Dmitry Duev

Spacecraft VLBI and Doppler tracking: algorithms and implementation

Aims. We present the results of several multi-station Very Long Baseline Interferometry (VLBI) experiments conducted with the ESA spacecraft Venus Express as a target. To determine the true capabilities of VLBI tracking for future planetary missions in the solar system, it is necessary to demonstrate the accuracy of the method for existing operational spacecraft. Methods. We describe the software pipeline for the processing of phase referencing near-field VLBI observations and present results of the ESA Venus Express spacecraft observing campaign conducted in 2010−2011. Results. We show that a highly accurate determination of spacecraft state-vectors is achievable with our method. The consistency of the positions indicates that an internal rms accuracy of 0.1 mas has been achieved. However, systematic effects produce offsets up to 1 mas, but can be reduced by better modelling of the troposphere and ionosphere and closer target-calibrator configurations.

Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma

Aims. The phase scintillation of the European Space Agencys Venus Express (VEX) spacecraft telemetry signal was observed at X-band (lambda = 3.6 cm) with a number of radio telescopes of the European Very Long Baseline Interferometry (VLBI) Network in the period 2009-2013. Methods. We found a phase fluctuation spectrum along the Venus orbit with a nearly constant spectral index of -2.42 +/- 0.25 over the full range of solar elongation angles from 0 degrees to 45 degrees, which is consistent with Kolmogorov turbulence. Radio astronomical observations of spacecraft signals within the solar system give a unique opportunity to study the temporal behaviour of the signals phase fluctuations caused by its propagation through the interplanetary plasma and the Earths ionosphere. This gives complementary data to the classical interplanetary scintillation (IPS) study based on observations of the flux variability of distant natural radio sources. Results. We present here our technique and the results on IPS. We compare these with the total electron content for the line of sight through the solar wind. Finally, we evaluate the applicability of the presented technique to phase-referencing VLBI and Doppler observations of currently operational and prospective space missions.

RadioAstron as a target and as an instrument: Enhancing the Space VLBI mission’s scientific output

Context. The accuracy of orbit determination has a strong impact on the scientific output of the Space VLBI mission RadioAstron. Aims. The aim of this work is to improve the RadioAstron orbit reconstruction by means of sophisticated dynamical modelling of its motion in combination with multi-station Doppler tracking of the RadioAstron spacecraft. Methods. The improved orbital solution is demonstrated using Doppler measurements of the RadioAstron downlink signal and by correlating VLBI observations made by RadioAstron with ground-based telescopes using the enhanced orbit determination data. Results. Orbit determination accuracy has been significantly improved from ~600 m in 3D position and ~2 cm/s in 3D velocity to several tens of metres and mm/s, respectively.

A tropospheric signal delay model for radio astronomical observations

In this work, a three-dimensional refraction model is proposed, which allows one to calculate the delay of signal due to the Earth’s troposphere—the main source of error limiting the accuracy of modern radio astronomical observations. The method of raytracing through the three-dimensional troposphere (numerical weather model) is used. The results of VLBI observations of spacecraft are presented, showing that, in terms of accuracy, the developed model performs at the level of the best modern analogues and in some cases even exceeds them.

Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos Flyby: II. Doppler tracking: Formulation of observed and computed values, and noise budget

Context. Closed-loop Doppler data obtained by deep space tracking networks, such as the NASA Deep Space Network (DSN) and the ESA tracking station network (Estrack), are routinely used for navigation and science applications. By shadow tracking the spacecraft signal, Earth-based radio telescopes involved in the Planetary Radio Interferometry and Doppler Experiment (PRIDE) can provide open-loop Doppler tracking data only when the dedicated deep space tracking facilities are operating in closed-loop mode. Aims. We explain the data processing pipeline in detail and discuss the capabilities of the technique and its potential applications in planetary science. Methods. We provide the formulation of the observed and computed values of the Doppler data in PRIDE tracking of spacecraft and demonstrate the quality of the results using an experiment with the ESA Mars Express spacecraft as a test case. Results. We find that the Doppler residuals and the corresponding noise budget of the open-loop Doppler detections obtained with the PRIDE stations compare to the closed-loop Doppler detections obtained with dedicated deep space tracking facilities.

RadioAstron gravitational redshift experiment : status update

A test of a cornerstone of general relativity, the gravitational redshift effect, is currently being conducted with the RadioAstron spacecraft, which is on a highly eccentric orbit around Earth. Using ground radio telescopes to record the spacecraft signal, synchronized to its ultra-stable on-board H-maser, we can probe the varying flow of time on board with unprecedented accuracy. The observations performed so far, currently being analyzed, have already allowed us to measure the effect with a relative accuracy of

PRIDE contribution to the European VLBI Network

4\times10^{-4}

Scintillation of Venus and Mars Express radio signal on interplanetary and ionosphere plasma

. We expect to reach

Single baseline GLONASS observations with VLBI: data processing and first results

2.5\times10^{-5}

The Wettzell-Onsala G130128 experiment – VLBI-observations of a GLONASS satellite

with additional observations in 2016, an improvement of almost a magnitude over the 40-year old result of the GP-A mission.