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|
NSSDCA ID: BEPICLMBO (https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=BEPICLMBO)
|Mission duration||Cruise: 7 years|
Science phase: 1 year
Elapsed: 2 years and 11 days
|Manufacturer||Airbus · ISAS|
|Launch mass||4,100 kg (9,000 lb) |
|BOL mass||MPO: 1,230 kg (2,710 lb)|
Mio: 255 kg (562 lb) 
|Dry mass||2,700 kg (6,000 lb) |
|Dimensions||MPO: 2.4 m × 2.2 m × 1.7 m (7 ft 10 in × 7 ft 3 in × 5 ft 7 in)|
Mio: 1.8 m × 1.1 m (5 ft 11 in × 3 ft 7 in) 
|Power||MPO: 150 W|
Mio: 90 W
|Start of mission|
|Launch date||20 October 2018, 01:45 UTC|
|Rocket||Ariane 5 ECA |
|Launch site||Centre Spatial Guyanais |
|Flyby of Earth (gravity assist)|
|Closest approach||10 April 2020 04:25 UTC|
|Distance||12,677 kilometres (7,877 mi)|
|Flyby of Venus (gravity assist)|
|Closest approach||15 October 2020 03:58 UTC|
|Distance||10,720 kilometres (6,660 mi)|
|Flyby of Venus (gravity assist)|
|Closest approach||10 August 2021 13:57 UTC (planned)|
|Distance||552 kilometres (343 mi)|
|Spacecraft component||Mercury Planetary Orbiter|
|Orbital insertion||5 December 2025 (planned)|
|Perihermion altitude||480 km (300 mi)|
|Apohermion altitude||1,500 km (930 mi)|
|Spacecraft component||Mercury Magnetospheric Orbiter|
|Orbital insertion||5 December 2025 (planned)|
|Perihermion altitude||590 km (370 mi)|
|Apohermion altitude||11,640 km (7,230 mi)|
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. The mission comprises two satellites launched together: the Mercury Planetary Orbiter (MPO) and Mio (Mercury Magnetospheric Orbiter, MMO). The mission will perform a comprehensive study of Mercury, including characterization of its magnetic field, magnetosphere, and both interior and surface structure. It was launched on an Ariane 5 rocket on 20 October 2018 at 01:45 UTC, with an arrival at Mercury planned for on 5 December 2025, after a flyby of Earth, two flybys of Venus, and six flybys of Mercury. The mission was approved in November 2009, after years in proposal and planning as part of the European Space Agency's Horizon 2000+ programme; it is the last mission of the programme to be launched.
BepiColombo is named after Giuseppe "Bepi" Colombo (1920–1984), a scientist, mathematician and engineer at the University of Padua, Italy, who first proposed the interplanetary gravity assist manoeuvre used by the 1974 Mariner 10 mission, a technique now used frequently by planetary probes.
Mio, the name of the Mercury Magnetospheric Orbiter, was selected from thousands of suggestions by the Japanese public. In Japanese, Mio means a waterway, and according to JAXA, it symbolizes the research and development milestones reached thus far, and wishes for safe travel ahead. JAXA said the spacecraft will travel through the solar wind just like a ship traveling through the ocean.
The mission involves three components, which will separate into independent spacecraft upon arrival at Mercury.
During the launch and cruise phases, these three components are joined together to form the Mercury Cruise System (MCS).
The prime contractor for ESA is Airbus Defence and Space. 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 were successfully launched together on 20 October 2018, on Ariane flight VA245. 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. ESA's Cebreros, Spain 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 Mio and MPO satellites will separate and observe Mercury in collaboration for one year, with a possible one-year extension. The orbiters are equipped with scientific instruments provided by various European countries and Japan. The mission will characterize the solid and liquid iron core (3⁄4 of the planet's radius) and determine the size of each. The mission will also complete gravitational and magnetic field mappings. Russia provided 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, but it has a "tenuous surface-bounded exosphere" containing hydrogen, helium, oxygen, sodium, calcium, potassium and other trace elements. Its exosphere is not stable as atoms are continuously lost and replenished from a variety of sources. The mission will study the exosphere composition and dynamics, including generation and escape.
The stacked 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.
The stacked spacecraft left Earth with a hyperbolic excess velocity of 3.475 km/s (2.159 mi/s). Initially, the craft was placed in a heliocentric orbit similar to that of Earth. After both the spacecraft and Earth completed one and a half orbits, it returned to Earth to perform a gravity-assist maneuver and is deflected towards Venus. Two consecutive Venus flybys reduce the perihelion near to the Sun-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 ). 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 maneuver is needed to bring the craft into an orbit around Mercury with an apocentre of 178,000 km. The orbiters then separate and will adjust their orbits using chemical thrusters.
As of 2020[update], the mission schedule is: 
|20 October 2018||Launch|
|10 April 2020||Earth flyby||1.5 years after launch|
|15 October 2020, 03:58 UTC||First Venus flyby, successful||According to Johannes Benkhoff of ESA, the probe may possibly be capable of detecting phosphine – the chemical discovered in the Venusian atmosphere in September 2020 – during this and the following flyby. He stated that "we do not know if our instrument is sensitive enough". On 15 October 2020, the ESA reported the flyby was a success.|
|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||Spacecraft separation; 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|
The BepiColombo mission proposal was approved in 2000 by the ESA, with a science payload proposal request issued in 2004. In 2007, Astrium was selected as the prime contractor, and the Soyuz-Fregat launcher was dropped in favor of Ariane 5 as the estimated mass increased. The initial target launch of July 2014 was postponed several times, mostly because of delays on the development of the solar electric propulsion. The total cost of the mission is estimated at US$2 billion.
|Type||Kaufman Ion Engine|
|Units on board||4|
|Diameter||22 cm (8.7 in)|
|Max. thrust||145 mN each|
|Total power||4,628 W|
The Mercury Transfer Module (MTM) is located at the base of the stack. Its role is to carry the two science orbiters to Mercury and to support them during the cruise.
The MTM is equipped with a solar electric propulsion system as the main spacecraft propulsion. Its four QinetiQ-T6 ion thrusters operate singly or in pairs for a maximum combined thrust of 290 mN, making it the most powerful ion engine array ever operated in space. The MTM supplies electrical power for the two hibernating orbiters as well as for its solar electric propulsion system thanks to two 14-meter-long solar panels. Depending on the probe's distance to the Sun, the generated power will range between 7 and 14 kW, each T6 requiring between 2.5 and 4.5 kW according to the desired thrust level.
The solar electric propulsion system has typically very high specific impulse and low thrust. This leads to a flight profile with months-long continuous low-thrust braking phases, interrupted by planetary gravity assists, to gradually reduce the velocity of the spacecraft. Moments before Mercury orbit insertion, the MTM will be jettisoned from the spacecraft stack. After separation from the MTM, the MPO will provide Mio all necessary power and data resources until Mio is delivered to its mission orbit; separation of Mio from MPO will be accomplished by spin-ejection.
The Mercury Planetary Orbiter (MPO) has a mass of 1,150 kg (2,540 lb) and uses 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.
The MPO will carry a payload of 11 instruments, comprising cameras, spectrometers (IR, UV, X-ray, γ-ray, neutron), a radiometer, a laser altimeter, a magnetometer, particle analysers, a Ka-band transponder, and an 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.
A high-temperature-resistant 1.0 m (3 ft 3 in) 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 Gbit/year. ESA's Cebreros, Spain 35-metre ground station is planned to be the primary ground facility for communications during all mission phases.
Mio, or 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. It has a mass of 285 kg (628 lb), including a 45 kg (99 lb) scientific payload consisting of 5 instrument groups, 4 for plasma and dust measuring run by investigators from Japan, and one magnetometer from Austria.
Mio 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. 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 ft 7 in) 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, Mio will be operated by Sagamihara Space Operation Center using Usuda Deep Space Center's 64 m (210 ft) antenna located in Nagano, Japan.
The Mercury Surface Element (MSE) was canceled in 2003 due to budgetary constraints. 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. Shaped as a 0.9 m (2 ft 11 in) 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 Mio. 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.
As with the Hayabusa 2 mission, the BepiColombo mission is the topic of artwork. The manga artist Masayuki Ishikawa created a piece featuring the character Mercury from the manga Madowanai Hoshi, as well as the BepiColombo spacecraft.
The flyby itself was very successful", confirms Elsa. "The only difference to normal cruise phase operations is that near to Venus we have to temporarily close the shutter of any of the star trackers that are expected to be blinded by the planet, similar to closing your eyes to avoid looking at the Sun