The x-ray multi mirror mission (XMM) is the second cornerstone mission of the ESA Horizon 2000 Science Programme, to be launched in late 1999. With its three mirror modules, each comprising of 58 concentric grazing incidence mirrors, it will provide unprecedented effective area for x-ray astronomy. Three x-ray CCD cameras and two reflection grating spectrometers will be positioned in the focal plane to collect the photons and generate the scientific data. Additionally, an optical monitor will provide optical and UV imaging and timing information, simultaneously to the x-ray measurements. This paper introduces the mission objectives and elaborates the driving requirements for the spacecraft and the resulting configuration and system design. The focal length of 7.5 m creates a tall spacecraft with the mirrors on one end and the instruments on the other end, connected by a thin walled tube. This drives design choices in may areas, such as structure, thermal and test concept. The required imaging and spectroscopy accuracy leads to highly stable design solutions for the telescope tube and the mirrors and instrument platforms as well as for the attitude control. The spacecraft subsystems are described and several key system aspects are highlighted, including design aspects related to contamination control and minimization of stray light.
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