BepiColombo: ESA Mission Reaches Key Milestone on Mercury Approach

BepiColombo Separation and Mercury Orbit Insertion Timeline

Spaceflight engineers at ESA’s ESOC control centre in Darmstadt, Germany, are preparing for mission separation on September 3, according to ESA Flight Director Ignacio Tanco. At 2:00 pm CEST, the spacecraft divides into two science probes while the large Mercury Transfer Module (MTM) drifts away. The MTM functions as a fully passive module without attitude control, according to ESA’s Flight Dynamics Manager Frank Budnik, meaning its trajectory will carry it past Mercury into interplanetary space rather than into orbit.

Following separation, the two science orbiters—ESA’s Mercury Planetary Orbiter (MPO) and the Japan Aerospace Exploration Agency’s Mercury Magnetospheric Orbiter (Mio)—remain locked together as a single composite spacecraft. Mission controllers will fire a critical sequence of chemical thruster burns in late November and early December to lower the spacecraft into Mercury’s grip. MPO and Mio will then separate into independent orbits, leading up to a dedicated science campaign starting in April 2027 after months of orbit fine-tuning.

Engineering Challenges of Operating Near the Sun

“Mercury is a challenging destination. It’s very difficult to reach, it’s very difficult to operate there,” said Santa Martinez, ESA mission manager, citing extreme temperature swings that go from -180 to 450°C and solar radiation up to ten times what we have on Earth. Ignacio Tanco compared the whole spaceflight experience to “operating with a very hot pizza oven running right on your back” and comparing it to “working on a knife edge,” noting particular concern over keeping the solar panels finely tilted to avoid losing power or getting roasted beyond repair.

Matching the planet’s velocity precisely is necessary to reach Mercury, making the transfer far more demanding energetically than journeys to larger, more distant planets. Instead of choosing a straightforward path, BepiColombo utilized an ion engine over the course of eight years and nine planetary flybys of Mercury itself, Venus, and Earth to gradually shed velocity.

Unsolved Scientific Mysteries of the Inner Solar System

Studying Mercury via telescope from Earth is an absolute headache because of the burning presence of the Sun in the background, according to BepiColombo Project Scientist Geraint Jones. The planet features an unusually heavy density for its size, likely because of an oversized iron core which makes up 60% of its volume, along with a magnetic field shared among rocky planets by only Mercury and Earth. Additional puzzles include the fact that the planet is literally shrinking as the inner core cools, surface ‘hollows’ first spotted by NASA’s MESSENGER mission to Mercury where the ground appears to be eaten away as volatile materials evaporate in the extreme heat, and strong evidence of water ice in some of the permanently shadowed craters at Mercury’s poles.

Frequently Asked Questions

When will BepiColombo enter orbit around Mercury?

The arrival sequence begins on September 3 with the separation of the transfer module, followed by critical thruster burns in late November and into early December to bring it into Mercury’s grip.

What agencies are involved in the BepiColombo mission?

BepiColombo is Europe’s first mission to Mercury, involving the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), which built the Mio orbiter.

When does the scientific study phase begin?

Following orbit capture, commissioning, and system fine-tuning that runs into March 2027, the mission’s dedicated science phase begins in April 2027.