ESA's BepiColombo spacecraft has fired up all four of its ion thrusters as it begins the first of 22 burn arcs. The high-tech engines that use xenon as a propellant were powered up on December 17 at 1:45 pm CET (12:45 GMT) and will fire for two months as they propel the unmanned probe on the start of its 9-billion-km (5.6-billion-mi) journey to explore the planet Mercury.

Monday's engine start comes in the wake of a series of tests carried out by mission control last month to make sure that the four T6 thrusters on the Mercury Transfer Module (MTM) carrying the Mercury Planetary Orbiter and Mercury Magnetospheric Orbiter were working properly. Satisfied with their performance, ESA gave the green light for routine operation.

According to the space agency, the engine start required a series of maneuvers, which included orienting the spacecraft into the correct attitude, aiming the high-gain antenna at Earth, and angling the solar panels that the ion thrusters rely upon for the 4.5 kW of electricity needed to power each one.

When activated, an electrically-charged grid ionized and accelerated xenon atoms until they shot out the stern at a speed of over 50 km/s (112,000 mph). The thrust was very small – only about 108 mN each, however, when running flat out, two of the thrusters can generate 250 mN. That's about the same force as being towed by 250 ants.

The current two-month burn will set BepiColombo on course for the first of nine flybys of Earth, Venus, and Mercury as it orbits the Sun 18 times over seven years on its way to Mercury. The first flyby will be of Earth in April 2020.

Launched on October 20 this year, BepiColombo is scheduled to arrive in orbit around Mercury on December 5, 2025. Once there, the two orbiters will detach from the MTM and begin their mission to study the smallest planet in the solar system.

Source: ESA

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