Trajectory Planning of Radio Source Tracking for the New Feed Cabin Mechanism in FAST

Bin Zhang, Zhaoyang Li, Xiaoyan Wang, Weiwei Shang, Xinyu Gao, Yifan Ma, Rui Yao, Hui Li, Jianing Yin, Qingge Yang, Qingwei Li

Abstract: To reduce the weight of the feed cabin and increase the observation range of the five-hundred-meter aperture spherical radio telescope (FAST) for reaching the galactic center, a new feed cabin mechanism (NFCM) with a lightweight nine-cable-driven structure has recently been proposed, which theoretically has satisfactory performance for the forthcoming upgrade of FAST. However, trajectory planning suitable for the NFCM is still lacking when tracking radio sources. Consequently, an optimal trajectory planning method is proposed in this article that can achieve smooth motion of the NFCM within a specific period by considering the observation requirements of FAST. Based on the motion analysis for radio source tracking, the trajectory relationship between the radio source and the NFCM is deduced by considering the rotation of the Earth. Then, based on the quintic B-spline, the observation-related cable force characteristics are designed as the objective function to obtain the optimal trajectory of the NFCM, where multiple constraints in different spaces are uniformly mapped to the observation space for optimization complexity reduction by using the graphic-based method. The simulation results show that the optimized observation trajectory of the NFCM using constraint mapping is smooth enough to track the radio source, which brings an acceptable continuity of cable length variation for effectively reducing the potential mechanical shock, and the cable force characteristics with constraints are also well guaranteed. In addition, the effectiveness of constraints, the optimality of cable force characteristics, and the feasibility of the planned trajectory are further demonstrated in simulations.