BepiColombo will be only the third mission ever to visit Mercury when its two satellites arrive in 2025. The aim is that it will solve many of the planet’s mysteries and potentially result in broader science benefits too. RHEA is supporting the mission with three staff working at the BepiColombo Space Operations Centre.

BepiColombo mission timescale

Mission launch: 20 October 2018
Mission arrival: Late 2025, reaching Science Orbit in March 2026
Nominal mission end: May 2027
Extension: Possibly until May 2028

About the BepiColombo mission

Artist's impression of BepiColombo at Mercury. Copyright - Spacecraft: ESA/ATG medialab; Mercury: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Artist’s impression of BepiColombo at Mercury showing the Mercury Planetary Orbiter (MPO) built by ESA and the Mercury Magnetospheric Orbiter (MMO) built by JAXA. © Spacecraft: ESA/ATG medialab; Mercury: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

BepiColombo is a joint mission to Mercury, the innermost planet of our Solar System, between ESA and the Japan Aerospace Exploration Agency (JAXA).

The mission consists of two satellites launched together: the Mercury Planetary Orbiter (MPO) built by ESA and the Mercury Magnetospheric Orbiter (MMO) built by JAXA.

Among the mission’s goals are to provide data that will help solve some of Mercury’s many mysteries:

  • Is there water or sulphur ice in the planet’s polar regions?
  • Is the unseen hemisphere of Mercury different from that imaged by Mariner 10?
  • Is the core of Mercury solid or liquid?
  • What happened to all the iron that models say should be the major component of Mercury but has so far remained undetected?
  • Is there any tectonic activity in Mercury today?
  • Given the small size of Mercury, why is there a magnetic field?
  • How does the magnetic field of Mercury interact with the solar wind?

In addition, the advance of the perihelium of Mercury (the point in its orbit closest to the Sun) was one of the early success stories of General Relativity. Can we take advantage of the proximity of Mercury to the Sun to further test General Relativity?

As always for a planetary mission, BepiColombo scientists will also use the observations of Mercury to learn more about how our Solar System formed.

About BepiColombo’s orbit

BepiColombo was launched on 20 October 2018. The mission’s cruise phase is a long and complex one lasting around 7 years and making use of several flybys: one of the Earth, one of Venus and six of Mercury.

Upon arrival in December 2025, the two spacecraft will separate and operate in different orbits:

  • the MPO will orbit closer to Mercury with a 480km periherm (closest point of orbit) and 1,500km apoherm (most distant point of the orbit)
  • the MMO will have an orbit with the periherm at 590 Km and apoherm at 11,639 Km.
This sequence of images was taken by one of the cameras on BepiColombo as it zoomed past the planet during its first and only Earth flyby. Copyright: ESA/BepiColombo/MTM, CC BY-SA 3.0 IGO
This sequence of images was taken by one of the cameras on BepiColombo as it zoomed past the planet during its first and only Earth flyby. © ESA/BepiColombo/MTM, CC BY-SA 3.0 IGO

BepiColombo’s main technical challenges

Exploring Mercury is difficult as the speeds required to reach it are high: Mercury travels very quickly in its orbit and so a spacecraft intending to orbit the planet has to travel very fast. However, because Mercury is so close to the Sun, the Sun’s gravitational pull is extremely strong and therefore once a spacecraft reaches Mercury, it has to be able to decelerate quickly as well.

Unfortunately, these two requirements imply significant fuel consumption. The designers were able to overcome this for BepiColombo with a combination of a cleverly designed transfer orbit and a solar electric propulsion system, allowing it to reach Mercury with a low relative velocity.

Being so close to the Sun, another concern is the high temperatures any Mercury orbiter has to face. In order to minimize the adverse effects of extremely high temperatures, the two satellites make use of advanced high temperature technologies in any elements where exposure to the harsh environment cannot be avoided, such as the solar panels.

For a solar panel on a mission to the outer reaches of the Solar System, the angle of incidence of the Sun should be as high as possible. But in the case of BepiColombo, we need to orient the solar panels so that the Sun is kept at a low incidence angle in order to avoid overheating the solar array. For this reason, the solar array needs to be continuously rotated.

Given these challenges, it is not surprising that Mercury is the least explored inner planet of the Solar System, with only two satellites visiting it before: Mariner 10 in 1974 to 1975 and Messenger from 2011 to 2015.

BepiColombo’s scientific payload

The MMO satellite carries instruments dedicated to the study of Mercury’s magnetic field and its interactions with the solar wind, namely a magnetometer, several high energy particle detectors, a dust monitor and an instrument to study electromagnetic fields in Mercury’s magnetosphere.

The MPO carries a range of science instruments including several spectrometers, a laser altimeter and an accelerometer, as well as a magnetometer. In order to perform General Relativity tests, there is also the Mercury-Orbiter Radio Science Experiment (MORE). This consists of several multifrequency transponders.

Did you know?

Sometimes the names of space missions are acronyms extracted from a generic description of what the mission does. However, often they honour people whose work has allowed space exploration to progress at the pace we experience today. BepiColombo is in the latter category.

The name BepiColombo is a tribute to the Italian mathematician and engineer Giuseppe (Bepi) Colombo. Among his many contributions to space science was his investigation of how to design the orbit that allowed Mariner 10 to visit Mercury.

Although it sounds as if the Japan Aerospace Exploration Agency’s (JAXA’s) MMO is in the former category, it turns out in Japan it is also known as Mio. The name, which was chosen from thousands of suggestions from the Japanese public, means ‘waterway’. According to JAXA, Mio will travel through the solar wind as a ship travelling through the ocean.

How RHEA is contributing to the BepiColombo mission

Three RHEA staff are working at the BepiColombo Space Operations Centre (SOC): a system and operations engineer, a test engineer and a software engineer.

The system and operations engineer is responsible for activities related to operations planning, from coordinating the design and development of the planning system to overseeing the planning of science operations during the cruise and science operations phase. In addition, this engineer is also responsible for liaison between the SOC and the scientists operating the instruments.

The test engineer is responsible for running test campaigns and preparing and maintaining testing documentation. As in other ESA mission SOCs, a large part of the testing is automated due to the complexity of the software involved. The test engineer also performs quality assurance functions and coordinates the help desk support.

RHEA’s software engineer is responsible for the development, maintenance and validation of a suite of planning tools, as well as providing support to the principal investigator (PI) teams on the use of the planning system.

Main image: Artist’s impression of the BepiColombo spacecraft in cruise configuration, with Mercury in the background. The Mercury Transfer Module is shown with ion thrusters firing and with its solar wings extended, spanning about 30 m from tip-to-tip. The 7.5m-long solar array of the Mercury Planetary Orbiter in the middle is seen extending to the top. The Mercury Magnetospheric Orbiter is hidden inside the sunshield in this orientation. © Spacecraft – ESA/ATG medialab; Mercury – NASA/JPL