As the telescopes of the future grow in size, survey spectrographs naturally follow that trend. The massive appearance of the instruments designed for the ELTs provides visualization of this inevitability. At some point, we hit the size ceiling, due to many reasons including available optics size, beyond which the traditional oneoff way of building an instrument might be much riskier than before, or more costly. One logical way to get around the limit is to break up an instrument into much manageable “replicated” units. The overall system size may still be the same, but the highly concentrated risk can now be diluted across the units so that, individually, it becomes much less risky although some types of risk may be transformed into something else that requires “consistency” across the replicated units. One specific area where this matters is the alignment quality across many spectrograph units. Spanning more than a decade, several replicated instrument projects forced us to go through evolution cycles to refine our approach to the alignment of replicated spectrographs. This report provides an overview of the methods and techniques we deployed over the years and how they could be applied to ELT-generation instruments yet to come.
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