Alignment and ground calibration of the Carruthers GeoCoronal Imager

The Carruthers Geocorona Observatory is a NASA Heliophysics mission designed to study the variability of Earth’s hydrogen exosphere. Launching in 2025, the Carruthers GeoCoronal Imager (GCI) will observe the exosphere at Far Ultraviolet wavelengths from an Earth-Sun L1 vantage point. The GCI consists of two co- aligned imagers that simultaneously provide both wide field observations of the entire exosphere, in addition to high spatial resolution observations near the Earth’s limb. The optical prescription for both the narrow field imager (NFI) and wide field imager (WFI) is discussed, including critical analyses that were performed during the design phase of the project. A deterministic alignment approach was adopted to verify performances of the imagers at visible wavelengths prior to verification in the vacuum ultraviolet. The details of this alignment plan, along with opto-mechanical considerations and requirements are discussed in detail. Finally, we discuss the imaging performance of the system in the ultraviolet utilizing a ground calibration facility previously developed for another NASA spaceflight mission.