VLBI and Doppler tracking of spacecraft for planetary atmospheric studies

The Planetary Radio Interferometry and Doppler Experiment (PRIDE) is a technique that can enhance the science return of planetary missions. By shadow tracking the spacecraft signal using radio telescopes from VLBI networks, the PRIDE technique provides precise open-loop Doppler and near-field VLBI observables (Duev et al. 2012, Bocanegra-Bahamon et al. 2018) to find the radial velocity of the spacecraft and its position in the plane of the sky. This information is not only important for navigation, but it can also be used for many science applications. One such case is the study of planetary atmospheres by means of radio occultation experiments. The application of PRIDE for atmospheric studies has been demonstrated by observing ESA's Venus Express (VEX) during multiple Venus occultation events (Bocanegra-Bahamon et al. 2019). From these observations density, temperature and pressure profiles of Venus were derived to characterize the planet's ionosphere and neutral atmosphere. The noise budget of the observations indicated that the quality of the detections are comparable to those of NASA's and ESA's deep space networks (Bocanegra-Bahamon et al. 2019). With PRIDE, making use of open-loop Doppler data, EVN stations were able to sound deeper layers of Venus' thick atmosphere when compared to closed-loop Doppler data provided by ESA's New Norcia.