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One of the largest challenges for optical systems is eliminating stray light generated by reflections off the walls and other optical elements of the device. Most black coatings are not sufficiently effective at grazing angles. Acktar's black coatings exhibit particularly low residual reflectance and have been implemented in various instruments. The new proposed material exhibits particularly low hemispherical and specular reflectanceespecially at grazing angles.

In the context of ESA's Cosmic Vision 2015-2025 scientific program, Solar Orbiter (SolO) represents the first M-class mission, currently under implementation for a launch planned in October 2018. One of the SolO solar remote-sensing instruments is the Multi Element Telescope for Imaging and Spectroscopy (METIS), under development by an Italian consortium ATI composed by CGS and TAS-I. METIS is a coronagraph that will perform simultaneously broad-band imaging in visible light and narrow-band imaging in UV of the Sun corona with unprecedented spatial resolution. The surfaces of several Ti-6Al-4V components of the METIS Optical Unit must have a very low reflectance in order to minimize straylight and therefore ACKTAR Magic Black™ coating was specified. An example is represented by the internal surface of the Inverted External Occulter (IEO) -the front part of the instrument -which is exposed to the direct solar flux and experiences challenging environmental conditions. Qualification for 450°C was required whereas Acktar's Magic Black™ qualified maximum temperature was 380°C. A dedicated thermal-vacuum cycling test (100 total cycles, -120°C -450°C) was conducted to qualify Magic Black™ to quantify any performance degradation under these conditions:• optical (reflectance) • thermal (α and ε values) to allow calculation of the radiative heat transfer of the METIS parts during mission • mechanical performancesThe following success criteria were established:• total reflectance at wavelengths of 400-1000nm <5% • degradation of absorptance α and emissivity ε to be <10% • surface resistivity < 5 kΩ/square