# Line-of-Sight Initial Pointing Model of Space Dynamic Optical Network and Its Verification
## 1 Introduction  
With the development of space optical technology, the demand for the dynamic networking of optical terminals is increasing. For example, inter-satellite networking optical communication, space optical time-frequency transmission and correction, and space gravitational wave detection have put forward increasingly high requirements for space optical networking systems. Early laser links were mainly \"point-to-point\". NASA first launched the \"Laser Communications Relay Demonstration Program\" [1] to test the capabilities of laser communications at about 22,000 miles from the Earth, conducting two-way laser-link-establishment and communication-demonstration experiments between geosynchronous orbit satellites and Earth.  
In 2013, ESA formulated the European Data Relay Satellite plan, which used microwave communications to transmit data between relay satellites and ground stations, and laser links were used to transmit data between relay satellites [2]. With the development of space science and technology, the demand for space networks is increasing day by day. The prerequisite for the application of optical networking is the establishment of network optical links. Russia planned to install spaceborne laser communication equipment on the GLONAS-K series satellites to build a laser communication network among multiple satellites [3]. The low-orbit satellite \"Starlink\" system performs optical link networking between the same orbit and different orbits to realize the interactive transmission of massive information between backbone networks [4]. In the gravitational wave detector plan, optical links and networks are established between three satellites in solar orbit to form a space triangle interferometer to achieve gravitational wave detection [5]. When a space optical link involves an atmospheric channel, the impact of atmospheric turbulence on the transmission beam cannot be ignored. The Gamma-Gamma model [6], lognormal model [7], etc., can usually be used to describe its power-spectrum distribution characteristics for analysis, and then analyze its impact on boresight capture and tracking accuracy.  
As one of the key technologies of space optical networking, LOS initial pointing technology is the prerequisite and a guarantee for various space applications. Reference [8] modified the LOS pointing model and verified its functions and indicators using Terra SAR-X and NFIRE. Taking aircraft-to-ground laser communications as the research background, reference [9] proposed an LOS pointing system that incorporated Kalman filtering technology, which improved the pointing accuracy of LOS pointing, but also reduced the size of the FOU of the LOS from 10.06 mrad to 5.06 mrad. Reference [10] proposed a dynamic initial pointing algorithm based on an integrated GPS/INS navigation system, and designed a hardware system for outdoor verification of the algorithm. The correctness and reliability of the pointing system were analyzed.  
This article studies the principle and implementation method of laser-link building between space networks based on existing \"point-to-point\" laser-link building techniques. Based on the impact of real-time position and attitude changes on the LOS pointing, and through the principle of coordinate conversion and transfer, a \"point-to-multipoint\" multi-link LOS initial pointing model was established. We completed model verification and indicator testing in the dynamic space optical networking test.