Click for original graphic.

After eight years of travel through the inner solar system to get to Mercury, the European/Japanese dual orbiter mission BepiColombo is finally getting close to arrival at Mercury in the fall, and the science team has been doing rehearsals to prepare for that orbital insertion.

Teams must align timelines, verify readiness criteria and maintain a common understanding of what constitutes a ‘go’ or ‘no-go’ decision. During one recent simulation, controllers were confronted with an anomaly that forced them to abort and re-schedule a planned separation scenario. “It generates continuous discussions and iterations between the different teams,” Nacho adds.

The exercise highlighted an essential aspect of Mercury arrival: success depends not only on operating the spacecraft, but on ESA and JAXA working together as one team.

That arrival is made more complicated in that BepiColombo is not a single orbiter. It is made up of the following parts:

• The Mercury Transfer Module (MTM), which provided the service module and ion engines for the journey, including six fly-bys of Earth, two ofVenus, and six of Mercury
• The Mercury Planetary Orbiter (MPO) from the European Space Agency (ESA)
• The Mercury Magnetospheric Orbiter (Mio) from Japan’s space agency JAXA
• The Mio Sunshield and Interface Structure (MOSIF), which protected everything during its journey in the inner solar system close to the Sun

The graphic to the right outlines the arrival plan. First the MTM must separate. Then the two orbiters enter Mercury orbit. Next Japan’s Mio separates and is deployed in its own orbit. Then the sunshield is ejected from Europe’s orbiter and it moves into its planned orbit.

As the spacecraft uses ion engines, with low but continuous thrust, these maneuvers can take weeks.

Both orbiters have complementary orbits to study different aspects of the planet. Europe’s orbiter will orbit closer to get a better look at the planet, while Japan’s Mio’s orbit is highly elliptical, to study the planet’s magnetic field.

During the journey to Mercury BepiColombo overcome several problems. First, the Covid panic threatened operations by limiting staffing and preventing normal behavior. Next the solar panels failed to produce the expected power, a problem that appears to still exist but which has not prevented operations. Finally, its thrusters produced less thrust than expected during a mid-course correction in 2024, causing an eleven month delay in arrival.

It is now however about to arrive. Let us hope that arrival proceeds as planned.