Deep-space optical communications link availability and data volume

Optical links from a spacecraft at planetary distance to a ground-based receiver presume a cloud free line of site (CFLOS). Future ground-based optical receiving networks, should they be implemented, will rely on site diversity of cloud cover to increase link availability. Recent analysis shows that at least 90% and as high as 96% CFLOS availability can be realized from a cluster comprised of 3-4 nodes. During CFLOS availability variations of atmospheric parameters such as attenuation, sky radiance and “seeing” will determine the link performance. However, it is the statistical distributions of these parameters at any given node that will ultimately determine the data volumes that can be realized. This involves a complex interaction of site-specific atmospheric parameters. In the present work a simplified approach toward addressing this problem is presented. The worst-case link conditions for a spacecraft orbiting Mars, namely, maximum range (2.38 AU) and minimum sun-Earth-probe (SEP) angle of 3-10° is considered. A lower bound of ~100 Gbits/day under the most stressing link conditions is estimated possible.