X-IFU system requirements breakdown justification

Abstract

This document justifies the flow down of the major X-IFU performance requirements among the main subsystems. The main goals of it are to explain how the input requirements are flowed down into several lower level requirements, to show that the “burden” is shared in an optimal way among the various subsystems, and that, from a system point of view, no subsystem is over specified. Another important aspect of this document is to detail the X-IFU understanding of the input requirements, to provide clear definitions and objective ways to interpret it. Sometimes, assumptions need to me made, that have still not been discussed with ESA and translated into requirements: these assumptions are also stated whenever they are needed to flow down the requirements. This document will be updated continuously during the development, so that subsystem requirements origin and justification can be found when the requirement engineering process goes on, and will be used in addition to the classical requirements traceability to guaranty that when a requirement changes, all the consequences are well understood.