Hull deformation measurement for spacecraft TT&C ship by Photogrammetry

When voyaging, ships are subject to inevitable hull deformations caused by the changes in the environmental temperature and external stress. These are a crucial source of errors when measuring data using a spacecraft tracking, telemetry, and control (TT&C) ship. A prototype system based on photogrammetry was developed for the real-time measurement of a spacecraft TT&C ship’s hull deformation. This system has high accuracy, a simple structure, and convenient maintenance, and requires few changes to the ship’s structures. To improve its performance, an estimation approach is proposed for hull deformation angles. With the proposed approach, the central positions of cross spots in successive frames can be predicted based on the prediction of the camera’s attitude, and their extract locations can be found by defining a series of small windows around each predictive location. Then, the optimal estimate of the camera’s attitude is updated by the designed extended Kalman filter using the extracted cross spots and their corresponding local coordinates, with which the hull deformation angles can be found. To verify the proposed measurement approach, its performance was tested during the normal sailing, floating, and rocking on the sea of a spacecraft TT&C ship. The experimental testing results demonstrated that the proposed approach performs well in terms of accuracy and robustness. It can satisfy the hull deformation measurement requirement for a spacecraft TT&C ship in real time.