# Trusted Autonomous Operations of Distributed Satellite Systems Using Optical Sensors +
## 2 Distributed Satellite Systems  
The current state-of-the-art DSS operation is completed when one of the satellites picks/detects the event, then it is sent to ground control, and the ground control operators conduct the reconfiguration, which is inefficient in time-critical applications. Figure 2a depicts the current state of the DSS. As shown, the highlighted satellite detects the event and transmits it to the ground station, where it is relayed to the remaining DSS satellites. With the ISL, the DSS operation can be improved, and real-time/near-real-time operations such as data sharing/processing can be performed without the ground segment as shown in Figure 2b. This provides enhanced performance for time-critical applications such as a rare event, disaster events, etc. With the ISL and the DSS, real-time operations are achieved by adding predictive and reactive elements [28; 29; 30] within the architecture that endows the iDSS. The DSS can communicate, interact, and cooperate with the ISL. ISL makes up for the lack of robustness in the DSS, which results in an increase in the amount of data exchanged and communication that takes place on-board the satellite in the DSS. [PERSON] et al. [31] provide the various strategies that are suited for DSSs. ISL can be classified as a (1) ring, (2) star, (3) mesh, and (4) hybrid configuration depending on the communication linkages that are established between the DSS. These topologies are depicted in Figure 3, with the ISL represented by the arrows. [PERSON] et al. provide a wide range of solutions in their article [31] that are ideal for DSSs. Communication by radio frequency, also known as RF, is a form of transmission that is used in wireless networks more commonly than any other method. However, current space optical communication systems promise a bigger number of benefits, such as an improved data rate, protection, lower power consumption, and a decrease in the weight of satellites. In the past, RF technology was used for intersatellite communication; however, these days, modern satellites are increasingly resorting to technology that is based on laser and optics in order to connect with one another. Utilizing technologies that are based on lasers comes with a multitude of advantages. To begin, infrared laser rays have a greater frequency when compared with RF, which results in a shorter wavelength. As a direct consequence of this, they are able to send a greater quantity of data in a single transmission. Second, in contrast with radio waves, lasers experience significantly less difficulty with dispersion when they are transmitted over extensive distances. Because of this, it is far more difficult to intercept them, which results in a large increase in the level of security guaranteed to the data transfer [32; 33; 34]. Figure 4 illustrates the applicability of RF and optical communication (using two versions, i.e., Avalanche Photodiode (APD) and Erbium-Doped Fibre Amplifiers (EDFAs)) by plotting data rate against distance. Laser-based mesh topologies are excellent for the iDSS operations due to the fact that they are more dependable and are well-suited for use in applications that require real-time processing [35]. Figure 2: (**a**) Current state-of-the-art DSS operations; (**b**) DSS operation with ISL, i.e., iDSS. Adapted from [3]. The DSS collaborates actively through the ISL where the information is shared to achieve a common mission objective. The ISL relationship between the ground station network, with the iDSS orbital plane and other orbits, is shown in Figure 5. Figure 5a shows the ISL relationship between the orbits and the ground segment, whereas Figure 5b shows the proposed iDSS constellation with ISL. Figure 4: Link distance against data rates for optical and RF ISL systems. Adapted from [36]. Figure 3: ISL classification [31].