Mercury-bound spacecraft gets an assist from Venus

A sequence of images taken by one of the monitoring cameras on board the European-Japanese BepiColombo mission to Mercury, as the spacecraft made a close approach of Venus on Oct. 15, 2020. Credit: ESA/BepiColombo/MTM

The European-Japanese BepiColombo spacecraft flew by Venus late Wednesday, using the planet’s gravity to help redirect the probe toward its ultimate destination of Mercury.

The encounter with Venus also provided an opportunity to collect bonus scientific observations in tandem with Japan’s Akatsuki orbiter, which has been studying the Venusian atmosphere and climate since arriving there in 2015.

A scaled-down team of engineers supported the BepiColombo flyby at the European Space Operations Center in Darmstadt, Germany. The test of the team monitored the encounter remotely due to restrictions related to the coronavirus pandemic, according to the European Space Agency.

BepiColombo’s closest approach to Venus occurred at 11:58 p.m. EDT Wednesday (0358 GMT Thursday) at a distance of 6,661 miles (10,720 kilometers), ESA said. The flyby was the first of two close encounters with Venus, which use the planet’s gravity to slingshot BepiColombo’s trajectory toward Mercury, the solar system’s innermost planet.

Named for Italian mathematician and engineer Giuseppe (Bepi) Colombo, The $1.8 billion mission launched from French Guiana aboard an Ariane 5 rocket in October 2018. BepiColombo’s two orbiters will become the first European and Japanese spacecraft to enter orbit around Mercury, and will become the second mission to ever orbit the solar system’s innermost planet, following NASA’s MESSENGER spacecraft.

In total, the BepiColombo mission needs nine planetary flybys to adjust its speed and allow it to enter orbit around Mercury on Dec. 5, 2025. The first of the nine flybys occurred April 10 with a swing by Earth.

This graphic shows the BepiColombo mission’s schedule of planetary flybys before entering orbit around Mercury in 2025. Credit: ESA

“The flyby itself was very successful,” said Elsa Montagnon, ESA’s BepiColombo spacecraft operations manager. “The only difference to normal cruise phase operations is that near to Venus we have to temporarily close the shutter of any of the star trackers that are expected to be blinded by the planet, similar to closing your eyes to avoid looking at the sun.”

Two of three black-and-white monitoring cameras outside the BepiColombo spacecraft were switched on for the Venus flyby, showing the planet’s disc growing larger as the probe approached. During the time when BepiColombo was closest to Venus, the planet is pictured passing behind the magnetometer boom of the mission’s European-built Mercury Planetary Orbiter.

Ten of the 16 science instruments on-board ESA’s Mercury Planetary Orbiter and the Japanese Mercury Magnetospheric Orbiter were collecting data during the flyby, according to ESA. The two orbiters are connected together with an electric propulsion module with ion engines to help reshape the mission’s trajectory toward Mercury.

The European orbiter’s main science camera was not taking images during the Venus flyby. Its position on the probe points toward one of the other elements of the three-module spacecraft, and it will only be able to begin taking pictures once the mission is in orbit at Mercury.

The use of planetary gravity assist maneuvers and efficient ion thrusters saves fuel. Otherwise, the spacecraft would have had to be much larger and heavier, exceeding the lift capacity of any operational rocket.

BepiColombo conducted simultaneous observations of Venus with Japan’s Akatsuki orbiter, which has been circling Venus for nearly five years. The Japanese Hisaki Spectroscopic Planet Observatory in Earth orbit and ground-based telescopes also participated in coordinated observations of Venus around the BepiColombo flyby.

“Akatsuki is currently the only spacecraft in orbit around Venus and because of its elliptical orbit it was actually 30 times further away from the planet than BepiColombo during the flyby, meaning we can compare close observations of BepiColombo with Akatsuki’s global-scale view,” said Go Murakami, JAXA’s BepiColombo project scientist.

Artist’s concept of the BepiColombo spacecraft during a Venus flyby. Credit: ESA/ATG medialab

“A large campaign of coordinated observations are ongoing, involving professional and amateur astronomers alike, that will build a three-dimensional picture of what’s happening over time in Venus’ atmosphere, something that cannot be achieved by one spacecraft or one telescope alone,” said Valeria Mangano, of the National Institute for Astrophysics in Italy, and chair of the Venus flyby working group.

“Following the successful Earth flyby where our instruments worked even better than expected, we are looking forward to see what will come out of the Venus flyby,” said Johannes Benkhoff, ESA’s BepiColombo project scientist.

“We’ll have to be patient while our Venus specialists look carefully into the data, but we hope to be able to provide some atmosphere temperature and density profiles, information about the chemical composition and cloud cover, and on the magnetic environment interaction between the sun and Venus,” Benkhoff said. “But we rather anticipate more results next year than now, given the closer flyby distance, so watch this space!”

BepiColombo’s next encounter with Venus is scheduled for Aug. 10, 2021, when the spacecraft will pass by the planet at a distance of 341 miles (550 kilometers). That will bend BepiColombo’s course toward Mercury, setting up the spacecraft for the first of six flybys with Mercury next October before entering orbit in late 2025.

The encounters with Mercury will give scientists a glimpse of the global measurements and observations BepiColombo will obtain once it is in orbit.

“With each flyby completed we get a step closer to answering some of these perplexing questions about mysterious planet Mercury,” Benkhoff said. “Learning more about Mercury will shed light on the history of the entire solar system, helping us to better understand our own place in space.”

Once in orbit around Mercury, the European Mercury Planetary Orbiter and the Japanese Mercury Magnetospheric Orbiter will separate to enter their own orbits and perform independent measurements. BepiColombo’s European-built science orbiter will map Mercury and study the planet’s geologic history, while the Japanese component of the mission will observe the solar wind’s influence on Mercury.

Email the author.

Follow Stephen Clark on Twitter: @StephenClark1.