Slashdot Mirror
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.)
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.
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.
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!
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.
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?
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.