Free space laser communications

Summary form only given. Increased data transfer demands, limited RF spectral allocations, and emphasis on smaller spacecraft platforms to keep launch costs down are forcing space mission planners to consider free-space optical communications for their space-ground and intersatellite communications links. Optical communications can provide a theoretical performance advantage over conventional RF communications by as much as 60-80 dB. This advantage can be used to decrease the size of the communications terminals located at the ends of the link, and still provide significant increase in data rate capabilities (several orders-of-magnitude). Furthermore, as near-Earth missions begin flying more data-intensive instruments like synthetic aperture radars or hyperspectral imagers, communications systems that circumvent the lack of available spectral allocations will be required. Optical communications offers both the ability to achieve very high data rates with decreased-size assets on the spacecraft, while at the same time there are currently no spectral allocation limitations to the use of the spectrum. This talk will cover the basics of free-space laser communications and will apply those basics to some specific applications. First, the motivations for using laser communications will be given. Next, the technology required for a spacecraft optical communications terminal will be described, followed by the companion description of the technologies and systems at the ground end. With these basics, a simplified process for determining the performance of an overall space-to-ground link will be given. Next, a description of several previously completed, and some planned future, space demonstrations will be discussed. Finally, the applications areas for this emerging technology will be presented. While most of this tutorial will concentrate on NASA applications examples, extensions to future DoD and commercial applications will also be included.