IXO telescope mirror design and its performance

The International X-ray Observatory IXO, a candidate follow-on mission for XMM/Newton and CHANDRA, has been studied in Europe in the frame of two parallel industrial assessment studies commissioned by ESA as part of the Cosmic Vision 2015-2025 programme. One of these studies was successfully carried out by EADS Astrium. The present paper is focussed on the results obtained by Astrium GmbH in this study, i.e. on the optical, mechanical and thermal design of the IXO telescope mirror and on the predicted telescope performance. The IXO telescope mirror consists of nearly 1700 Silicon Pore Optics (SPO) mirror modules [1] accommodated on eight identical petal-shaped support structures. These petals are themselves supported by an optical bench. Design drivers proved to be the allowable mass, the required optical throughput as well as the axial and lateral stiffness required by the launch vehicle. To ensure light-weighting, low thermal gradients as well as robustness during AIV, the petals and the optical bench are deliberately made of a high-modulus carbon fibre material with high thermal conductivity. The telescope optical performance achievable with this design has been analysed based on rigorous finite element, thermal and optical modelling. It has been found to be fully compliant with the required optical throughput and image quality, thus enabling the scientific benefit of the IXO mission.