The fate of our mission to Mercury is uncertain

BepiColombo, a joint collaboration between the European and Japanese space agencies ESA and JAXA, is scheduled to reach Mercury in 2025. Nearly a month ago, the team unfortunately identified a problem that caused its thrusters to run out of power, potentially putting the mission in jeopardy.

Studying Mercury from every angle

BepiColombo is an ambitious, collaborative space mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). Its goal is to explore Mercury, the planet closest to the Sun, and provide crucial information about its composition, atmosphere, magnetosphere and geological history. Launched on 20 October 2018 from the Kourou Space Center in French Guiana, BepiColombo is the first mission to Mercury since NASA’s MESSENGER mission, which ended its exploration in 2015. It promises to transform our understanding of Mercury. The data collected will help answer fundamental questions about the origin and evolution of the planet, as well as the processes that govern celestial bodies close to the Sun. This information could also provide comparative insights for the study of other rocky planets, including Earth. BepiColombo is distinguished by its structure, which consists of three main modules:

Mercury Planetary Orbiter (MPO) : Built by ESA, this orbiter is equipped with scientific instruments to study the surface and interior of Mercury. It will focus on mapping the surface, analyzing the chemical composition, and studying the internal structure and magnetic field of the planet.
Mercury Magnetospheric Orbiter (MMO) : Developed by JAXA, this orbiter is designed to study Mercury’s magnetosphere, that is, the surrounding region where the planet’s magnetic field interacts with the solar wind.
Mercury Transfer Module (MTM) : This module carries the two orbiters to Mercury. It uses ion thrusters to adjust the mission’s trajectory and perform the maneuvers necessary to reach Mercury’s orbit.

In October 2020, BepiColombo took advantage of a first gravitational slingshot offered by Venus to gain speed and correct its trajectory leading it towards Mercury. Credits: ESA / BepiColombo / MTM, CC BY-SA 3.0 IGO

The challenges and trajectory of the mission

Traveling to Mercury is particularly complex because of the Sun’s strong gravitational pull. To reach the planet, BepiColombo must therefore follow a trajectory that includes several gravitational assists : one around the Earth, two around Venus and six around Mercury itself. These maneuvers allowed the spacecraft to gradually reduce its speed and position itself correctly for its entry into orbit around Mercury scheduled for December 2025. However, BepiColombo must also rely on its thrusters to lose speed. On April 26, in fact, a critical maneuver involved burning these engines. Unfortunately, the transfer module did not was unable to provide sufficient electrical energy to the thrusters of the spacecraft. It took an ESA team, working with the mission’s industrial partners, nearly two weeks to finally partially resolve the problem. Indeed, although a partial solution was found, allowing the restoration 90% of propulsion powerthe problem persists. Continued efforts are therefore needed to ensure the success of the mission. The researchers are working in parallel on two problems: understanding how current propulsion levels could affect upcoming maneuvers and determining what exactly happened to the thrusters. In terms of timing, two Mercury flybys will take place on September 5 and December 2. A final flyby will then take place on January 9, 2025, after which the spacecraft will separate and enter orbit on December 5, 2025, for the start of the science mission.