Nearly every six months, a team of world-class experts, is regularly meeting to discuss the calibration plan of the Athena telescope. As almost any aspect of this ESA mission, it is a challenging and unprecedented undertaking to build a mirror of ~3m diameter, with ~1100 individual modules.

The last meeting was held at SRON on May 31-June 1 2017, gathering 15 scientists from Europe, US, and Japan. The meeting aimed at: a) discussing the impact of different telescope calibration schemes (full versus partial illumination) on the calibration accuracy; b) consolidating the requirements for a long-beam facility and for the associated detector; c) discussing and define the telescope calibration timeline; d) consolidating the estimate of the required calibration resources, and identifying possible avenues through which additional resources could be pooled from the science community to cover the aforementioned activities.