The comet interceptor mission navigation camera and star tracker system

The ESA lead Comet Interceptor Mission (Comet-I), to be launched 2029, is destined for a close encounter with a pristine comet or an interstellar body to be identified post launch [1]. With a fly-by trajectory swiftly passing through the target body coma, the probe will characterize the body surface and coma composition in-situ gaining unprecedented insight into the early formation of celestial bodies. The huge relative velocity between Comet-I and the target body renders ground control and intervention impossible. Homing in and passing through the fierce environment formed by the gas coma and spallated fragments and particles, the navigation relies solely on on-board autonomy. Particles colliding with the probe’s shield will cause torque jerks challenging both GNC and attitude sensors. Sun light scattered within the coma resembling a faint daylight atmosphere, will challenge both the vision based navigation cameras and star trackers. In this work we describe the navigation camera and star tracker system and its adaptation to cope with the unwelcoming environment. The navigation camera system, recovering line-of-sight of the target body to GNC, is realized in three stages to cover the enormous illumination dynamic range from early distant pickup to final approach. The star tracker system, recovering the inertial attitude of the Comet-I, is internally augmented with both gyros and accelerometers to maintain attitude track within the highly dynamic torque conditions and low signal to noise from the faint atmospheric daylight conditions.