Radio spectroscopy and space science with VLBI radio telescopes for Solar System research

Only a tiny fraction of the universe has been studied even though the possibilities are unlimited given the current technologies, the resources and the time. To optimize the use of resources, the Metsähovi antenna and the existing VLBI processing hardware were exploited to study a broad variety of space phenomena. The research began with radio spectroscopy of the celestial bodies of our Solar System. Every object emits certain spectral signatures at several radio frequencies depending on its chemical molecules. Earth-based observations of the emitted radio spectral signal help to determine the composition of the structure and atmosphere of the planets. A unique method for processing the data captured by VLBI radio telescopes for radio spectroscopy purposes was developed during this work. Although the initial research focused on planetary bodies, it later shifted to the spacecraft motion. This new aim included studying ground support to planetary and deep-space mission spacecraft with VLBI radio telescopes, which opened up possibilities for collaboration between space agencies and radio astronomers. In addition, with VLBI phase-referencing, a high accuracy estimation of the spacecraft state vectors could be obtained. These new tools provide an opportunity for studying a broad variety of physical processes, including the dynamics of planetary atmospheres, geodynamical diagnostics of the interior of planets, fundamental physics effects of spacecraft motion and solar wind characterization. For instance, we organised a VLBI tracking session of Venus Express that involved 10 antennae and it estimated the spacecraft position with a precision of few hundred metres. The most interesting physical process for further investigation was the characterisation of the solar wind along the propagation path. The phase fluctuations on the signal allowed us to study essential parameters of the interplanetary scintillations, such as the phase scintillation index, bandwidth of scintillations or spectral broadening and their dependence on the solar elongation, distance to the target, celestial position of the spacecraft and radio telescopes. A scintillation and electron density model as a function of solar elongation was developed based on the data collected during two years. This model is powerful for improving the accurate determination of the spacecraft state vectors

Using software spectrometer to ensure VLBI signal chain reliability

Software spectrometer (SWSpec) developed for spacecraft tracking can be used to assure VLBI signal chain reliability, and phase stability of a VLBI receiver. Testing performed with SWSpec during pre-operations both saves time, and eases the tests as one does not need to gather, couple and setup the hardware.Comment: 4 pages, 4 figures, 12th European VLBI Network Symposium and Users Meeting, 7-10 October 2014, Cagliari, Ital

Study of ICME by spacecraft radio signals

Tracking radio communication signals from planetary spacecraft with ground-based telescopes offers, among others, the possibility to study the electron density and the interplanetary scintillation of the solar wind. Observations of the telemetry link of spacecraft have been conducted regularly with ground antennae from the European Very Long Baseline Interferometry Network (EVN), aiming to characterize the propagation of radio signals in the solar wind at different solar elongations and distances from the Sun. We have studied the phase fluctuations of Mars Express spacecraft radio signal while an interplanetary coronal mass ejection (ICME) crossed the radio path during one of our observations on 6 April 2015. Our measurements showed that the Doppler measurements and phase scintillation indices increased by a factor of 4 during the passage of the ICME. Thus, it is confirmed that the phase scintillation technique based on spacecraft signals provides information of the properties and propagation of the ICMEs in the heliosphere, and can be used to detect and monitor the presence of ICMEs in the near future.Peer reviewe

Contribution of simultaneous PRIDE observations of JUICE and Clipper spacecraft to the Galilean satellites' ephemerides

International audienc

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

VLBI20-30: a scientific roadmap for the next decade -- The future of the European VLBI Network

This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and provides suggestions towards upgrade paths for the European VLBI Network (EVN). The EVN is a distributed long-baseline radio interferometric array, that operates at the very forefront of astronomical research. Recent results, together with the new science possibilities outlined in this vision document, demonstrate the EVN's potential to generate new and exciting results that will transform our view of the cosmos. Together with e-MERLIN, the EVN provides a range of baseline lengths that permit unique studies of faint radio sources to be made over a wide range of spatial scales. The science cases are reviewed in six chapters that cover the following broad areas: cosmology, galaxy formation and evolution, innermost regions of active galactic nuclei, explosive phenomena and transients, stars and stellar masers in the Milky Way, celestial reference frames and space applications. The document concludes with identifying the synergies with other radio, as well as multi-band/multi-messenger instruments, and provide the recommendations for future improvements. The appendices briefly describe other radio VLBI arrays, the technological framework for EVN developments, and a selection of spectral lines of astrophysical interest below 100 GHz. The document includes a glossary for non-specialists, and a list of acronyms at the end

VLBI20-30: a scientific roadmap for the next decade -- The future of the European VLBI Network

This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and provides suggestions towards upgrade paths for the European VLBI Network (EVN). The EVN is a distributed long-baseline radio interferometric array, that operates at the very forefront of astronomical research. Recent results, together with the new science possibilities outlined in this vision document, demonstrate the EVN's potential to generate new and exciting results that will transform our view of the cosmos. Together with e-MERLIN, the EVN provides a range of baseline lengths that permit unique studies of faint radio sources to be made over a wide range of spatial scales. The science cases are reviewed in six chapters that cover the following broad areas: cosmology, galaxy formation and evolution, innermost regions of active galactic nuclei, explosive phenomena and transients, stars and stellar masers in the Milky Way, celestial reference frames and space applications. The document concludes with identifying the synergies with other radio, as well as multi-band/multi-messenger instruments, and provide the recommendations for future improvements. The appendices briefly describe other radio VLBI arrays, the technological framework for EVN developments, and a selection of spectral lines of astrophysical interest below 100 GHz. The document includes a glossary for non-specialists, and a list of acronyms at the end