Search

We introduce new observables of the cosmic microwave background radiation, which can be measured through the detection of high order modes excited within an antenna feed system, coherently combined with those currently detected by space observatories. The use of such observables could potentially further constrain the validity of cosmological theories.

Solar phase scintillation and solar amplitude scintillation are fundamentally important in deep space mission operations for designing a communication system capable of transmitting signals when the signal path is close to the Sun. The ESA’s BepiColombo measurement data were analyzed in a previous paper in terms of the power spectral density of the solar phase scintillation, also with a comparison with Woo’s solar phase scintillation theory, when X-band and Ka-band signals propagate close to the Sun with a small Sun-Earth-Probe (SEP) angle during the superior solar conjunction campaign in March 2021 in its cruise phase to Mercury. In this paper the solar amplitude scintillation is analyzed both by calculating the power spectral density and the scintillation index. The results of scintillation index, derived from these measurement data, fit the NASA JPL’s scintillation index model.

This paper reports on an internal study carried out at the European Space Agency (ESA) for assessing the reference performance of Payload Data Transmitters achieved in the mid-term. This assessment is meant to provide input to the ESA roadmaps for the 2023 time frame. The assessment is carried out for various space missions, from low Earth to deep space orbits. Taking advantage of technology evolution combined with innovative architectures and advanced digital signal processing, the paper shows how the data return in several space missions can be dramatically increased by reasonably extrapolating existing RF technology.

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.

The European Space Agency (ESA) is today autonomously flying three interplanetary missions: Rosetta traveling to the comet Churyumov-Gerasimenko and the two orbiters Mars Express and Venus Express. The capability of supporting these and future deep-space missions is the consequence of a farsighted decision taken in 1996 to expand the ESA network of 15-m tracking antennas into the deep-space domain. The ambitious plan to provide around-the-clock coverage to all ESA interplanetary missions is almost completed: two deep-space antennas, located in New Norcia (Australia) and Cebreros (Spain), have been in operation since 2002 and 2005, respectively, while a third antenna is planned for 2011. This paper presents the two existing antennas starting from the underlying system requirements originated from the Rosetta mission, which was the most demanding in terms of required performance. The selected architecture is then described, followed by a detailed discussion about the critical performances that play a major role in deep-space support and the associated design issues.

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft has embarked the Massachusetts Institute of Technology (MIT) Lincoln Laboratory’s (LL) Lunar Lasercom Space Terminal (LLST) as a secondary payload and part of the Lunar Laser Communications Demonstration (LLCD) experiment. The LLST was operated on four out of every seven days for one month during the commissioning phase of the LADEE spacecraft in lunar orbit, and then again for a shorter period of time, after the end of the primary scientific mission. ESA's Optical Ground Station (OGS) on the Canary island of Tenerife was one of two secondary participating ground stations – together with JPLs Table Mountain facility – involved in the experiment. We present, from ESA's perspective, the Lunar Optical Communications Link (LOCL) project including first results and lessons learned of the short-duration experiment using the OGS. The success of LOCL is of strategic importance for ESA for the development of future optical communications over "deep-space" distances.

The paper describes the operations of ESA’s Optical Ground Station (OGS) during the Lunar Laser Communications Demonstration (LLCD) experiment, performed in October and November 2013 with NASA’s Lunar Atmospheric and Dust Environmental Explorer (LADEE) spacecraft. First the transmitter and receiver designs at the OGS telescope are described, which are geometrically separated to prevent cross-talk. Problems encountered and the lesson learned will be explained. As it turned the chosen arrangement was not sufficiently stable in terms of alignment and the paper will describe the solution found. A new industrial contract has been placed for improvement of the design of two solutions will be presented, which will both be tested in a follow-up laser communication campaign, scheduled for end March 2014.

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.

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.

We study the reconstruction of a Gaussian random signal, subject to extreme clipping. The reconstruction is achieved by adding a high frequency sinusoidal reference signal prior to the hard-limiter, and by low pass filtering the output. Such a scheme belongs to the area of signal reconstruction from Sine Wave Crossings (SWC). In the present paper we study in detail the effect of sampling in time domain on the reconstruction algorithm, and we carry out an analysis, valid for high sampling rates, leading to approximate analytical expressions of the cross-correlation coefficient between the signal and its reconstructed version. As a result of our analysis, the best achievable cross-correlation coefficient, together with the corresponding setting of the configuration parameters, i.e., the frequency and power of the reference signal, is obtained as a function of the sampling rate. Asymptotic closed form formulas are derived in the limit of very large sampling rates.

We present the modification of two ESA ground stations carried out in order to support the in-flight RF validation of the Proximity Communication Equipment (PCE), part of the International Space Station (ISS). This subsystem plays a critical role during the docking of the Automated Transfer Vehicle (ATV), and has to be tested prior to each ATV launch, to ensure that the RF performance is as expected. For the check-out, an unmodulated signal is transmitted by the PCE during an ISS pass, and received by the two ground stations. Based on the strength of the received signal, the radiation characteristic of the complete PCE can be assessed, and compared with the nominal performance. The measurement process requires calibrating the receiving subsystem, including antenna, front-end and back-end equipment. The adopted calibration procedure, only relying on radio stars measurement, does not require the use of a calibrated source external to the ground station.

The Rosetta mission due for launch in January 2002 has been delayed as precautionary measure after the failure of the previous launch with the European Ariane 5 launcher. Due to that, a new mission plan targeting comet Churyumov-Gerasimenko (C-G) instead of the initially baselined Wirtanen, has been devised. For the new trajectory and launch window, it is possible that the angular offset between the probe and the Sun becomes as small as 1 deg. The present paper describes the computation of the effects of the thermal noise generated by the Sun at the ground station antenna, the options identified to minimise the problem including launching the spacecraft in the opposite direction and the final mission operation profile selected.

In Very Large Baseline Interferometry, signals from far radio sources are simultaneously recorded at different antennas, with the purpose of investigating their physical properties. The recorded signals are generally modelled as realizations of Gaussian processes, whose power is dominated by the system noise at the receiving antennas. The actual signal coming from the radio source can be detected only after cross-correlation of the various data-streams. The signals received at each antenna are digitized after low noise amplification and frequency down-conversion, in order to allow subsequent digital post-processing. The applied quantization is coarse, 1 or 2 bits being generally associated to the signal amplitude. In modern applications the sampling is typically performed at a high rate, and subchannels are then generated by filtering, followed by decimation and re-quantization of the signal streams. The re-digitized streams are then cross-correlated to extract the physical observables. While the classical effect of quantization has widely been studied in the past, the de-correlation induced by the filtering and re-quantization process is still characterised experimentally, mainly due to its inherent mathematical complexity. In the present work we analyze the above problem, and provide algorithms and analytical formulas aimed at predicting the induced decorrelation for a wide class of quantization schemes, with the unique assumption of weakly correlated signals, typically fulfilled in VLBI and radio astronomy applications.