Design Requirements: Faster, Better, Cheaper...pick 2

One NASA adage is:

Better, Faster, Cheaper…pick 2

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