On Monday 01 September 2003 00:04, Pat Naughtin wrote: > Dear John and All, > > I have interspersed some notes from an Australian perspective. > > on 2003-09-01 03.13, John S. Ward at [EMAIL PROTECTED] wrote: > > Hi, > > > > I'm a scientist/engineer working for NASA. The metric system is used > > extensively at the Jet Propulsion Laboratory, but inch-pounds are still > > dominant. > > What do you mean by the word, 'dominant'? Could you guess what proportion > of measures (and calculations) are done in metric measures and what > proportion are done in old (USA or UK) measures? Do you know of anyone who > calculates the chemistry of fuels (for example) in kilograms and then > changes their results to pounds when they have their results. I know thatin > the brewing trade, there is a tendency to do this because the calculations > are so easy in metric and so difficult in Imperial (or USA sustomary) > measures.
Hi Pat, The short answer is, everything made out of metal is made in inches, and the large majority of most spacecrafts are metal. The large majority of mechanical drawings are in inches, and most fasteners are "standard" (i.e. they don't make sense in any units, but are specified in inches.) JPL is the most-metric NASA lab, and yet inches dominate here. Other labs deal mainly with manned space flight and legacy programs (Space Shuttle, Space Station), which done almost completely in inch-pounds units. There is a very strong correlation between education level and metric usage within NASA. Most scientists and Ph.D. engineers strongly prefer metric. Thus, the really high-tech stuff like electronic device design and fabrication is done all metric. Higher level requirements and interfaces are also often all-metric. However, we eventually turn these designs and requirements into inches drawings, because as far as I can tell no NASA machinists think metric. Machinists make a big point to not do anything in metric, and if you give them a metric drawing, they will pencil in inches everywhere, and make the part in inches. To me, this seems like a lot of extra work and creates opportunity for error. Yet most machinist bear a grudge against the metric system, and make it a point to avoid it as much as possible. They also make it a point to train new machinists inches-only, indoctrinate the anti-metric grudge, and avoid buying metric tooling. Therefore, most engineers draw inches drawings. The real reason the JPL is not metric is because there is no organized conversion effort. Everyone is left to fend for himself. There is no clear message what units or parts are preferred, or when to use which system. There is no training. There appear to be no rules, and no deadlines. Most people blindly continue to design and buy all inch-pounds hardware and equipment, apparently oblivious to two acts of Congress and an Executive Order requiring NASA go metric. Yet at some point most hardware is truly mixed. I'm sure its very common to have a 1/4" screw and an M6 in close proximity in the same component. The crazy thing is, practically everyone here has high exposure to the metric system and has had to learn to cope with dual systems. A well-planned, organized conversion would be relatively painless and in the long run would make practically everything easier for everyone. Unfortunately, the will to get it over with does not seem to exist. John
