The end is only the beginning for Europe’s long-distance space traveler

After eight years in space, BepiColombo is approaching the most demanding stage of its journey to Mercury. On Thursday, Sept. 3, the spacecraft’s two probes are due to separate from their transport module.

Ignacio Tanco, ESA’s flight director for the mission, says the separation will be a major challenge because it resembles launching a new spacecraft, except that it will happen around another planet. And separation will only open the next chapter of the mission’s difficulties.

“

It is almost easier to say what cannot go wrong.

Mercury offers an exceptionally hostile environment. Temperatures range from minus 180 to 450 degrees Celsius, while solar radiation can reach ten times the level found on Earth. The spacecraft’s solar panels create one of the tightest margins. They must generate enough electricity while avoiding direct heating from the Sun. A slight change in angle can either cut power or cause the panels to overheat and deteriorate.

“

It is a significant challenge. It is equivalent to launching a new spacecraft. But this one happens to be around another planet.

Much of the technology, including the power supply, thermal protection and control systems, has never faced these conditions in operation. Santa Martinez, the mission manager, says the team expects that not everything will follow the plan and is prepared to adapt.

If the probes succeed, scientists could finally examine the planet we know least about among the rocky worlds. Cameras will map its surface in high resolution, including mysterious depressions that appear to be caused by volatile substances escaping as gas. Craters near the north pole may also contain ice because sunlight never reaches their floors, even though the surrounding surface exceeds 400 degrees Celsius.

“

We have extremely tight margins. If we tilt it too little, not enough power is produced. If we tilt it too much toward the Sun, the temperature immediately rises and it begins to deteriorate.

Launched from ESA’s spaceport in French Guiana on Oct. 20, 2018, BepiColombo has already flown past Earth once and Venus twice. The mission consists of ESA’s Mercury Planetary Orbiter and Japan’s Mio probe, which will study Mercury and its surrounding space environment.

“

It is likely that everything will not go according to plan. We are of course ready, flexible and prepared for the unexpected.