BepiColombo made a quick visit to Venus in August and is on to its next rendezvous. On October 1st it’ll perform a flyby of Mercury, the spacecraft’s eventual destination. This visit is just a little flirtation—one of six—ahead of its eventual orbital link-up with Mercury in late 2025.
The quick visit will yield some scientific results, though, and they’ll be just a taste of what’s ahead in BepiColumbo’s one-year mission to Mercury.
BepiColombo is on a bit of a tour of the inner regions of the Solar System on its way to Mercury. The complicated route full of flybys of Earth, Venus, and Mercury is the only way to get the spacecraft into orbit at Mercury. BepiColombo launched in October 2018 from Europe’s Spaceport in French Guiana. Then it travelled through space for a year and a half before returning to Earth for a gravity-assist manoeuvre that directed it toward Venus.
Then came two consecutive flybys of Venus to reduce its perihelion to Mercury distance. Those are both in the past now and next come six consecutive flybys of Mercury, each one helping to lower the spacecraft’s eventual relative velocity to only 1.84 km/s. After the flybys are complete, BepiColombo will perform four thrust arcs to lower its velocity some more. Only at that point will the spacecraft be in a position for Mercury’s weak gravity to play its role in all this. On December 5, 2025, the spacecraft will enter orbit around Mercury without a traditional orbital insertion. Quite a feat.
This complicated route is necessary because Mercury’s puny gravity is dwarfed by that of the Sun.
But before all that can happen it’s going to give us its first taste of Mercury science by swooping past the planet at about 200 km (124 mi) altitude. What’ll it find during that brief visit?
“We’re really looking forward to seeing the first results from the measurements taken so close to Mercury’s surface…It’s a fantastic feeling!”
Johannes Benkhoff, ESA’s BepiColombo project scientist.
BepiColombo won’t be in full-blown science mode during the flyby. That’s because of the spacecraft design. The mission is a joint effort between the ESA and JAXA, the Japan Aerospace Exploration Agency. So the spacecraft is actually two orbiters in one: the ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (Mio) wedded to the Mercury Transfer Module (MTM.) The two orbiters will be separated once in orbit at Mercury, but during these flybys, they’re together. Because of that, there’s a limit to the data and images they can gather.
There’ll be no high-resolution images because the main science camera is shielded by the MTM during cruise operations. But the three monitoring cameras (MCAM) will be operating. They’re the cameras that have provided mission images of the flybys of Earth and Venus so far.
When BepiColombo flew past Earth its monitoring cameras were active. Image Credit: ESA/BepiColombo/MTM, CC BY-SA 3.0 IGO
Unfortunately, BepiColombo will be arriving on the planet’s nightside during the flyby, so it’s not an ideal situation for capturing images. The three MCAMs will be operating from five minutes after the closest approach until four hours later. That means the closest image will be captured from about 1,000 km (620 mi.)