BepiColombo

BepiColombo is a joint European Space Agency (ESA) and Japanese mission to Planet Mercury for exploration. BepiColombo is ESA’s first mission to Mercury. It is also ESA’s first mission conducted in co-operation with Japan.

BepiColombo was launched on 20 October 2018 on an Ariane 5 rocket from ESA’s Spaceport in Kourou, French Guiana. The spacecraft will arrive at Planet Mercury in late 2026, with its nominal orbit insertion scheduled for November 21, 2026. To complete this long journey, the spacecraft executed nine total planetary flybys—one of Earth, two of Venus, and six of Mercury—to shed speed against the Sun’s immense gravity.

The two science orbiters—ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mio (Mercury Magnetospheric Orbiter)—will separate from each other on December 9–10, 2026. Following final orbit adjustments, routine science operations are scheduled to begin in April 2027.

BepiColombo used the gravity of the Earth, Venus and Mercury in combination with solar-electric propulsion (SEP) to journey to Mercury. When approaching Mercury, the spacecraft will use the planet’s gravity plus conventional rocket engines to insert itself into a polar orbit.

The main contractor for BepiColombo project is Airbus Defence and Space. It is building the European Mercury Planetary Orbiter and the Mercury Transfer Module.

Mission:

The aim of the BepiColombo mission is:

1. To investigate Planet Mercury’s magnetic field, magnetosphere and both its surface and interior.

2. To make a complete map of Mercury at different wavelengths. This will allow to map the planet’s mineralogy and elemental composition and determine whether the interior of the planet is molten or not.

3. To examine Mercury as a planet: composition, craters, geology and interior structure.

4. To examine Mercury’s thin atmosphere.

5. To use the spacecraft’s proximity to the Sun to test the predictions of General Relativity theory with improved accuracy.

6. To understand the origin and evolution of a planet close to its parent star (our Sun).

Total Cost: Originally estimated at €650 million in 2013, the baseline cost grew to €1.65 billion ($1.8B USD) due to thermal engineering challenges and launcher changes. Total lifecycle costs exceed €3 billion when including JAXA and instrument funding.

Specs:

General Spacecraft

Total Launch Mass: 4100 kg (9,040 lb)
Dry Mass (without fuel): Around 2,700 kg (5,950 lb)
Overall Dimensions (composite stack): 6.3 m × 3.9 m × 3.6 m stowed for launch

Individual Orbiter Specs

Mercury Planetary Orbiter (MPO):

– Mass: 1,230 kg
– Dimensions: 2.4 m × 2.2 m × 1.7 m
– Scientific Payload: 11 instruments (including BELA, MERTIS, and MIXS)

Mio (Mercury Magnetospheric Orbiter):

– Mass: 275 kg
– Dimensions: 1.8 m × 1.1 m
– Scientific Payload: 5 instruments (including MGF, MPPE, and PWI)

Spacecraft

The BepiColombo spacecraft consists of:

1. Mercury Transfer Module:

Developed by ESA, this high-power propulsion module provided the solar-electric power and thrust required to navigate the inner Solar System. Equipped with four T6 ion engines, it successfully carried both science orbiters through their eight-year cruise phase before separating from the stack on September 3, 2026.

2. Mercury Planetary Orbiter (MPO)

Developed by ESA, this three-axis stabilized spacecraft will enter a low polar orbit around Mercury in December 2026. Equipped with a protective sunshield to withstand extreme heat, the MPO will use 11 scientific instruments over its one-year mission to map the planet’s surface, topography, and internal composition.

3. Mio Mercury Magnetospheric Orbiter (MMO)

Developed by JAXA, the Mio spin-stabilized spacecraft will separate from the MPO on December 9–10, 2026, to enter a distinct elliptical orbit around Mercury. It is specifically designed to study the planet’s environment, utilizing five advanced scientific instruments to investigate Mercury’s magnetic field, magnetosphere, and surrounding space plasma.

The name “Mio” was chosen from public suggestions. Mio means a waterway or fairway in Japanese. JAXA chose the name to symbolize navigating milestones and traveling safely through the solar wind like a ship on the ocean.

Name

BepiColombo mission is named after Giusseppe (Bepi) Colombo (1920-1984) a scientist, engineer and mathematician at the University of Padua, Italy. He was the first to see that an unsuspected resonance is responsible for Mercury’s habit of rotating on its axis three times for every two revolutions it makes around the Sun. He also suggested to NASA how to use a gravity-assisted swing-by of Planet Venus to place the Mariner 10 spacecraft in a solar orbit that would allow it to fly by Mercury three times in 1974-5.

Operations Centre

Mission operation centre will be located at the European Space Operations Centre (ESOC) in Darmstadt, Germany. The ground telemetry station for the MPO and MMO spacecraft will be the Cebreros (Spain) 35m antenna (8 hours/day) and the Usuda (Japan) 64m antenna (6-8 hours/day) respectively.

History

The European mission to Planet Mercury was first proposed in May 1993. ESA included a Mercury orbiter in one of the three new Cornerstones missions when the Horizon 2000 science programme was extended in 1994. ESA approved a package of missions for 2008–2013 including BepiColombo and Gaia in October 2000.

In 2003 an original plan to include a lander was shelved.

In 2008 following an increase in BepiColombo mission’s mass the launch vehicle was changed from Soyuz-Fregat to Ariane 5.

Japan sent the Mercury Magnetosphere Orbiter (MMO) in April 2015 to the European Space Research and Technology Centre (ESTEC), Netherlands for testing.

In November 2016 the launch was rescheduled to October 2016 because an electrical fault was found during preparations for the Mercury Transfer Module thermal test.

Years later during its flight, in April 2024, the spacecraft’s thrusters suffered another electrical power glitch. While engineers successfully implemented a lower-thrust trajectory workaround to preserve the mission, the adjustment delayed final Mercury orbit insertion from late 2025 to November 2026.

The Mercury Transfer Module (MTM) successfully separated from the science stack on 3 September, 2026, concluding its 8-year cruise phase using solar electric propulsion.

Books:

Europe’s Space Programme: To Ariane and Beyond by Brian Harvey
from Amazon.com, Amazon.co.uk, Amazon.ca

Did you know?

* The proximity of Mercury to the Sun makes it difficult to observe and hard to reach by space flight.

* BepiColombo and Solar Orbiter are ESA’s first long-range science missions designated to use an ion engine.

*  NASA’s Mariner 10 was the first spacecraft to flyby Planet Mercury. It made three fly-bys in 1974 /75. It returned the first close-up pictures of the planet. The next spacecraft to orbit Mercury was NASA’s MESSENGER spacecraft in 2011.

* Magnetosphere is the region of space around the planet that is dominated by its magnetic field.

BepiColombo Links

ESA Science & Technology: BepiColombo: The official site for this European Space Agency mission to Mercury. Includes mission summary, background science, and current status.

Mercury project: BepiColombo: The official site for the Institute of Space and Astronautical Science (ISAS) and Japan Space Exploration Agency (JAXA) portion of the BepiColumbo mission

L’Europe ira sur Mercure by ESA (Photo reference – 2 Oct 2011)

JAXA | Mercury Exploration Mission “BepiColombo”: Japan Aerospace Exploration Agency

BepiColombo Overview: Picture source – Artist’s view of BepiColombo at Mercury (released 26/02/2007) by EADS Astrium.

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