The Solar Transition Region UltraViolet Explorer

We present the proposed Solar Transition Region UltraViolet Explorer (STRUVE) CubeSat mission. STRUVE is a slit-scanning, full-Stokes spectropolarimeter that observes the Sun in the near-UV in the wavelength band recently identified by Judge et al. (2021) as a particularly promising region for diagnostics of chromospheric magnetic field. The observed wavelength region contains the well-known Mg II h and k lines as well as a plethora of Fe I and Fe II lines that together will allow diagnostics of the magnetized plasma in the volume of the solar atmosphere from the photosphere through the chromosphere, and into the transition region at the base of the corona. This capability is unprecedented, and highly relevant for an improved description of the magnetically connected solar atmosphere. The main objective of STRUVE is to advance our understanding of the energy build-up and storage in the solar atmosphere, and its eventual release through flares and coronal mass ejections. STRUVE data will be interpreted using inversion codes that take into account the proper physics of chromospheric line formation, and employ machine learning techniques to keep computational cost at manageable levels.