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0 pointstjradcliffe11y ago0 comments

That is precisely the policy adopted by NASA, and it lead to the Mars disaster, so you are suggesting as a solution the exactly policy that caused the problem.

Furthermore, you are suggesting that the same entities--highly trained engineers and scientists and project managers--that proved inadequate to follow the policy you are suggesting last time can somehow be expected to follow the policy correctly at all times in the future.

Reducing needless complexity--in this case by enforcing a standard of common units so that when the inevitable inevitably occurs and someone forgets to label things--there is a much reduced (but still non-zero) chance of undetected mis-matches occurring.

Furthermore, it is very difficult to confuse milli-newtons with newtons even if a project was for some reason using both, because they differ by three orders of magnitude, which tends to get noticed. Whereas kilograms and pounds differ only by a factor of 2.54, which might be--and in fact has been--missed.

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Ankaios11y ago

Are you seriously claiming that a policy of labeling and testing units caused MCO to be lost?

Have you actually studied the mishap? If labeling and verifying the units was done carefully it would have prevented the accident.

A millinewton/newton mix-up could easily occur in a case like this one, too. The particular numbers which were misinterpreted in MCO's case were often small, and I can easily believe no one noticing similar ones being a few orders of magnitude off. (I do have a hard time imagining it with MCO's particular numbers, though.) Similarly, you can be bitten by a meters/centimeters switch or accidentally using different representations of the same quantity, such as specific impulse and its corresponding characteristic exhaust velocity, which only differ by a factor of about 10 when both are expressed in SI units.

I maintain that the key lesson is to always label your units, and to test them carefully and routinely, including at interfaces. I believe that claiming that using English units (as gross as they often are) caused the failure misses the more fundamental root problem.

(Also, I'm not claiming that labeling and verifying units is easy. I emphasize it partly because it's hard. Little of our current software ecosystem includes any concept of dimensionful numbers.)