We report progress in the design of the BepiColombo Mercury Imaging X-ray Spectrometer (MIXS). This instrument consists of two modules; a Wolter I soft X-ray telescope based on radially packed microchannel plate optics (MIXS-T) and a profiled collimator which uses a square pore square packed microchannel plate array to restrict its field of view (MIXS-C). Both instrument modules have identical focal planes (DEPFET macropixel array) providing an energy resolution of better than 200 eV FWHM throughout the mission. The primary science goal of MIXS is to perform X-ray fluorescence spectroscopy of the Hermean surface with unprecedented spatial and energy resolution. This allows discrimination between different regolith types, and by combining with data from other instruments, between competing models of crustal evolution and planetary formation. MIXS will also probe the complex coupling between the planet's surface, exosphere and magnetosphere by observing Particle Induced X-ray Emission (PIXE).

We report progress in the design, theoretical modeling and experimental characterisation of microchannel plate (MCP) X-ray optics for the BepiColombo Mercury Imaging X-ray Spectrometer (MIXS). We show that MCP optics technology allows the design of a highly capable imaging telescope with 1 m focal length, a 1° field of view and approximately 50 cm2 of on-axis effective area at 1 keV. Of a total instrument mass budget 7.3 kg, less than 2.3 kg is allocated to the optics assemblies, telescope tubes, support structures and the electron diverters (used to deflect electrons from the focal plane). The instrument science goals require an imaging resolution of 9 arcminutes, with a design goal of 2 arcminutes. Recent experimental data, taken from individual optic elements is presented to show that MCP quality is in good agreement with the error budgets assumed in theoretical calculations of performance.