Mercury Mission: launch of two satellites for a seven-year journey to the planet

A powerful European rocket Ariane 5 took off last Friday from French Guiana and propelled a pair of satellites into space for a seven-year plunge into the interior solar system, a trip requiring seven planetary flyovers to slow down enough under the clutch of the sun. orbiting Mercury in hell.

The $ 1.9 billion BepiColombo project is only the second, after NASA's MESSENGER mission, to attempt to place a spacecraft in orbit around the innermost planet in the solar system. one of the most difficult technical missions of the European Space Agency and the Japanese Aerospace Exploration Agency, or JAXA.

The Ariane 5 rocket, the most powerful inventory in Europe and one of the most reliable boosters in the world for large aircraft, came to life at 9.45pm. ETH 22:45 local time and has moved majestically away from the Guiana Space Center on the north coast of South America.

The rocket was lighting up the European space base for tens of kilometers, east of the Atlantic Ocean, above a brilliant jet of flame emanating from its two solid fuel boosters. It accelerated quickly by burning five tons of propellant per second.

"It was fantastic!" Johannes Benkhoff, the scientist of the BepiColombo project, said after its launch. "I had never seen this before and it was awesome – it was like a big fireball crossing the sky, it was really nice."

The spacewalk went well and 27 minutes after take-off, the JAXA's Mercury Planetary Orbiter and Mercax Magnetospheric Orbiter satellites, both attached to a carrier, dubbed the Mercury Transfer Module, were released from platinum. top of the Ariane 5 to fly in their turn. own.

"Arianespace is delighted to announce that BepiColombo is in its targeted leak orbit and is now heading for Mercury," said Stéphane Israël, Arianespace's chief executive officer. "Today's new success marks the beginning of a seven-year journey for BepiColombo, taking advantage of the gravitational assistance of the Earth, Venus and Mercury – what an exciting journey!" "

While this may seem counterintuitive, it will take more energy to reach Mercury (11.5 mph shifts) than NASA's New Horizon spacecraft, which was to reach Pluto.

The transfer module carrying the two satellites is equipped with ionic thrusters and more traditional liquid fuel rocket engines. But most of the necessary energy will come from planetary overflights, using the gravity of the Earth, Venus and Mercury to help define trajectory and slow down, slowing the BepiColombo probe enough to reach an orbit around Mercury.

The inland journey actually begins only in April 2020, when the BepiColombo probe runs over the Earth, using the gravity of the planet to bend the trajectory on a route routing satellites to Venus. Two overflights of Venus are planned, one end 2020 and the other in August 2021, to deviate the trajectory towards Mercury.

But it's still not enough to do the job. Six overflights of Mercury are needed over the next four years to slow down the probe enough for it to be captured by the relatively low gravity of the planet.

This step will be taken in December 2025 when the ESA's MPO satellite and the JAXA MMO, then released from the spacecraft, will install on different orbits around the Mercury poles.

"The cruise will be a little over seven years old," said Ulrich Reininghaus, project manager at ESA. "We will fly over the Earth (once), twice Venus and six times Mercury itself before entering orbit, allowing us to capture with the low gravity of the planet Mercury against the great sun.

"It means that when we fly, we constantly brake against the sun," he said. "When you fly to the heavier element (of the solar system), you are constantly accelerating, we do not want it, that's why we are decelerating."

The orbit of the DFO satellite will have a low point of about 300 miles and a high point of about 930 miles. The JAXA MMO will orbit at a higher altitude, up to 7,200 miles above the surface.

Once in position, the spacecraft will have to withstand temperatures of up to 660 degrees, at an average distance of 37 million miles from the Sun.

"The mercury is three times closer to the sun and therefore the radiation and heat we receive from Mercury are 10 times higher," said Johannes Benkhoff, project scientist. "So, everything … had to withstand the higher temperatures, but also the higher radiation doses we received from the solar wind, and for that we needed special insulation from our spacecraft, of special materials for the antenna, for solar panels.It was a very big challenge. "

Only two other spacecraft have already visited Mercury and only one of them has entered orbit.

The NASA Mariner 10 spacecraft was the first spacecraft to make this trip. He flew over the planet three times in 1974 and 1975 and collected the first close-ups and other data at altitudes as low as 200 miles. Mariner 10 was also the first interplanetary spacecraft to use gravity-assisted overflights, a procedure that quickly became commonplace.

Launched in 2004, the NASA Spacecraft Messenger was orbiting Mercury in 2011 and spent four years studying the surface environment and space of the planet with a sequel. sophisticated instruments. Although extremely fruitful, scientists still have important issues unresolved.

Enter BepiColombo, named after Giuseppe "Bepi" Colombo, Italian mathematician and engineer who discovered that Mercury was spinning on its axis three times for two sun orbits and suggested how gravity assistance could be used to reach the planet.

ESA's Mercury Planetary Orbiter contains 11 instruments, including cameras, spectrometers, a radiometer, a laser altimeter, a magnetometer and others, which will focus on the surface and the internal composition of the planet. .

The JAXA Mercury Magnetospheric Orbiter is equipped with five instruments, including a magnetometer, an ion spectrometer, an electronic energy analyzer, plasma detectors and a camera. It is designed to map the planet's magnetic field and its interactions with the sun.

Scientists hope to answer the following questions:

• Mercury has a higher overall density than any other terrestrial world. Why?
• Is the core of the planet at least partially liquid or solid?
• The planet is tectonically active?
• How does such a small planet maintain an intrinsic magnetic field and how does it interact with the solar wind?
• Iron is probably the main constituent of mercury, but it is not seen in spectroscopic analysis. Why?
• Do the craters permanently shaded near the Mercury poles contain ice or sulfur reservoirs?
• What produces a thin "exosphere" around the planet?

"The study of Mercury is crucial to better understand the formation of our solar system, how the Earth has formed and evolved and where we have come from," said Benkhoff.

BepiColombo, he said, will help scientists "understand the nature of the planet itself".

"We want to characterize the surface, what material is on the surface, we would like to measure temperatures, we would like to see the interaction with the solar wind, which is special about Mercury because it is so close to the sun," he said. "Mercury has a magnetic field similar to Earth's, a dynamo field, we would like to understand it."

Once in orbit, BepiColombo's orbiters should collect data for one year, possibly with a one-year mission extension.