Detection of tropospheric propagation effects from deep space links of the Cassini spacecraft

The bandwidth allocations for frequencies that lie below 10 GHz are limited, and thus they cannot accommodate high rate communications requirements for future deep space missions. The transition to higher‐frequency bands where there are higher bandwidth allocations is being considered for such missions. As communications frequencies increase, the degradation effects due to weather also increase. The statistics of such effects have been documented in a variety of experimental programs using geostationary satellites. Deep‐space missions operate at much weaker received signal levels than near‐Earth missions because of very large interplanetary distances. These weaker signal levels result in lower operating margins, and thus it becomes important to characterize propagation effects at these higher microwave frequencies. The Ka band frequency allocation (27–40 GHz) offers increased advantages over the X band allocation (8–12 GHz) for telecommunications. Such advantages include increased gain (using directional antennas) and increased bandwidth. Knowledge of weather degradation effects is essential for developing optimum telemetry return strategies at Ka band. This article will report on atmospheric induced effects that have been observed on a deep‐space Ka band carrier signal (32 GHz) emitted by the Cassini spacecraft between December 2002 and January 2003. The results of such work will be beneficial in the planning of operations on future spacecraft with Ka band telemetry links.