Star tracker focal plane evaluation for the JIMO mission

The Jupiter Icy Moon Orbiter (JIMO) mission was planned as the first implementation of Prometheus, an ambitious space exploration project proposed by NASA. The mission would provide a rigorous scientific investigation of Jupiter and three of its moons Callisto, Ganymede, and Europa. To safely and efficiently power and maneuver the spacecraft in deep space, novel technologies would be incorporated. Though launch is currently indefinitely postponed, this mission, as conceived, already presents a significant technical challenge for a robust attitude control system (ACS) design due to severe radiation environment of the Jovian system, and because navigation sensors must survive and function properly throughout the mission. It is particularly relevant to a spacecraft´s ACS that relies on star trackers for an accurate attitude determination. A star tracker focal plane is very susceptible to impinging charged particles and cosmic gamma rays. The radiation will degrade the device performance through false signal appearance and increased noise. At Jet Propulsion Laboratory, California Institute of Technology an extensive study has been initiated to understand available visible imager technologies such as charge coupled device (CCD), charge injection device (CID), active pixel sensor (APS) in applications for radiation-tolerant star trackers. More specifically, this paper includes the results of a detailed technical study and presents relevant parameters and performance characteristics (e.g., read noise, dynamic range, dark current, hot pixel rates, quantum efficiency, linearity) that must be considered in a challenging star tracker design