ESA's first mission to the planet Mercury lifted off today from Europe's spaceport in Kourou, French Guiana. At 10:45 pm GFT (October 20, 01:45 GMT), the BepiColombo spacecraft rose on a tail of fire into the night atop an Ariane 5 booster on the start of a voyage that will take seven years and a total travel distance of 9 billion km (5.6 billion mi) to cover the 240 million km (149 million mi) between Earth and the closest planet to the Sun.

Under partly cloudy skies, the joint ESA-JAXA mission made a near-flawless launch. At two minutes into the flight, the two solid rocket boosters fell away from the Ariane 5 first stage and the fairing protecting the stacked spacecraft separated a minute later.

At the nine-minute mark, the main stage shut down and fell away, leaving BepiColombo, its transfer module, and upper stage to coast into low Earth orbit before the final firing of the upper stage to escape the Earth's gravity. Spacecraft separation occurred at 27 minutes after lift off. The first signals showing that the probe is alive and functional came at the 40-minute mark as it passed over ground stations tracking the flight.

According to ESA, the solar arrays that power the mission to the smallest planet in the solar system will complete deployment 74 minutes after launch and within 18 hours the instruments will begin deployment. The craft will then undergo three days of system checks as it coasts into interplanetary space before the main ion thrusters on the transfer module power up.

Because of the Sun's massive gravitational pull, the energy needed to reach Mercury is equivalent to getting to Pluto. The Ariane 5 isn't nearly powerful enough to achieve this by itself, nor are the onboard ion thrusters, but BepiColombo will reach the necessary speed by means of a series of slingshot maneuvers that involve a flyby of Earth in April 2020, two of Venus in October 2020 and August 2021, and six flybys of Mercury itself between 2021 and 2025, before the probe finally arrives in orbit on December 5, 2025.

Once BepiColombo is on station, it will split into two separate orbiters, ESA's Mercury Planetary Orbiter (MPO) and JAXA's Mercury Magnetospheric Orbiter (MMO). The first time a pair of spacecraft has been sent to Mercury, they will carry out complementary studies of the planet to learn about its structure, magnetic field, and its almost non-existent atmosphere.

To protect themselves against the intense solar radiation 113 million km (70 million mi) from the Sun, both spacecraft will keep their solar panels at an oblique angle to the sunlight. The MPO will be protected by a sun shield, while the MMO will keep spinning to maintain an even temperature.

The BepiColombo mission is named at the Italian mathematician and engineer Giuseppe "Bepi" Colombo (1920 – 1984). He's best known for his descriptions of the link between Mercury's orbit and its rotation as well as his calculations of trajectories for NASA's Mariner 10 mission in the 1970s to Venus and Mercury.

Source: ESA

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