Development of a multispectral stereo-camera system comparable to Hayabusa2 Optical Navigation Camera (ONC-T) for observing samples returned from asteroid Ryugu

Hayabusa2 collected 5.4 g of samples from the asteroid Ryugu and brought them back to Earth. Measuring these samples using a camera system comparable to that used for remote-sensing observations is important for characterizing the collected samples, examining sample representativeness, and identifying materials collected from the asteroid. In this study, we constructed an instrument that enables both visual multispectral imaging and 3D shape reconstruction of samples based on stereo imaging. The imaging system has the pixel resolution of 1.93 {\mu}m/pix and field of view of 7.9 mm x 4.2 mm. Our validation measurements demonstrate that our multispectral imaging system, comparable to the telescopic optical navigation camera (ONC-T) on Hayabusa2, yields reflectance spectra with an accuracy of 3% and a 3D model with a precision of 5%. Using this instrument, we conducted multispectral measurements of two Ryugu samples acquired from two locations on the asteroid. The average spectra of the samples are consistently flat with v-band reflectance of 2.4%, higher than the overall average of Ryugu as observed with ONC-T. This apparent difference could be attributed to the potentially reflective surface of the returned grain samples.