In-Flight Performance of the ICON EUV Spectrograph.

We present in-flight performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field ( ${17}^{\circ }\times {12}^{\circ }$ ) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the Oii emission lines at 61.6 nmand 83.4 nm. In flight calibration and performance measurement has shown that the instrument has met all of the science performance requirements. We discuss the observed and expected changes in the instrument performance due to microchannel plate charge depletion, and how these changes were tracked over the first two years of flight. This paper shows raw data products from this instrument. A parallel paper (Stephan et al. in Space Sci. Rev. 218:63, 2022) in this volume discusses the use of these raw products to determine O⁺ density profiles versus altitude.