[PPS02-P03] Conceptual Study of Deployable Camera 5 for Martian Moons Exploration mission
Keywords:DCAM5, Deployable Camera, MMX, Martian Moons Exploration, Phobos
DCAM is a series of cylindrical-shaped small camera units of 10-cm-order length. The concept of the DCAM series is that a small unit separates from mother spacecraft and takes images with cameras at a distance away from the spacecraft for several hours. Data of the images are immediately sent to the spacecraft via one-way radio communications. DCAM1 and DCAM2 were initially developed by JAXA and mounted on Japanese solar-sail mission IKAROS, and they took images of the IKAROS spacecraft itself to demonstrate the sail deployment. DCAM3 is currently onboard the asteroid probe, Hayabusa2. It will capture the images of the Hayabusa2's impact experiment on the asteroid at a close distance, while the mother spacecraft is at a safe distance to avoid contamination due to the impact fragments.
The new DCAM5 system is designed for MMX to deploy several small units from orbits down to the Phobos surface. Each unit has two visible-infrared multi-band cameras, close-up cameras, and a tri-axial accelerometer in a small cylindrical-shape chassis. The following scientific observations are conducted by DCAM5: (1) imaging the various scales of Phobos surface at visible-infrared at different altitudes on the descent trajectory, (2) measuring the acceleration response of a collision with the Phobos surface, which reflects the physical condition of the top surface layer, (3) taking close-up images of the regolith particles after the probe comes to rest on the surface, and (4, extra) imaging of flying dust from the impact point. Potential landing sites for DCAM5 will be selected in regions where the mother spacecraft cannot approach, due to, for example, high slope or complex topography.
While the most of the system and the electrical design of DCAM5 inherit from DCAM3 on Hayabusa2, main issues in the current conceptual studies are the radio communication antenna and transmitter on the separation unit, and the separation mechanism. Radio communications from the DCAM5 unit to the mother spacecraft must be omnidirectional since the attitude of the unit is not controllable after landing or bouncing on the Phobos surface. The antennas of the unit must be carefully designed to capture the mother spacecraft in the antenna pattern with a sufficient S/N, with considering radio reflection at the ground surface. The omnidirectional antenna on the unit was designed and selected via trade-off studies, and its performance was investigated by numerical simulations. Specifications of the separation mechanism affect a subsequent trajectory of the DCAM5 unit to Phobos. According to the results of the numerical studies for the descent trajectories of DCAM5, a relatively high separation velocity of 40-100 cm/s is desired for the separation mechanism. Therefore, a new separation mechanism was designed to satisfy this requirement.