Since its takeoff in 2018, the European and Japanese BepiColombo mission has been making its way through the Solar System to slow down before it can enter orbit around Mercury. But this spring, there is a problem with the propulsion module, the electric motors are not receiving enough power!
The BepiColombo mission, to travel to Mercury, is made up of a somewhat unusual assembly, with a Japanese orbiter (MMO) attached to a European orbiter (MPO). So that these two precious elements can reach the planet closest to the Sun, they are installed in front of a third block, which is only used for the 7 years of transport and the final braking, called the MTM (Mercury Transfer Module). Equipped with solar panels, it uses the energy it collects to power its four very low thrust ionic electric motors. Very efficient, these engines continuously produce, for weeks and months, a few tens of millinewtons of thrust.
Over time, this allows BepiColombo to be slowed down with a huge mass saving, although it is still insufficient to reach Mercury. These brakes therefore complement the gravitational assistance, for which the different planets of the inner Solar System slow down the mission by several thousand kilometers/hour… Unfortunately, when the teams wanted to begin a new sequence of maneuvers over several weeks on the 26 April 2024, a power problem occurred and the MTM only provided a few fractions of the power needed for its 4 engines, which were unable to operate properly.
A very limited right to error
This is an important problem, because the maneuvers with the ion electric motors and the gravitational flybys are a ballet that must be executed in a precise manner: a missed meeting and Mercury will no longer be in the “right place” to the next orbit, which will involve other needs with engines, etc. BepiColombo has already flown past Mercury three times, with two more remaining in September and December 2024, then a final flyby in January 2025. A delicate orbital billiards table that BepiColombo must not fail, otherwise it will at least have to postpone its entry into orbit until after December 2025 or worse, to call into question the entire mission six years after leaving Guyana.
Immediately detected, immediately repaired?
Fortunately, the news so far is rather reassuring. Less than two weeks after discovering the failure, the teams (who immediately set up working groups to understand the power problem) managed to restore the power level, and therefore the thrust of the engines to 90%. This is temporarily sufficient to ensure the maneuver for the gravitational assistance planned for next September. But the situation is uncomfortable, it is important to understand as much as possible what could have happened so as not to suffer from the same problem in the months to come, while ensuring that no other breakdown will degrade the action of the engines. The ESA, which communicated on the problem on May 15, has freed up “listening time” on its network of large antennas for more exchanges with BepiColombo. We must hope that this is only a serious alert: after all this journey and 18 months before the goal, the 2 probes and their instruments are in remarkable condition.
Source : esa
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