5:00 PM - 5:15 PM
[PCG30-14] Imaging strategy of DCAM3 equipped on Hayabusa2 based on radiance prediction of imaging objects
Keywords:asteroid, planetary exploration, Hayabusa2, scientific payload
SCI is approximated by a cylinder of 15 cm x φ 30 cm, smaller than the pixel resolution of DCAM3-D located at a distance of ≃ 1 km, but Beta cloth with a diffusive reflectance of ≃ 80 % is attached on the lateral surface of SCI. Assuming SCI surface is a uniform diffuse reflector (i.e., lambertian), we estimate the radiance of SCI and the signal to be detected with DCAM3-D. Since 1999JU3 is a C-type asteroid, its surface is dark with a geometric albedo ~ 0.05. We estimate the radiance of the surface of 1999JU3, assuming Hapke model with Hapke parameters for 1999JU3  as well as other C-type asteroids [4, 5] and comets [6, 7]. It is difficult to predict the radiance of ejecta because we have not yet known the surface condition producing ejecta and the size and the material property of grains consisting of ejecta from 1999JU3. On the other hand, a preliminary trial to generally construct a light scattering model of impact ejecta is in progress by means of Monte Carlo method . We use such preliminary results to estimate the ejecta radiance.
These radiance predictions were checked by some experimental tests and reflected to the imaging strategy of DCAM3-D, namely to decide imaging parameters such as timing, exposure time, and gain setup. Consequently, we prepared three imaging modes specialized for each imaging object: SCI mode, ejecta mode, and 1999JU3 mode. These modes were adequately mixed in a sequence of 1 fps imaging to cope with every situation we can assume at around the time of SCI impact. Since we have no route to access the FPGA of DCAM3 in space, its imaging parameters had to be completely set up before launch. That is, we have already released the shutter of DCAM3. GOOD LUCK!
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