Universal Principles of Design, Updated and Expanded Third Edition

123 No Single Point of Failure

The design of systems to be able to continue operating even when components fail.

A single point of failure is an element of a system that, if it fails, will cause the entire system to fail. Therefore, the no-single-point-of-failure principle (NSPF) refers to the design of systems such that they can continue operating at a safe level — i.e., without harm to people and property — despite the failure of one or more constituent elements.1

The key to eliminating single points of failure is adding redundancy, but this is not always possible. Adding redundancy invariably increases cost, complexity, size, and weight, which often cannot be accommodated in a design. For example, the James Webb Space Telescope has 344 single ...