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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]."
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.
Which is the difference between scientists and engineers.... Sometimes the right decision is to listen to the engineers and not the scientists.
The scientists have it easy. They work in theories and numbers. The engineers have to produce usable physical objects. They have to do so in an environment that had significantly established manufacturing infrastructure before the SI standard existed. The countries that have converted to SI are the countries that were late to the industrial revolution party. It is expensive and difficult to overcome a massive established base of equipment. And it's a self perpetuating problem, because you can't just replace individual tools and machines as they wear out. An individual replacement has to be compatible with the rest of your infrastructure.
Sigh all you like. Short of a massive cash investment (Many Trillions of Dollars), or all manufacturing leaving the US and UK for good, Imperial units will stay and be indifferent to the sighs of the "rest" of the world.
(Incidentally, this would have been a *great* thing to spend stimulus money on instead of government employee salaries and other stupid programs.)
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?
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.
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.
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.
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.
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.
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?
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.
That *is* the lesson learned, and being followed.
There are other issues. A machine setup that can make a .5 inch bore to ten-thousandths of an inch precision, cannot necessarily be changed to make a 1.27cm bore with the same precision. Many of the machine tools used in aerospace are calibrated in SAE units, and the machines cannot be replaced economically, if at all -- lathes, milling machines, grinders etc., still in service since the 1960s or even 1940s, refit for CNC, still turning out high-precision work, and some of these cannot really be replaced.
Yes, you can calibrate a CNC milling machine to work in metric units, but precision in one system is not equivalent to precision in another system, especially when you're talking about a screw-calibrated device that is extremely accurate at whole units in its reference scale.
I'm only considering linear measurement here. When you're talking about rocket engines, I can only wonder how many physical equations have to change if you change the reference units of all the components.
In an ideal world, changing between measurement scales creates an equivalence set, but in the real world this is not such a foregone conclusion.
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