Measurements of atmospheric dynamics and composition from radiometric tracking of an ice giant entry probe

The dynamics of planetary atmosphere including winds, waves, tides, and turbulence is a tie-point between multiple aspects of planetary structure and processes, including atmospheric composition and compositional gradients, thermal and energy structure, and the location and properties of the clouds. Radiometric tracking of an ice giant entry probe provides the only direct measurements of the atmospheric dynamics along the probe descent path, as well as measurements of the abundance of microwave absorbing molecules along the probe relay signal raypath, expected to be primarily ammonia (NH₃) or hydrogen sulfide (H₂S).

The technique of Doppler tracking of a descent probe has been demonstrated at Jupiter with the Galileo probe and at Titan with the Huygens probe. By utilizing an ultrastable oscillator on both the transmit and receive sides of the probe telemetry relay signal, the time variation of the measured relay signal frequency provides a direct measure of the line of sight component of probe speed. Careful analysis of the Doppler residuals can provide the signature of atmospheric waves, convection, and turbulence, along with other probe dynamical effects such as pendulum motion under the parachute, probe spin, and aerodynamic buffeting.

Measurements of the time-varying received signal strength would provide a profile of atmospheric absorbers along the probe radio signal raypath, . This measurement would complement composition measurements made the probe mass spectrometer. A more difficult measurement would be to characterize the scale size of atmospheric turbulence along the probe relay signal raypath by measuring the effect of atmospheric scintillation on the probe relay signal strength measured at the receiver.

This presentation will present the scientific objectives, measurement requirements, and expected measurement accuracies of the profile of zonal winds and atmospheric absorption, with a preliminary attempt to quantify the effect of variations in probe descent trajectory reconstructions and carrier overflight trajectory.