Re:Urban Legend

[N. Criss]

The official report mentions this - but glosses over its importance.

Sounds to me like you have a problem with the official report, not Wikipedia.

Wikipedia places a high level of importance on citations. Were you able to come up with credible citations to backup your alternate conclusions? If not, you should start a "NASA MCO Conspiracy" page on MySpace instead editing the Wikipedia topic.

Re:Another pointless "victory"

[Anonymous Coward]

Using the metric or imperial system would not matter one bit if all you're measuring is distance or volume. But as soon as you start converting distance into volume (quick question: how many cubic inches in a pint?), or thrust into velocity (quick: you apply a one-pound force to a one-pound object for one second. What's the resulting speed, measured in mph?), or torque into power, or energy into force or power, the beauty of the SI (metric) system really stands out. In the imperial system, the only way to get these calculations right is to insert all sorts of wacky numbers. Which you need to remember with potentially infinite precision.

Try this beauty: 1 Nm (Newton-meter) equals 1 J (Joule) equals 1 Ws (Watt-second). In the imperial system you'd have to insert all sorts of wacky numbers to go from pount-feet to calories to, strangely enough, Watt-seconds again. (Electricity, even in the US, is always measured in metric.)

Or more practical: Ever tried to convert the torque that your car engine delivers (measured in pound-feet) at a certain rpm (rounds per minute) to the horsepower (hp) that it delivers? In SI, it's a simple multiplication: Power (measured in W, or more commonly kW) = 2 * pi * torque (measured in Nm) * rotation speed (measured in 1/s). No wacky, imprecise numbers. Just 2 * pi due to the rotation and that's it.

The SI system and all the calculations you do with them are completely void of wacky numbers, with only a few exceptions:
- 2 times pi for anything that involves rotation.
- Natures constants like c (lightspeed), g (gravitational accelleration), e (elementry electric charge) and a few others, about half an A4 page full of them.
- Natural properties (like density) of materials that you use.

Since NASA does *a lot* of these calculations (how much force do you need to accelerate/decelerate the lunar lander, what's the effect of gravity?) I can understand why they switch to metric.

Re:Good start

[argStyopa]

".. but when is the rest of the USA going to follow suit?"

Well, why does everyone seem to care so much?

I mean, the US is particularly full of people that don't like governments telling them what to do - hell, the US was FOUNDED by people like that.

It's simply not practicable for the US gov't to say "you must all do it this way" for something so trivial.

Re:Urban Legend

[Anonymous Coward]

I'm sorry, but you're quite wrong.

The divergence you mention, as it was abnormal behaviour, should have led to a delay in the mission to ascertain the situation, performing some analysis and tests that could have pinpointed the culprit (flaky software and data) and saved the probe. This was an operational error - which the report quite rightly pointed out.

The root cause of the crash, however, is the conversion issue. Better testing should have caught it, and operational vigilance might have saved the day, yes, but the best way to eliminate bugs remains not to have them in in the first place. And pointless unit conversions is a designed potential bug that was just waiting to happen, as it did. Just like the 2 supply voltage design that led to the Apollo 13 incident, for what matters.

Re:American metric system

[Alinabi]

In my experience, most Americans under 30 can't even convert from miles to yards. Yes all systems of units are arbitrary conventions, but some of them are better designed than others. You don't need a calculator to find out how many centimeters are there in 174.56 m. That makes it particularly well suited for every day use. By the way, the eV is as much of a metric system unit as the degree Celsius. See this [nist.gov].

Re:Yay!!!

[spagetti_code]

If you're going to do something poorly, at least by consistent.

Yeah, because we know how consistent the imperial system is...

Let me see...

16 ounces to the pound
14 pounds to the stone
2240 pounds to the ton (more correctly a long ton)
1000 pounds to the short ton
40 cubic feet to the freight ton

And this is my favourite:
Both the long and short ton are 20 hundredweights, but the
hundredweight differs from 100 to 108 pounds.

Dont forget the furlong, rood, pole, chain, link, inches, feet, yards...

Yeah... that looks pretty consistent. /sarcasm.

Re:Yay!!!

[kjots]

But if they were only going to do it half-assed (0.196850394-assed for metric folks)

Shouldn't that be 0.196850394-arsed?

How many days in a year?

[mangu]

Why not use: 100 sec an hour, 10 hour a day, 100 hours a month and so on?

Yeah, right, so that would make it 1000 days in a year? And PI==10.0, I guess. The problem with imperial unit apologists is that they make such unreasonable arguments to try to justify an unreasonable system.

Now, let's get this straight, write it down carefully: the International System unit of time is the second. Minutes, hours, days, weeks, and months are ***NOT*** metric units

We have such weird units of time partly because neither the lunar month nor the solar day are exact divisors of the year and partly because of an old tradition on dividing the day. But, no matter how hours and minutes are counted, these are not part of the International System. You may buy eggs and beer cans by the dozen, but a kilogram is still a thousand grams.

Re:Imperial Staying Power

[JanneM]

You do realize, of course, that using metric units in no way stops you from using fractions rather than decimal whenever it is convenient?

You may use 3/4 cups of something; I'll use 1 1/2 dl. And one pint is a fairly good size for a beer, but then, so is 40cl, the normal size in Sweden. But of course we don't call it "40cl"; it's a "large beer".

If I estimate people's height, I'll just estimate to the nearest 5cm. That is a pretty convenient scale; fine enough to get close, and rough enough for me to have a good chance of being right.

Pretty much none of your arguments have anything to do with the units used, but with how you use them - and you can do it equally with either measurement system. As a guess, you have not had to use metric very much so you just have never built up a collection of mental tools equal to the one's you use for inches and stuff, and so you see it as clumsy and ill-fitting.

NOT English Units

[Roger W Moore]

I wish Americans would stop calling them "English" units. Not only are they no longer generally used in England (with the odd exception like pints of beer and miles) but the even when they were used they were different from the American system. For example there are 20 fluid ounces in an Imperial pint vs. 16 fluid ounces in a US pint....so it is a very good thing than NASA is no longer using them for international missions since there isn't even an Imperial standard that anyone can agree on!

"Err...Houston we may have a problem, when you told us to burn 10 pints of fuel was that Imperial pints or US pints?"

Re:Hopfuly this is a trend

[Abcd1234]

To your first reply: 1/3 of a meter is about 33cm. Oddly enough, 1/3 of a foot is exactly 4 inches.

If you need more accuracy, that's what decimals are for.

1 Gallon of water? About 7 pounds.

a) that's rote memorization. b) It's "about" 7 pounds. Oddly enough, 1L of water is exactly 1kg. :) Well, ignoring temperature and impurities...

Yards of cloth are a gross measure -- it's linear yards

Well that makes things even worse! Honestly, WTF is a linear yard?? :) And why should I *need* a specialized measuring tool? Oh yeah... because it's Imperial. Why can't I just use a regular ol' meters and centimeters with a straight-up tape measure?

I'm making pastry, so I can't have any of this "about 333mL" stuff

Bah, since when did you need sub-mL accuracy for making pastry? That's a 1/5th of a teaspoon, for you metric-crippled folks. It's not *that* sensitive (it's far more sensitive to temperature).

I've seldom needed tablespoon to teaspoon conversions, but it's 3 teaspoons to the tablespoon. However, I don't know the tablespoon to cup conversion. Something like 32 or so.

And that's exactly my point. If I don't have a particular measure, I need to make it up with others. For example, I lost my 1/3 cup measure, so I need to make it up with my others. With Imperial, that's practically impossible without a conversion table. With metric, it's easy-peasy.

As for your 3 tsp = 1 tbsp, again, that's rote memorization, and it's a pain in the ass. OTOH, if you're dealing with metric, it's 15mL and 5mL. Again, simple.

Re:American metric system

[Gavin Rogers]

One day the world will rise up and say in one voice, "No! Screw you guys! From now on everything we export to your country is in metric. Deal with it."

I think you just quoted the EU, without realising it.

Re:Metric would work better in base 12

[saforrest]

I've often wondered if metric would be better long term if everyone counted in base 12, instead, and if the relationships between metric units were based on multiples of 12 instead of 10.


First off, there is an error in your list:

1/5 is not 0.24 in base 12. 0.24 in base 12 is 2*(1/12)+4*(1/12)^2 = 7/36, which is 0.1944, not 0.20 as it should be. In fact, 1/5 does not have a terminating representation in base 12, for exactly the same reason as 1/3 does not have a terminating representation in base 10. For a fraction to have a terminating representation, all the prime factors of the denominator have to evenly divide the base. And of course 5 doesn't divide 12.

On your proposal, I recall reading in E. T. Bell's Men of Mathematics that this was actually proposed in revolutionary France, where SI was first invented. It was rejected after being argued down by Lagrange, who argued as a sort of "modest proposal" that base 13 would be better because all denominators would then be 13.

Note that the main convenience you cite is the existence of a terminating representation for fractions who denominators are multiples of 3. The choice of 12 here is arbitrary, because this also true of base 6:

1/1 in base 10 is 1.0, in base 6 is 1.0.
1/2 in base 6 is 0.5, in base 6 is 0.3.
1/3 in base 10 is 0.333333..., in base 6 is 0.2.
1/4 in base 10 is 0.25, in base 12 is 0.13.
1/6 in base 10 is 0.166666.... in base 12 is 0.1.

If you wanted the best of both worlds, you could go to base 30 (since 30=2*3*5) and you would be able to represent 1/2, 1/3, and 1/5 with terminating representations.

Why aren't we using base 30 then? It's probably too big to be a convenient base, so we have to choose something smaller. We have to then make the sacrifice of giving one of 1/2, 1/3, or 1/5 a nonterminating representation in the base. Whether we sacrifice 1/3 (as we do with base 10) or 1/5 (as we would with base 6 or 12) seems to me an arbitrary enough choice that there's no clear gain in making a change.

Re:Yay!!!

[1u3hr]

..reprogramming vast amounts of software that makes use of these conversions. The short-term chaos probably would not be worth it.
Exactly, which is why America hasn't adopted the metric system wholesale.

Seems to make sense, until you wonder why it didn't stop every other country in the world from converting to metric decades ago. Also, it causes untold grief for everyone else when their American software always defaults to Imperial units ("PC LOAD LETTER" is a familiar message to many who have an A4 size paper tray). And while you're at it, change the date notation to DMY or YMD, MDY is another continuous irritation. After you've done that, we can discuss your spelling.

Re:American metric system

[Braino420]

I think you've missed the point entirely. Your confusion over the parent's posting would have been cleared up had you just followed the link. From the wiki:

Both systems derive from the evolution of local units over the centuries, as a result of standardization efforts in England; the local units themselves mostly trace back to Roman and Anglo-Saxon units. Today, these units are defined in terms of SI units.

In other words, no longer are things described as being "the length from forearm to elbow". Didn't you even read the summary? Converting between the two has the potential to cause problems.

Personally I don't think it is bad that we still use inches sometimes because it just goes to show that all units are just made up. It starts to get you used to switching between different units which you even have to do if everything is metric.

Again, I believe you have missed the issue here. Of course you have to convert to bigger/smaller units even in metric, but the thing is that it's easier to do if you are using the metric system! Dividing or multiplying by ten is a hell of a lot easier than finding the correct imperial conversion and then doing the math without nice round numbers. Also, as the article mentions, even when not doing simple conversions, it helps not to have to keep up with two sets of tools. I really don't understand why people are clinging on to this imperial system, it's not that hard to learn the metric system!

Re:Imperial Staying Power

[JanneM]

"You do realize, of course, that using metric units in no way stops you from using fractions rather than decimal whenever it is convenient?"

Actually, it does because ten has less factors (1,2,5,10) than twelve (1,2,3,4,6,12) or sixteen (1,2,4,8,16).

Huh? What stops you from counting in whatever fractions you're comfortable with? If you want to use 4 3/12 deciliters or something, just go ahead.

If I take a stick that's 1 foot long and cut it into four pieces, I have four sticks that are 3 inches long. If I take a stick that's one meter long and cut it into four pieces, I have four sticks that are 25 centimeters long.

You have four stick of 1/4 meter each. If you take one meter and cut into five pieces you get five sticks of 2dm. What does cutting a one foot stick in five pieces get you?

I think you need to calm down a bit; you're sounding quite obsessive about this, to the point of being irrational.

Re:Another pointless "victory"

[Anonymous Coward]

Or more practical: Ever tried to convert the torque that your car engine delivers (measured in pound-feet) at a certain rpm (rounds per minute) to the horsepower (hp) that it delivers? In SI, it's a simple multiplication: Power (measured in W, or more commonly kW) = 2 * pi * torque (measured in Nm) * rotation speed (measured in 1/s). No wacky, imprecise numbers. Just 2 * pi due to the rotation and that's it.

I agree with your post except for this part. I never understood why the SI system was considered better when talking about an engine's power and torque.

First, you really should have the conversion factor for changing 1/min to 1/s (i.e. 60s/1min). As you already stated rotational velocity is almost always given in RPM.

Secondly, the equation for converting torque (lbf-ft) and rotation (RPM) to power (hp) is nearly identical. You just need to multiply by a factor of 1/550, hardly an imprecise number.

Typically, this is generalized by the equation: hp = (lbf-ft * RPM) / 5252.

The SI equivalent is: W = (N-m * RPM) / 9.549.

We don't use l/km because ...

[Anonymous Coward]

The only reason we don't use l/km (litre per kilometre) because the numbers are far below zero and would make results like : 0.085 (my gaz consumption on moterways running over the limites, oups ...) !

But multiplying this by 100, and you get 8.5 l/100km which is better to remember (usualy people would round this saying I "consume" 9 litre per 100 kilometer with my wrek ... ok, I know this is huge, but Prius is way too expensive for me (what are the non japanese car maker doing in their labs, ey ?).

AFAIK, gas kilometrage is the only mesure that is commoly using such an hundred trick ...

Another funny things, here in europe people are used to talk about computer screens in inches (maybe simply because it is written on the box so), but they are used to talk about TV screens in cm ! I would preffer to see people use cm as well in IT, because on some screens the roundings make a 1cm difference (where inches roundings does not make it different).