Simultaneous multi-spacecraft observations with VLBI radio telescopes to study the interplanetary phase scintillation

N. M. M. Said

In this study, we simultaneously observed radio signals transmitted by two co-orbiting spacecraft: the ESA Mars Express (MEX) and the CNSA Tianwen-1 (TIW-1). The objective is to improve our understanding of interplanetary phase scintillation caused by time-dependent variations of electron density across the sounding line-of- sight due to plasma inhomogeneities and the speed of the solar wind carrying the disturbances across the radio sound path.

Figure 1. Highly elliptical polar orbit of MEX and TIW-1 space missions. Spacecraft operate in one or two-way coherent mode with ground stations.

This work complements previous investigations on interplanetary plasma scintillation reported by Kummamuru et al. (2023) utilising a single spacecraft: MEX. These simultaneous multi-spacecraft observations allow us to analyse plasma properties and the propagation medium between two different point measurements of the plasma environment close to Mars and investigate the correlation between the RMS phase fluctuation with the solar radio flux at 10.7 cm (2800MHz). Furthermore, these sessions can help to distinguish signals from radio frequency interference (RFI), evaluate the robustness of our software for extracting phase residual and Doppler measurements for different spacecraft orbits, and conduct regular spacecraft performance assessments by comparing its providing power and data receiving and transmitting capability.

Figure 2. Full spectrum including a 32 MHz bandwidth centred at 8426 MHz at Hobart- 12. The two spacecraft carrier signals of MEX at 8420.3 MHz and TIW-1 at 8431.7 MHz are shown. The remaining peaks are radio frequency interference (RFI), harmonics of the carrier, or products of the FFT.

We employed the Planetary Radio Interferometer and Doppler Experiment (PRIDE) technique developed by the Joint Institute for VLBI ERIC (JIVE) to determine the topocentric Doppler measurements and residual phase of the carrier signal. This technique uses the standard telecommunication system of the spacecraft and radio telescopes on Earth to produce precise measurements of the spacecraft state vectors (lateral position and radial Doppler) based on Very Long Baselines Interferometry (VLBI) phase referencing (Duev et al., 2012) and topocentric Doppler measurements (Molera Calvés et al., 2021). Several science experiments used the PRIDE technique including the ESA’s Jupiter Icy Moons Explorer (JUICE) mission, which launched on 14 April 2023.

References:

Kummamuru et al., 2023, PASA, 40, 013

Duev et al., 2012, A&A, 541, 43

Molera Calvés et al., 2021, PASA, 38, 065

Link to the paper:

N.M.M. Said et al., 2025, Exp. Astron, 59, 19

Contact:  

N.M.M. Said, Joint Institute for VLBI ERIC. Email: said@jive.eu