BepiColombo
A collaborative effort between ESA and JAXA, the spacecraft will provide the best understanding of Mercury to date
Scheduled to launch on 19 October 2018, BepiColombo will be a first-of-its-kind mission for both the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA). This mission will explore Mercury – the least explored terrestial planet in our Solar System. Only two spacecraft have ever paid the tiny planet a visit: NASA’s Mariner 10 and MESSENGER probes.
The BepiColombo mission is named after Professor Giuseppe (Bepi) Colombo (1920–1984), a mathematician and engineer at the University of Padua, Italy, who was the first person to see that there was an unusual resonance between Mercury’s three rotations to every two orbits of the Sun. His namesake will be launched from Europe’s spaceport in Kourou, French Guiana, aboard an Ariane 5 rocket. The four-part BepiColombo spacecraft ‘stack’ will travel for over seven years through the inner Solar System before it arrives at Mercury after a series of flybys of Earth, Venus and Mercury.
This four-part spacecraft includes the Mercury Transfer Module (MTM), which will transport the two orbiters safe and sound to their intended destination. The MTM can be thought of as the bottom of the stack. On top of the MTM sits one of the orbiters, the Mercury Planetary Orbiter (MPO), led by the ESA, which includes 11 instruments that will probe every aspect of Mercury. The Mercury Magnetospheric Orbiter (MMO), led by JAXA, will sit at the tip of the BepiColombo stack, and has a further five instruments in order to do a bit more probing. It will be protected by the MMO Sunshield and Interface Structure (MOSIF) during the journey, but MOSIF will be jettisoned upon the spacecraft’s planned arrival at Mercury in December 2025.
Although Mariner 10 and MESSENGER learnt a lot about the surface of Mercury and its unusual magnetic field, there is so much more still to be discovered. This is why ESA and JAXA put their heads together to birth this mission that will put two separate orbiters around Mercury in a journey never undertaken by either space agency before.
The journey to the innermost planet is a difficult one, as the huge gravity of the Sun becomes more and more intense on the spacecraft at it makes the 77-million-kilometre (48-million-mile) approach towards the centre of our Solar System. On its approach to Mercury the spacecraft will inevitably accelerate as the Sun’s gravity pulls it in. This is a challenge that neither ESA or JAXA have encountered before, as they usually send spacecraft in the opposite direction, away from the Sun. To
slow down the spacecraft upon arrival at Mercury, six Mercury flybys and ion thrusters will allow the spacecraft to be captured, placing the orbiters into their intended orbits.
On 5 December 2025, BepiColombo is due to finally arrive at Mercury and can begin the highly anticipated mission that will reveal previously unknown details about the planet’s composition, geophysics, atmosphere, magnetosphere and its evolution. The mission has been scheduled for one Earth year (about four Mercurian years), with the possibility of another Earth year extension. Before this mission begins, the two orbiters must be carefully placed into their different orbits, which requires a fine level of precision.
Upon arrival the MTM is separated from the stack, sending the other three sections onward.
The first orbiter to be released will be the MMO, which is an octagonal prism with a diameter of 1.8 metres (5.9 foot) and 1.1 metres (3.6 foot) in height and has a mass of 255 kilograms (562 pounds). It will be placed into a polar orbit, taking 9.3 hours per orbit. Due to the elliptical nature of this orbit, the spacecraft can come as close as 590 kilometres (367 miles) of the planet’s surface, or as far as
11,640 kilometres (7,233 miles). While making its way around Mercury MMO will continuously spin, completing 15 rotations per minute. The spin axis will make sure that the top and bottom of the spacecraft (where the instruments show) will never be pointed at the Sun, while simultaneously making sure the orbiter’s antennae are pointed towards Earth for constant communication.
Next to be jettisoned is the sunshield after its job has been completed in keeping the MMO safe on its travels. The final module is the MPO, which measures 2.2 metres (7.2 foot) wide, 2.4 metres (7.9 foot) long and 1.7 metres (5.6 foot) tall, and a rough mass of 1,230 kilograms (2,712 pounds). This orbiter is placed in a much closer orbit, flying between 480 and 1,500 kilometres (298 and 932 miles) of the surface and completing one orbit every 2.3 hours.
The MPO incorporates a different design to the MMO, as it will sit closer to Mercury. Mercury radiates copious amounts of heat due to its close proximity to the Sun and reflective surface, which means that scientists and engineers had to design MPO so that the planet’s – and the Sun’s – heat isn’t a problem. To do so, engineers constructed MPO in a double-H configuration that contains a large radiator with connecting pipes so that it can collect the heat and dispose of it efficiently.