• Aschenbach, B.
• Braeuninger, H.
• Mazzoleni, F.
• Ghigo, Mauro
• Citterio, O.
• Pareschi, Giovanni

Abstract

One of the major components of the XEUS scientific payload is given by the X-ray optics that, in spite of its enormous size, has even to be characterized by optimal imaging capabilities (the HEW goal is of just 2 arcsec). The enormous mirror dimensions give rise to a number of problems that make very challenging to meet a so ambitious request. It is impossible to realize so large mirror shells with a close symmetrical Wolter I structure (which would guarantee a high mechanical stiffness), but instead they will be formed by a series of segments (size of the order of 1 m x 0.5 m), known as petals, to be assembled together. Moreover, the Mass/Geometric-Area ratio foreseen for the mission is very small (just of 0.08 Kg/cm2), much lower than for the XMM-Newton (0.24 Kg/cm2). Finally, the optics will operate in prohibitive thermal conditions (the mirror temperature will oscillate between -30 and -40<SUP>o</SUP> C), that tend to exclude the epoxy-replication approach because of the mismatch between the CTE of the substrate and that of the resin, that would cause a deformation of the mirror profile. These considerations make very attractive the use of light weight materials with high thermal-mechanical parameters like glass or ceramics to realize the XEUS petals. In particular, in this paper we will describe the basic ideas concerning an on-going development activity devoted to the realization of the XEUS petal by large segments of thin borofloat glass. The technique to be explored is based on a thermal precision slumping of flat glass panels to produce the optics. To get the right final mirror profile, the segments will be directly grinded and superpolished. After the evaporation of the reflecting coating, the segments will be integrated in the mounting structure in appropriate way, in order not to deform the mirror profile. Some elements for the evaluation of the real feasibility of the process will be also given....

Topics

• impedance spectroscopy
• glass
• glass
• ceramic
• resin
• evaporation