Deep-Space Optical Communications Downlink Budget from Mars: System Parameters,” The Interplanetary Network

This article describes the elements of a design control table for an optical commu-nications link from a spacecraft in Mars orbit to a ground-based receiving station on Earth. A fixed average laser transmitter power of 5 W transmitted through a 30-cm-diameter near-diffraction-limited telescope is assumed, along with a 10-m-diameter ground receiving antenna. Pulse-position modulation of the laser with direct de-tection also is assumed. An end-to-end systems analysis is presented to provide the expected signal and background-noise photons as a function of the Earth–Mars range. The signal and noise photons received are treated using an ideal Poisson channel model in order to predict data rates when Mars is close to conjunction. The data rates range from 5 to 40 Mb/s with a large part of the uncertainty owing its origin to variability of the atmosphere. The article also concludes that further work is required in order to narrow the rather wide range of preliminary data rates presented. I