Post-arrival calibration of Hayabusa2's optical navigation cameras (ONCs): Severe effects from touchdown events

Accurate measurements of the surface brightness and its spectrophotometric properties are essential for obtaining reliable observations physical material planetary bodies. To measure Ryugu accurately, we calibrated optical navigation cameras (ONCs) Hayabusa2 using both standard stars itself during rendezvous phase including two touchdown operations sampling. These calibration results showed that nadir-viewing telescopic camera (ONC-T) wide-angle (ONC-W1) experienced substantial variation in sensitivity. In particular, ONC-W1 significant sensitivity degradation (~60%) after first operation. We estimated degradations to be caused by front lens contamination fine-grain materials lifted from due thruster gas ascent back maneuver sampler projectile impact upon touchdown. While ONC-T is located very close W1 on spacecraft, was only ~15% over entire phase. If fact dust really main cause degradation, this lighter damage likely resulted protection long hood attached ONC-T. However, because large variations absolute occurred events, which should effect, uncertainty rather (3–4%). On other hand, change relative spectral responsivity (i.e., 0.55-?m-band normalized responsivity) small (1%). The proximity has been well have a (< 1%). Furthermore, increase) full width at half maximum point spread function almost negligible, although blurring effect scattering confirmed W1. events were carefully monitored as time along with time-related deteriorations, such dark current level hot pixels. also conducted new flat-field detector temperature observing onboard lamp validating Ryugu's disk images. these calibrations maintained their scientific performance updating parameters. • Touchdown Hayabusa-2 affected sensor performances largely. Variations sensitivities calibrated. Through calibration, qualities ONC images maintained.