Well, I can see not having cameras on heat shields simply because NASA
has never done it before and it worked. They didn't have camera heat
shields on Mercury, Gemini, or Apollo so the idea of monitoring the
heat shield probably seemed not as important for the Shuttle. They
probably had it in their organizational experience that the heat
shielding works ok so you don't need to worry about it as much.

I wouldn't have been so quick to laugh at the Shuttle engineer. Using
metric shuttle parts would have been an organizational disaster at the
time: 1976-1979. Mountains of subcontractors worked for NASA, in a
country that used predominantly english units at the time of the
shuttle manufacture, would have had all of these specifications coming
in metric. It would mean that the tooling cost would go up - if people
had rules on their cutting or grinding or milling machines in english,
and had to convert to metric, you would either have to get a new tool
or do some kind of a conversion. There would be errors in parts. It
would have been a zoo.

Also, if the bulk of your engineering talent, at the time of the
shuttle, was born in the 1930s and were schooled by all those X
programs, they were probably visualizing problems in english terms, and
making someone switch to metric to make the French happy might make the
guy a lot less effective. After every problem he or she would have to
do conversions in his or head.

Given that computers do all the calculations these days, I really don't
see a need to switch to metric at all. Metric was elegant when its
measurements were all based roughly on a block of water, but, it isn't
anymore.