The BepiColombo spacecraft separated from its Mercury Transfer Module on Sept. 3 at 1400 CEST, with controllers confirming successful separation by 1552 CEST. The separation marks the end of a nearly eight-year cruise phase that began with the mission's October 2018 launch.
The transfer module's jettisoning is a required step: it carried the solar-electric propulsion system that shepherded the two science orbiters across the inner solar system but has no role once the spacecraft enters Mercury orbit. The next critical event is orbital insertion on Nov. 21. The Mercury Magnetospheric Orbiter, or Mio, will separate between Dec. 9 and 10. The larger Mercury Planetary Orbiter will then move to its final operational orbit, ranging from 480 to 1,500 kilometers altitude, with science operations commencing in April 2027.
The mission is roughly one year behind its original December 2025 arrival date. Problems with the spacecraft's solar electric propulsion system required trajectory revisions that extended cruise duration.
BepiColombo has already conducted six Mercury flybys since 2021, gathering preliminary data. The mission also used gravity assists from Venus and Earth to shape its trajectory through the inner solar system.
The MPO, built by ESA, measures 2.4 by 2.2 by 1.7 meters and weighs 1,230 kilograms including an 85-kilogram science payload. JAXA's Mio is 1.8 meters in diameter, 1.1 meters tall and weighs 255 kilograms with a 45-kilogram science payload. The MPO operates as a 3-axis stabilized platform; Mio will spin-stabilize at 15 revolutions per minute with its spin axis oriented 90 degrees to the Sun.
The primary mission objectives are to map Mercury's magnetosphere structure, study how it interacts with the solar wind, characterize its large iron core, and determine the origin of its magnetic field. The initial science mission is planned for one Earth year, with a provision to extend operations for another year.
