Design and Performance of the ICON EUV Spectrograph.

We present the design, implementation, and on-ground performance measurements of the Ionospheric Connection Explorer EUV spectrometer, a wide field (17° x 12°) 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 Oil emission lines at 61.6 nm and 83.4 nm. Its design, using a single optical element, permits a 0°.26 imaging resolution perpendicular to the spectral dispersion direction with a large (12°) acceptance parallel to the dispersion direction while providing a slit-width dominated spectral resolution of ~ 25 at 58.4 nm. Pre-flight calibration shows that the instrument has met all of the science performance requirements.