Vision-Based Rapid Target Tracking Method for Trajectories Estimation and Actuator Parameter Uncertainties for Asteroid Flyby Problem

Flyby imaging has attracted attention as a method for small body exploration and the requirement for an accurate target tracking system becomes higher for the mission quality. A relative trajectory that is either designed or estimated offline contains uncertainties, and they cause errors in the targeting profile generated for imaging missions. Online relative trajectory parameter estimation is required to obtain high-quality imaging, and visual-based tracking systems are popular for estimating the relative trajectory. In addition to the uncertainties in the measured or estimated relative parameters of trajectories, the high relative velocity between the spacecraft and the asteroid, as well as the actuator driving characteristics have a negative impact on asteroid tracking. To overcome the problems, this paper proposes a control system with two degrees of freedom, which includes a vision-based feedback controller and feedforward controller. The feedforward controller contains two compensators: the first utilizes a real-time vision-based relative trajectory estimator and predicts the future relative trajectory from the results of the estimation, and the other compensates for the actuator characteristics. The applicability of the proposed control system is discussed by using a case study based on numerical simulation. The results show the effectiveness of the proposed concept.

I. Introduction

Small bodies, such as asteroids and comets, are likely to retain the conditions under which they were formed owing to the absence of atmospheric and crustal movements. Thus, they are expected to provide data that are useful for elucidating the conditions at the time of the birth of the solar system and the process of its evolution [1]–[5]. Flyby, which is one of the methods that is employed to explore celestial bodies entails spacecraft to collect various types of information while passing near the target body. Starting with the Halley's Comet flyby observation in 1986, many spacecraft have since succeeded in the flyby observation of small bodies. Generally, the quality of the image is proportional to the size of the telescope and in reverse proportion to the relative distance from the target body. Recently, the spacecraft tends to become smaller and the telescope size is limited under the resource constraints. Achieving precise observation with a small telescope means that the required relative distance becomes smaller and the importance of a precise navigation system becomes higher. At the same time, a target tracking system is required to enlarge the observation opportunities. In this regard, visual-based tracking systems are popular. Figure 1 shows an overview of the flyby imaging. The telescope's line-of-sight is controlled to track the target body direction during the flyby. Fig. 1.

Target body tracking during the flyby.