An artist rendering of the BepiColombo mission, a joint ESA/JAXA project that will take two spacecraft into the harsh environment of Mercury.
ESA
This week, the European Space Agency released a slightly ominous note about its BepiColombo spacecraft, which consists of two orbiters traveling to Mercury.
The online news release cited a “problem” with the spacecraft that was disrupting its ability to generate thrust. The problem was first noticed on April 26 when the spacecraft’s main propulsion system was due to undertake an orbital maneuver. At that time, insufficient electrical energy was supplied to the solar-electric drive system.
According to the space agency, a team including its own engineers and those of its industrial partners has begun work on the problem. By May 7, they had made some progress, restoring the spacecraft’s thrust to about 90 percent of its original level. But it’s not a full force, and the root cause of the problem is still poorly understood.
It’s an ambitious mission with an estimated cost of $2 billion. Undertaken in conjunction with Japan’s JAXA space agency, BepiColombo launched on an Ariane 5 rocket in October 2018. So there’s a lot to do with those thrusters. The critical question is whether, at this power level, BepiColombo can still perform its primary mission of reaching orbit around Mercury?
The answer to this question is not so clear.
A three-part spaceship
The spacecraft consists of three components. The “transfer module” is where the current problems occur. It was built by the European Space Agency and is designed to power the other two components of the spacecraft until October 2025. It is essential for positioning the spacecraft to enter orbit around Mercury. The other two mission elements are the European MPO orbiter and the Japanese Mio orbiter. After their planned arrival in orbit around Mercury in December 2025, the two orbiters will separate and make observations for at least a year, including characterizing the small planet’s magnetic field.
The news release is ambiguous about BepiColombo’s fate if its propulsion system cannot be restored to full power.
Ars reached out to the European Space Agency and asked if BepiColombo could still reach orbit around Mercury in this condition. The answer, said Elsa Montanon, the space agency’s chief of mission operations, is not entirely clear.
“Thank you for your legitimate questions about the current uncertainty,” Montanon said. “We are working hard to resolve these uncertainties.”
There should be a delta-V
What is clear, she said, is that the current level of thrust can support the next critical stage, BepiColombo’s fourth spin of Mercury, due on September 5 this year. This is the first of three wobbles planned to occur in quick succession from September to January, which will slow the spacecraft relative to Mercury.
“This spin sequence provides a braking delta-V of 2.4 km/s and provides a change in the direction of the velocity vector with respect to the Sun as required for the endgame trajectory in 2025,” Montanon said.
A team of experts is currently working on the implications of reduced thrusters for the other two parts of this spin sequence and other propulsion needs in 2025.
This transfer module is scheduled to be ejected from the rest of the stack in October 2025, and then the remaining Mercury approach and orbit maneuvers will be performed with the European spacecraft’s chemical propulsion subsystem MPO.
