On the 20. October 2018 at 03: 45 CEST launched the four-part spacecraft Bepi Colombo in the Ariane 5 launch vehicle her journey to Mercury. Also on board: Rolling of Minebea Mitsumi Subsidiary Cerobear. The launch of the space mission took place in Kourou (French Guiana).

The mission is a collaboration between the Japanese Space Agency JAXA (Japan Aerospace Exploration Agency) and ESA (European Space Agency). The spacecraft, named after the Italian mathematician Giuseppe Colombo, is expected to be underway for seven years.

With a diameter of 4.878 km, Mercury is the smallest and least explored planet of our solar system. This is due to the inhospitable conditions for space probes in Mercury and thus close to the sun. The solar radiation in the Mercury orbit is about ten times higher than on Earth. And the long Mercury days and nights also matter: The change between day and night lasts on the Mercury 176 days, which is why the temperature on the sunny side with about 430 ° C extremely high and on the dark side with minus 180 ° C extreme is low. Due to the high thermal loads, all devices and components have to meet special requirements for heat management.

With the Bepi Colombo, Mariner 10 and the Messenger Orbiter are the third spacecraft on the Mercury Expedition. The participating scientists expect a comprehensive description of the planetary properties and history of Mercury. One of the two satellites, which will separate from the probe at the target, will examine the surface, the second the magnetic field.

According to calculations, Bepi Colombo should reach the finish in December 2025. On the way, nine "swing-by-maneuvers" have to be carried out. The space probe passes once the Earth in April 2020, then twice Venus and six times Mercury itself. These maneuvers are used to slow down, so that the 4,1 t heavy probe does not crash into the interior of the solar system.

Rolling bearings in the satellite

The rolling bearings are used in the current Mercury mission, among others, in the Solar Array Drive Mechanism of the MPO (Mercury Planetary Orbiter), ie in the satellite, which is to explore the surface. Due to the long journey and the extreme conditions, special demands are placed on the rolling bearings: after seven years of standstill, the bearings must function properly and withstand the high temperature fluctuations in orbit of Mercury. Therefore, this mission uses hybrid bearings in which the rings are made of steel and the balls of silicon nitride. This is the only way to ensure that the start and the long journey, even without lubricant, do not lead to cold welding between rings and balls.

Cerobear's history in aerospace began in early 2000 with the first flight of ceramic cylindrical rollers in the bearings of the space shuttle's liquid hydrogen pumps. The ceramic rollers worked at 36.200 rpm at temperatures of minus 1 °C and were only filled with liquid Hydrogen lubricated. The use of Cerobear rolling elements improved the engines' service interval by a factor of 12, while at the same time increasing the payload by 9%. The maintenance times between missions have been reduced from 1000 hours to less than 50 hours.

In space applications, the bearings must be tailor-made and tuned for a long life with the highest accuracy and low friction. Low-speed bearings typically used in space mechanisms have space-efficient materials and coatings available. New rolling bearing steels and ceramics are used for the extreme requirements.

Picture above: ESA - S. Corvaja

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