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In this article, coded space communication links impaired by solar scintillation are investigated followed by a comprehensive end-to-end approach. With respect to baseband analyses, this allows for a more realistic modeling of actual communication links in these scenarios, though at the cost of longer simulation times and higher minimum values of the error rates assessable. The effect of solar scintillation on both signal amplitude and phase is studied, by considering the potential use of noncoherent demodulation to withstand phase synchronization impairments. This article allows optimizing some receiver parameters, such as the phase-locked loop bandwidth, in a way to face critical contingency scenarios as well.

The growing number of deep space exploration missions operating simultaneously in the solar system triggers an increasing demand for large ground antennas capable of tracking distant spacecraft. Several space agencies have their own deep space tracking networks, where each antenna belonging to a ground station complex is meant to be shared among different deep space missions in flight, significantly constraining the tracking schedule. A typical ranging and Doppler radio tracking session requires long tracking passes and a single ground antenna, while angular (Delta-DOR) observations require at least two antennas but usually for much shorter tracking sessions. However, during Delta-DOR observations, the baseline between the two receiving antennas should be kept as large as possible, thus reducing the time windows in which Delta-DOR observations are actually feasible. This leaves little room for adaptation of the tracking schedules of these antennas and calls for the need for possible alternatives for the receiving stations. The antennas belonging to the very long baseline interferometry (VLBI) network worldwide meet the requirements to carry out Delta-DOR tracking sessions. Here, we present an experimental activity carried out tracking ESA’s GAIA spacecraft using a mixed deep space antenna configuration involving an ESA ESTRACK antenna at New Norcia (Australia) and a VLBI antenna at Medicina (Italy). This baseline was used to form Delta-DOR observables with the aim of demonstrating that VLBI antennas offer the capability to track deep space missions, thus increasing the number of possible baselines and observation time windows.

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.

The Mercury Orbiter Radio Science Experiment (MORE) of the ESA mission BepiColombo will provide an accurate estimation of Mercury’s gravity field and rotational state, improved tests of general relativity, and a novel deep space navigation system. The key experimental setup entails a highly stable, multi-frequency radio link in X and Ka band, enabling two-way range rate measurements of 3 micron/s at nearly all solar elongation angles. In addition, a high chip rate, pseudo-noise ranging system has already been tested at 1-2 cm accuracy. The tracking data will be used together with the measurements of the Italian Spring Accelerometer to provide a pseudo drag free environment for the data analysis. We summarize the existing literature published over the past years and report on the overall configuration of the experiment, its operations in cruise and at Mercury, and the expected scientific results.

This paper illustrates the design, implementation and testing of a prototype of an off-line correlator for large dish antenna array, in the frame of the ESA-funded study “Prototype of off-line Correlator for Arraying of Large Aperture Antennas” In order to improve the performance of downlink reception, a four 35-m antenna array is a valid alternative to a single large 70-m dish, offering the same performance with remarkable advantages, such as being more fail-safe against the failure of components. The concept is to acquire two or more replicas of the same signal at different Ground Stations and combine them after delay and phase correction, due mainly to media and clock offset. After a first study phase of the best combination and correlation methods, as well as of the requirements driven by the analysis of the error sources of delay and phase misalignment, the tool has been designed, implemented and successfully tested. Together with the correlator, a simulator has also been developed, in order to better test the performance of the combination tool. Tests with simulated, static (generated in ESOC) and real mission data have been carried out. The improvement in the Signal-to-Noise Ratio has been demonstrated, and the information bits have been successfully reconstructed after the combination of the deep space signal acquired in Cebreros and Malargue stations from Exomars and Mars Express spacecraft, endorsing the tool for an off-line use in the near future.

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.

Spacecraft communication systems operating at X band are strongly affected when the propagation path passes close to the Sun (which can be characterized by the Sun-Earth-Probe, SEP, angle). In this paper, a channel model that can generate a time series of signal amplitude and phase, and hence the signal in-phase and quadrature values, is presented. For X band, the channel model reproduces the observations well for SEP > 0.8°. While the model has not been experimentally validated at SEP angles below 0.8°, the behavior is consistent with measurements reported in the literature and is therefore likely to be suitable for use, with caution, in that region too.

Some results so far achieved in the framework of the HELIOS (Highly rEliable Links during sOlar conjunctions) Project, founded by the European Space Agency (ESA), are presented. The purpose of the project is the definition of a TT&C communication subsystem architecture (including both ground and space segments, as well as operational methods) being robust to impairments due to superior solar conjunction, especially when the Sun-Earth-Probe angle is below 5 degrees.

The move towards higher frequency bands like 26GHz or 32GHz for scientific satellite data downlinks calls for the need to better characterise the atmosphere at the sites where ground antennas are located. For this reason ESA is undertaking the deployment of microwave radiometers at its Deep Space station locations. This paper reports the results of the first two years of site characterisation at the ESA Deep Space antenna 2 located in Cebreros, Spain.

We discuss the results achieved so far in the RESCUe (Reliable TTC b) non-coherent modulation schemes, like Frequency Shift Keying (FSK) and Differentially Encoded Phase Shift Keying (DPSK), as an alternative to coherent modulation schemes, like Phase Shift Keying (PSK); c) diversity techniques (space, time and frequency).

This work aims at verifying an innovative approach for link-design optimization of deep-space missions working at Ka band. The presented approach exploits a weather forecast (WF) model coupled with a radiopropagation model to maximize data-transfer during a Ka-band downlink transmission. First, we exploit radiosounding data to tune the WF model on the geographical site of interest. As second step, we use microwave radiometric measurements to verify both WF and radiopropagation models. A final goal is obtained applying the WF-based approach to optimize the link and then computing the yearly data return on the basis of the actual atmospheric scenario measured by the microwave radiometer. On a test period of three years of transmission, WF-based approach provides a gain, in terms of yearly received data-volume, of about 15% up to 24% if compared to traditional link-design techniques. This gain is combined with a corresponding reduction of yearly lost data. These interesting results make the WF-based approach an appealing alternative for deep-space applications.

This paper describes the implementation of delta-DOR (delta-differential one-way ranging) receivers within the ESA Deep Space ground station network. Delta-DOR provides very accurate plane-of-sky measurements of spacecraft position which complement existing line-of-sight ranging and Doppler measurements. We discuss how this technique has been adapted and implemented at the two ESA deep-space ground stations using existing equipment and infrastructure. These new capabilities were added by writing new software modules for the standard ESA digital receiver (the intermediate frequency modem system—IFMS). With these upgrades the receiver has the ability to record accurately timetagged signals from up to eight IF sub-channels. These sub-channels can have bandwidths of 50 kHz–2 MHz with a sample quantization of 1–16 bits per component. The IF samples are stored locally for subsequent retrieval over a WAN by the correlator facility at ESOC.

Navigation of deep-space probes is accomplished through a variety of different radio observables, namely Doppler, ranging and Delta-Differential One-Way Ranging (Delta-DOR). The particular mix of observations used for navigation mainly depends on the available on-board radio system, the mission phase and orbit determination requirements. The accuracy of current ESA and NASA tracking systems is at level of 0.1 mm/s at 60 s integration time for Doppler, 1–5 m for ranging and 6–15 nrad for Delta-DOR measurements in a wide range of operational conditions. The ASTRA study, funded under ESA's General Studies Programme (GSP), addresses the ways to improve the end-to-end accuracy of Doppler, ranging and Delta-DOR systems by roughly a factor of 10. The target accuracies were set to 0.01 mm/s at 60 s integration time for Doppler, 20 cm for ranging and 1 nrad for Delta-DOR. The companies and universities that took part in the study were the University of Rome Sapienza, ALMASpace, BAE Systems and Thales Alenia Space Italy. The analysis of an extensive data set of radio-metric observables and dedicated tests of the ground station allowed consolidating the error budget for each measurement technique. The radio-metric data set comprises X/X, X/Ka and Ka/Ka range and Doppler observables from the Cassini and Rosetta missions. It includes also measurements from the Advanced Media Calibration System (AMCS) developed by JPL for the radio science experiments of the Cassini mission. The error budget for the three radio-metric observables was consolidated by comparing the statistical properties of the data set with the expected error models. The analysis confirmed the contribution from some error sources, but revealed also some discrepancies and ultimately led to improved error models. The error budget reassessment provides adequate information for building guidelines and strategies to effectively improve the navigation accuracies of future deep space missions. We report both on updated error budget for radio-metric observables and the system configurations proposed for the upgrade of ESA's tracking and orbit determination systems.

In a suggested radio propagation experiment using a deep space antenna, accurate calibration of the propagation delay through the Earth's atmosphere is essential. One or two microwave radiometers can be used for this purpose. Differences in precise locations of the radiometer(s) and antenna to be calibrated leave a residual wet path delay value. We computed the Allan Standard Deviation (ASD) of this residual, as well as the one resulting from different pointing positions in the plane of the sky, by simulations. Pointing offsets, e.g., to avoid solar radiation into the radiometer beam, lead in general to an increased ASD. However, for many observation geometries a deliberate pointing offset can compensate for the location differences. In the case studied we found a reduction of the ASD with up to 45% compared to the ASD obtained for a zero pointing offset. The size of the calculated ASD depends strongly on the model parameters used, e.g., the turbulence strength parameter Cn^2, which has a significant natural variation over a year.

Deep space exploration is aimed at acquiring information about the solar system and a significant communication capacity has to be planned for such very large distances. The concept of the RadioMeteorological Operations Planner technique (RadioMetOP) is described together with its main modelling components and objectives. Numerical results, in terms of received frame data using a statistical estimation methodology, is also illustrated using the BepiColombo mission as a baseline example. Preliminary results, using raingauge data and radiometeorological forecast simulations, are discussed taking the fully-adaptive bit-rate test case as a benchmark.

The Portable Radio Science Receiver (PRSR) is a suitcase-sized open-loop digital receiver designed to be small and easy to transport so that it can be deployed quickly and easily anywhere in the world. The PRSR digitizes, down-converts, and filters using custom hardware, firmware, and software. Up to 16 channels can be independently configured and recorded with a total data rate of up to 256 Mbps. The design and implementation of the system's hardware, firmware, and software is described. To minimize costs and time to deployment, our design leveraged elements of the hardware, firmware, and software designs from the existing full-sized operational (non-portable) Radio Science Receivers (RSR) and Wideband VLBI Science Receivers (WVSR), which have successfully supported flagship NASA deep space missions at all Deep Space Network (DSN) sites. We discuss a demonstration of the PRSR using VLBI, with one part per billion angular resolution: 1 nano-radian / 200 µas. This is the highest resolution astronomical instrument ever operated solely from the Southern Hemisphere. Preliminary results from two sites are presented, including the European Space Agency (ESA) sites at Cebreros, Spain and Malargue, Argentina. Malargue's South American location is of special interest because it greatly improves the geometric coverage for spacecraft navigation in the Southern Hemisphere and will for the first time provide coverage to the 1/4 of the range of declination that has been excluded from reference frame work at Ka-band.

Turbulence is an important effect for different applications including different aspects of electromagnetic propagation in the atmosphere, especially for frequencies in the microwave part of the spectrum. Our parameter of interest is an integrated effect, namely the propagation delay of a signal propagating through the Earth's atmosphere to a receiver on the ground. A simulation method has been implemented in order to predict the statistics of atmospheric turbulence. For systems where calibration for the wet delay is done by means of radiometric measurements there is an uncalibrated remainder of the variability due to imperfections of the method: (1) the radiometer location, which may not be identical to the location of the receiving antenna that is subject to calibration, (2) a pointing offset on the sky, and (3) the radiometer beam that may sense another volume of the air than does the original signal. The size of the remainder depends on the assumptions made about the atmospheric variability when the instrument is calibrated. The analysis shows that the overall performance of the system to a significant level depends on the uncertainty in the true range of variation for the turbulence strength parameter C n 2.

This paper presents the preliminary design of the Beam Waveguide (BWG) system of the 64-m diameter paraboloidal reflector antenna Sardinia Radio Telescope (SRT). The project is aimed at providing the antenna with Telemetry, Tracking & Command (TT&C) capabilities in order to support present and future deep-space missions. The synthesis of the BWG layout has been carried out according to the Gaussian Beam theory, which represents a reasonable compromise between accuracy of the results and computational time to set up the initial specifications of large reflector antennas. According to this assumption, the best design parameters of the antenna feeding system have been achieved through an accurate optimization analysis and verified by Physical Optics simulations. The proposed BWG architecture and the corresponding simulated antenna performance are shown in this paper.

The main focus of this study is the characterization of internal noise of the Microwave Radiometer (MWR) to be located at an ESA Deep Space Antenna (DSA) site, to accurately retrieve the tropospheric path delay along the line-of-sight of the deep space probe. This would enable precise tropospheric calibration of radiometric observables (range and range-rate) with particular reference to the BepiColombo SIC and the Cebreros (S) DSA. The characterization of current MWRs technologies has been based on a detailed analysis of data collected at Cabauw (NL) remote sensing site with the available instruments.

This paper describes the techniques currently in use and those proposed for a precise estimation of the Earth troposphere path delay for Deep Space probe tracking purposes. The different proposed techniques could be selected according to the to the mission goals and tracking accuracy requirements. In this paper, they are sorted by an increasing accuracy but also level of complexity.

Delta-DOR (Differential One-Way Ranging) measurements generate very large data volumes that have to be transferred over ground communications networks from deep space ground stations to a site where the data are processed by a correlator. The two ESA deep space stations New Norcia, Australia, and Cebreros, Spain, have been fitted with Delta-DOR systems, the correlator is located in the control centre ESOC, Germany. The interconnecting ESA mission operations network (known as OPSNET) has been used for the data transfer. Although OPSNET capacity was and is for economic reasons sized for throughputs considerably lower than for Delta-DOR needs, OPSNET has been successfully used to support the ESA Delta-DOR campaigns. The pertinent capability of the overall solution was the result of combined optimizations of the OPSNET IP network, of the TCP/IP stacks in the source and destination systems, and of the file transfer multiplexing utility.