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 |
| Website | sci global |
| Mission duration | Cruise: 7 years Science phase: 1 year |
| Spacecraft properties | |
| Manufacturer | Airbus · ISAS |
| Launch mass | 4,100 kg (9,040 lb) |
| BOL mass | MPO: 1,230 kg (2,710 lb) Mio: 255 kg (560 lb) |
| Dry mass | 2,700 kg (5,950 lb) |
| Dimensions | MPO: 2.4 × 2.2 × 1.7 m (7.9 × 7.2 × 5.6 ft) Mio: 1.8 × 1.1 m (5.9 × 3.6 ft) |
| Start of mission | |
| Launch date | 20 October 2018, 01:45 UTC |
| Rocket | Ariane 5 ECA (VA245) |
| Launch site | Guiana Space Centre |
| Contractor | Arianespace |
| Mercury orbiter | |
| Spacecraft component | Mercury Planetary Orbiter (MPO) |
| 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 (MMO) |
| Orbital insertion | Planned: 5 December 2025 |
| Orbit parameters | |
| Perihermion | 590 km (370 mi) |
| Apohermion | 11,640 km (7,230 mi) |
| Inclination | 90° |
 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 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+ program; it is the last mission of the programme to be launched.
Mission
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, which will separate into independent spacecraft upon arrival at Mercury.
- Mercury Transfer Module (MTM) for propulsion, built by ESA
- Mercury Planetary Orbiter (MPO) built by ESA
- Mercury Magnetospheric Orbiter (MMO) or Mio built by JAXA
During launch and cruise phase, 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 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.
Objectives
The main objectives of the mission are:
- Study the origin and evolution of a planet close to its parent star
- Study Mercury's form, interior, structure, geology, composition and craters
- Investigate Mercury's exosphere, composition and dynamics, including generation and escape
- Study Mercury's magnetised envelope (magnetosphere) - structure and dynamics
- Investigate the origin of Mercury's magnetic field
- Verify Einstein's theory of general relativity by measuring the parameters gamma and beta of the parameterized post-Newtonian formalism with high accuracy.
Design
Planned orbits for Mio and MPO satellites, the two probes of the BepiColombo mission
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 is
placed in an orbit similar to that of the Earth. After both the
spacecraft and the Earth 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.
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 orbiters then
separate and will adjust their orbits using chemical thrusters.
Schedule
As of 2018, the planned mission schedule is:
| Date | Event | Comment |
|---|---|---|
| 20 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 | 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 |
Timeline of BepiColombo from 20 October 2018 to 2 November 2025. Red circle indicates flybys.
History
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 USD$2 billion.
Components
Mercury Transfer Module
Mercury Transfer Module in The Large Space Simulator at ESTEC.
| QinetiQ T6 | Performance |
|---|---|
| Type | Kaufman Ion Engine |
| Units on board | 4 |
| Diameter | 22 centimetres (8.7 in) |
| Max. thrust | 145 mN each |
| Specific impulse (Isp) |
4,300 s |
| Propellant | Xenon |
| 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 pair for a maximum combined thrust of 290 mN,[25]
making it the most powerful ion engine 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.
Mercury Planetary Orbiter
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.
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 (3.3 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 Gbit/year. ESA's Cebreros 35-metre ground station is planned to be the primary ground facility for communications during all mission phases.
Science payload
The science payload of the Mercury Planetary Orbiter consists of eleven instruments:
- BepiColombo Laser Altimeter (BELA), developed by Switzerland and Germany
- Italian Spring Accelerometer (ISA), developed by Italy
- Mercury Magnetometer (MPO-MAG, MERMAG), developed by Germany and UK
- Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS), developed by Germany
- Mercury Gamma-ray and Neutron Spectrometer (MGNS), developed by Russia
- Mercury Imaging X-ray Spectrometer (MIXS), developed by UK and Finland
- Mercury Orbiter Radio-science Experiment (MORE), developed by Italy and the United States
- Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS), developed by France and Russia
- Search for Exosphere Refilling and Emitted Neutral Abundances (SERENA), a neutral and ionised particle analyser, developed by Italy, Sweden, Austria and the United States, which contains the Strofio mass spectrometer from NASA's Discovery programme
- Spectrometers and Imagers for MPO BepiColombo Integrated Observatory System (SIMBIO-SYS), high resolution stereo cameras and a visual and near infrared spectrometer, developed by Italy, France and Switzerland
- Solar Intensity X-ray and Particle Spectrometer (SIXS), developed by Finland and UK.
Mio (Mercury Magnetospheric Orbiter)
Mio in ESTEC before stacking
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 (2.6 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, 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 Magnetospheric Orbiter was given the nickname Mio on 8 June 2018. In Japanese, Mio
means a waterway for ships, and symbolizes the research and development
milestones reached thus far, as well as wishes for a safe travel ahead.
The spacecraft will explore the solar wind as it flows through and is
interfered by Mercury's magnetosphere, just like a ship voyaging through
water currents. Mio was chosen from among 6,494 submissions from the public.
Science payload
Mio carries five groups of science instruments with a total mass of 45 kg (99 lb):
- Mercury Plasma Particle Experiment (MPPE), studies the plasma
& neutral particles from the planet, magnetosphere, and
interplanetary solar wind. It will employ these instruments:
- Mercury Electron Analyzers (MEA1 and MEA2)
- Mercury Ion Analyzer (MIA)
- Mass Spectrum Analyzer (MSA)
- High-Energy Particle instrument for electrons (HEP-ele)
- High-Energy Particle instrument for Ions (HEP-ion)
- Energetic Neutrals Analyzer (ENA)
- Mercury Magnetometer (MMO-MGF), studies Mercury's magnetic field, magnetosphere, and interplanetary solar wind
- Plasma Wave Investigation (PWI), studies the electric field, electromagnetic waves, and radio waves from the magnetosphere and solar wind
- Mercury Sodium Atmosphere Spectral Imager (MSASI), studies the thin sodium atmosphere of Mercury
- Mercury Dust Monitor (MDM), studies dust from the planet and interplanetary space.
Mercury Surface Element (cancelled)
The Mercury Surface Element (MSE) was cancelled 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 (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 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.
