1.1. The BepiColombo Mission Planet Mercury, the closest planet to the Sun, (0.30 AU - 0.46 AU), orbits in an environment exposed to intense particle’s fluxes and to a solar constant ranging from approximately 6,000 to 14,000 W/m2, which is up to ten times that at Earth. Therefore, reaching Mercury with a spacecraft needs a complex design, accurate operation planning and years of navigation to win
Preprint submitted to Acta Astronautica September 4, 2024

Nevertheless, Mercury is still a key scientific element for the understanding of Solar System evolution. The knowledge of its interior, the presence of a significant magnetosphere, the nature of some surface features (such as the hollows and the clusters of rimless depressions) are still open points for the Mercury science. To this aim, already in 2000, and then in 2008 with a complete review of size, targets and budget, the BepiColombo mission was approved as joint mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) Benkhoff et al. (2010). The mission is dedicated to Giuseppe ”Bepi” Colombo (1920-1984), a Paduan mathematician and engineer, who specialised in celestial mechanics. He discovered the Mercury’s spin-orbit 3:2 resonance and contributed to the calculation of the NASA Mariner 10 probe’s orbit, by suggesting to exploit this peculiarity to carry out three fly-bys at Mercury instead of one alone. The BepiColombo mission hosts 16 payloads and aims at hundreds of scientific goals for a complete characterisation of the planet’s interior, its surface, the exosphere, and the magnetosphere and to test Einstein’s theory of General Relativity. To fulfil those ambitious scientific goals, the overall assembly is designed in a modular configuration of four parts: the Mercury Transfer Module (MTM), the Mercury Planetary Orbiter (MPO), the Mercury Magnetosphere Orbiter (MMO or Mio) and the Magnetospheric Orbiter Sunshield and Interface Structure (MOSIF). Launched on the 20th of October 2018 from French Guiana spaceport on board the VA-245 Ariane 5 ECA 5105, the spacecraft is currently facing the cruise phase in the Mercury Composite Spacecraft (MCS) configuration, as shown in Figure (1). The whole MCS is propelled by four, max thrust 145 mN each, solar electric thrusters mounted on board the MTM module, also housing 40 m2 solar panels, 10 meters tip-to-tip long, able to generate up to 13,000 W. The arrival at Mercury is foreseen in December 2025, after about seven years in the interplanetary space on a trajectory designed to exploit ∆V from one flyby with the Earth, two with Venus and six with
(a)
(b) (c) Figure 1: BepiColombo Mercury Composite Spacecraft (MCS). a) A diagram of BepiColombo at launch b) MCS in cruise configuration, backward view. c) MCS in cruise configuration, upward view.
Mercury. At the end of the last electric thrust arc, the MCS will detach the MTM module and the MPO chemical propellers will start the Mercury Orbit Injection (MOI). MPO and Mio will move to high eccentricity 11500 km apoherm, 400 km periherm, polar orbit, that will be the Mio final orbit. Finally, after the Mio/MPO separation, MPO will reduce its orbit eccentricity reaching 1500 km apoherm - 400 km periherm orbit. The Mio spacecraft with its five payloads (Table 1) is dedicated to the measurement of the exosphere and magnetosphere of the Mercury environment. At the contrary, the MPO will Type position BELA Laser Altimeter MPO ISA Three Axis Accelerometer MPO MERMAG Magnetometer MPO MERTIS-TIS IR spectrometer MPO MGNS Gamma ray and neutron spectrometer MPO MIXS X-ray spectrometer MPO Ka-T Radio science Ka-band transponder MPO PHEBUS UV spectrometer MPO SERENA Neutral and ionised particle analyser MPO SIMBIO-SYS High resolution + stereo camerasVisual and NIR spectrometer MPO SIXS Solar monitor MPO MDM Dust Monitor Mio MGF Magnetometer Mio MPPE Plasma, high-energy particle and energetic neutral atom detector Mio MSASI Mercury Sodium Atmospheric Spectral Imager Mio PWI Sets of Electric Field sensors Mio focus on the planetary complete characterisation, using payloads (Table 1)

[Table: Table 1: MPO and Mio Payloads list
BepiColombo Payloads list]