BepiColombo is Europe’s first mission to Mercury, the innermost planet of the Solar System. It consists of two orbiters, one for planetary investigation and one for magnetospheric studies. They will reach Mercury in 2019 after a six-year journey towards the inner Solar System to make the most extensive and detailed study of the planet ever performed.

The 'Mercury Planetary Orbiter' (MPO), under ESA’s responsibility, will study the surface and the internal composition of the planet at different wavelengths and with different techniques. The Mercury Magnetospheric Orbiter (MMO), under the responsibility of the Japan Aerospace Exploration Agency (ISAS/JAXA), will study the magnetosphere, that is the region of space around the planet that is dominated by its magnetic field.

Only two spacecraft have visited Mercury so far. NASA's Mariner 10 provided the first close-up images of the planet when it flew past three times in 1974-75. More than 30 years later, on 14 January 2008, NASA’s MESSENGER swung-by Mercury, in the course of its journey to eventually settle in orbit around the planet in 2011. The spacecraft provided new close-up images and scientific data of the planet. When it reaches its destination in 2019, BepiColombo will be only the second spacecraft to orbit Mercury in the history of planetary exploration.

The difficulty of reaching, surviving and operating in the harsh environment of a planet so close to Sun makes BepiColombo one of the most challenging long-term planetary projects undertaken by ESA so far.

BepiColombo was named after Giuseppe (Bepi) Colombo (1920-84), a scientist who studied Mercury's orbital motion in detail and greatly contributed to the study of orbits and interplanetary travel.
 
Objectives
 
BepiColombo will study and understand the composition, geophysics, atmosphere, magnetosphere and history of Mercury, the least-explored planet in the inner Solar System. In particular, the mission objectives are to:

• understand why Mercury's density is markedly higher than that of all other terrestrial planets, Moon included;
• understand if the core of Mercury is liquid or solid, and if the planet is still tectonically active today;
• understand why such a small planet possesses an intrinsic magnetic field, while Venus, Mars and the Moon do not have any, and investigate if Mercury's magnetised environment is characterised by features reminiscent of the aurorae, radiation belts and magnetospheric substorms observed at Earth;
• understand why spectroscopic observations do not reveal the presence of any iron, while this element is supposedly the major constituent of the planet;
• investigate if the permanently shadowed craters of the polar regions contain sulphur or water ice;
• observe the yet unseen hemisphere of Mercury;
• study the production mechanisms of the exosphere and to understand the interaction between planetary magnetic field and the solar wind in the absence of an ionosphere;
• obtain new clues about the composition of the primordial solar nebula and about the formation of the Solar System;
• test general relativity with improved accuracy, taking advantage of the proximity of the Sun and considering that the advance Mercury's perihelion was explained in terms of relativistic space-time curvature.

Launch and journey

BepiColombo is currently scheduled for launch in 2013 from ESA’s Kourou station in French Guiana, on board a Soyuz-Fregat 2-1B rocket provided through Arianespace.

During the voyage to Mercury, which will last about six years, the two orbiters and a transfer module will form one single composite spacecraft. After launch, the composite will be pushed by the chemical propulsion engine to a 420 000 km high orbit around Earth, and will make a lunar swing-by to reach the interplanetary trajectory. Once in cruise, the composite spacecraft will be accelerated by solar-electrical propulsion (SEP) – a technique already tested on ESA’s SMART-1 mission to the Moon - and by five gravity-assist manoeuvres (one at Earth, two at Venus, and two at Mercury itself). Upon arrival at Mercury, the transfer module with the electrical propulsion system will be jettisoned. At this point the composite spacecraft will use conventional rocket engines and the so-called 'weak stability boundary capture technique' to enter a polar orbit around the planet. When the MMO orbit is reached, the MPO will separate and lower its altitude by means of chemical propulsion to its operational orbit.

Orbit

The MPO and MMO final orbits will both circle above Mercury’s poles. The MPO orbit will range between 400 km and 1500 km above the surface of the planet, while the MMO orbit will range between 400 km and 12 000 km above the surface.
 
Planned mission lifetime
 
The BepiColombo scientific mission at Mercury is planned to last at least one Earth year. In principle the mission can be extended by an additional Earth year.
 
Spacecraft
 
Design: Operating a spacecraft in the harsh environment of Mercury represents a true technological challenge. The direct solar radiation hitting the spacecraft is about ten times more intense than in Earth's proximity. Furthermore Mercury's surface, whose temperature can reach up to 470 °C, not only reflects solar radiation but also emits thermal infrared radiation. Therefore, the probe will have to withstand extreme thermal conditions.

Dimensions: The body of BepiColombo’s MPO will measure 2.0 x 1.7 x 1.7 m (excluding solar wings), while the radiator on one side of the spacecraft measures 2.8 m. With the solar wings extended, it measures about 7 m across. BepiColombo’s MMO will measure 1.8 x 1.0 m.

Mass: The MPO spacecraft will weigh 550 kg, including 60 kg of instruments. The MMO spacecraft will weigh about 250 kg, including about 45 kg of scientific instruments.

Industrial involvement: Astrium (Germany) is prime contractor for the design and procurement of the 'cruise-composite' spacecraft, including the ESA’s MPO, the Mercury Transfer Module, the MMO’s sunshield and the interface between the MPO and the MMO. Furthermore it provides the design and development of the attitude and orbit control subsystem, and the integration of the engineering model. The Italian branch of Thales Alenia Space Italy will be the co-prime contractor for the development of the MPO’s electrical power, thermal control and communications systems and for the integration and test activities. In the UK, Astrium is co-prime contractor for the electrical and chemical propulsion systems, for the structure of all modules, including the launch vehicle adapter, and for the thermal control of the Mercury Transfer Module. Astrium in France will develop the on-board software. MMO and its scientific payload are designed and developed by JAXA.
 
What’s on board?
 
Mercury Planetary Orbiter (ESA)
MPO will carry a highly sophisticated suite of eleven scientific instruments, ten of which will be provided by Principal Investigators through national funding by ESA Member States and one from Russia:

BepiColombo Laser Altimeter (BELA)
BELA will characterise the topography and surface morphology of Mercury. It will also provide a digital terrain model that, compared with the data from the MORE instrument, will allow to obtain information about the internal structure, the geology, the tectonics and the age of the planet’s surface.
Co-Principal Investigators: N. Thomas, University of Bern, Switzerland, and T. Spohn, DLR, Germany.

Italian Spring Accelerometer (ISA)
The objectives of the ISA accelerometer are strongly connected with those of the MORE experiment. Together the experiments can give information on Mercury’s interior structure as well as test Einstein’s theory of the General Relativity.
Principal Investigator: V. Iafolla, CNR-IFSI, Italy.

Mercury Magnetometer (MERMAG)
MERMAG will provide measurements that will lead to the detailed description of Mercury’s planetary magnetic field and its source, to better understand the origin, evolution and current state of the planetary interior, as well as the interaction between Mercury’s magnetosphere with the planet’s itself and with the solar wind.
Principal Investigator: K.H. Glassmeier, Technical University of Braunschweig, Germany.

Mercury Thermal Infrared Spectrometer (MERTIS)
MERTIS will provide detailed information about the mineralogical composition of Mercury’s surface layer with a high spectral resolution, crucial for selecting the valid model for origin and evolution of the planet.
Principal Investigator: H. Hiesinger, University of Münster, Germany.

Mercury Gamma ray and Neutron Spectrometer (MGNS)
MGNS will determine the elemental compositions of the surface and subsurface of Mercury, and will determine the regional distribution of volatile depositions on the polar areas which are permanently shadowed from the Sun.
Principal Investigator: I. Mitrofanov, Institute for Space Research, Russia.

Mercury Imaging X-ray Spectrometer (MIXS)
MIXS will use the ‘X-ray fluorescence’ analysis method to produce a global map of the surface atomic composition at high spatial resolution. This technique has been also used by the D-CIXS instrument on ESA’s SMART-1 mission to the Moon.
Principal Investigator: G. Fraser, University of Leicester, UK.

Mercury Orbiter Radio science Experiment (MORE)
MORE will help to determine the gravity field of Mercury as well as the size and physical state of its core. It will provide crucial experimental constraints to models of the planet’s internal structure and test theories of gravity with unprecedented accuracy.
Principal Investigator: L. Iess, University of Rome ‘La Sapienza’, Italy.

Probing of Hermean Exosphere by Ultraviolet Spectroscopy (PHEBUS)
The PHEBUS spectrometer is devoted to the characterisation of Mercury’s exosphere composition and dynamics. It will also search for surface ice layers in permanently shadowed regions of high-latitude craters.
Principal Investigator: E. Chassefière, Université P&M Curie, France.

Search for Exosphere Refilling and Emitted Neutral Abundance (SERENA)
SERENA will study the gaseous interaction between surface, exosphere, magnetosphere and solar wind.
Principal Investigator: S. Orsini, CNR-IFSI, Italy.

Spectrometers and Imagers for MPO BepiColombo Integrated Observatory System (SYMBIO-SYS)
SIMBIO-SYS will examine (also in stereo and colour) the surface geology, volcanism, global tectonics, surface age and composition, and geophysics.
Principal Investigator: E. Flamini, ASI, Italy.

Solar Intensity X-ray Spectrometer (SIXS)
SIXS will perform measurements of X-rays and particles of solar origin at high time resolution and a very wide field of view.
Principal Investigator: J. Huovelin, Observatory University of Helsinki, Finland.

Mercury Magnetospheric Orbiter (JAXA)
MMO will carry five advanced scientific experiments that will also be provided by nationally funded Principal investigators, one European and four from Japan. Significant European contributions are also provided to the Japanese instruments:

Mercury Magnetometer (MERMAG)
MERMAG will provide a detailed description of Mercury’s magnetosphere and of its interaction with the planetary magnetic field and the solar wind.
Principal Investigator: W. Baumjohann, Austrian Academy of Sciences, Austria.

Mercury Plasma Particle Experiment (MPPE)
MPPE will study low- and high-energetic particles in the magnetosphere.
Principal Investigator: Y. Saito, ISAS, JAXA, Japan.

Mercury Plasma Wave Instrument (PWI)
PWI will make a detailed analysis of the structure and dynamics of the magnetosphere.
Principal Investigator: H. Matsumoto, RISH, University of Kyoto, Japan.

Mercury Sodium Atmospheric Spectral Imager (MSASI)
MSASI will measure the abundance, distribution and dynamics of sodium in Mercury’s exosphere.
Principal Investigator: I. Yoshikawa, University of Tokyo, Japan.

Mercury Dust Monitor (MDM)
MDM will study the distribution of interplanetary dust in the orbit of Mercury.
Principal Investigator: K. Nogami, Dokkyo Medical University, Japan.
 
Operations
 
Ground control: ESA is responsible for the whole mission design, and for the cruise operations up to the insertion of the MPO and MMO into their orbits. During the cruise, the operations of the full composite spacecraft will be coordinated by the European Space Operations Centre (ESOC) in Darmstadt, Germany, using the Cebreros 35 m antenna in Spain. Once in orbit around Mercury, the ISAS/JAXA Sagamihara Space Operation Centre using the Usuda 64 m antenna (Japan) will take over the MMO operations, while ESOC will remain in charge of the MPO spacecraft operations.

Science operations: ESA is responsible for the mission and scientific operations of the MPO. The BepiColombo Science Operation Centre will be at the European Space Astronomy Centre (ESAC) in Villafranca, near Madrid, Spain. It will define and coordinate the scientific observations and assisting the teams in operating their instruments.

ESA Project Manager: Jan van Casteren
ESA Project Scientist: Johannes Benkhoff
ESA Spacecraft Operations Manager: Elsa Montagnon

 
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