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Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter
Artist's depiction of the BepiColombo mission, with the Mercury Planetary Orbiter (left) and Mercury Magnetospheric Orbiter (right)
Mission type Planetary science
Operator ESA · JAXA
Mission duration Planned: 1+ year
Spacecraft properties
Manufacturer EADS Astrium · ISAS
Launch mass 4,100 kg (9,039 lb)[1]
BOL mass MPO: 1,230 kg (2,712 lb)[1]
MMO: 255 kg (562 lb)[1]
Dry mass 2,700 kg (5,952 lb)[1]
Dimensions MPO: 2.4 × 2.2 × 1.7 m[1]
     (7.9 × 7.2 × 5.6 ft)
MMO: 1.8 × 1.1 m[1]
     (5.9 × 3.6 ft)
Power MPO: 150 W
MMO: 90 W
Start of mission
Launch date Planned: October 2018 (2018-10)[1]
Rocket Ariane 5 ECA
Launch site Guiana Space Centre[2]
Contractor Arianespace
Mercury orbiter
Spacecraft component Mercury Planetary Orbiter
Orbital insertion Planned: 5 December 2025
Orbit parameters
Perihermion 480 km (300 mi)
Apohermion 1,500 km (930 mi)
Inclination 90°
Mercury orbiter
Spacecraft component Mercury Magnetospheric Orbiter
Orbital insertion Planned: 5 December 2025
Orbit parameters
Perihermion 590 km (370 mi)
Apohermion 11,640 km (7,230 mi)
Inclination 90°

BepiColombo mission insignia
ESA solar system insignia for BepiColombo

BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury.[3] The mission comprises two satellites to be launched together: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (MMO). The mission will perform a comprehensive study on Mercury, including its magnetic field, magnetosphere, interior structure and surface. It is scheduled to launch in October 2018, with an arrival at Mercury planned for December 2025, after a flyby of Earth, two flybys of Venus, and six flybys of Mercury.[1][4] The mission was approved in November 2009, after years in proposal and planning as part of the European Space Agency's Horizon 2000+ program;[5] it will be the last mission of the program to be launched.[6]


BepiColombo is named after Giuseppe "Bepi" Colombo (1920–1984), a scientist, mathematician and engineer at the University of Padua, Italy, who first implemented the interplanetary gravity-assist manoeuvre during the 1974 Mariner 10 mission, a technique now commonly used by planetary probes.

The mission involves three components:[7]

  • Mercury Transport Module (MTM) for propulsion, built by ESA
  • Mercury Planetary Orbiter (MPO) built by ESA
  • Mercury Magnetospheric Orbiter (MMO) built by JAXA
Planned orbits for MMO and MPO satellites, the two probes of the BepiColombo mission.

The prime contractor for ESA is Airbus Defence and Space.[8] ESA is responsible for the overall mission, the design, development assembly and test of the propulsion and MPO modules, and the launch. The two orbiters are planned to be launched together on an Ariane 5 launch vehicle in October 2018. The spacecraft will have a seven-year interplanetary cruise to Mercury using solar-electric propulsion (ion thrusters) and gravity assists from Earth, Venus and eventual gravity capture at Mercury.[1] ESA's Cebreros 35-metre ground station is planned to be the primary ground facility for communications during all mission phases.

Arriving in Mercury orbit on 5 December 2025, the MMO and MPO satellites will separate and observe Mercury in collaboration for one year, with a possible one-year extension.[1] The orbiters will be equipped with scientific instruments provided by various European countries and Japan. They will characterise the huge liquid iron core (​34 of the planet's radius) and will complete gravitational and magnetic field mappings. Russia will provide a gamma ray and neutron spectrometers to verify the existence of water ice in polar craters that are permanently in shadow from the Sun's rays.

Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have a "tenuous surface-bounded exosphere"[9] containing hydrogen, helium, oxygen, sodium, calcium, potassium and others. Its exosphere is not stable; atoms are continuously lost and replenished from a variety of sources, and the mission will study its composition and dynamics, including generation and disappearance.


The main objectives of the mission are:[2][10]

Mission design[edit]

The spacecraft will take seven years to position itself to enter Mercury orbit. During this time it will use solar-electric propulsion and nine gravity assists, flying past the Earth and Moon in April 2020, Venus in 2020 and 2021, and six Mercury flybys between 2021 and 2025.[1]

The spacecraft will leave Earth with an hyperbolic excess velocity of 3.475 km/s (2.159 mi/s). Initially the craft is in an orbit similar to that of the earth. After both the spacecraft and the earth have completed one and a half orbits, it returns to Earth to perform a gravity-assist manoeuvre and is deflected towards Venus. Two consecutive Venus flybys reduce the perihelion nearly to Mercury distance with almost no need for thrust. A sequence of six Mercury flybys will lower the relative velocity to 1.76 km/s (1.09 mi/s). After the fourth Mercury flyby the craft will be in an orbit similar to that of Mercury and will remain in the general vicinity of Mercury (see video). Four final thrust arcs reduce the relative velocity to the point where Mercury will "weakly" capture the spacecraft on 5 December 2025 into polar orbit. Only a small manoeuvre is needed to bring the craft into an orbit around Mercury with an apocentre of 178,000 km. The spacecraft then will be lowered using chemical thrusters.[12][13]

The planned mission schedule is:[1]

Date Event Comment
~5 October 2018 Launch
6 April 2020 Earth flyby 1.5 years after launch
12 October 2020 First Venus flyby
11 August 2021 Second Venus flyby 1.35 Venus years after first Venus flyby
2 October 2021 First Mercury flyby
23 June 2022 Second Mercury flyby 2 orbits (3.00 Mercury years) after 1st Mercury flyby
20 June 2023 Third Mercury flyby >3 orbits (4.12 Mercury years) after 2nd Mercury flyby
5 September 2024 Fourth Mercury flyby ~4 orbits (5.04 Mercury years) after 3rd Mercury flyby
2 December 2024 Fifth Mercury flyby 1 orbit (1.00 Mercury year) after 4th Mercury flyby
9 January 2025 Sixth Mercury flyby ~0.43 orbits (0.43 Mercury years) after 5th Mercury flyby
5 December 2025 Mercury orbit insertion 3.75 Mercury years after 6th Mercury flyby
14 March 2026 MPO in final science orbit 1.13 Mercury years after orbit insertion
1 May 2027 End of nominal mission 5.82 Mercury years after orbit insertion
1 May 2028 End of extended mission 9.98 Mercury years after orbit insertion


Mercury Transport Module[edit]

Mercury Transport Module in ESTEC before stacking

The Mercury Transport Module (MTM) is at the base of the 'stack' and provides propulsion for Earth-Mercury transfer and to slow down its approach to Mercury. It carries no significant scientific instruments.

The Transport Module is equipped with two propulsion systems: a solar electric ion drive engine and a standard bipropellant chemical propulsion system using MMH / MON3. The chemical propulsion system will be used for Earth escape and then it will be pyrotechnically isolated, and the solar electric ion engine will take over for the cruise phase. The twin QinetiQ T6 ion thrusters operate at maximum combined throttle of 290 mN.[14] The MTM supplies electrical power for the two hibernating orbiters as well as for its solar electric propulsion system.[15]

The solar electric propulsion will be used for the cruise phase. The ion drives have very high specific impulse and very low thrust. This leads to a flight profile with long continuous low-thrust braking to gradually reduce the velocity of the spacecraft. Moments before Mercury orbit insertion, the MTM will be jettisoned from the spacecraft stack.[15] After separation from the MTM, the MPO will provide the MMO all necessary power and data resources until MMO is delivered to its mission orbit; separation of MMO from MPO will be accomplished by spin-ejection.

Mercury Planetary Orbiter[edit]

Mercury Planetary Orbiter in ESTEC before stacking
Radio testing of BepiColombo orbiter

The Mercury Planetary Orbiter (MPO) will have a mass of 1,150 kg (2,540 lb) and will use a single-sided solar array capable of providing up to 1000 watts and featuring Optical Solar Reflectors to keep its temperature below 200 °C (392 °F). The solar array requires continuous rotation keeping the Sun at a low incidence angle in order to generate adequate power while at the same time limiting the temperature.[15]

The MPO will carry a payload of 11 instruments, comprising cameras, spectrometers (IR, UV, X-ray, γ-ray, neutron), radiometer, laser altimeter, magnetometer, particle analysers, Ka-band transponder, and accelerometer. The payload components are mounted on the nadir side of the spacecraft to achieve low detector temperatures, apart from the MERTIS and PHEBUS spectrometers located directly at the main radiator to provide a better field of view.[15]

A high-temperature-resistant 1.0 m (3.3 ft) diameter high-gain antenna is mounted on a short boom on the zenith side of the spacecraft. Communications will be on the X and Ka band with an average bit rate of 50 kbit/s and a total data volume of 1550 Gb/year. ESA's Cebreros 35-metre ground station is planned to be the primary ground facility for communications during all mission phases.[15]

Scientific payload[edit]

The scientific payload of the Mercury Planetary Orbiter consists of eleven instruments:[16][17]

  • BELA — BepiColombo Laser Altimeter, developed by Switzerland and Germany
  • ISA — Italian Spring Accelerometer, developed by Italy
  • MERMAG — Mercury Magnetometer, developed by Germany and UK
  • MERTIS — Mercury Thermal Infrared Spectrometer, developed by Germany
  • MGNS — Mercury Gamma ray and Neutron Spectrometer, developed by Russia
  • MIXS — Mercury Imaging X-ray Spectrometer, developed by UK and Finland
  • MORE — Mercury Orbiter Radio science Experiment, developed by Italy and the United States
  • PHEBUS — Probing of Hermean Exosphere by Ultraviolet Spectroscopy, developed by France and Russia
  • SERENA — Search for Exosphere Refilling and Emitted Neutral Abundances (Neutral and ionised particle analyser), developed by Italy, Sweden, Austria and the United States, contains the Strofio mass spectrometer from NASA's Discovery program[18]
  • SIMBIO-SYS — Spectrometers and Imagers for MPO BepiColombo Integrated Observatory System (High resolution and stereo cameras, visual and near infrared spectrometer), developed by Italy, France and Switzerland
  • SIXS — Solar Intensity X-ray Spectrometer, developed by Finland and UK

Mercury Magnetospheric Orbiter[edit]

Mercury Magnetospheric Orbiter in ESTEC before stacking

The Mercury Magnetospheric Orbiter (MMO), developed and built mostly by Japan, has the shape of a short octagonal prism, 180 cm (71 in) long from face to face and 90 cm (35 in) high.[2][19] It has a total mass of 285 kg (628 lb), including a 45 kg (99 lb) scientific payload.[2][20]

The MMO is spin stabilized at 15 rpm with the spin axis perpendicular to the equator of Mercury and it will enter polar orbit at an altitude of 590 × 11,640 km (370 × 7,230 mi), outside of MPO's orbit.[20] The top and bottom of the octagon act as radiators with louvers for active temperature control. The sides are covered with solar cells which provide 90 W. Communications with Earth will be through a 0.8 m (2.6 ft) diameter X band phased array high-gain antenna and two medium-gain antennas operating in the X band. Telemetry will return 160 Gb/year, about 5 kbit/s over the lifetime of the spacecraft, which is expected to be greater than one year. The reaction and control system is based on cold gas thrusters. After its release in Mercury orbit, the MMO will be operated by Sagamihara Space Operation Center using Usuda Deep Space Center's 64 m (210 ft) antenna located in Nagano, Japan.[16]

Scientific payload[edit]

The Mercury Magnetospheric Orbiter will carry five groups of instruments with a total scientific payload mass of 45 kg (99 lb):[2][16]

  • MPPE — Mercury Plasma Particle Experiment, studies the plasma & neutral particles from the planet, magnetosphere, and interplanetary solar wind. It will employ these instruments:
    • Mercury Electron Analyzer (MEA)
    • Mercury Ion Analyzer (MIA)
    • Mass Spectrum Analyzer (MSA)
    • High-Energy Ions (HEP-ion)
    • High-Energy Electrons (HEP-ele)
    • Energetic Neutrals Analyzer (ENA)
  • MGF — Magnetic Field Investigation, studies Mercury's magnetic field, magnetosphere, and interplanetary solar wind
  • PWI — Plasma Wave Investigation, studies the electric field, electromagnetic waves, and radio waves from the magnetosphere and solar wind
  • MSASI — Mercury Sodium Atmosphere Spectral Imager, studies the thin sodium atmosphere of Mercury
  • MDM — Mercury Dust Monitor, studies dust from the planet and interplanetary space

Mercury Surface Element[edit]

The Mercury Surface Element (MSE) was cancelled in 2003 due to budgetary constraints.[6] At the time of cancellation, MSE was meant to be a small, 44 kg (97 lb), lander designed to operate for about one week on the surface of Mercury.[12] Shaped as a 0.9 m (3.0 ft) diameter disc, it was designed to land at a latitude of 85° near the terminator region. Braking manoeuvres would bring the lander to zero velocity at an altitude of 120 m (390 ft) at which point the propulsion unit would be ejected, the airbags inflated, and the module would fall to the surface with a maximum impact velocity of 30 m/s (98 ft/s). Scientific data would be stored onboard and relayed via a cross-dipole UHF antenna to either the MPO or MMO. The MSE would have carried a 7 kg (15 lb) payload consisting of an imaging system (a descent camera and a surface camera), a heat flow and physical properties package, an alpha particle X-ray spectrometer, a magnetometer, a seismometer, a soil penetrating device (mole), and a micro-rover.[21]

See also[edit]


  1. ^ a b c d e f g h i j k l "BepiColombo Factsheet". European Space Agency. 6 July 2017. Retrieved 6 July 2017. 
  2. ^ a b c d e "MMO/BepiColombo". JAXA. 2008. Retrieved 7 February 2014. 
  3. ^ Amos, Jonathan (18 January 2008). "European probe aims for Mercury". BBC News. Retrieved 21 January 2008. 
  4. ^ "BepiColombo Launch Rescheduled for October 2018". European Space Agency. 25 November 2016. Retrieved 14 December 2016. 
  5. ^ "BepiColombo Overview". European Space Agency. 5 September 2016. Retrieved 13 March 2017. 
  6. ^ a b "Critical Decisions on Cosmic Vision" (Press release). European Space Agency. 7 November 2003. No. 75-2003. Retrieved 14 December 2016. 
  7. ^ Hayakawa, Hajime; Maejima, Hironori (2011). BepiColombo Mercury Magnetospheric Orbiter (MMO) (PDF). 9th IAA Low-Cost Planetary Missions Conference. 21–23 June 2011. Laurel, Maryland. 
  8. ^ "BepiColombo to Enter Implementation Phase". European Space Agency. 26 February 2007. 
  9. ^ Domingue, Deborah L.; Koehn, Patrick L.; et al. (August 2007). "Mercury's Atmosphere: A Surface-Bounded Exosphere". Space Science Reviews. 131 (1–4): 161–186. Bibcode:2007SSRv..131..161D. doi:10.1007/s11214-007-9260-9. 
  10. ^ "BepiColombo: Fact Sheet". European Space Agency. 1 December 2016. Retrieved 13 December 2016. 
  11. ^ "BepiColombo - Testing general relativity". European Space Agency. 4 July 2003. Retrieved 7 February 2014. [permanent dead link]
  12. ^ a b "BepiColombo". National Space Science Data Center. NASA. 26 August 2014. Retrieved 6 April 2015. 
  13. ^ "Mission Operations - Getting to Mercury". European Space Agency. Retrieved 7 February 2014. 
  14. ^ Clark, Stephen D.; Hutchins, Mark S.; et al. (2013). BepiColombo Electric Propulsion Thruster and High Power Electronics Coupling Test Performances. 33rd International Electric Propulsion Conference. 6–10 October 2013. Washington, D.C. IEPC-2013-133. 
  15. ^ a b c d e "Mercury Planetary Orbiter - Spacecraft". European Space Agency. 20 October 2011. Retrieved 6 February 2014. 
  16. ^ a b c "MMO (Mercury Magnetospheric Orbiter) : Objectives". JAXA. 2011. Retrieved 7 February 2014. 
  17. ^ "Mercury Planetary Orbiter - Instruments". European Space Agency. 15 January 2008. Retrieved 6 February 2014. 
  18. ^ "Strofio". Discovery Program. NASA. Retrieved 7 January 2017. 
  19. ^ Yamakawa, Hiroshi; Ogawa, Hiroyuki; et al. (January 2004). "Current status of the BepiColombo/MMO spacecraft design". Advances in Space Research. 33 (12): 2133–2141. Bibcode:2004AdSpR..33.2133Y. doi:10.1016/S0273-1177(03)00437-X. 
  20. ^ a b "Mercury Exploration Project "BepiColombo"" (PDF). JAXA. 2014. Retrieved 6 April 2015. 
  21. ^ "BepiColombo's lander". European Space Agency. 20 February 2002. Retrieved 7 February 2014. 

External links[edit]