Deep-Space Ka-band Link: Design, Continuity and Completeness

The Mars reconnaissance orbiter (MRO) Ka-band demonstration has been indefinitely postponed and its objectives must now be met through other means. One of these objectives is the evaluation of the continuity and completeness performance of the deep-space Ka-band link for different link design criteria. To meet this objective, the data from the water vapor radiometers (WVR) and the advanced water vapor radiometers (AWVR) at the three deep space network (DSN) communication complexes were used. Along with these data, MRO´s DSN antenna allocation schedule, Earth-MRO geometry and telecom parameters from MRO were utilized to emulate the Ka-band link performance over a ten-month period. One pass per week per complex was selected for a total of 129 passes (43 passes per complex). For each pass, at most two data rates were chosen such that the expected data return relative to the monthly atmospheric noise temperature distribution for the given complex would be maximized subject to different minimum availability requirements (MARs). The performance of the link was measured in terms of data return, data loss, effective data rate, link availability, number of good periods, number of bad periods, good and bad period duration statistics, number of passes with outages and link stability. As expected, as the MAR was increased, the link availability and link stability increased. However, even with a MAR of 99%, 16 passes suffered outages due to weather effects. The data return remained relatively the same for MARs between 10% and 80% but it declined rapidly as the MAR approached 99%. These results indicate that a simple margin policy cannot guarantee data completeness and retransmissions must be used. Given that some form of retransmission has to be used with Ka-band, it is also recommended that the link be designed with approximately 80% MAR so that the data loss could be reduced substantially without incurring a significant penalty in data return.