Word
Redundancy
Extra capacity or an additional route that can preserve a function when something fails
Examples
A second power source provided redundancy only if the same fault could not disable both.
The spare pump added little redundancy because it depended on the broken controller.
Origin
In ordinary language, redundancy can mean something unnecessary or repetitive. Engineering gives the apparent excess a purpose: capacity that seems idle during normal operation may become essential after a failure. The distinction is between extra parts and an available extra function.
How it connects
The word distinguishes purposeful extra capacity from mere duplication.
This word appeared in The spare that can actually help, the Involves connection for September 15, 2026, which asked: When does having more than one system make you safer?
Check yourself
Which backup provides the strongest redundancy against a power failure?
A second system with a separately protected power source. Exactly. A backup must avoid the failure that disabled the primary path.
What the sources establish
Redundant capacity must remain usable after a failure; Apollo's separate systems provided emergency resources.
Sources
Apollo 13: Mission Details (NASA), Accident, lunar module lifeboat, and incompatible canisters
Apollo 13 Review Board Report, Appendices B–E (NASA), Lunar Module Lifeboat: interchange of oxygen, water, power, and canisters