Complexity in the MATISSE cold optics: a risk or a tool?

Abstract

MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) will be a mid-infrared spectro-interferometer combining the beams of up to four telescopes of the European Southern Observatory Very Large Telescope Interferometer (ESO VLTI), providing phase closure and image reconstruction. MATISSE will produce interferometric spectra in the LM and N band (2.8 to 13 micron). Building the cryogenic interferometer section of an instrument like MATISSE is inherently complex. During the preliminary design phase it became clear that this inherent complexity should not be seen as a hurdle but rather a tool; to keep project risks low it is vital to first comprehend the complexity and second to distribute these complexities to areas of expertise, i.e. fields of low risk. With this approach one prevents the typical reaction of either steering away from complexity or digging narrow and deep to find only a local solution. Complexity can be used to achieve the project goals with a reduced overall project risk. For example two alternative options: either a complex single structure with limited interfaces or an assembly of many simpler parts with, in total, much more interfaces. Although simpler in approach, the latter would be a burden on the overall tolerance chain, assembly procedures, logistics & overall cost, culminating in a higher overall risk to the project; the unintended shift of complexity and risk to a later project phase. In addition, this fragmentation would reduce the overall grip on the project and would make it more difficult to identify showstoppers early on. And solving these becomes exponentially more difficult in later project stages. The integral multidisciplinary approach, earlier discussed in “MATISSE cold optics opto-mechanical design” Proc. SPIE 7734, 77341S (2010), enables optimal distribution of complexity and lowering of overall project risk. This current proceeding presents the way in which the high level of opto-mechanical complexity and risks were distributed and dealt with during the MATISSE Cold Optics Bench instrument development.