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Europe flies to Mercury – What you should know about the BepiColombo mission



T On 20 October, the European Space Agency (ESA) launched its BepiColombo mission on the planet Mercury from its spaceport near the equator in Kourou, French Guiana. My involvement in the mission means I will be concerned after the trip as the spaceship performs a series of intricate maneuvers culminating in its final access to Mercury in 2025.

The mission comes 25 years after a group of ESA scientists proposed to send a probe to Mercury for the first time, and 18 years after the ESA approved the project as a "cornerstone". This is the category of scientifically awarded world-class missions that require significant development of new technologies. Previous ESA missions include the Rosetta Comet Mission and the LISA Pathfinder Gravitational Wave Observatory

But why Mercury? It is a mysterious planet. The NASEN MESSENGER Orbiter (201

1-2015) revealed many reasons why scientists want to know more about it. This includes the unusually large core of the planet – we do not know why it is still molten and unlike Mars or Venus can create a magnetic field. Another mystery is the abundance of (largely unknown) volatile substances on their surface. These should not have been taken into a planet as close to the sun as Mercury is now.

The Rocket Science

BepiColombo will be an elliptical orbit around the planet after three days of orbiting the Earth for checkouts. This will begin by putting it into Earth orbit. But in early 2019, it will be out most of the year. It will then move in again before it comes very close to Earth in April 2020.

  BepiColombo's startup and disconnect timeline
BepiColombo's startup and disconnection timeline

Back then It will bring a "gravity wizard" to pass – with Help Earth's gravity to swing inward towards Venus. There will also be a gravity assisted flyby of Venus when it is 2020, followed by another in 2021 to send it to Mercury. Then, in the years 2021-2025, there will be a series of six similar Mercury fly-bys needed to ensure that the spacecraft eventually closes slowly enough on its target to be placed in orbit around it in December 2025.

Every flyby, as shown in the animation above, must be executed perfectly. Especially at the start it can go wrong, but I have great confidence in the capabilities of the ESA flight control in Darmstadt.

Stacked Spacecraft

The mission, named in memory of Giuseppe (Bepi) Colombo (19659002), who first proposed gravity-assisted spacecraft fly-bys, is a joint venture between ESA and its Japanese counterpart JAXA.

The stacked spacecraft carries two orbiters. The ESA is a two meter long unit weighing more than one ton called the Mercury Planetary Orbiter (MPO). I suspect that after it begins to circle Mercury, it will inherit the name BepiColombo, or perhaps just Bepi. The Japanese orbiter is smaller and its mass is about a quarter of the ESA orbiter. Originally referred to as Mercury Magnetospheric Orbiter, MMO, it received the name Mio in June, which carries the connotation of safe navigation in Japanese. During the cruise to the Mercury Mio is housed in a sun shield and attached to one side of the European orbiter.

  Artist's impression of BepiColombo during his flyby on Earth in April 2020. Mio can be seen in his sunscreen.
Artistic representation of BepiColombo during his earthly flyby in April 2020. Mio can be seen in his sunscreen.

On the other side of the orbiter is the Mercury Transfer Module, MTM. Powered by ESA, it powers propulsion to transport stacked spacecraft to their Mercury orbit. It has a 7.5 meter long "wing" of solar panels, whose job it is to convert sunlight into electricity to power its "ion drive". This is a propulsion device that generates thrust by accelerating xenon gas that is positively charged stripping its atoms from electrons). This technique can deliver much more thrust per mass of fuel than conventional chemical rockets.

The enormous gravity of the sun means that more energy is needed to get into a stable orbit around Mercury, as Pluto would have to send the same spacecraft more distant. For this reason, ion propulsion is operated at intervals that are approximately half the travel time, primarily to slow down the spacecraft.

Unfortunately, the stacked configuration of the combined spacecraft hampers its ability to science during the planetary fly-bys. Some scientific data is collected, but the best pictures we are likely to get in passing are from the selfie cams mounted on the MTM

Arriving at Mercury

Arriving at Mercury in late December 2025, the Transfer module is solved. Mio, which rotates at 15 rpm for stability, is then released into a highly elliptical orbit around Mercury. Once this is the case, JAXA takes over the operation of Mio and leads it through its tasks by examining the planet's magnetic field and the associated space environment.

The ESA orbiter will then discard the sunroof, its last obstacle, and use its own chemical thrusters to achieve a closer, circular orbit around Mercury. From there, he examines the surface of the planet with a selection of cameras and other instruments. This should describe the composition and geological history much more accurately than the smaller and less complex MESSENGER. The orbiter will also carry a magnetometer so that both he and Mio can report magnetic conditions in two places at the same time – an important premiere for a space mission to inform us about the speed at which disturbances travel through the planet's magnetic field.

It's exciting to think that BebiColombo could change our knowledge of Mercury in just a few years. And while you wait, from October 23, you can hear beautiful, atmospheric music inspired by the planet as part of the Planets 2018 project. This was set up to commemorate the centenary of Gustav Holst's Planets Suite with music inspired by planetary science.


This article was originally published on The Conversation by David Rothery. Read the original article here.


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