## 1 Introduction
### Motivation and Related Work  
Understanding the system requirements to maintain connectivity throughout a constellation is crucial. Several studies have examined the structure of satellite constellations and communications between different satellite layers. In [16], a classification of both RF and OIL links is presented, focusing on links between satellites at the same or different altitudes and between high-altitude platforms (HAPs). In [17], a satellite network utilizing OILs is examined and compared to a terrestrial network in terms of latency. In [18], the phasing parameter \(F\) is introduced to determine the relative initial satellite positions to avoid collisions. In [19; 20], OIL connection strategies are explored, focusing on efficient routing schemes with low latencies. In [20], the authors introduced a latitude parameter to examine the relationship between satellite distance and the number of connections that could be established. The authors in [6] focused on the trade-off between physical layer parameters and network latencies in intercontinental satellite links. In [21], a methodology is proposed to minimize the average network latency in intercontinental connections. In [22], the authors proposed a methodology for utilizing OILs to reduce latencies and determine the most efficient routing. In [23], the impact of atmospheric effects on optical space communications--such as signal attenuation and scintillation--is analyzed, along with their potential utilization for atmospheric measurements. The work also explores the adaptability of laser communication terminals and highlights the synergy between satellite technologies and atmospheric research. However, such factors are not considered in the present study. The primary contribution of this work is the application of a comprehensive network model to analyze optical power requirements at OIL terminals in LEO Walker delta-type constellations [24] that are widely being considered in commercial applications. The required optical power is a crucial factor that directly affects terminal design, influencing transmitter and receiver specifications, power acquisition and tracking system precision, thermal management strategies, and overall power consumption. Previous studies have typically considered the link budget without (a) accounting for the precise constellation dynamics and (b) the actual network requirements for connectivity, which involves reliable intra- and inter-orbit communication. Our approach incorporates the full constellation dynamics and is applicable to commercial constellations such as Kuiper and Starlink [6; 18]. We use the Starlink Phase 1 V2 constellation as a realistic scenario to illustrate the practical applicability of our model. We applied it in two different scenarios with varying satellite densities and estimated the power requirements for high-speed optical inter-satellite links (OILs). Our results are comparable to [19; 20] in terms of minimum distances between satellites and indicate that a 100 Gbps network can be sustained across a dense constellation of approximately 6000 satellites using transmission powers in the 300 mW range. This is an important finding, since such power levels can be supported by high-power distributed feedback (DFB) lasers [25], possibly removing the need for optical amplification,simplifying the terminal design and reducing power consumption. Such levels of satellite population are well within the planning of commercial satellite internet carriers [22; 26]. Our comprehensive model is implemented as a Python module that encompasses various constellation parameters, such as satellite count, initial positioning, inclination, and phasing, as well as terminal characteristics, including beam divergence, targeted bit error rate (BER), receiver aperture, etc., to precisely calculate physical layer performance. Also, in a straightforward way, it optimizes satellite phasing in a standard manner following [4; 18].