ICON FUV Imager

A novel design FUV spectrographic imager is currently under construction at UC Berkeley for the payload of the Ionospheric Connection Explorer (ICON). This instrument will image the limb-view atmosphere/ionosphere with a FOV of 24x18 degrees (vertical and horizontal) tilted down by 20⁰ and looking in a direction nominally perpendicular to the spacecraft velocity. From the spacecraft altitude (575 km) the view provides coverage from sub-limb up to ~500 km limb tangent height. There is a steering mirror assembly that allows steering the view ±30⁰ with respect to the nominal direction in order to observe the nightglow emissions along the local magnetic meridian. The instrument uses the spectrographic imager principle first used on the IMAGE spacecraft in which several full two-dimensional instantaneous images are formed in specific wavelength bands. One of the two bands on ICON contains the 135.6 nm atomic oxygen emission while the other band covers the N2 LBH emission region near 157 nm. When the imager is viewing the sunlit atmosphere the instrument provides the limb altitude profile of the atmospheric O/N2 ratio. On the night side the instrument observes the 135.6 nm emission that is produced by the recombination of O+ and therefore provides a good proxy for the nighttime ionospheric density. To minimize data downlink, 6 parallel vertical stripe segments will be transmitted to the ground from both channels every 12 seconds. In addition the nighttime 135.6 nm data will be integrated as two dimensional (spacecraft orbit latitude and longitude) maps. One map is projected on a sphere at 300 km altitude while the other map projects at a surface defined by the tangent height of observation from the ICON satellite. Both maps will be integrated with motion compensation to minimize blurring due to the satellite motion.