In article ,
Derek Lyons wrote:
Being able to implement your design change tomorrow, so you can start
testing it the day after, does wonders for cost-effective engineering.

That sounds suspiciously circular; "the secret to building stuff
cheaply is to buy stuff cheaply". (Setting aside the fact that
cost-effectiveness and total cost are only loosely coupled.)

It's not so much whether the parts are *cheap* -- although that helps --
but whether you can get them quickly. It's a question of the speed of
design iterations, and the ease of building multiple copies early so you
can get them into testing early and make bench-test hardware widely
available.

When parts availability is a major bottleneck, the engineering process is
much less flexible. You have to make commitments far in advance, and a
lot of man-hours get spent inefficiently on reviews and double-checking
because design mistakes cost a lot of time. There is great pressure to
sign off on poor designs, even if they're likely to cause problems later,
because there is too much invested in them and no time for more design
iterations. Testing has to be delayed until near the end, and if it finds
problems -- which it almost always does -- you may be in deep trouble.
Related development tasks (e.g. software) have to start long before real
hardware is available, so a lot of effort gets put into simulators and
fake testbed hardware, which may or may not be representative. Access to
real hardware is limited, and you have to be careful with it because it's
not easily replaced if you break it, and that too limits testing. "Real
hardware" problems like incompatible materials or fabrication problems
may not be found until very late. There is pressure to cut corners when
another design rev is really needed but there isn't quite time.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |