  Free space optics (FSO) refers to optical wireless communications in outdoor
environments. The aim of this paper is to analyze the role that FSO is
envisaged to play in the creation of next-generation satellite networks. To
begin with, the reader is introduced to the types of FSO links and
functionalities of a basic FSO system. Next, a comparison of FSO and radio
frequency (RF) technologies for inter-satellite links (ISLs) is provided,
including a comparison between FSO and RF links when employed between low Earth
orbit satellites. After that, the types of FSO or laser ISLs are considered,
and the challenges in establishing laser ISLs, the properties of laser ISLs,
and the capabilities of terminals for laser ISLs are discussed. Then, the
parameters of a satellite constellation are highlighted, and different aspects
of SpaceX's upcoming mega-constellation Starlink are explored. In addition, the
optical wireless satellite network that is created by utilizing laser ISLs is
examined. Finally, a use case is investigated for next-generation optical
wireless satellite networks that are envisioned by the mid to late 2020s.
