The European-Japanese collaborative mission BepiColombo has completed its scheduled flyby of Earth on its way to its target planet, Mercury. The flyby, which took place on April 10, was a necessary maneuver to use Earth's gravity to sling the spacecraft towards the center of the Solar System.
You might think this would be counterintuitive; shouldn’t it be easy to just go towards the Sun? The answer is no: Anything launched from Earth starts from the same speed that keeps our planet from falling into the Sun. To move inward in the Solar System, spacecraft have to be slowed down, and scientists worked out this can be done with carefully planned flybys of planets. So the mission used Earth as a celestial brake, using our planet's gravitational pull to slow down and bend its trajectory towards the inner portions of the Solar System. Luckily it was successful, as this was just the first of BepiColombo's nine flybys to get to Mercury.
It took some beautiful images of our planet as it made its closest approach, coming less than 12,700 kilometers (7,890 miles) from Earth’s surface at 04:25am UTC, before bidding farewell to Earth.
The maneuver did not require any intervention from the team monitoring it from Earth, though they had to keep a close eye on it as the spacecraft crossed Earth's shadow for 34 nerve-wracking minutes, where it stopped receiving energy from the Sun.
“This eclipse phase was the most delicate part of the flyby, with the spacecraft passing through the shadow of our planet and not receiving any direct sunlight for the first time after launch,” Elsa Montagnon, BepiColombo Spacecraft Operations Manager for ESA, said in a statement.
“It is always nerve-wracking to know a spacecraft’s solar panels are not bathed in sunlight. When we saw the solar cells had restarted to generate electrical current, we knew BepiColombo was finally out of Earth’s shadow and ready to proceed on its interplanetary journey.”
The flyby allowed the spacecraft to “stretch its leg” as it conducted measurements using its suite of 16 instruments. The measurements will be used to refine the calibration of the instruments that will be used when it finally starts its mission in 2025. Made up of two satellites, the mission will study the magnetic field of Mercury, as well as its interior structure and surface to understand how the smallest planet in the Solar System came to be.
“Today was of course very different to what we could have imagined only a couple of months ago,” said Johannes Benkhoff, ESA’s BepiColombo Project Scientist, who followed the operation from home due to the current lockdown. “We are all pleased that the flyby went well and that we could operate several scientific instruments, and we are looking forward to receiving and analysing the data. These will also be useful to prepare for the next flyby, when BepiColombo will swing past Venus in October.”
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