1 Introduction

The EPIC instrument on XMM-Newton (Jansen et al. 2001) provides focal plane imaging and spectrometry for the three X-ray telescopes. Each telescope has an objective comprising a nested, 58 shell, Wolter 1 X-ray mirror (Aschenbach et al. 2000), of focal length 7.5 m, and geometric effective area 1500 cm²; there is one EPIC at the focus of each telescope. Two of the telescopes are fitted with the X-ray gratings of the Reflection Grating Spectrometer (den Herder et al. 2001). The gratings divert 50% of the flux out of the EPIC beams; with allowance for structural obscuration, 44% of the original flux reaches two of the EPIC cameras; these contain MOS CCDs (Short et al. 1998) and are referred to as the MOS cameras. The third telescope has an unobstructed beam; the EPIC instrument at the focus of this telescope uses PN CCDs (Strüder et al. 2001) and is referred to as the PN camera. All three cameras have an identical forward section that contains a filter wheel, door, calibration source, radiation shielding, the interface to the spacecraft focal plane bulkhead, and the internal bulkhead that forms part of the camera vacuum enclosure. The rear part of each camera that contains the CCDs and the cooling system is different in construction for the MOS (Fig. 1) and PN cameras. EPIC also includes the EPIC Radiation Monitor System, to record the ambient proton and electron flux (Boër et al. 1996). It provides warning of a radiation flux increase to provide for automatic shut down of the instrument. This paper describes the common items and the MOS cameras, while an accompanying paper, by Strüder et al. (2001) describes the PN camera.

Figure 1: The long conical radiators of the MOS enable the radiating surface to reach the plane of the spacecraft thermal shield to avoid parasitic heat-loads