The HySICS Pointing System: Precision Pointing of CLARREO Pathfinder from the ISS

The CLARREO (Climate Absolute Radiance and Refractivity Observatory) Pathfinder (CPF) mission will measure Earth-reflected sunlight with unparalleled accuracy over existing reflected solar (RS) sensors and will also serve as an on-orbit inter-calibration reference to other orbiting sensors. In order to achieve these goals, the HySICS (HyperSpectral Imager for Climate Science) instrument will need to be pointed at a diverse set of targets including: nadir Earth, co-aligned Earth scans with other orbiting sensors, the Sun, and the Moon. The HySICS Pointing System (HPS) was developed to provide independent pointing at these targets from its mounting location on the ISS. This paper describes the various HPS pointing modes that support CPF science, challenges and solutions of implementing the HPS on the ISS, HPS test results, and lessons learned through the design and test phases.