Mission To Mercury

... BepiColombo will set off in 2014 on a journey lasting approximately six years. When it arrives at Mercury in mid 2020, it will endure temperatures as high as 350 °C and gather data during its one year nominal mission, with a possible 1-year extension.

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About the mission

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.

Only one probe has visited Mercury so far, NASA's Mariner 10 which flew past three times in 1974-5 and returned the only close-up images of the planet so far. 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 MPO will study the surface and internal composition of the planet, and the MMO 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 programme. 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.

The journey from Earth to Mercury will also be a first. 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 MMO will be released into its operational orbit, then the Sunshield and the MMO interface structure will be separated while the chemical propulsion system will bring the MPO to its lower orbit. The mission design and deployment sequence is schematically depicted in the above figure. Observations from orbit will continue for one Earth year.

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