Comparison of Ka-band link design strategies for solar probe plus

This study compares different strategies for planning and controlling the Ka-band downlink for NASA's upcoming Solar Probe Plus mission. This downlink provides the science data return: as such the availability of a specific pass is of less importance than the average performance of the link over an entire orbit. Three options for setting the link data rate were considered in this study: 1) a single data rate optimized for maximum effective data rate at the beginning of the pass, 2) a single data rate set to optimize return over the entire pass, and 3) a stepped data rate which optimizes the return over consecutive portions of the pass. In each case, the data return is characterized using a statistical model for the Ka-band link parameters, including weather and elevation-dependent G/T, yielding a cumulative distribution function for available data rate. It is important to the mission to minimize the contact time needed to meet the mission's science data requirement. Hence we propose a downlink methodology that minimizes contact time subject to constraints on data delay and complexity.