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The European Space Agency (ESA) will launch its BepiColombo mission on the Mercury planet from its spaceport near the Equator in Kourou, French Guiana, on 20 October. My involvement in the mission means that I will be anxiously following the voyage as the spaceship makes a series of tricky maneuvers, culminating in its final approach to Mercury in 2025.
This mission comes 25 years after a group of scientists proposed to ESA to send a probe to Mercury, and 18 years after ESA approved the project as a mission "fundamental". This is the category of world-class missions, scientifically excellent, that require significant technological development. Previous ESA missions in Cornerstone include the Rosetta Comet Mission and the LISA Pathfinder Gravitational Wave Observatory.
But why Mercure? It's a confusing planet. NASA's MESSENGER satellite (2011-2015) has revealed many reasons why scientists want to know more about it. These include the abnormally large nucleus of the planet – we do not know why it is still melted and capable of generating a magnetic field, unlike that of Mars or Venus. Another mystery is the abundance of volatile substances (largely unidentified) on its surface. These should not have been integrated into a planet as close to the sun as Mercury.
The science of rocketry
The initial trajectory of BepiColombo, after three days of orbiting the Earth to perform verifications, will be an elliptical orbit around the sun. It will begin by taking it inside Earth's orbit. But in early 2019, it will go on the outside for most of the year. He will then return to the interior before moving closer to Earth in April 2020.
At that time, he will perform a gravity-assisted overflight, using Earth's gravity to move towards Venus. There will also be a gravitational flyby of Venus when he arrives there in 2020, followed by another in 2021 to send him to Mercury. Then there will be a series of six similar Mercury overflights in 2021-2025, necessary for the satellite to finally get closer to its target at a speed slow enough to be captured in orbit around it in December 2025.
Each hover, shown in the animation above, should be executed perfectly. Things could go wrong, especially during the launch, but I have every confidence in the capabilities of the ESA flight control team in Darmstadt, Germany.
Stacked Spaceship
The mission, named in memory of Giuseppe (Bepi) Colombo, who had offered for the first time overflights by gravitational assistance, is a joint venture of ESA and its Japanese counterpart, the JAXA.
The stacked spaceship carries two orbiters. ESA is a two-meter long unit with a mass greater than one tonne, called Mercury Planetary Orbiter (DFO). I suppose that after starting around Mercury, he will inherit the name BepiColombo or maybe just Bepi. The Japanese orbit is smaller and its mass is about a quarter of the ESA's orbit. Originally called Mercury Magnetospheric Orbiter, MMO, the name Mio was awarded in June. In Japanese, it carries the security connotations of navigation. During the cruise to Mercury, Mio will be housed in a sun visor and attached to one of the sides of the European orbiter.
On the other side of the orbiter is the Mercury Transfer Module, MTM. This is operated by the ESA and provides propulsion to bring the stacked spacecraft to its orbit at Mercury. It has a "wing" of solar panels 7.5 meters long, whose role is to turn the sunlight into electricity to power its "ionic drive". This is a propulsion device that creates a boost by accelerating the Xenon positively charged its electron atoms). This technique can provide much more thrust per fuel mass than conventional chemical rockets.
The enormous gravity of the sun means that it takes more energy to enter a stable orbit around Mercury than to send the same spacecraft to Pluto, much farther away. For this reason, the ion control will operate at intervals of about half the duration of the cruise, primarily to slow down the spacecraft.
Unfortunately, the stacked configuration of the combined spacecraft prevents it from doing science during planetary flyovers. Some scientific data will be collected, but the best images that we will probably have during the flybys will come from the selfie cameras mounted on the MTM.
To reach Mercure
Upon arrival at Mercury at the end of December 2025, the transfer module will be detached. Mio, spinning at 15 rpm for stability, will then be released into a highly elliptical orbit around Mercury. As soon as this happens, the JAXA will support Mio operations and guide it in its tasks of studying the magnetic field of the planet and the associated spatial environment.
The ESA orbiter will then drop the sunshade, its last obstacle, and use its own chemical thrusters to achieve a more circular and circular orbit around Mercury. From there, he will study the surface of the planet using an assortment of cameras and other instruments. This should allow to better detail the composition and the geological history of the MESSENGER, smaller and less complex. The orbiter will also be equipped with a magnetometer, which will allow Mio and himself to report magnetic conditions simultaneously in two locations – an important first for a deep space mission that should inform us of the speed at which which disturbances cross the magnetic field of the planet.
It's exciting to think that BebiColombo could transform our knowledge of Mercury in just a few years. And in the meantime, from October 23rd, you will be able to listen to some beautiful and evocative music inspired by the planet as part of the Planets 2018 project. It was created to commemorate the centenary of Gustav Holst's Planets Suite with music inspired by the science of planets.
David Rothery is a professor of planetary geosciences at the Open University.
This article is republished from The conversation under Creative Commons license. Read the original article.
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