Deep-Space Optical Communications Link Availability and Data Volume

Optical links from a spacecraft at planetary distances to a ground-based receiver presume a cloud-free line of sight (CFLOS). If a network of ground-based optical receivers is used for providing a data service from deep space, site diversity of cloud cover will be exploited in order to improve availability. In this article, a preliminary estimate of achievable data volumes, downlinked from Mars distances to a 5-mdiameter telescope similar to the Hale telescope, is undertaken. The data volume is affected by the CLFOS duration and the variation of atmospheric parameters during the CFLOS. Simplified analysis using a cluster of ground stations to comprise each node of the global network provides conservative estimates of the data volumes, to range from 60 to 90 Gbits/day when Mars is at maximum range and the Sun– Earth–probe angles are 3 to 10 deg. On the other hand, when the spacecraft range is closer, the data volumes, constrained by the maximum data rate that the Mars Laser Communications Demonstration Project can support, will be approximately 450 Gbits/day.