AWARDS: Advanced microwave radiometers for deep space stations

Abstract

The objective of this study, named AWARDS (Advanced microWAve Radiometers in Deep space Stations), is the preliminary design of a transmission Media Calibration System (MCS) to be located at an ESA Deep Space Antenna (DSA) site. The crucial aspect is the capability to accurately retrieve the tropospheric path delay along the line-of-sight of the deep space probe in order to allow precise tropospheric calibration of deep space observables (range and range-rate) with particular reference to the BepiColombo spacecraft and its primary DSA at Cebreros (ES).The study focuses on two main aspects which lead to the preliminary design of the Mercury Orbiter Radioscience Experiment (MORE) MCS: the characterization of current microwave radiometers (MWRs) available at ESA/ESTEC and the atmospheric fluctuation effects on the MCS error budget, in terms of the Allan standard deviation (ASD).In the course of the study, further critical aspects have been identified (effects of Sun contamination, effects of ground noise emission), and mitigation strategies have been proposed.The final outcome is a preliminary design of the MWR (and the entire MCS) to be deployed at the ESA/ESTRACK (ESA Tracking station network) sites and being compliant with MORE requirements.

Performance Characterization of ESA's Tropospheric Delay Calibration System for Advanced Radio Science Experiments

“…This observation prompted JPL to propose a new design for its next generation of a tropospheric calibration system, which foresees a direct integration of the water vapor radiometer within the antenna receiver (Tanner et al, 2021). While a direct integration was not possible for the current setup, the selected mounting location for the TDCS is well within the 50 m distance limit proposed by Tortora et al (2013) and represents a tradeoff between calibration performances and operational constraints (i.e., availability of supporting infrastructures and visibility during tracking).…”

“…Later, the European Space Agency (ESA) performed a preliminary study named AWARDS (Graziani, et al, 2014;Tortora, et al, 2013) for the definition of the requirements and preliminary system design of a tropospheric delay calibration system (TDCS). In addition, media calibration performance requirements for accurate spacecraft tracking were studied in detail in another ESA study called ASTRA (Iess et al, 2012(Iess et al, , 2014.…”

Assessment of Ground-Based Microwave Radiometry for Calibration of Atmospheric Variability in Spacecraft Tracking

“…There are three main different effects that need to be simulated: (A) the differences between the true beam shapes, of the DSA and the MWR antennas, vs. a pencil beam; (B) the site position offset(s) between the DSA and the MWR(s) on the ground, and (C) the pointing offsets in the plane of the sky. Tortora et al [16] studied these effects and found the following. The effect due to antenna beams is small and actually it reduces the residual ASD by 10-20 % due to averaging of the variations within the volume of air sensed by the antennas.…”

“…However, the extensions of the actual antenna beams studied lead to spatial averaging of the measured wet delay. Hence the ASD of the residual wet delay measured is 0.8-0.9 times the ASD calculated for the pencil shaped beams [16]. We have therefore multiplied the pencil beam results with ~0.85 in order to compensate for the expected spatial averaging.…”

“…The maximum contributions from the residual troposphere (after calibration) allowed in the MORE error budget are reported in Table I, where different integration times are defined in order to have reference values for both deep-space ranging and Doppler observables. On the other hand, the same values are used as design requirements for the definition of the studied MCS [16]. There are three main different effects that need to be simulated: (A) the differences between the true beam shapes, of the DSA and the MWR antennas, vs. a pencil beam; (B) the site position offset(s) between the DSA and the MWR(s) on the ground, and (C) the pointing offsets in the plane of the sky.…”