Metal-coated carbon nanotube ultrathin pellicles: a high-performance solution for the optical blocking filters of the NASA MIDEX solar mission MUSE

The NASA MIDEX mission MUSE (MUlti-slit Solar Explorer), presently under development with a launch scheduled no earlier than 2027, will focus on high spectral and time resolution imaging of the solar corona by use of two separate instruments sensitive in the EUV wavelength range ~ 10 - 30 nm: a multi-slit spectrograph (SG) and a context imager (CI). Both instruments use back-illuminated CCD detectors and thus need optical blocking filters, mounted both on the telescope entrance pupil and on a filter wheel close to the detector plane, to strongly attenuate the UV/Vis band of the solar spectrum. As part of the Italian contribution to the MUSE mission, funded by the Italian Space Agency, we have proposed to use an innovative filter technology based on metal-coated Carbon Nanotubes (CNT) pellicles. We present the current design of the optical blocking filters for MUSE based on this innovative CNT technology, discuss potential advantages with respect to the baseline design, and report first results on the technology readiness assessment activity performed on manufactured small filter samples and fully representative filter models.