The objective of this paper is to familiarize weight engineers with the powerful influence that reliability and
safety requirements can have on the weight and cost of aerospace vehicles.

Results of typical reliability/safety analyses are used to illustrate the relationships between various levels of
potential reliability/safety achievement and the associated program costs. Examples are used to illustrate how the
safety requirements are first integrated into the design and how implementation of safety requirements can enhance,
or detract from, system reliability. Once the safety requirements have been provided for, system reliability is
systematically increased, at increasing cost and weight, until an optimum level is reached that is consistent with
minimum total program costs. The manner in which this optimization is achieved is described through the development
of typical reliability/weight/cost analyses.

It is also pointed out that the detailed implementation of redundancy can involve complexities that transcend the
mere addition of backup units. These complexities include the requirement that monitoring devices, with the attendant
increases in cost and weight, may also have to be added to the system to attain component redundancy.

Emphasis is placed on the necessity for ensuring that reliability and safety analyses are initiated at the start of
the design process. It is pointed out that this practice results in the early implementation of reliability/safety
design features and in the development of cost and weight statements that reflect the impact of those design features.