Re: Changing Cycles 'till it Hertz

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> > Bottom line is that, as Faraday said, "names are one thing and science
> > is another".  I doubt that any competent engineer anywhere in the world
> > was ever confused by the expression of units in either the english or
> > metric systems.  The changes were silly and didn't help the engineering
> > profession at all!  There are alleged to have been some colossal butches
> > made by confusing metric and english units, as for example in the loss
> > of one of the Mars probes, but I don't believe that.  Careless
> > arithmetic, perhaps.........
> >
> 
> I feel compelled to defend our (JPL) honor here....
> 
> JPL has used metric units (km, Newtons, etc.) for navigation of spacecraft
> for decades (probably as long as the lab has been here, but certainly since
> the 70's).  The same is not true of mechanical dimensions (although,
> currently, most (if not all) released drawings are metric), and, more to the
> point, it is not necessarily true of various and sundry vendors and
> suppliers to JPL (in this particular case, Lockheed-Martin).
> 
> The Nav guys get data from the vendor, which according to the
> specification/contract/whathaveyou is in metric, in this case, thrust in
> Newtons (impulse in Newton seconds), which is fairly standard in the rocket
> propelling business (for instance, if you buy "Estes" rocket engines,
> they're marked in metric units).
> 
> Turns out though, that nobody on either side actually checked the data to
> make sure it was really being supplied in Newtons, rather than pounds (which
> is what it was).  On the JPL side, I'm sure it never occurred to them that
> anyone would do anything else (the last navigators to use non-metric units
> probably having retired, died, or moved into senior management years ago).
> I'm not sure on the LMA side, but probably, nobody really looked at it
> carefully, it being just one set of numbers out of the pallet loads
> (literally.. I get documentation delivered to me on pallets), and everyone
> just assuming that everybody is doing the "right thing".

Jim et al:

	I wasn't intending to impune anyone's honor, just pointing out the
problems when one mixes the systems of units AND DOESN'T REALIZE IT!!! 
I never read the complete story spelled out so clearly, but at least
around Northrop the assumption always was that Lockheed had probably
goofed.  The tragedy was what happened and the loss of something
irreplaceable which could have returned fascinating information.  By the
way, assume your reference to navigators means guys controlling space
craft, as guys on earth still use lat-long of course.  Since I first got
involved with the NASA Deep Space Network way back when I've always been
fascinated with what can be done using only range/doppler information.

	Couple of other examples of stuff from my personal experience.  One is
a MIL spec on maximum microwave RF power density in regions where fuel
mixtures might be ignited.  Someone long ago converted maximum allowable
values in metric to values in english units (watts/cm^2 to watts/in^2)
but used the cm - in factor backward, with the result that the spec is
almost 10 dB too low!  Still bugs us.  Second thing is in the expression
of radar range.  All of us "old" radar guys use feet and nautical miles,
but the specification of range in kilometers is becoming common.  As a
result, guys read range in km as range in miles, and make severe
over-estimates of radar performance.  Again, no problems if one keeps
his head screwed on tight, something which seems to be rarer than it
used to be. 

	This is far off the TC subject so Terry will probably kill it, but
wanted to make it clear that no finger pointing was involved...

Ed