One NASA adage is:

Better, Faster, Cheaper…pick 2Image 740b

The premise is that the third desire is mutually exclusive. This is obviously an oversimplification of the process however it quickly brings to light the interplay between goals.

I like to think of design requirements from an optimization standpoint. There are constraints and goals. Constraints are those that the design must meet otherwise it is not a viable product. Goals are parameters that you would like to improve.

Constraints usually read black and white. ‘The design shall have a fatigue life exceeding 1 million cycles as dictated by ISO##.’

Goals usually read as a desired direction with a target goal. ‘Unit cost should be minimized with a goal of $$’

Often the constraints get merged together. ‘Unit cost shall be less than $$’

Higher cost could be justifiable and a viable product as long as all constraints are met and the goals are favorable. However, most requirements are written as individual statements which must be checked off for a design to be finalized. Unfortunately, this leaves many great designs only living in the musings of the inventor thinking ‘what if’. Don’t turn away a golden square peg because your requirements are a round hole.


This can be accomplished by creating a goal function which wraps up all of the goals into a weighted global goal. This allows cost in this case to increase with increasing performance.

Design teams need to know  where they should go in the vast design space. I would rephrase

Better, Faster, Cheaper…pick 2

to read

_%Better, _%Faster, _%Cheaper…fill in the blanks

Image 740

Thank you.

Rob Stupplebeen