SAE 2008-01-2160 : 2008

Ultra reliable space life support systems can be built with small additional mass for direct material supply or about twice the minimum mass for recycling equipment. The required direct supply of a material such as oxygen, water, or food for space life support can be provided in some number “r” of identical packages. If only one of the r packages fails, the life support system fails. But by providing n > r packages, so that there are n - r spare packages to make up for failures, the reliability of direct material supply can be greatly increased. Ultra reliability can be achieved if the required direct supply is provided in 10 to 100 or more packages with 1 or 2 spare packages, so the additional mass required for ultra reliable direct life support is only a few percent. Recycling equipment for oxygen or water recovery can be designed to have a large number of subsystems and components so that the failure modes are localized, separated, and contained, and so that the failure rate of each component is small because the failures are distributed over a large number of components. Ultra reliability can be achieved if a sufficient number of spare components is provided. A simple model of this process, a worst-case because of a uniform distribution of fault sources, shows that ultra reliability can be achieved by providing a single spare for each component if the number of components is large enough. Ultra reliability for recycling equipment can be achieved by only doubling the equipment mass. Mathematical analysis and example data expand and confirm this surprising result.

Cross Reference: