Does space effect reliability? In design we are given requirements and often the space we use in the design is well defined. Sometimes it is the size of the mechanical packaging, often a circuit card has given dimension or the device design requires that it fit inside something like the palm of a human hand. So how do these spatial constraints effect the reliability of the design and eventually the product?
Once the physical envelope is defined, the ability of the reliability engineer to impact the robustness of design is limited. The size and design margins of the components are restricted by the dimensional envelope provided. As an example an electronic component will need to be smaller to fit the design space available which results in higher power stress ratios. A simple derating analysis will show an increase of failures in time (FIT) for that component. The amount of “real estate” and layering available on a circuit card impacts the reliability of every component. With increased need for miniaturization, reliability is thus severely impacted.
Consider a transponder module on a satellite. The space for the transponder that is available is limited by the size of the payload. The payload size is not just based on the functional demands of the satellite but is also constrained by the payload capability of the launch vehicle. The “real estate” available is constrained and that has an adverse impact on the reliability of the transponder, especially where higher reliability off the shelf components are the mainstay of low earth orbit (LEO) design.
Dimensional constraints can effect whether redundancy is incorporated into the design. The reliability of the same transponder can be increased by an order magnitude simply by introducing a redundant functional pathway. But, any single failure mode in a single transponder will results in loss of mission. With a redundant transponder, a single failure results in a switch to the parallel pathway and continuation of the mission. The satellite must be able to dimensionally support two transponders and it is the reliability specialists responsibility to introduce these concepts early in the requirements phase.
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