Dust Monitoring Instrument on Cubesat for Small Body Mission

Introduction: NEAR Shoemaker and HAYABUSA landed on asteroids and Philae of Roset-ta mission and HAYABUSA-2 are going to land on Churyumov-Gerasimenko comet and 1999 JU3 asteroid , respectively, as of writing this abstract. For such missions in the future, we suggest dust monitoring instrument on a CubeSat dispatched to the target body from the main spacecraft. CubeSat is a type of minia-turized satellite for space research and launching pod system is reliable. Using such small probe, we are able to investigate obviously-dangerous field where the main spacecraft does not approach. In this paper, we describe a concept idea of dust monitoring by CubeSat probe in small body mission. Purpose of dust monitoring: Environment survey. Dust particles may exist on the surfaces of or around bodies, asteroids and comets. Those dusts could affect spacecraft approaching the bodies for landing. Those dust can be risk on the spacecraft operation. For more security, the risk that the spacecraft would be damaged by dust impact, adhesion , and other effect has to be assessed and preliminary environment survey has to be conducted before approaching to the target body. The spacecraft must have navigation cameras and observe the surrounding space of the target bodies from remote position. But it is difficult to recognize small dust particles as mm to cm size from distant position unless the spatial density of the dust is sufficiently thick so that scattered sunlight can be detected. Impact ejecta monitoring. In Hayabusa-2 mission, an impactor of 2 kg will be ignited to aim at the surface on 1999JU3 at 2 km/s. The imapct experiment will excavate the subsurface materials to be sampled. In such impact experiment, detecting ejecta grains will give us meaningful information on the surface and the interior of asteroids [1]. Recording the position and the time when ejecta grains are detected with DM, we reconstruct the trajectories of the grains and obtain their ejection speed and angle. In particular, the ejection angle is informative since the ejection angle reflects the porosity around the impact site: The ejection angle tends to become high for fluffy target [2]. In addition, the trajectory reconstruction enables us to determine the speed of the ejecta at the moment of detection. Assuming that DM detects the momentum of colliding grains, the grain mass (or size) turns out with the colliding speed determined.