Each of the three XMM-Newton telescopes consists of:

• the mirror assembly door, which protected the optics during integration, launch and early orbit phase
• the entrance baffle, which provides visible straylight suppression at angles larger than 47°
• the X-ray baffle
• the mirror module
• an electron deflector, which produces a circumferential magnetic field which prevents low energy electrons reflected by the mirrors reaching the focal plane detectors
• the Reflection Grating Array (only in two of the three telescopes)
• the exit baffle, which provides an appropriate thermal environment

Scheme of one of the XMM-Newton telescopes

The 58 Wolter I mirrors of each telescope are bonded on their entrance aperture to the 16 spokes of a single spider made out of Inconel (a nickel alloy). The spider is connected to the support platform via an aluminium interface structure (the MIS: Mirror Interface Structure) consisting of an outer cylinder and an interface ring. On two of the modules, the ring interfaces the mirror module to a Reflection Grating Assembly (RGA). To minimise the mechanical deformation of the mirrors and therefore the optical degradation, the flatness of the interface between the spider and the MIS had to be better than 5 micron.

X-ray baffles are located in front of the mirror systems. They act as collimators and reduce considerably the amount of straylight in the field of view of the focal plane cameras.

Light path in the XMM-Newton telescope with only an EPIC camera in its primary focus (left), and in the two telescopes in which a RGA is mounted into the optical path (right).

The XMM-Newton X-ray baffle was constructed as two sieve-plates made out of circular strips. The plates were mounted coaxial to and coaligned with the front aperture cross section of the 58 mirror shells, such that they block single-reflection rays, but do not eclipse two-reflection rays. Each sieve plate is a disk 1 mm thick with 59 circular strips and 16 radial spokes. The offset of the two sieve plates from the front of the mirror system is 385 mm and 439 mm, respectively. All the baffle surfaces facing the mirrors are blackened.

	Introduction
	Optical Design