Short-distance equivalent test of acquisition, pointing, and tracking process for space laser communication

The function and performance of acquisition, pointing, and tracking (APT) for the space laser communication terminals must be characterized on the ground before the launching. However, short working distance causes the terminals to not be viewed as a point, leading to the challenge for the whole-process equivalent test. A novel equivalent test method is proposed, to the best of our knowledge, by using a narrow laser beam and the imaging relationship between two terminals. The communication terminal is transformed to a virtual point by establishing an imaging relationship between the antenna of the transmitter and the tracking detector of the receiver. Thus, the deviation angle between the optical axis of the receiver and the centroid line of two terminals can be measured accurately. Furthermore, the acquisition process of searching the small-size antenna in the receiver with an extensive coverage beam in the transmitter is replaced by searching a large receiver surface with a narrow beam. This point-searching-surface method is equivalent to the surface-searching-point method in actual space communication. With this method, two terminals spaced 5 m apart were employed to construct the short-distance verification platform, and the APT function verification and performance test were completed.