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NASA Sticking To Imperial Units For Shuttle Replacement
JerryQ sends in a story at New Scientist about the criticism NASA is taking for deciding to use Imperial units in the development of the Constellation program, their project to replace the space shuttle. "The sticking point is that Ares is a shuttle-derived design — it uses solid rocket boosters whose dimensions and technology are based on those currently strapped to either side of the shuttle's giant liquid fuel tank. And the shuttle's 30-year-old specifications, design drawings and software are rooted in pounds and feet rather than newtons and meters. ... NASA recently calculated that converting the relevant drawings, software and documentation to the 'International System' of units (SI) would cost a total of $370 million — almost half the cost of a 2009 shuttle launch, which costs a total of $759 million. 'We found the cost of converting to SI would exceed what we can afford,' says [NASA spokesman Grey Hautaluoma]."
How many cwts of Mars Orbiters must be lost before we learn?!
My work here is dung.
You know, a lot of Europeans probably think that U.S. reluctance to embrace the metric system is just another example of our arrogance. But a lot of Americans (like me) are genuinely interested in adopting this system. We even passed a law in 1975 trying to mandate it.
The real problem is that it is surprisingly hard to embrace a new system of measurement when you've spent your entire life thinking in different terms. Try as I might, I still can't picture a kilometer without converting it to a mile first, and still can't picture a centimeter without converting it to inches. The meter is a lot easier because it's pretty analogous to the yard. I think maybe your brain gets locked into a certain measurement pattern pretty early in life and it's very difficult to get out of it, even though many of us would happily embrace it. I'm still trying to think more in metric, but it requires a surprising amount mental effort to do so.
It's not that Americans are really all that arrogant or stubborn about the imperial system. We've actually been trying to embrace the metric system for some time.
SJW: Someone who has run out of real oppression, and has to fake it.
1 foot = 0.3048 meters
There you go, NASA. That one's for free.
The sticking point is that Ares is a shuttle-derived design â" it uses solid rocket boosters whose dimensions and technology are based on those currently strapped to either side of the shuttle's giant liquid fuel tank. And the shuttle's 30-year-old specifications, design drawings and software are rooted in pounds and feet rather than newtons and meters.
And in 20 years, that'll be the same excuse given for building Ares's replacement with imperial units.
Dewey, what part of this looks like authorities should be involved?
Rhapsody in Numbers
Abe Simpson: The metric system is the tool of the devil! My car gets forty rods to the hogshead and that's the way I likes it.
I work for an engineering company, and unit conversions are not a trivial operation. All of our drawings are created in autocad, and after several years it becomes difficult if not impossible to find the original file. As such, converting achieved documents requires recreating the document entirely from scratch. We also use a fairly vigorous quality control system that requires 3 engineers to check every document change, verify the calculation, and repeat the calculation using a different method to ensure that no mistakes were made.
We recently acquired an older project where we needed to simply change the title block on each page, and this process took roughly 5000 hours. For something on the scale of the space shuttle, 370 million isn't unheard of.
You make it sound so simple...when, in fact, this is quite literally rocket science here.
One of the common stories here is people needing to rewrite an entire project because of a new language fad. The old project worked. Rewriting it first means you have to replicate the old project and then deal with new bugs while the old project had all the bugs mostly ironed out.
Why do we insist NASA to reinvent the wheel when we're so against it in our own profession?
Most systems engineers in the space industry know that it's difficult to completely use metric for space missions. There are usually many components and subsystems that are designed by different vendors that have their own paradigms set up. These paradigms are usually kept do a legacy of proven use, and engineers will agree with me that if a product works well on-orbit, why on earth would you want to change a product simply due to unit conversions. You simply take note of the units and move on. I never thought I'd have to deal with microinches, to be honest, but it's no big deal since everyone knows 1 uin = 0.0254 microns.
the issue isn't just one of redoing the drawings along with the various checks and cross checks to make certain the units were converted properly. I'm sure they could that, but the resulting set of new drawings would be extremely prone to encouraging mistakes. As a minor example. Let's assume that on one piece they currently have a dimension of 12 inches +/- 0.01 inches. So they convert this dimension to metric giving a new value of 30.48 cm +/- 0.025 cm. Excuse me?!?!? That's a rather odd and strange dimensional target to hand off to the machinest. And you'll be getting these rather strange dimensions for everything on the original design. Frankly using the metric measurements would make that rocket utterly hell to construct. So the "proper" solution would be to use the original design and then stretch/shrink various dimensions in order to make the dimensions "rounder" and easier to manufacture. But upon doing that, they have effectively come up with a new design that has to be recertified.
I prefer imperial units for lots of everyday tasks like cooking. Imperial units are much closer to a binary-based system, which is very convenient for human beings. Two cups in a pint. Two pints in a quart. An ounce of water weighs about an ounce. A pint of water weighs about a pound. Human beings are very good at halving or doubling things by eyeball, but we're lousy at dividing into tenths.
But if you're building a fucking spaceship, use SI units for Christ's sake.
Yes...stored in electronic form. That's right. Wait, remind me again, what file format did Autocad use in the 1960s? 1970s? 1980s? Was it DWG back then?
Plus we're not building another shuttle. We're going back to the days of Apollo, with a capsule^Wspacecraft on top of a rocket. Apparently, though, they found that they can utilize the SRB design for part of the new project. (The big white rockets that get reused after launches.) The SRBs date from the start of the Shuttle era which...erm, yeah. 1970s.
So here we have a rocket booster already designed that works like a champion. The blueprints are all done. They work. They're reusable. They've been fieldtested over 100 times.
And you want to redesign them essentially from scratch? As many coders here want to say to their bosses when upper eschelon wants to recode an application in the new flavor of the month language: if it is not broken, do not fix it.
after several years it becomes difficult if not impossible to find the original file...We also use a fairly vigorous quality control system
How do you keep quality on your products, but not even keep your original documentation files? What happens if there is a change?
our drawings are created in autocad... unit conversions are not a trivial operation
The engineering team where I work uses Solidworks, and there are macros to do the conversions. Of course, those macros only work on the original files, not the printed documents... :-) So that brings us back to having lost the files...
It's not like they're building anything new or buying raw materials; they just need someone to re-draw plans with new measurements in a different system.
Frankly, and without trying to be insulting, you're so ignorant of what the issue is that it's laughable that you even have an opinion on it.
This isn't a matter of trivia, where we are worried if plans are marked in inches or mm. Change to metric, now every bolt must be metric pitch thread, every nut must be changed to accomodate. Every calculation of mass and structural integrity has to be reexamined and recalculated for new components. You don't just magically say "ok, our 3/8" bolts are now to be called 9.525mm bolts" and call it a day.
Not sure if you are joking or not, but 1 foot is exactly .3048 meters, because 1inch is exactly 2.54 centimeters.
We're just talking about units of measure. If it is easier to use imperial units because previous design and drawings were done in imperial, then that's the smart choice. I would be upset if NASA was wasting taxpayer money just so that the design could be done in metric. I actually applaud NASA for making a smart, cost/benefit engineering decision.
The fact of what it's based off of is irrelevant, everything comes down to the metric system being consistent in staying in base 10, and the imperial system is not.
Next time you should replace 4999 of those hours with a simple BASH script.
The original files were not available. What shell do you use that compiles to paper?
Write your representatives! Repeal the 2nd Law of Thermodynamics!
both SI and Imperial units are pegged to arbitrary things. In the case of Imperial units it was some king's foot. In the case of SI it is the distance light travels in some amount of time. whatever.
That's beside the pont. Yes the SI units are pegged to arbitrary things but they are not arbitrarily pegged to *eachother*.
Converting from centimeters to kilometers requires dividing by 100,000. I can do that in my head.
Converting from miles to inches requires dividing by 63,360. I can't do that in my head.
You don't seem to understand, even a little. These numbers are on a piece of paper that no longer exists on a computer. Not even the most advanced computer script in the world can adjust paper. So okay, I understand part of your point, put it into the computer first, and then run the script. These documents are crawling with numbers. Line numbers, electrical classifications, instrument identifiers. Even if I had a script to manage the process, you then have the problem of units. I'm not doing 5000 ft to meter conversions. We have lengths (using both ft, in, ',and "), weights, volumes, temperatures, powers (hp, MMBtu/hr, kW, MW) and so forth. Even if you could have a script smart enough to check for units, how would it tell the difference between a temperature and a temperature change? If I have a heat exchanger with a temperature change of 50ÂF, the correct metric temperature change is 27.8ÂC. If you got 10ÂC, you used the wrong method. The sheer amount of back checking I would have to do to make sure a rogue script didn't destroy my drawings would be insane.
This is not a simple database you're playing with.
The problem with imperial is not what it is based upon (actually, these days the US units are all defined by reference to the SI units anyway - since 1959 an inch is defined as 2.54 cm - see http://en.wikipedia.org/wiki/Inch ) the problem with the imperial system is the arbitrariness and inconsistency of the relationships between the units. The SI system has a consistent relationship between all of the units, and a consistent naming system and a consistent abbreviation system. In the imperial system, the relationships between units are not only arbitrary, but they are also inconsistent, there are multiple uses of the same word (ounces for example) used to describe different measurements (weight as well as volume) or dry vs liquid volumes.
Except unit conversions are not the norm. When a grocery store manager orders potatoes, it doesn't really matter if he orders 200 10 pound bags (which is really tough to convert to 2,000 pounds) or if he orders 200 5 kilogram bags (which is really tough to convert to 1,000 kilograms).
Sure, sometimes someone has to get a calculator to figure out how many inches are in 200 feet (but hopefully not most people) before they figure out how many 1.65 inch pieces they can cut that 200 feet into, but the other guy is going to need a calculator (or some scratch paper, whatever) to figure out how many 4.191 cm pieces they can get from 60 meters anyway.
Nerd rage is the funniest rage.
Yes the SI units are pegged to arbitrary things but they are not arbitrarily pegged to *eachother*.
Actually "imperial" units are pegged to SI units. Since July 1, 1959, the the inch, foot, yard, and mile have been defined on the basis of 1 yard = 0.9144 meters. The pound is defined as exactly 453.59237 grams.
When our name is on the back of your car, we're behind you all the way!
And a liter of water weight exactly a kg. There are exactly 1,000 meters in a kilometer. And there's exactly a year in a light year.
Wait ... one of those is wrong.
Damn right.
Consistently and accurately labeling numbers with their units is a lot more important than making sure that it is easy to convert between units and occasionally be able to quickly do math.
SI is certainly easier to work with, but the constant implication that this makes it hard to work in Imperial units is ridiculous. If someone has trouble with inches and feet, I'm not going to pay them to do any work on my rocket.
Nerd rage is the funniest rage.
There's a VERY good reason to re-use the SRB's, they are a well tested design with the flaws worked out and the real operating parameters known.
We would be remiss if we did not note that the engineering kinks of the SRBs have been ironed out, by that they killed seven people in the process.
Don't blame me, I voted for Baltar.
It never ceases to amaze me the resistance to going to metric here in the states for measurements but no one bats an eyelash at the fact our money is basically metric (base 10).
It is in fact soo damn easy that we can instinctively give somone a $5 and a penny for something that costs $4.01 so we can get back a dollar rather then 3 quarters 2 dimes and 4 pennies....
Boo metric it's too damn easy to use! Forget cutting a board 1.46 meters in half. it's too damn hard to cut it .73 meters! Better yet that 3 5/8th inch board needs to be cut in half so we need umm... err... need some scratch paper here....
-=[ Who Is John Galt? ]=-
And once the drawings are re-drawn, you have to verify the individual drawings. Then you have to verify the interfaces to make sure that vendor 'A' didn't round his tolerances in a direction that means his part will no longer properly mate with a part from vendor 'B'. Then you have to withdraw the old drawings from service and replace them with the new in an orderly fashion. Somewhere along the way you also have to not only update the references between drawings, but also the hundreds of thousands of pages of documentation, specifications, etc... that reference these drawings.
The individual steps are bone simple - but there are a lot of individual steps and they interact in various complicated ways.
An additional problem is that all this has to be done while those drawings, specifications, etc... etc... are in daily use at facilities scattered across the country, which means you have a fairly difficult problem not only in making these changes - but in ensuring everybody is 'on the same page'...
If you're dividing meters into centimeters, you can really only talk about tenths, hundreds, etc. If you're dividing yards into feet and inches, or pounds into ounces, etc. you have thirds, 16ths, 12ths, and all kinds of other useful fractions to use to think about the divisions.
And that would be an advantage for the imperial system? Really? Having to keep in mind always different fractions, instead of just 1000 (as in kilo, mega, giga... and milli, micro, nano, pico...)?
"The agriculture ministry is not in charge of Gundam" - Japanese ministry official.
I know exactly what you are talking about. We had 2000 logic diagrams to change once, and we used a script to do it in AutoCAD. Took the farm 3 hours to do, but it took us 4 weeks to check over. It's even worse when the drawings didn't come from your department, or (god help us) an outside source. We got drawings from a sister company once that were not to scale, and the title blocks were scaled by hand to 'look' right. Half of them don't even use the same blocks either, so when you write the script it only works on half of them and you are left saying 'WTF?'. Then you add in a layer filter, for example, to help the script find the right block. Guess what? Some trade school graduate from drinkachusetts screwed up the layers on every individual drawing. So you add a filter for linetype. Turns out the linetypes are all different to, and in order to make each drawing look consistent they changed the linetype scale so the .5 linetypes look ok. ARGHH we should have just redrawn them.
Speaking of databases, have you ever designed in AutoCAD using Bently AutoPlant? It links the drawings to a database. We use it where I work to design for power plants. It sucks, but we have tried many other solutions over the years and it works the best. Trying to link Pro-E or Microstation or Solidworks to a database we can use to generate Process Flow Diagrams, Piping and Instrumentation Diagrams, and Logic Diagrams is nigh impossible. Sure they are perfect for modeling, but taking the model data and converting it to schematic line drawings is a technological boundary for sure. Oh well.
If they paid their engineers $150,000/year, they could hire almost 2500 engineers for a year-long project.
Or, pay 10 engineers to make sure that the adapter between the (imperial) boosters and (metric) Ares is properly sized and be done with it. If you're pulling a boat behind a truck, you don't care if the truck engine's bolts are metric and the boat's are imperial because they don't have anything to do with each other. As long as the hitch pieces are compatible, you're golden.
Dewey, what part of this looks like authorities should be involved?
Next time you should replace 4999 of those hours with a simple BASH script.
The original files were not available. What shell do you use that compiles to paper?
lpr
So your owner there... he wants 200 10 pound bags, good... good...easy enough...
How many ounces is that? Tons?
It's a stupid system which is held onto simply because it's what we're used to. (and yes, it's easy to google the answer, but I could give you the kilogram converstions faster then you could type it)
Beware of he who would deny you access to information, for in his heart, he dreams himself your master.
Please advise us on how you're going to train every machinist, and QC agent, just to name two job categories on how to measure 30.22mm with calipers that are intended to measure in Imperial? If they can't do this, do it reliably, and do it accurately then you're going to have some funny fitting parts on those Ares.
That is just one very simple example in two very limited job categories where changing from SI to Metric would introduce horrible, and potentially disastrous, difficulties.
humans find it much easier to divide into halves than into tenths [...] Give me a gallon of liquid and a set of unmarked jugs and I'll probably have pretty darn close to 1 fl. oz. long before you can cut 1 L down to 1 mL.
a) Wow. Ok. Is that a problem you encounter frequently? This seems a bit artificial. :)
b) Yeah, I'll grant you that dividing something physically in half is easier. But while YOU might be able to pull a fluid ounce from a gallon using unmarked jugs, lets be honest most people would still really struggle with that.
c) Next, people like you and I who could solve this problem are also smart enough to realize that they don't have to physically divide into 10ths, but halves and fifths. So to cut 1L down to 1mL they need to divide by 1000... or 2x2x2x5x5x5. Fifths is harder than halves but not THAT hard.
d) Further its bit of an unfair problem. The SI problem is a 1000th cut, your imperial problem is considerably less. Its only a 128th cut. A closer problem (both in difficulty, and in the actual amounts of liquid involved would be: 4L to 50mL, which 2x2x2x2x5.
e) Further you are cherry picking imperial units. Tablespoon to Teaspoon is 3rds. Feet to inches is 12ths (2x2x3). Yards to feet is 3rds. And from yards to feet is 1760ths... and 1760 factors to 2x2x2x2x2x5x11. Yeah there's an 11 in that one. How many people do you know who are facile at 11ths? I suppose we could dig through rods and chains etc but I'd have to look up what those actually are...
f) decimal is easier for any serious work, where you have paper and calculators and computers instead of sets of unmarked jugs and cherry picked problems.
The Imperial System of measurements is not the same as the customary measurements used in the United States. The legal arbiter of measurements in the United States is the National Institute of Standards and Technology. Apendixes B [PDF] and C [PDF] to their Handbook 44 provide a good overview of the structure of the respective standards and their relationship to SI (the science based International System, which was based on the Metric System).
The word system seems misleading when applied to US customary measures. For example:
Does this make a difference? From one viewpoint, no, when do you ever need to keep something accurate within 2 mm over a mile? From another, yes, repeated iterations of computations based on incorrect conversions can produce just plain gibberish. Another bit of measurement chaos to keep in mind:
We also must remember that NASA has proven itself incapable of managing the different systems of measurement before. Ten years ago NASA crashed a Mars bound probe because of botched conversions from customary to SI units. You would think that having paid $125 million for that lesson, they would want to avoid a recurrence. But, I suppose that they are from the government and they do not have to care.
In the land of the blind, the one-eyed man is king.
Seeing the discussion here, I wonder why nobody has brought this up yet:
http://xkcd.com/526/
I grew up in rural Canada, and can assure you that you can, indeed, tip a cow. Certain breeds are more difficult to sneak up on and others wake up before they hit ground, but it is certainly not difficult once someone has shown you how. If you really are from a farm and have never done it or even seen it done, I suggest you visit us up north and we'll take you out one night and show you the finer points.