BepiColombo: Another flyby of Mercury Only three years until launch into orbit

After an Earth flyby, two Venus flybys and two Mercury flybys, BepiColombo is scheduled for another trial visit to its target planet. On 19 June, the satellite will fly past Mercury again, the closest planet to the sun in our solar system. On board: measurement technology from TU Braunschweig.

On the evening of 19 June 2023, the BepiColombo probe will perform a crucial manoeuvre: It will approach within 240 kilometres of Mercury’s surface, picking up additional momentum for the final shot into orbit around Mercury in 2025. During this flyby, the probe will switch on the magnetometer developed in Braunschweig by the Institute of Geophysics and Extraterrestrial Physics (IGEP) to further measure the planetary magnetic field.

The research team led by Dr Daniel Heyner, who heads the magnetometer team for the European satellite at IGEP, will then be able to analyse its own data from Mercury’s magnetosphere. So far, only the northern hemisphere of the planet has been magnetically explored as part of NASA’s MESSENGER mission (2004-2015). With the data from the first two flybys of the BepiColombo probe, the scientists hope to be able to determine whether Mercury’s magnetic field has changed since the partial investigation by the NASA-MESSENGER mission.

Separation still to come

BepiColombo consists of three parts until it is launched into its final orbit: The European Mercury Planetary Orbiter (MPO), the Japanese Mercury Magnetospheric Orbiter (also called “Mio”) and the Mercury Transfer Module (MTM) – the latter, with an ion engine, is the motor to bring the mission to Mercury. Shortly before reaching the target orbit, the transfer module, which is then no longer needed, is separated. Shortly afterwards, the two probes MPO and Mio also separate from each other and continue their journey on different orbits around Mercury, which is close to the Sun. They are exposed to extremely high temperatures of up to 300 degrees Celsius.

During the primary mission, which lasts about one year, the satellites also have to withstand solar radiation and infrared radiation emitted by Mercury’s surface, which is up to 470 degrees Celsius hot. When the satellites enter Mercury’s shadow, there is a rapid change in temperature to very cold conditions. This poses an enormous challenge for the technology on board the spacecraft. It will be the first time that a planet other than Earth is surveyed simultaneously by two satellites.

“Naked” in the solar wind

This dual approach, in which the Mio satellite measures the solar wind in front of Mercury and the MPO simultaneously measures Mercury’s magnetosphere, offers decisive advantages. It allows scientists to observe how the magnetosphere reacts to events such as solar storms. Near Mercury, these massive particle ejections set the magnetosphere in motion. In some cases, these solar storms are so strong that the magnetosphere collapses, leaving the planet “naked” in the solar wind, lacking its magnetic shield and unable to maintain its own atmosphere.

However, the primary goal of the Braunschweig researchers remains to complete the magnetic map of the planet as precisely as possible. Of course, such precision requires sophisticated sensor calibration. Among other things, the Braunschweig calibration laboratory “Magnetsrode”, which even calibrates sensors on behalf of NASA, was used for this purpose. This magnetic field map of Mercury can then be compared with the dynamo models created at IGEP. This allows important conclusions to be drawn about Mercury’s long-term thermal evolution.

Close European-Japanese cooperation

The overall management of the mission lies with the European Space Agency (ESA), which was also responsible for the development and construction of the Mercury Planetary Orbiter (MPO). The Mercury Magnetospheric Orbiter (Mio) was provided by the Japanese space agency JAXA. This second satellite is also equipped with magnetometers, for which IGEP cooperates with Japanese institutes. The German contribution to BepiColombo is predominantly financed by DLR Space Management with funds from the Federal Ministry of Economics and Climate Protection (BMWK).