Abstract
This paper describes the design of MEFISTO (Mercury Electric Field In-Situ Tool) and WPT (Wire Probe Antenna) electric field sensors for Plasma Wave Investigation (PWI) on the BepiColombo Mio spacecraft (Mercury Magnetospheric Orbiter, MMO). The two sensors will enable the first observations of electric fields, plasma waves and radio waves in and around the Hermean magnetosphere and exosphere. MEFISTO and WPT are dipole antennas with 31.6 m tip-to-tip length. Each antenna element has a spherical probe at each end of the wire (15 m length). They are extended orthogonally in the spin plane of the spacecraft and enable measurements of the electric field in the frequency range of DC to 10 MHz by the connection to two sets of receivers, EWO for a lower frequency range and SORBET for higher frequencies. In the initial operations after the launch (20 Oct. 2018), we succeeded to confirm the health of both antennas and to release the launch lock of the WPT. After Mercury orbit insertion planned at the end of 2025, both sensors will be fully deployed and activate full operations of the PWI electric field measurements.
Highlights
The BepiColombo project is a Euro-Japanese joint mission for the investigation of Mercury, the innermost planet in our solar system (Benkhoff et al 2010, 2020, this issue)
The Mio (Mercury Magnetospheric Orbiter (MMO)) spacecraft is a part of this project (Hayakawa et al 2004; Yamakawa et al 2008; Murakami et al 2020, this issue), and will enable a comprehensive study of the Hermean environment, which is strongly influenced by the Sun, by combined observations with the Mercury Planetary Orbiter (MPO) (Milillo et al 2010, 2020, this issue)
Each dipole antenna is a pair of top-hat wire probe antennas, with a sphere attached at the end of the wire, and its total length after deployment is 31.6 m tip-to-tip
Summary
The BepiColombo project is a Euro-Japanese joint mission for the investigation of Mercury, the innermost planet in our solar system (Benkhoff et al 2010, 2020, this issue). For the electric field measurement, the PWI has two pairs of wire dipole antennas, MEFISTO (Mercury Electric Field In-Situ Tool) and WPT (Wire Probe Antenna) (Fig. 1) Both sensors with their deployment units are orthogonally installed on the outer side of the spacecraft lower deck. By biasing the MEFISTO-S and WPT-S antennas, PWI EWO-EFD can measure the electric field in the frequency range of DC to 32 Hz with dynamic amplitude range from −500 to +500 mV/m and with a resolution of 0.015 mV/m This range is enough to cover the expected fields in the exosphere, magnetosphere and solar wind around Mercury (e.g. Blomberg et al 2006). By the combination of MEFISTO and WPT, the PWI measurements can investigate the Hermean environment and the inner heliosphere in combination with to the magnetic field measurement by MGF and PWI SC-LF and SC-DB
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