BepiColombo spacecraft launch: A long mission to Mercury begins | Science| In-depth reporting on science and technology | DW | 19.10.2018
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BepiColombo spacecraft launch: A long mission to Mercury begins

BepiColombo is set to begin its long journey to one of the least studied of Earth's seven neighboring planets. It is hoped the probe will offer insights into how our solar system was formed.

 Artist's image of spacecraft BepiColombo at Mercury

The Mercury Planet Orbiter (left) is designed to separate from the Magnetospheric Orbiter

A seven-year journey to Mercury, one of the solar system's least studied planets, is about to get underway.

The space probe duo BepiColombo, named after Italian engineer and mathematician Giuseppe Colombo, is considered one of the most demanding space missions the European Space Agency (ESA) has ever undertaken.

This might sound surprising, because at first glance the project appears to be a simple one — at least when compared to missions such as Rosetta's landing on comet Chury in 2014.

After all, it's just an orbiter probe — albeit one with two components — like many others before it that have visited planets in our solar system.

Read more: Towards the Moon: Why Europe wants to work with China

Mercury: Planet of opposites

Watch video 02:49

BepiColombo lifts off for seven-year trip to Mercury

But getting a probe to Mercury is not as easy as it sounds. ESA has teamed up with the Japanese space agency JAXA for this technically challenging mission. Extreme climatic conditions around the planet will add an element of difficultly to the study, as Mercury has virtually no atmosphere.

At the same time, it is the planet closest to the sun. As a result, the planet can heat up to around 430 degrees Celsius (806 degrees Fahrenheit) during the extremely long days that prevail there. At night, it drops to temperatures as low as minus 180 degrees Celsius.

Little is known about Mercury. Its conditions make it inhospitable and with a diameter of 4,878 kilometers (3,031 miles), it is only slightly larger than our Earth's moon.

Only two NASA probes — the Mariner in 1975 and Messenger between 2011 and 2015 — have ever visited the planet named for the Roman deity and messenger of the gods. Messenger's main focus was on the planet's northern hemisphere. Now BepiColombo is to fill the gap and provide data for the southern hemisphere. 

Read more: 8 facts about the tiny planet Mercury and its rare transit across the sun.

BepiColombo: Two orbiters traveling together

BepiColombo consists of two orbiters, which will only separate from each other as it approaches Mercury. The first, Mercury Planet Orbiter (MPO), will investigate the surface and composition of the planet with the aim of obtaining a complete three-dimensional image.

While the Mercury Magnetospheric Orbiter (MMO) will measure magnetism. Both probes will also collect data on solar winds and examine the interactions between the Sun and Mercury.

Unique measuring instruments

Sixteen measuring instruments are on board two probes.

"With some of them, we can even take a look beneath the planet's surface and learn about the minerals there — iron-sulfur compounds, for example,"  ESA project scientist Johannes Benkhoff told DW in an interview.

The German Aerospace Center (DLR) is directly involved with three of the instruments: A laser altimeter (BELA), a magnetometer (MPO-MAG) and a combined radiation measuring device with an infrared spectrometer (MERTIS).

The instruments had to be specially designed to withstand the temperature fluctuations and radiation.

For example, the sensor for the MERTIS radiation measuring device is tiny — 1 by 3 millimeters (0.04 by 0.12 inches) in size. It was made from a single piece of silicon and at the same time serves as a tiny opening for the spectrometer with which it's combined. The outer part of the instrument must be able to withstand the temperature extremes.

The inside of the probe is less extreme. It is encased in a specially developed 6-centimeter-thick insulating layer. This is intended to cool the central devices to a moderate 20 degrees Celsius. 

Read more: NASA spacecraft Messenger ends its voyage on the planet Mercury

Images of both sides of the planet mercury, taken by the Messenger spaceship

It's hoped BepiColombo will complement these infrared images provided by NASA's Messenger probe

Long, complicated approach

The probe also has to have enough energy to fuel its long journey.  

"We need a lot of energy to reach Mercury," says planetary researcher Benkhoff. "We obtain this energy in two ways. First, we have solar-electric propulsion that is very energy-efficient. But solar energy alone is not enough to reach Mercury. Secondly, we must get help from the planets."

BepiColombo will perform a series of swing-by maneuvers to gain the necessary speed. But the planetary constellation must be just right for this, meaning the journey will take some time. The probe will fly past Earth once and past Venus twice. "In total, BepiColombo must orbit the Sun 18 times before it reaches Mercury," says Benkhoff.

Read more: 5 things Alexander Gerst will have to do as International Space Station commander

To be able to complete its journey, BepiColombo has to be slowed down too. Swing-by maneuvers are also used here — six times on Mercury itself. Only in this way can the probe reach its desired orbit around the planet.

On the outbound flight, BepiColombo will collect data from Earth and Venus. After the probe begins operations in early 2026, its two orbiters will collect data for about a year, before sending the information back to Earth.

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