The BepiColombo mission, a joint effort between the European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA), began its critical Mercury arrival phase on September 3, as its two orbiters separated from the propulsion module after an eight-year journey.
A Challenging Arrival Sequence
The separation of the MPO and MMO from the Mercury Transfer Module (MTM) marked the start of what ESA described as its most operationally challenging planetary arrival sequences ever attempted.
Santa Martinez, the mission manager at ESA, highlighted the difficulties of maneuvering near Mercury, which has a weak gravitational pull and extreme temperatures due to its proximity to the Sun. It's a very ambitious mission,
Martinez said. Mercury is a challenging destination… because of the extreme environment so close to the Sun.
The spacecraft had to travel more than 10 billion kilometres, executing a series of nine flybys, to speed up, slow down and perfect its trajectory. The MPO and MMO, attached to the MTM, separated at 8 a.m. EDT (1200 GMT) on Thursday (Sept. 3). ESA’s Ignacio Tanco, head of inner solar system mission operations, compared the maneuver to launching a new spacecraft. Only this spacecraft happens to be around a different planet.
The orbiters will now begin a months-long process of adjusting their trajectories before entering their final science orbits.
Key Milestones and Future Steps
The next major milestone is Mercury orbit insertion, scheduled for November 21, when the MPO and MMO will be captured by the planet’s gravity. Following this, the MPO will release the MMO into its final orbit on December 9 or December 10, after which the MMO will begin its study of Mercury’s magnetosphere. The MPO is set to reach its final orbit—an ellipse with altitude extremes of 298 miles and 932 miles (480 by 1,500 km)—on March 10, 2027.
The science phase of the BepiColombo mission (which is named after Italian mathematician and engineer Giuseppe “Bepi” Colombo), which will last at least one Earth year, is scheduled to begin on April 6, 2027. During this time, the MPO will map Mercury and Mio will study its magnetosphere, working together to shed light on the least explored planet in the inner solar system,
with the MPO and MMO working together to address fundamental questions about Mercury’s formation and evolution.
Preparation and Team Coordination
To ensure the success of the arrival phase, ESA and JAXA teams have spent months conducting simulations at the European Space Operations Centre (ESOC) in Darmstadt, Germany. These rehearsals, which began last month, tested every step of the complex arrival sequence, from module separation to orbit insertion. People working together is what makes this mission work, especially when facing challenges,
said ESA BepiColombo Flight Director Ignacio Tanco. If you see something that you don't understand during the simulation, you have to drill into it and treat it as you would in reality.
The mission’s complexity is further compounded by the need for coordination between ESA and JAXA teams across Europe and Japan. The separation of the MMO from the MPO requires precise timing and synchronization, with activities on both spacecraft needing to align. Many steps need to happen on both sides in a specific order, and we need to be synchronized.
Despite the risks, mission officials remain confident. So, what can go wrong?
It's probably easier to list the things that cannot go wrong, which are very few,
Tanco said. But of course, we are ready, we are flexible, and we need to be prepared for the unexpected.
However, the teams have adapted, and the current phase marks a critical step toward unlocking Mercury’s secrets.
It is the world’s first dual-spacecraft mission to Mercury, besides being only the second mission ever to orbit around the planet. With its sixteen instruments and advanced technology, the mission is expected to provide unprecedented insights into Mercury’s geology, magnetic field, and space environment, opening a new chapter in solar system exploration.
