# The Impact of Space-Based AIS Antenna Orientation on In-Orbit AIS Detection Performance
###### Abstract
Quantitative AIS performance can be measured by comparing the number of messages received by the space-based AIS system to another AIS system such as terrestrial-based AIS [14]. The other one, qualitative AIS performance, can be assessed by comparing the portion of valid messages to all received messages containing erroneous data [15]. In order to study the in-orbit performance of the LAPAN-A2 AIS system, in this paper, a quantitative LAPAN-A2 AIS performance in terms of message reception has been performed based on its AIS  
Figure 1: Illustration of the LAPAN-A2 microsatellite. antenna orientation. Since LAPAN-A2 is also equipped with another payload, i.e., multispectral camera, in some cases, in order to point a camera lens to a specific target, the satellite has to be maneuvered into the desired angle. This maneuver will set the AIS antenna position to be oriented, causing a shift angle towards its default position. Since the difference in antenna orientation produces variations of covered ground area, we have hypothesized that satellite maneuver can affect the number of receive message and the message reception performance. Therefore, in this paper, the measurement of LAPAN-2 AIS receiver performance was carried out by varying the antenna orientation. Since this research is intended to study the impact of different AIS antenna orientations on its message reception performance, there is no ground truth or other AIS data involved in this research. This data may be required if one desires to compare LAPAN-A2 AIS performance to other AIS systems. In case no specific maneuver is required, the LAPAN-A2 satellite is set to nadir pointing mode. In the nadir pointing mode, the spacecraft's camera or \(z\)-axis is oriented to the center of the Earth, and this mode is defined as the nominal pointing of LAPAN-A2 satellite. During this nominal pointing, LAPAN-A2 AIS antenna is oriented to the south direction or 90\({}^{\circ}\) from its nadir direction. Since the antenna is mounted fixedly on the satellite's body, to provide different antenna orientation, we have maneuvered the attitude of the satellite so that the AIS antenna will orient to 135\({}^{\circ}\) and 180\({}^{\circ}\) from nadir direction or 45\({}^{\circ}\) and 90\({}^{\circ}\) from its flight direction. All AIS messages collected during those maneuvers are analyzed and compared to messages collected in the nominal pointing (nadir pointing). The AIS datasets collected during the maneuvers are then analyzed to study the impact of antenna orientation on its reception performance quantitatively. The details of AIS antenna orientation and flight configuration are shown in Figure 2 below. Finally, the result of this research is organized to produce an essential recommendation related to orienting and positioning the AIS antenna. Even though this research has been performed on LAPAN-A2 satellite, the result is suitable to be used as a reference by other typical small satellites which already exist in the orbit. Moreover, the result can also be used in determining the right AIS  
Figure 2: Nominal flight configuration of LAPAN-A2. antenna position and orientation for any satellite being developed which plans to carry similar AIS antenna to LAPAN-A2 or other typical omnidirectional antenna.