On 15 June 2026, at 15:24 Central European Summer Time, a faint blue glow in space went dark for good. That glow came from the ionized xenon gas streaming out of BepiColombo's solar electric thrusters, a propulsion system that had pushed the spacecraft across the inner Solar System for nearly eight years. With the final thrust arc complete, the European Space Agency and Japan Aerospace Exploration Agency mission ended its long cruise phase and began its arrival at the Solar System's innermost planet, Mercury.
Eight years, nine flybys, one engine
BepiColombo launched in October 2018 from Earth. To reach Mercury, the spacecraft needed an unusually efficient engine. Traditional chemical rockets burn a lot of fuel quickly, but BepiColombo used solar electric propulsion, or SEP. The system, built into the Mercury Transfer Module, contained four QinetiQ T6 thrusters. These thrusters took electricity generated by the spacecraft's solar arrays and used it to ionize xenon gas, turning it into plasma. That plasma was then accelerated and fired out at very high speeds. The result was a gentle but constant push that required far less propellant than chemical alternatives. The thrusters could also adjust their power based on how much sunlight the solar panels received. This flexibility allowed BepiColombo to complete one of the most complex interplanetary journeys ever attempted. Over the course of its cruise, the spacecraft performed nine planetary flybys: one past Earth, two past Venus, and six past Mercury itself.
A final shutdown in Darmstadt
On the morning of the shutdown, lead SEP thruster engineer Neil Wallace met with the mission team and industry partners at ESA's European Space Operations Centre in Darmstadt, Germany. They reviewed lessons learned from the SEP system, a step meant to help design future missions that might use similar technology. The commands to turn off the thrusters had been sent from Earth well in advance. They were timed so that the engines would stop at the exact right moment during the spacecraft's last thrust arc. At the scheduled afternoon moment, the blue glow ended.
What comes next for BepiColombo
With its electric propulsion switched off permanently, BepiColombo now has no source of thrust. It will follow a ballistic, or free falling, trajectory toward Mercury. The next major event is the separation of the Mercury Transfer Module on 3 September 2026. After that module is ejected, the remaining spacecraft composite, which includes the Mercury Planetary Orbiter and the Mio orbiter, will rely on MPO's chemical propulsion system to adjust its path and enter orbit around Mercury. Local people in Darmstadt and across the European space community cared about this moment because it marked the end of a long, challenging engineering effort and the beginning of the mission's primary science phase. The team gathered at ESOC to witness the end of one chapter and the start of another.
