The International X-ray Observatory (IXO) is a candidate mission in the ESA Space Science Programme Cosmic Vision
1525, and was studied as a joint mission with NASA and JAXA. Considering the programmatic evolution of the
international context, the mission is being reformulated as an ESA-led mission, under the name of ATHENA (Advanced
Telescope for High Energy Astrophysics), with possible participation of NASA and JAXA.
The mission is building on the novel Silicon Pore Optics (SPO) technology to achieve the required performance for this
demanding astrophysics observatory. This technology is being developed by an industrial consortium, and involves also
several research institutes [1-12]. A second optics technology, slumped glass optics (SGO), which is being developed in
Europe and the USA, was the backup technology for IXO, and additionally work is progressing on improved reflective
coatings and X-ray test facilities [13-17].