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 (950539)]

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 /.

Re:Yay!!!

[pilgrim23 (716938)]

as I recall, the fittings on the Apollo 13 launch were metric, the Comamnd Module English. Some fittings were square, others round.... If I was on the moon I would hate to need to change my O2 bottle and in an emergency, the one from contractor B has a English nozzle fitting. Consisitency is not just a good idea here....

Re:Yay!!!

[el_womble (779715)]

I'm British, so I deal with both systems on a daily basis and I think we've got it pretty sorted. Doing something important, where you need accuracy do it in metric doing something fun, do it in imperial.

Distance to the shops in miles, distance to the sun in kilometers
I measure my weight in stones and pounds, but I cook in grams.
Size of my wang in feet (ok, ok inches) size of my windows in cm.

I'm not sure why Americans feel the need to stick to imperial, especially in light of computers. At least NASA has now seen the light.

Re:Yay!!!

[illegalcortex (1007791)]

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:Yay!!!

[itlurksbeneath (952654)]

Consistent? We (the US) buy soft drinks by the liter, booze by the milliliter and milk by the gallon. Where's the consistency there?

Re:Yay!!!

[bckrispi (725257)]

Just like we buy meat by the pound, but cocaine by the kilo!

Thank You!

[spun (1352)]

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

I've always heard people talking about "a metric buttload" or "a metric assload" of this, that or the other thing. I never knew how much they were talking about, and I've been too embarassed to ask. Thank you for clearing up the conversion factor between a metric and imperial ass load!

Re:Yay!!!

[spagetti_code (773137)]

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!!!

[tobiasly (524456)]

16 ounces to the pound

Not so fast... that's only true if you're using the regular "Avoirdupois" [wikipedia.org] pounds. In the Troy [wikipedia.org] system, which is used for precious metals and gems, a pound is only 12 ounces!

I read a "brain teaser" once that asked: Which is heavier, a pound of gold or a pound of feathers? Of course, we've all heard a variation of this question (usually bricks and feathers), and know that the answer is that they weigh the same -- one pound. However, a pound of feathers weighs more than a pound of gold, because feathers are measured using the avoirdupois system (1 pound = about 453.59 g) while gold uses Troy (1 pound = about 373.24 g).

Re:Yay!!!

[Zaatxe (939368)]

And until last week, the speed of light for NASA was 1.8026174997852541159627773801002 terafurlongs per fortnight...

Re:Yay!!!

[Bent Mind (853241)]

It is plain old stupid. 60 sec for a minute, 60 min in a hour, 24 hours per day, 12 months? That is nuts. Why not use: 100 sec an hour, 10 hour a day, 100 hours a month and so on?

Absolutely! I also don't know why we used such an awkward value for PI. It would make much more sense if PI = 1.

On the other hand, I've always liked the idea of lunar months. Thirteen months of 28 days makes a lot more sense than twelve months that are anywhere from 28 to 31 days long.

How many days in a year?

[mangu (126918)]

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:Yay!!!

[Martin Blank (154261)]

Better to use 100 hours per week, or tenday (some fiction writers have used this term, but I don't recall names offhand). I figure that you meant 100 seconds per minute, 100 minutes per hour, ten hours per day (which makes a metric second equal to 0.864 standard seconds). Otherwise, 100 seconds per hour makes for one metric second every 86.4 standard seconds.

There are two problems with changing to metric time.

1) The year does not fit neatly into a base-10 meter. You can do 36 tendays in a year, but there's still five days left to factor in, aside from the fact that 36 isn't really close to an exponentially-derived value of ten. This is the minor one, since the original 12 months of 30 days each didn't fit neatly into an actual year, either.

2) Redefining the second means redefining a significant number of constants. The speed of light, for example, would go from 299,792.452 km/s to 259,020.684 km/s. That requires redefining the meter, which leads to redefinitions of even more things, and reprogramming vast amounts of software that makes use of these conversions. The short-term chaos probably would not be worth it.

Re:Yay!!!

[1u3hr (530656)]

..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:Yay!!!

[mpe (36238)]

Watching that would be ever so slightly more amusing than watching one of my European customers when maintaining one of my employer's half-metric half-imperial products. It's fun hearing things like "This wrench won't fit, and this one is too big. Is this a 9.5mm nut? Oh shit. It's American."

They'd read the instructions, but when they tried to print them out the printer just sat there flashing "PC LOAD LETTER"...

Re:Yay!!!

[Spritzer (950539)]

What the fuck does that mean?!

Re:Yay!!!

[bgarcia (33222)]

Both of my "American cars" were actually made in Canada, and are already metric.

I think the only car companies still making cars in America are the Japanese. :-D

Re:Yay!!!

[Simon Garlick (104721)]

I mess around with electric guitars in my nonexistent spare time. Last time I ordered a guitar neck from a US manufacturer it was described as being 43 millimetres wide and 0.85 inches thick, with tuning-machine holes pre-drilled at 11/32 inches.

Re:Yay!!!

[mollymoo (202721)]

My grandfather's 1976 John Deere tractor (how much more American can you get?) was metric.

[my emphasis]
How about a really fat John Deere tractor, with a gun?

Wait a minute.....

[lbmouse (473316)]

The metric system is the tool of the devil! My spaceship gets forty rods to the hogshead and that's the way I likes it!

Re:Wait a minute.....

[the dark hero (971268)]

for all of you that don't know, a rod was originally measured from the tip of the donkey's nose to the back of the plow. go america...

American metric system

[camperdave (969942)]

It secretly amuses me when Americans (one of only three backwards countries that haven't converted) argue about keeping the "imperial" system. All of your current units of measurement have been defined relative to the metric system for the past 50 years or so. From the wiki [wikipedia.org]: "One inch international measure is exactly 25.4 millimeters, while one inch U.S. survey measure is defined so that 39.37 inches is exactly 1 meter". "The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams".

Re:American metric system

[immel (699491)]

The conversion from electron volts to Joules is the value of a coulomb, which is another important metric unit in electrical calculations (although "metric" and "electrical" may be redundant; I have yet to encounter english units in circuits). The point is, if you know what a coulomb is (and you should, if you are doing this sort of calculation), you know how to convert between electron volts and Joules.

Now the english unit for energy, on the other hand, is the Btu. Converting it to the next "logical" english unit is a factor of about 778 Btu in a ft*lbf. Anyone who has taken thermodynamics knows the Btu as an enemy because using it with things like pressure (usually lbf/in^2) and mass flow rate (remember, there are many types of pounds in English, some for mass and some for force) requires inches, feet, and two types of pounds. Now let's try to convert from Btus to electron volts for even more fun! Because english has failed to come up with any useful electric units (even in the US), this calculation gets extra-nasty.

I suppose my point is as follows: Does the metric system always mesh nicely with physics? No. That's just the way the universe works. FSM made it that way. But some English units just seem to fit together with no rhyme or reason whatsoever! It's as if they made it up as they went along.

and to think

[User 956 (568564)]

The loss of the Mars Climate Orbiter was blamed on an error converting between English units and metric units.

And to think when we were learning the metric system in school, the teacher told us it didn't take a rocket scientist to figure it out.

I guess he was wrong.

Hopfuly this is a trend

[VEGETA_GT (255721)]

Metric is a very easy system to deal with and has been adopted over a large portion of the world. Technically Canada has been metric for over 20 years. Tho things like construction has remained Imperial as we are next to the US. If not for the Us Canada would be completely metric, but since the Us is right next door, we end up in the metric camp with one foot still over in the Imperial side o things. But I don't see the Us converting to metric any time soon, but the scientific community moving to metric to do its work instead of continually converting would be a great leap in the right direction.

Re:Hopfuly this is a trend

[Stanistani (808333)]

Confusion can be fatal or just embarassing, such as in the Gimli Glider [wikipedia.org] incident, which was partially due to a units conversion error.

Re:Hopfuly this is a trend

[KH (28388)]

we end up in the metric camp with one foot still over in the Imperial side o things.

That's 30.48 cm, correct?

Re:Hopfuly this is a trend

[808140 (808140)]

That boneheaded vendor being Lockheed Martin, unfortunately...

Soo..

[dbatkins (958906)]

when the first McD's is built on the moon, I have to order a "Royal With Cheese" ?

I have a bad feeling about this

[Decaffeinated Jedi (648571)]

I have a bad feeling about this. Has this whole metric thing been thoroughly tested?

"NASA Will Go Metric On The Moon"?

[TheWoozle (984500)]

I'm confused - are they only going to use the Metric system on the Moon?

or is it more like: "Dude, did you see that?! NASA totally went Metric on the Moon's ass!"

Good start

[gregmac (629064)]

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

According to wikipedia, As of 2005 only three countries, the United States, Liberia, and Myanmar (Burma) [wikipedia.org] have not converted to metric yet. Canada officially converted in 1970, but both systems get used on a day-to-day basis. Most tape measures, rulers, etc have both systems. Most older people still use imperial for most things, and younger generations seem to be mixed.

It's actually interesting that a lot of people here (Canada) use mixed units. Personally, I usually use feet if I'm estimating a distance (it's just a very convienient size - the closest metric equivalent is a decimeter, just doesn't quite cut it), and pounds and feet/inches for human weight/height. We still order a pound of wings and a pint of beer (I think you get beat up if you ask for 568mL of beer in a bar). Most other things are metric: road signs are km/h, the weather report is in celcius. Most stores sell things by the kilogram, meter, or liter/milliliter. I'm not sure what they teach kids in school now, but my generation (mid 20's) seems to be decently fluent in both systems (I remember learning how to add inches as part of learning fractions).

Re:Good start

[Freultwah (739055)]

I'm European and I've never been exposed to the imperial system. I am thus not tempted to use my hands or feet for measuring anything but the runway length for my long jumps. I've heard of no-one that uses decimetres for measuring distance, either. It's pretty much "metre twenty" or "two forty" everything. The pound thing, I think, would be "half a kilo", the beer issue is solved by asking "a beer". Or "a small beer" for a 0.33 l glass. (Other beer countries' customs and glass sizes do vary.) People weigh something like "75 kilos" and are "metre eighty" tall.

I guess it shows that even if you would think one system is harder or more cumbersome for certain things than the other, people who have had exposure to only one of them tend to come up with a very flexible and convenient way of measuring stuff. I still get dizzy when a translator fails to translate all the measurements to the target culture's system (all right, there are those rare times when it's desirable to have cubic feet and furlongs in literature), but the North Americans don't.

My favourite (not) is the standard PC case and its measurements. Have a metric ruler handy and go over it. Everything is very much metric. The 3.5 inch floppy? It's not 8.89 cm, it's exactly 9 cm. The 3.5 inch drive bay? Exactly 10 cm wide. The 5 1/4 inch bay? Not 13.335 cm, exactly 15 instead. Etc. Everything metric from the beginning, re-measured and rounded to fit the imperial system (what with the US probably being the biggest target market in the beginning of the PC). The sad thing is, the rest of the world seems to be accepting it unconditionally. It's as if no-one has had a ruler handy for quite some time.

Metric would work better in base 12

[jesterzog (189797)]

It's actually interesting that a lot of people here (Canada) use mixed units. Personally, I usually use feet if I'm estimating a distance (it's just a very convienient size - the closest metric equivalent is a decimeter, just doesn't quite cut it), and pounds and feet/inches for human weight/height.

I've grown up using Metric, since New Zealand's been standardised on it since well before I was born. I use it all the time, and I love it. So many different units of measurement go between each other in logical ways, many of which aren't noticed by most, right down to things like standard pencil widths being designed to match standard paper sizes. There are definitely problems with using it for day-to-day use, though, which I think most people just put up with. (The metre is often too big, the centimetre isn't big enough, and so on. Blocks of 10 cm would make a lot of sense, and I'm a bit surprised they don't get used.)

What imperial really has going for it, though, and one of the reasons it's so convenient, is that the units make it easier to divide things up for day-to-day tasks. In metric, it's easy to divide by 10, and often by 5 and 2, but outside of that the decimal places start getting long and often end up recurring. Dividing things into threes, fours and sixes really doesn't work if you also want twos and fives.

This is more to do with base 10 than with metric. 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. For day to day use, simpler fractions translate to decimals (or whatever decimals are called in base 12) more nicely with base 12 than base 10. eg.

1/1 in base 10 is 1.0, in base 12 is 1.0.
1/2 in base 10 is 0.5, in base 12 is 0.6.
1/3 in base 10 is 0.333333..., in base 12 is 0.4.
1/4 in base 10 is 0.25, in base 12 is 0.3.
1/5 in base 10 is 0.2, in base 12 is 0.24.
1/6 in base 10 is 0.166666.... in base 12 is 0.2.

Base 12 makes the first 6 fractions easy to write as a decimal, whereas base 10 becomes a real problem. This probably wouldn't be practical because it's a huge learning curve for everyone, but it'd be quite interesting all the same.

Re:Good start

[Dunbal (464142)]

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:Imperial Staying Power

[JanneM (7445)]

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.

Necessary but difficult

[carambola5 (456983)]

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:Necessary but difficult

[Zackbass (457384)]

To follow up on this one of the other big difficulties with the switch is the need for metric tools. I'm not talking about a set of wrenches but the seriously expensive machine tools and metrology equipment that prototyping shops across the county rely on. I personally have several thousand dollars of just measuring equipment like micrometers, dial indicators, and gage blocks before even looking at the milling machine and lathe which have inch threaded screws. In a well equipped shop this could add up to several hundred thousand dollars of equipment that simply doesn't work in metric. To a shop that is perfectly happy using inch measurements there is no incentive to switch. On top of this, almost all machined parts are done in decimal inches. The whole power of ten advantage means nothing to a machinist because all the work is already done in decimal.

As more modern NC equipment trickles down to the smaller shops that form of the base of American manufacturing the problem is getting less severe because it's as easy to programming a few lines to switch to metric or pressing a button on digital measuring equipment. I wouldn't hold my breath though.

They weren't using metric?!

[wile_e_wonka (934864)]

I should preface this post with the fact that I'm in the US. When I took physics and chemistry in college we barely discussed English units. There was one class period that we talked a little about conversion from English to metric units (I don't believe we even did the opposite), and that was about it. It was just assumed that we knew metric very well already. If I graduated and went to work for NASA and had to use English measures, I think I would have to almost relearn some of the physics--it would be awkward for me to work with the non-SI units, and even more awkward to have to learn new constants (I learned the constants in metric units). So I assumed that NASA had moved away from English units long ago since it hasn't been taught in so long.

We must strike now, before it is to late

[PingSpike (947548)]

These NASA rebels must be stopped. The moon was claimed in the name of the United States by Neal Armstrong, we can't allow them to fruit it up by going all metric on its ass the next time they land there. We should nuke all of NASA's bases from orbit. Some one see about coordinating that with our national space agency.

Urban Legend

[DerekLyons (302214)]

The loss of the Mars Climate Orbiter [wikipedia.org] was blamed on an error converting between English units and metric units.

Exhibit #1 for why Wikipedia is not to be trusted - they continue to tell half the story. (On this and many other topics, they prefer the simple and popular explanation over completeness and accuracy. [1])
 
MCO was lost not because of a metric conversion error - but because an increasing divergence between the planned and actual performance was ignored. The official report mentions this - but glosses over its importance. MCO was lost because NASA attempted to fly the mission on the cheap, because of this testing and analysis during the cruise phase was cut from the budget. Some analysis was done on the side by a few engineers - and their calls for a formal analysis went unheeded until too late.
 
[1] And before the Wikipedia cheerleaders chime in, yes - I have tried to fix many articles to correct this problem. Without exception the corrections were either reverted out or edited into meaninglessness. On Wikipedia the win goes to the editor with time on his hands or who can cite a lightweight popular article as the source of his 'facts'.

Countries NOT using the metric system

[banditski (163064)]

From Wikipedia:

http://en.wikipedia.org/wiki/Image:Metric_system.p ng [wikipedia.org]

about time

[smash (1351)]

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*.

Mixed opinions

[evanbd (210358)]

As someone working on an early prototype for one of the engines involved, I'd like to say I have mixed opinions on this.

Metric is good for all the obvious reasons -- SI units haver fewer weird things going on, conversions are easier, interoperable tools and fittings, etc etc. For all things like discussing distances, velocities, thrust levels, trajectory simulations, and more, I'm completely in favor of metric everywhere.

The one place I don't like this is when it comes to fittings, fasteners, plumbing, etc. Partly it's that metric nuts, bolts, and fittings are harder to find. You can't buy metric pipe fittings around here. Sure, you can order them, but that takes longer and costs more. The cost isn't a big issue on most things, but turnaround time is -- if you find a problem, it's really nice to be able to order a different part and have it the next day, rather than waiting a few days for something from Europe to clear customs and arrive. On some things, though, it actually makes a big difference. A lot of things like large pressure regulators, specialty valves, and more are even harder to find with metric fittings on them -- specifically, they become custom parts, with associated cost increases and weeks of lead time, which is frequently unacceptable.

And before anyone says you can buy metric parts in the US -- sure, you can, as long as they're "normal." It's the specialty parts that are hard. For example, McMaster-Carr stocks 3798 different socket cap screws in English sizes, but only 1610 in metric. If you need a weird metric screw, you may very well be out of luck.

The other major thing is subcontracts -- if I hire a consultant or send a part out to be machined, the machinist needs to have metric tools. Again, most machinists have a basic set of metric tools, but not an entire shop's worth. If the consultant or machinist has to start buying new tooling, your costs and the delivery time start going up.

I'll say it again -- having to buy parts from out of the country is not just a minor nuisance; it has a direct impact on how quickly you can revise a design and do the next test, which directly translates into how long it takes to complete the project.

I'm in favor of working toward compatibility, but it's not nearly as obvious an answer as it looks when it comes to tooling, since the installed base of English tooling and suppliers is *so* *huge* while metric is really only supported because of a few foreign-made parts.

they've got a list, and they're working on it

[User 956 (568564)]

I imagine this will assist the U.S. is its conversion to the metric system, something it has been trying to do for many years now.

Yeah, they started with the 2-liter bottles of soda about 20 years ago, so it looks like they're working their way down the list.

I wonder what comes next, after beverage containers, and interplanetary spacecraft.

Re:Why are we still using the US system?

[porcupine8 (816071)]

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:Metric system is not just for scientific commun

[mengu (452383)]

It was actually mandated back in 1975 that the US needs to convert to the metric system, check out http://www.pueblo.gsa.gov/cic_text/misc/usmetric/m etric.htm [gsa.gov] Quote: Congress passed the Metric Conversion Act of 1975 "to coordinate and plan the increasing use of the metric system in the United States." but it all fell apart since there where no deadline and all based onm voluntary conversion.

Re:Obligatory Quote

[amliebsch (724858)]

That's no moon!

But the Death Star would almost certainly use Imperial units, would it not?

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

[Malc (1751)]

The bigger irony is that they're not even proper "english" units! The fl. oz. is slightly bigger, there are fewer fl. oz. in a pint, the ton is lighter, and have you ever heard Americans measuring their weight in stones? Perhaps they were looking for somebody else to blame for the twisted unit system, and chose the name of the country they rejected in 18th century!

Re:Another pointless "victory"

[by 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.