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Media propagation noises are amongst the main error sources of radiometric observables for deep space missions, with fluctuations of the tropospheric excess path length representing a relevant contributor to the Doppler noise budget. Microwave radiometers currently represent the most accurate instruments for the estimation of the tropospheric delay and delay rate along a slant direction. A prototype of a tropospheric delay calibration system (TDCS), using a 14 channel Ka/V band microwave radiometer, has been developed under a European Space Agency contract and installed at the deep space ground station in Malargüe, Argentina, in February 2019. After its commissioning, the TDCS has been involved in an extensive testbed campaign by recording a total of 44 tracking passes of the Gaia spacecraft, which were used to perform an orbit determination analysis. This work presents the first statistical characterization of the end-to-end performance of the TDCS prototype in an operational scenario. The results show that using TDCS-based calibrations instead of the standard GNSS-based calibrations leads to a significant reduction of the residual Doppler noise and instability.

Nanosatellite missions represent a promising option for the exploration of the near-Earth asteroid population since they provide low-cost versatile platforms for scientific observations. This paper describes the preliminary orbital and navigation analyses for the DustCube mission, which was pre-selected to reach the binary asteroid system Didymos on-board ESA’s AIM spacecraft. Possible candidate orbits that exploit the binary nature of the system are identified and traded off to produce a preliminary concept of operations. The overall feasibility of the proposed scenario is then addressed by integrating the spacecraft trajectories in a realistic dynamical environment, evaluating their sensitivity to state errors, and estimating the accuracy of the orbit determination system. Preliminary results suggest that autonomous navigation of a Cubesat platform within a binary asteroid system is technically feasible. The proposed solution, which combines an initial parking orbit at the L4 equilibrium point with a Distant Retrograde Orbit for proximity operations, is shown to be consistent with the estimated orbit determination accuracy and allows to fulfil the mission requirements.

To accurately estimate the mass of a comet, is a challenging task, given the complexity of its dynamical environment, and particularly so while close to perihelion, where the coma emissions are stronger. This study describes an operational approach for simultaneous orbit determination and mass estimation of a cometary target, using detailed dynamical models and combining measurements from multiple instruments. The testbed for the proposed approach is represented by the Proteus mission towards the main belt comets 288P and 238P-Read, for which formal uncertainties for the mass and other parameters of interest are estimated though a covariance analysis. It will be shown that the required relative accuracy of 10% in mass estimation can be achieved for both cometary targets under realistic operational conditions.