Mechanical and thermal design of XMM.

Introduction Once the scientific requirements (and goals) for a spacecraft are set, the system-level requirements follow. A global configuration is then selected that would, in principle, allow the realisation of the spacecraft within these constraints. So far, the constraints are mainly geometrical. The satellite should fit in a launcher, the (focal) distance between optics and detectors should be respected, Structural design constraints and requirements The spacecraft structure, like any other structure, is there primarily to guarantee the integrity of the spacecraft under any loading, such as during handling, testing and launch. In addition, it must allow the spacecraft to serve as an optical bench for a telescope and therefore the structure must provide the necessary thermo-elastic stability in orbit. In the case of XMM, this led immediately to the selection of ultra-high-modulus carbon-fibre composites (low thermal expansion) for the main structural elements. Another advantage of this material is its very high modulus of elasticity, which limits structural mass for a structure like this, which is (also) designed for stiffness.