BepiColombo visited Venus briefly in August, and now it is ready for its next rendezvous. It will fly by Mercury on October 1, the spacecraft's eventual destination. This is just a small flirtation, one of six before its eventual orbital connection-up with Mercury in the latter part of 2025.
However, the quick visit will yield some interesting scientific results and is just a glimpse of what lies ahead in BepiColumbos 1-year mission to Mercury.
BepiColombo is taking a trip through the Solar System's inner regions on its way towards Mercury. It is only possible to launch the spacecraft at Mercury orbit using a complicated route that includes flybys of Venus, Earth, and Mercury. BepiColombo was launched from Europe's Spaceport in French Guiana in October 2018. It then traveled through space for about a year before returning to Earth for a gravity assist manoeuvre that directed the craft toward Venus.
To reduce the spacecraft's perihelion distance to Mercury, Venus flew two more times. These are all in the past. Next, six flybys of Mercury will be performed consecutively. Each one helps to reduce the spacecraft's eventual relative velocity to 1.84 km/s. BepiColombo will then perform four thrust arcs in order to further lower the spacecraft's velocity. The spacecraft will be able to allow Mercury's weak gravity to play its part in this. The spacecraft will orbit Mercury around December 5, 2025 without any traditional orbital insertion. It's quite an achievement.
Because Mercury's tiny gravity is dwarfed in comparison to that of the Sun, this complicated route is necessary.
It will, however, give us its first taste at Mercury science by flying past Mercury at 200 km (124 miles) altitude. What will it discover during this brief visit?
We are eager to see the first results of the measurements taken so close at Mercury's surface. It is a wonderful feeling! Johannes Benkhoff - ESAs BepiColombo scientist.
BepiColombo will not be in full science mode during the flyby. This is due to the spacecraft design. The mission is a joint effort of the ESA and JAXA (the Japan Aerospace Exploration Agency). The spacecraft actually consists of two orbiters: the Mercury Transfer Module, (MTM) and the Mercury Planetary Orbiter(ESA). They will be separated at Mercury orbit, but they will remain together during flybys. There is a limit on the amount of data and images that they can collect.
High-resolution images won't be available because the MTM shields the main science camera during cruise operations. The MCAM (monitoring cameras) will still be operational. These are the cameras that provided mission images of Venus and Earth's flybys so far.
BepiColombo flew past Earth with its monitoring cameras activated. Image Credit: ESA/BepiColombo/MTM CC BY -SA 3.0 IGO
BepiColombo, unfortunately, will arrive on the planets' nightsides during the flyby. This makes it difficult to capture images. From five minutes after closest approach, the MCAMs will operate until approximately four hours later. This means that the nearest image will be captured at approximately 1,000 km (620 miles).
BepiColombo's Mercury flyby was marked by some important moments. These are the active and inactive instruments. Image credit: ESA
MCAM images show the spacecraft as it is positioned on the MTM. At 10241024, the cameras will capture black-and-white images. These images will begin to arrive about 30 minutes after closest approach. They will be arriving in a steady stream on Saturday morning in Central European Summer Time. They will arrive on the west coast, around 11:00 pm.
MCAMs are not perfect, but the images will be fascinating. According to the ESA, we should be able see large impact craters at Mercury's surface.
It is a similar situation when it comes to BepiColombos scientific instruments. While some of the science instruments aboard both orbiters may be functional, there will be limitations. When it samples Mercury's magnetic, particle and plasma environment, the spacecraft will provide a glimpse of what is to come. The spacecraft finally begins to study its target after years of planning and space travel.
Johannes Benkhoff (ESA's BepiColombo Project Scientist) says that they are eager to see the first results of measurements taken so close by Mercurys surface. In January 2008, NASA's Messenger mission made its first flyby of Mercury. This was when I began my work as a project scientist for BepiColombo. It's now our turn. It's an amazing feeling!
BepiColombo is the third spacecraft that has visited Mercury. This is despite the fact that Mercury is 77 million kilometers (48 million miles) away. Spacecraft have been sent further into the Solar System. Jupiter, for example, is 715 million kilometers (484 million miles) away. We have sent two missions to the gas giant (Galileo & Juno). Five additional missions included flybys to Jupiter.
Because Mercury is so close to the Sun, it can be difficult to visit. Any spacecraft must contend with the Sun's gravity, which is much stronger than Mercury's weak gravity. Mercury orbits the Sun at a very fast rate, so any spacecraft wishing to rendezvous with it must have high velocity.
It is also why landing on Mercury is so difficult. The typical sequence of planetary exploration is: flybys, an orbiter and a landing craft, followed by a lander on the surface. We will one day be able to land on Mercury.
The issue was addressed in depth in a 2018 white paper. The relative velocity and the immense launch energy are the main issues. The authors noted that launch vehicle capabilities have improved and will continue to improve. Launch vehicles such as the NASA Space Launch System, SpaceXs Falcon Heavy and the Ariane 6 should help overcome the obstacles to reaching Mercury's surface.
A sample return to Earth would be the gold standard for a mission on Mercury's surface. It's unlikely that this is possible for a while.
We can now look forward to what BepiColombo has to say about Mercury.
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