The European Space Agency (ESA) has announced a significant delay in the BepiColombo mission's planned orbital insertion around Mercury due to unforeseen problems with the spacecraft's electric propulsion system.
Originally set to enter orbit in December 2025, the mission’s insertion is now scheduled for November 2026, nearly a year later than expected. This adjustment, while substantial, is not anticipated to impact the overall scientific goals of the mission, which is a collaborative effort between ESA and the Japan Aerospace Exploration Agency (JAXA).
Thruster Complications and the Need for a New Trajectory
The BepiColombo mission has encountered a major technical issue with its Mercury Transfer Module (MTM), which has necessitated a change in trajectory. In April 2024, during routine checks, engineers discovered that the spacecraft’s electric thrusters were not receiving sufficient power to function at their full capacity. This problem was traced back to unexpected electrical currents between the spacecraft’s solar arrays and a power distribution unit. These currents interfered with the amount of power available to the electric thrusters, reducing their output to 90% of the original thrust—insufficient for the complex orbital maneuvers required to insert the spacecraft into Mercury’s orbit as originally planned.
Santa Martinez, ESA’s BepiColombo Mission Manager, stated, “Following months of investigations, we have concluded that MTM’s electric thrusters will remain operating below the minimum thrust required for an insertion into orbit around Mercury in December 2025.” This conclusion led to the development of an alternative mission profile that will see the spacecraft taking a revised trajectory, ultimately delaying its arrival in orbit by 11 months. Despite these challenges, the mission team remains optimistic, with Martinez adding, “The new trajectory maintains the baseline scientific mission at Mercury but allows the spacecraft to use lower thrust during the cruise phase.”
Fourth Mercury Flyby: A Critical Adjustment
On September 4, 2024, BepiColombo is scheduled to execute its fourth flyby of Mercury, a maneuver critical to adjusting its trajectory after the thruster issues were discovered. During this flyby, the spacecraft is expected to pass just 165 kilometers above Mercury’s surface—35 kilometers closer than initially planned. This closer approach is part of the revised trajectory designed by ESA’s flight dynamics team to compensate for the reduced thrust. The flyby will be essential not only for the trajectory correction but also for reducing the spacecraft's speed to better match Mercury’s orbit in preparation for future maneuvers.
This fourth flyby marks a pivotal point in BepiColombo’s journey to Mercury, allowing the spacecraft to gather valuable data from the planet’s environment and magnetosphere. Although the mission’s main science camera will remain inoperative during the cruise phase, ten other instruments will be active during the flyby. These instruments are expected to provide crucial data that will help refine scientific operations once the spacecraft enters its final orbit. Johannes Benkhoff, BepiColombo Project Scientist, emphasized the importance of these observations: “We get to fly our world-class science laboratory through diverse and unexplored parts of Mercury’s environment that we won’t have access to once in orbit, while also getting a head start on preparations to make sure we will transition into the main science mission as quickly and smoothly as possible.”
Maintaining the Mission’s Scientific Integrity
Despite the delay in orbital insertion, ESA has assured that the overall scientific objectives of the BepiColombo mission remain intact. The spacecraft is expected to fulfill its mission to study Mercury’s surface, magnetic field, and exosphere—key areas of interest that will provide insights into the planet’s formation and its role within the broader context of the solar system. The spacecraft’s primary mission phase, once it finally enters orbit in November 2026, will involve detailed mapping and analysis, utilizing a suite of 16 sophisticated instruments spread across two orbiters: ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter.
The scientific community eagerly anticipates the wealth of data that BepiColombo will provide, which is expected to surpass previous missions to Mercury in both scope and detail. The flybys conducted en route to Mercury, including the recent fourth flyby, have already offered tantalizing glimpses of what is to come. Benkhoff expressed excitement about these preliminary findings, noting, “It’s so exciting that BepiColombo can boost our understanding and knowledge of Mercury during these brief flybys, despite being in ‘stacked’ cruise configuration.”
Preparing for the Main Mission
The adjusted timeline has provided the mission team with additional time to prepare for the main science phase of the mission. This extended preparation period is seen as an opportunity to fine-tune the spacecraft’s instruments and systems, ensuring they are fully operational when BepiColombo finally settles into its orbit around Mercury. The flybys also serve as a testing ground for these instruments, allowing the team to verify their functionality in Mercury’s harsh environment.
One of the key aspects of the upcoming science phase will be the detailed imaging and analysis of Mercury’s surface features, including large craters, wrinkle ridges, and lava plains. While the main science camera remains inactive until the spacecraft reaches its orbit, the three engineering cameras aboard the Mercury Transfer Module (M-CAMs) have already captured significant images during the flybys, offering valuable data and a preview of the geological features that will be studied in greater detail later.
The mission team remains committed to overcoming the technical challenges posed by the thruster issue and is confident that the BepiColombo mission will ultimately achieve its scientific objectives. As the spacecraft continues its journey, the data gathered during the remaining flybys will provide essential information that will contribute to the success of the mission, offering new insights into one of the least explored planets in our solar system.
BepiColombo’s journey to Mercury has been fraught with challenges, but each hurdle has also provided an opportunity for learning and adaptation. The mission exemplifies the resilience and ingenuity required in space exploration, where unexpected issues can lead to innovative solutions and new discoveries. As the mission progresses, the scientific community and space enthusiasts alike eagerly await the groundbreaking findings that BepiColombo is poised to deliver.