Several spacecraft mated together in deep space.

Artist's impression of the BepiColombo spacecraft in cruise configuration. The Mercury Transfer Module is at the bottom. The Mercury Planetary Orbiter is in the middle. The Mercury Magnetospheric Orbiter sits inside the sunshield, visible at the top. Credit: ESA/ATG medialab

BepiColombo is an international mission that combines two spacecraft to explore Mercury from unique vantage points. ESA is leading the mission and provided one orbiter (with a NASA instrument aboard). The Japan Aerospace Exploration Agency (JAXA) built the second orbiter. Their data will be combined to provide a more complete understanding of Mercury.

  • ESA's Mercury Planetary Orbiter (MPO) will study the the surface and interior of the innermost planet.
  • NASA's Strofio mass spectrometer is among MPO's scientific instrument suite. Strofio will study the chemical and geological history of Mercury's surface.
  • JAXA's Mercury Magnetospheric Orbiter (MMO), also known as Mio, will study the planet's magnetic field, known as a magnetosphere.
  • The two orbiters are riding together for the seven-year trip to Mercury.
  • These are the first Mercury missions for the ESA and Japan. Only two other spacecraft have visited Mercury: NASA's Mariner 10 and MESSENGER.

The spacecraft are en route to their destination.

Mission Elapsed Time
Launch Date Oct. 20, 2018 | 01:45:28 UT
Launch Site Guiana Space Centre, Kourou, French Guiana
Launch Vehicle Ariane 5
Destination Mercury
Type Orbiters
Status En Route to Mercury
Nation Europe / Japan
Alternate Names Mercury Magnetospheric Orbiter (MMO), Mercury Planetary Orbiter (MPO)

Key Dates

Oct. 20, 2018 | 01:45:28 UT​: Launch

April 13, 2020: Earth Flyby

Oct. 16, 2020: Venus Flyby

Aug. 11, 2020: Venus Flyby

Oct. 2, 2021: Mercury Flyby

June 23, 2022: Mercury Flyby

June 20, 2023: Mercury Flyby

Sept. 5, 2024: Mercury Flyby

Dec. 2, 2024: Mercury Flyby

Jan. 9, 2025: Mercury Flyby

Dec. 5, 2025: Mercury Orbit Insertion

In Depth

BepiColombo, an ESA mission in cooperation with Japan, will explore Mercury, the planet closest to the Sun. Europe's space scientists have identified the mission as one of the most challenging long-term planetary projects, because Mercury's proximity to the Sun makes it difficult for a spacecraft to reach and survive in the harsh environment. The scientific interest to go to Mercury lies in the valuable clues that such a mission can provide in understanding the planet itself as well as the formation of our solar system; clues which cannot be obtained with distant observations from Earth.

BepiColombo will be the third mission to visit the planet Mercury. NASA's Mariner 10, flew past Mercury three times in 1974-5 and returned the first close-up images of the planet. NASA's MESSENGER spacecraft will enter Mercury orbit in March of 2011, and already has returned many images of the planet, as well as data. The information gleaned when BepiColombo arrives will throw light not only on the composition and history of Mercury, but also on the history and formation of the inner planets in general, including the Earth.

The mission will consist of two separate spacecraft that will orbit the planet. ESA is building one of the main spacecraft, the Mercury Planetary Orbiter (MPO), and the Japanese space agency ISAS/JAXA will contribute the other, the Mercury Magnetospheric Orbiter (MMO).

The Mercury Planetary Orbiter will study the surface and internal composition of the planet, and the Mercury Magnetospheric Orbiter will study Mercury's magnetosphere, that is the region of space around the planet that is dominated by its magnetic field.

Technological Challenges:

With two spacecraft, BepiColombo is a large and costly mission, one of the 'cornerstones' in ESA's long-term science program. The mission presents enormous, but exciting challenges. All of ESA's previous inter-planetary missions have been to relatively cold parts of the solar system. BepiColombo will be the Agency's first experience of sending spacecraft to 'hot' regions.

After launch into a geostationary transfer orbit, the Mercury Composite Spacecraft will be boosted to the phasing orbit using chemical propulsion. From here the spacecraft will be set on its interplanetary trajectory through a flyby of the Moon. On its way to Mercury, the spacecraft must brake against the Sun's gravity, which increases with proximity to the Sun, rather than accelerate away from it, as is the case with journeys to the outer solar system. BepiColombo will accomplish this by making clever use of the gravity of the Earth, Venus and Mercury itself and by using solar electric propulsion (SEP). This innovative combination of low thrust space propulsion and gravity assist has been demonstrated by ESA's technology mission, SMART-1.

When approaching Mercury, the spacecraft will use the planet's gravity plus conventional rocket engines to insert itself into a polar orbit. A special Weak Stability Boundary Capturing technique is employed. This gives flexibility and is more robust against failures compared to using the more traditional "big kick" approach (single burn capture). The Mercury Magnetospheric Orbiter will be released into its operational orbit, then the Sunshield and the Mercury Magnetospheric Orbiter interface structure will be separated, while the chemical propulsion system will bring the Mercury Planetary Orbiter to its lower orbit. Observations from orbit will continue for one Earth year.


Launch Vehicle: Ariane 5

Spacecraft Mass: 9,040 pounds (4,100 kilograms)

Spacecraft Instruments

Mercury Planetary Orbiter: 520 kg
Mercury Magnetospheric Orbiter: 250 kg

Mercury Planetary Orbiter:

  1. Cameras
  2. Spectrometers (IR, UV, X-ray, neutron)
  3. Radiometer
  4. Laser altimeter
  5. Magnetometer
  6. Particle analysers
  7. Ka-band transponder
  8. Accelerometer

Mercury Magnetospheric Orbiter:

  1. Magnetometer
  2. Ion spectrometer
  3. Electron energy analyser
  4. Cold and energetic plasma detectors
  5. Plasma wave analyser
  6. Imager

Spacecraft Power:

Solar Panels

Max Power:

Mercury Planetary Orbiter: 600 W
Mercury Magnetospheric Orbiter: 325 W

Antenna Diameter:

Mercury Planetary Orbiter: 1.0 M
Mercury Magnetospheric Orbiter: 0.8 m

Max Data Rate:

Mercury Planetary Orbiter: 50 kb/s
Mercury Magnetospheric Orbiter: 5 kb/s

Additional Resources

European Space Agency: BepiColombo

Japan Aerospace Exploration Agency: BepiColombo

National Space Science Data Center Master Catalog: BepiColombo

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