# NASA sticking to pounds & inches

Tags:
1. Jun 24, 2009

### Staff: Mentor

2. Jun 24, 2009

### JaredJames

How many countries still use imperial? Seems a bit of a silly decision to stick to them.

3. Jun 24, 2009

### mgb_phys

So a shuttle at take-off weighs 49666 firkins and climbs to an orbit of 1588 furlongs where it flies at around 46000 furlong/fortnight
Couldn't be simpler.

4. Jun 24, 2009

### negitron

They have a good reason for it, though. Remember the Mars Climate Orbiter?

Last edited: Jun 24, 2009
5. Jun 24, 2009

### mgb_phys

The USA and Burma.

Actually the US has always been metric. After their little tiff with Britain they weren't allowed into the British Parliament to compare their measuring stick with the standard British yard ( they didn't wipe their feet and had a tendancy to throw all the tea into the harbour).
So they borrowed a metric standard from the French and based their inch on that, which wasn't quite correct. Finally in the 60s the UK and the US agreed on a standard average inch (25.4mm) just in time for the Brits to stop using them.

Just to add to the confusion the American call feet/inches 'English' units but they are sometimes different from the English 'Imperial' units. A US pint is smaller, because you wouldn't want to have to drink 562ml of Budeweiser.
This also annoys the Scots and Welsh - so can't be all bad!

6. Jun 24, 2009

### Astronuc

Staff Emeritus
I have to use both units in my work because technology companies still use English units in much of their data transmittal, but our code uses SI units internally. Plus we report to European and Asian companies, so we prefer metric.

We also use the odd mixed units like kW/ft or mg/in.

7. Jun 24, 2009

### JaredJames

I get annoyed with Budweiser, it is because one bottle of Bud (330ml) costs the same as a pint. Two bottles of Bud fill a pint glass. It's all I drink when I go out so I'm pretty good on this particular brand. I would love to see a pint of Bud. How big are the bottles out in the US? (in ml please so I can compare). We can get 250ml bottles here, but I never see the point. All pubs serve 330ml bottles. And as before, two bus to every (British) pint.

And by the way, I'm Welsh and I've only heard of the units referred to as 'British Imperial' and well, whether English or British I can't say it bothers me at all.

8. Jun 24, 2009

### FredGarvin

It doesn't matter either way. Agencies/Companies have to pick a way of doing business and it only has to make sense to the way they operate.

Most engineers could care less what units they work in.

9. Jun 24, 2009

### mgb_phys

Mostly not - it doesn't matter if a a CNC machine is reading out to 0.001" or 0.01mm
But there are problems eg. does a pound mean mass or force, is a BTU energy or power?

10. Jun 24, 2009

### Cyrus

I suggest you read the manual of the CNC machine then....

A lbf is force and a slug is mass.

11. Jun 24, 2009

I'm glad that NASA decided not to waste the estimated $370 million that it would cost to convert units. I wish I could say that I hope the money they saved is well spent towards space exploration, but NASA has long ago abandoned that dream...it's no wonder the government has repeatedly slashed their budget. Somewhere between the space race and now, the higher ups over there decided that accountability is more important than space exploration. If you ask me, there is no more honorable calling than exploring the nature of the universe we live in. This does not mean sending repeated shuttle missions to the same space station for god-knows-what. I want to see a colony on mars in the time it takes to travel to the moon + the time it takes to develop the technology - the date we started thinking about it. That means we should have been there years ago. More likely, none of us will live to see the day. Pathetic! 12. Jun 24, 2009 ### Cyrus Wrong thread, wrong argument. 13. Jun 24, 2009 ### mgb_phys They seem a little confused about that: http://www.spaceflight.nasa.gov/shuttle/reference/basics/index.html Weight At liftoff: 2,041,166 kilograms (4.5 million pounds) End of mission: 104,326 kilograms (230,000 pounds) Maximum cargo to orbit 28,803 kilograms (63,500 pounds) "Since 1981, it has boosted more than 3 million pounds of cargo into orbit" 14. Jun 24, 2009 ### Cyrus It should read, errrrrr edit: Newtons. So actually, its you people around the world calling everything 'kilograms' that's the problem. Start calling it what it is, 'newtons'. 15. Jun 24, 2009 ### JaredJames Ooh yeah, that post above, WEIGHT AT TAKEOFF and then it is quoted in KILOGRAMS. Who writes these documents? If it's NASA I would be a tad concerned. 16. Jun 24, 2009 ### Moonbear Staff Emeritus At least by the time my generation was going through school, we learned both the English and metric systems. Most people who know how to use any reasonable amount of math could work with either system. If the US switched over to the metric system, most people would probably need a fairly short adjustment period just to get a general feeling of, for example, how many grams of lunch meat to order to make their sandwiches for the week, or learn to gauge how hot or cold it is outside when temperature is reported in celsius. There's no really good reason to stick with a system of measures that's so much more complicated. As for things like engineering projects, though, I think the best policy would be to say that existing projects will continue to be supported with the English system to ensure there are no errors due to attempts to convert units as parts are replaced, etc. And then all new projects could be started with the metric system. Gradually, as things become obsolete, the English units will naturally be phased out. For the few areas where they can't easily be phased out, such as water mains, sewer systems, things where you really never replace the whole thing at once, but just parts, then once everyone is comfortable using primarily the metric system, you spend the time doing the conversions for those. 17. Jun 24, 2009 ### Chi Meson Unless you're talking about a lbm which is the mass and a poundal is the force. 18. Jun 24, 2009 ### xxChrisxx On saying that being in the UK I was brought up with metric, so for engineering work thats what I use. In every day life I use imperial, if someone asked me what my height and weight are in metric I wouldnt have a bloody clue. EDIT : I also drink pints, beer just tastes so much better in pints. 19. Jun 25, 2009 ### Blenton lol Cyrus banned. It seems theres a 'glass ceiling' to these forums. Post for long enough and you're bound to be banned. Anyway$370 million to convert units? What the hell are they doing there? I would assume everything now is in digitized format, so conversion would be as simple (or simpler) than pushing a button.

20. Jun 25, 2009

### D H

Staff Emeritus
A slug is a rarely used non-imperial unit of mass invented in the early 1900s. The US aerospace community does use the slug, but only for moments and products of inertia. For mass, the aerospace community uses the avoirdupois pound, abbreviation lb, or lbm to be pedantically clear on the distinction between pounds-force and pounds (mass). The poundal? I don't know anyone who uses poundals.

The term "pound" used without a qualifier refers to the avoirdupois pound, 0.45359237 kilogram (exactly) -- unless of course you are talking about precious metals, in which case the term "pound" without a qualifier refers to the troy pound. A pound of feathers weighs quite a bit more than a pound of gold.

============================================

Back to the main topic of this thread. A lot of the software for these new vehicles, including the flight software, is in metric because as far as software is concerned, converting to metric is a simple matter of multiplying by the appropriate conversion factor.

The hardware is a beast of a completely different color. Converting to metric involves a lot more than simply multiplying by the appropriate conversion factor. Consider something as simple as a fastener, for example. Metric fasteners have head sizes, shaft diameters, yield strength, and lead and pitch all expressed in nice even metric steps. The same goes for imperial fasteners. Simply scaling an imperial fastener to metric units does not work because the scaled fastener does not exist.

The same concerns apply to a lot of other hardware element. Converting to metric entails a complete redesign.