## 1 Introduction  
The development of next-generation wireless communication systems has increased interest in satellite communication systems. It aims to achieve ambitious goals, such as providing universal connectivity to reduce the gap in the connectivity, offering coverage anywhere and anytime, improving reliability, and promoting sustainability. It also aims to deliver much faster data speeds and lower latency compared to those of current technologies. Achieving these goals requires advancements not only in communication technologies but also in improving the user experience, often referred to as quality of service (QoS) [1]. These requirements have caused a rapid increase in network connections, making it hard for terrestrial networks alone to handle the growing demand efficiently. As a result, integrating terrestrial networks with non-terrestrial networks (NTNs), like satellite systems, is becoming essential to meet these needs in a cost-effective way. Satellite communication in space, especially using inter-satellite links (ISLs), offers unique benefits over ground-based networks and has attracted significant interest. ISLs can act as space-based base stations, helping to ensure high QoSs for users [1, 2]. ISLs are categorized based on orbital height, with low-Earth orbit (LEO) being one of the key classifications. Positioned at altitudes ranging from 350 to 2000 km, LEOconstellations are actively being developed by various companies and organizations. The low altitude of LEO provides distinct advantages, including shorter propagation distances and latency, reduced energy requirements for satellite launches, and cost efficiency. The advent of reusable launch systems has also drastically reduced overall costs [3]. The transition to next-generation communications introduces unprecedented demand for connectivity, driven by emerging applications, such as augmented reality (AR), virtual reality (VR), autonomous systems, and the advanced Internet-of-Things (IoT) network. The third-generation partnership project (3 GPP) also explores methods to align ISLs with requirements. One promising approach involves optical inter-satellite links (O-ISLs), which leverage optical wireless communications (OWCs) for satellite communications. O-ISLs, using free-space optic (FSO) technologies, offer numerous advantages, including high channel capacities, secure data transmission, rapid data rates, immunity to electromagnetic and radio frequency interference, and low beam divergence [4; 5]. Compared to traditional radio-frequency (RF) systems, O-ISLs exhibit superior economic and spatial efficiencies because of compact antenna sizes, reduced signal power loss resulting from shorter wavelengths (approximately 1000 times shorter than microwaves), and cost advantages. Small satellites, crucial to O-ISL systems, are considerably more economical to deploy than their full-sized counterparts. O-ISLs also support high data rates of up to 2.5 Gb/s, and propagation distances exceeding 5000 km, with freedom from frequency regulation constraints [6; 7]. Despite these advantages, several factors disrupt optical signals in O-ISLs. Solar irradiance can be a primary source of such interference. Although sunlight is attenuated on the surface of the Earth through the atmosphere, satellites' optical receivers in space are directly exposed to intense solar radiation, potentially affecting O-ISL performances. To address these challenges, this work presents a systematic analysis of the effects of solar irradiance on O-ISLs. A multi-directional field-of-view (FoV) model and a communication environmental analysis framework proposed in reference [8] are applied in this work. This model is designed to flexibly incorporate practical factors, such as multiple optical modules, FoVs, beam divergence, maximum laser propagation distance, and altitude constraints. More importantly, using an ego-centric coordinate system, the model allows for geometrical investigations based on the satellite's orientation and position at a user-specified time.