# Test Method for Single Satellite's Inter-Satellite Link Pointing and Tracking via Ground Station
###### Abstract  
An inter-satellite link is a key technology that improves control accuracy, transmission efficiency, and autonomous capability of constellations. A satellite's pointing and tracking abilities mainly determine the inter-satellite link's performance, which should be validated through an in-orbit test. However, during the construction of the constellation, the distribution of satellites does not satisfy the constraints of establishing the inter-satellite link. A test method for inter-satellite link pointing and tracking is developed with respect to a single satellite. A practical mission scenario for testing inter-satellite links' performance is constructed. A virtual satellite is introduced as the target satellite to establish an inter-satellite link with the local satellite. The orbit of the virtual target satellite between two ground stations is characterized based on the Newton-Raphson method. By comparing the predicted and actual time differences between two ground stations receiving the signals from the local satellite, the inter-satellite link pointing and tracking abilities are evaluated independently. Numerical simulations verify the design of the virtual satellite. The single satellite test method for inter-satellite link pointing and tracking abilities is available. virtual satellite; inter-satellite link; pointing and tracking; in-orbit test; ground station +
Footnote †: journal:  
0000-0002-1199-22001/0000-00002-1199-2001/00000-00002-1199-2001/0000002-1199-2001/000002-1199-2001/000002-11999-2001/0  
redundant observations. [PERSON] et al. eliminated the effect of empirical weight on the fusion data processing, thereby increasing the orbit determination accuracy [11]. [PERSON] et al. [12] and [PERSON] et al. [13] studied high-precision clock synchronous correction methods. According to previous studies, a precondition for employing an inter-satellite link is that the link equipment of the constellations is in a consistent state, which guarantees continuity and reliability. Therefore, high-confidence verifications of the performance of an inter-satellite link should be conducted. However, current studies do not involve an efficient in-orbit test method for the performance of a constellation's inter-satellite link, especially when the constellation is still under construction. This restricts the rapid iteration and further development of the inter-satellite link technology for mega-constellations. In practical missions, the in-orbit test of an inter-satellite link's performance concentrates on the pointing and tracking abilities of a satellite in an operation state. Typical inter-satellite link transmission mainly involves microwave and laser equipment, which are widely used for data projection and relay [14; 15]. The microwave beam is wide, but the transmission rate is low [16; 17; 18]. Laser beams show high-speed and strong anti-interference ability, enabling efficient and accurate transmissions between satellites. The test methods for this equipment have been studied. [PERSON] et al. completed the test of orbit determination for the Galileo spacecraft based on two-way laser inter-satellite links [19; 20]. The results show that the orbit determination efficiency via an inter-satellite link is related to the visibility of the other satellites in the constellation. [PERSON] et al. analyzed multiple search methods, such as scan/gaze and scan/scan [21]. The influences of a satellite's structural vibration on the inter-satellite links were studied. A compensatory method was then developed to eliminate deviations between the pointing vectors of the transmitter and the receiver telescope. To achieve high-accuracy signal capture and tracking, both the microwave and laser in the above research required the altitude of the satellite to calculate the inter-satellite link pointing angle [21; 22]. In-orbit tests are carried out accordingly [23]. [PERSON] et al.