Future optical ISL characteristics from the perspective of large commercial constellations

The birth of large LEO constellations dedicated to personal communications in the past few years has created formidable new tasks for the space industry. Systems such as the IRIDIUM ^{\scriptsize{\circledR}} Program, Globalstar ^{\scriptsize{\circledR}} , and Odyssey ^{\scriptsize{\mathrm{TM}}} challenge the long standing paradigm on how to design, build, and launch satellites. A second generation of big LEOs is now being planned to offer broadband services for Internet access, cellular backhaul, videoconferencing and distance learning. Systems such as Teledesic ^{\scriptsize{\mathrm{TM}}} and M‐Star are planned to make extensive use of inter‐satellite links.

Until now, these crosslinks have been implemented using RF technology, but as the data rate of these systems increases, serious consideration must be given to the use of optical inter‐satellite links. Much has been discussed in the media over the past years about the relative merits of both optical and RF approaches. This paper avoids this debate, and examines the reasons that RF technology currently dominates inter‐satellite links. The cost of existing optical terminals for space has is measured in the millions to tens of millions of dollars. These figures often compare to the total on‐orbit cost of the satellites in commercial constellations. Clearly, a significant paradigm shift will be required in order for producers of optical ISLs to realize a business from these commercial satellite programs. This paper discusses both the technical and programmatic requirements of terminals for such systems in order to provide the industry a better understanding of upcoming needs and constraints essential for their success.