  Free-space optical satellite networks (FSOSNs) will employ free-space optical
links between satellites and between satellites and ground stations, and the
link budget for optical inter-satellite links and optical uplink/downlink is
analyzed in this paper. The satellites in these FSOSNs will have limited energy
and thereby limited power, and we investigate the effect of link distance and
link margin on optical inter-satellite link transmission power, and the effect
of slant distance, elevation angle, and link margin on optical uplink/downlink
transmission power. We model these optical links and compute the results for
various parameters. We observe that the transmission power increases when the
link distance increases for inter-satellite and uplink/downlink communications,
while the transmission power decreases when the elevation angle increases for
uplink/downlink transmission. We also observe an inverse relationship between
link margin and link distance. Furthermore, we highlight some practical
insights and design guidelines gained from this analysis.
