RF Power Variations during Atmospheric Probe Descent

Radio links from probes descending into deep planetary atmospheres (Venus, Titan and Outer Planets) show power fluctuations on short timescales (seconds – minutes). These are due to several factors: generally the most significant is the vehicle dynamics which may cause antenna depointing. Propagation factors such as absorption by certain atmospheric gases like ammonia (Jupiter) or sulfuric acid (Venus) can play a role on long timescales. Additional factors, prominent in grazing incidence raypaths, are refractive bending and multipath due to atmospheric inhomogeneities (turbulence, gravity waves) which can cause strong scintillation. The signal power histories from Pioneer Venus, Galileo and Huygens will be reviewed, and expectations for DAVINCI discussed.