Improvement of Trajectory Estimation Considering Imaging Delay for Autonomous Image Tracking System in Flyby Observation

In recent years, close approach exploration, called flyby, of asteroids by small spacecraft has attracted attention. In flybys, guidance based on a spacecraft trajectory pre-calculated on the ground is problematic because the accuracy of tracking and imaging is degraded due to uncertainty in geometric parameters during spacecraft navigation. In particular, recent missions tend to fly at higher speeds and shorter proximity distances to the target asteroid. Therefore, the effects of camera measurement error and delay time cannot be ignored, making it difficult to achieve the required performance with simple feedback control. To improve the flyby accuracy, highly accurate trajectory estimation based on measured relative trajectory and the design of a precise control system for the actuator is effective. This paper focuses on accurate trajectory estimation, where a trajectory estimation method based on an online autonomous imaging algorithm is proposed. The least-squares method estimates the relative velocity between the spacecraft and the asteroid. Based on the estimated relative velocity, an accurate target trajectory is generated. In addition, a target trajectory with improved accuracy is generated by correcting the camera's delay time, and the imaging system's actuators are controlled based on the trajectory. The accuracy of the tracking system is evaluated through experiments using an experimental setup that simulates a flyby exploration.