VLBI tracking of the Huygens Probe in the atmosphere of Titan

We present results of an assessment study of VLBI (Very Long Baseline Interferometry) observations of the Huygens probe during the probe's descent through the atmosphere to the surface of Titan. The aim of the study was to assess the feasibility of a direct receipt, detection and VLBI processing of the probe's S-band radio signal. The direct receipt of the probe signal by Earth-based tracking stations was not foreseen in the original mission scenario but has proven to be possible owing to recent developments in radio astronomy, and particularly in VLBI. We analyze the power budget of the "Huygens-Earth" radio link, the potential accuracy of the VLBI determination of the probe's coordinates in the atmosphere of Titan, and some scientific applications of these measurements. We also discuss prospects for VLBI tracking of future deep space missions using the next generation Earth-based radio telescopes, in particular the Square Kilometer Array (SKA)

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.Department of Astrodynamics and Space MissionsAerospace Engineerin

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

Aims: The phase scintillation of the European Space Agency's Venus Express (VEX) spacecraft telemetry signal was observed at X-band (λ = 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° to 45°, 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 signal's phase fluctuations caused by its propagation through the interplanetary plasma and the Earth's 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.Peer reviewe

Planetary Radio Interferometry and Doppler Experiment (PRIDE) of the JUICE Mission

Planetary Radio Interferometry and Doppler Experiment (PRIDE) is a multi-purpose experimental technique aimed at enhancing the science return of planetary missions. It is based on the near-field phase-referencing Very Long Baseline Interferometry (VLBI) and evaluation of the Doppler shift of the radio signal transmitted by spacecraft by observing it with multiple radio telescopes. The methodology of PRIDE has been developed initially at the Joint Institute for VLBI ERIC (JIVE) for tracking the ESA’s Huygens Probe during its descent in the atmosphere of Titan in 2005. From that point on, the technique has been demonstrated for various planetary and other space science missions. The estimates of lateral position of the target spacecraft are done using the phase-referencing VLBI technique. Together with radial Doppler estimates, these observables can be used for a variety of applications, including improving the knowledge of the spacecraft state vector. The PRIDE measurements can be applied to a broad scope of research fields including studies of atmospheres through the use of radio occultations, the improvement of planetary and satellite ephemerides, as well as gravity field parameters and other geodetic properties of interest, and estimations of interplanetary plasma properties. This paper presents the implementation of PRIDE as a component of the ESA's Jupiter Icy Moons Explorer (JUICE) mission

Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: a test case of the Mars Express Phobos fly-by

The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency's Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet-satellite systems. Aims. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. Methods. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. Results. We achieved, on average, mHz precision (30 mu m/s at a 10 s integration time) for radial three-way Doppler estimates and sub-nanoradian precision for lateral position measurements, which in a linear measure (at a distance of 1.4 AU) corresponds to similar to 50 m

Probing the gravitational redshift with an Earth-orbiting satellite

International audienceWe present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order 10−5 , a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle