GSO4SCHOOL Summer School 2020
Final system acceptance tests are underway. The mission of the European Space Agency to Mercury is on track for launch in 2018. All eyes are now on BepiColombo.
Aiming to a closer observation of Mercury, the BepiColombo mission of the European Space Agency (ESA) inaugurates a new era for European Astronomy. In contrast with other planetary missions of ESA, which have visited relatively colder parts of the Solar System, BepiColombo, is going to operate very close to the Sun. In the years
to come this planetary mission will enrich our knowledge about the least explored planet of the inner solar system with new information about its geophysics, composition, exosphere, magnetosphere and history. The two orbiters of the mission, Mercury Planetary Orbiter-MPO and the Mercury Magnetospheric Orbiter-MMO, will be largely operating in the realm of the unknown, observing and collecting data for one Earth year of an uncharted territory. Jan van Casteren, Special advisor of the BepiColombo mission, talks about this astronomical challenge. The launch date is April 2018, arriving at Mercury in late 2024.
Interview & introduction by Amalia Drosou,
Science Communication
-Mr. Van Casteren, which are the scientific objectives of the mission?
We go with BepiColombo to the planet Mercury, which is the inner-most planet of our solar system. Due to the fact that it is very close to the Sun, Mercury is very difficult to observe. Scientists, have always been interested in understanding how planets are formed, how they evolve and how it is possible for life to emerge. In fact to gain a deeper understanding, we look at the earth-like planets of our solar system: Mars, Earth, Venus and Mercury. They are actually totally different from each other and the reason they are, is one of the fundamental questions. ESA had missions to Mars and Venus, but not yet to the inner-most planet, so the science of Mercury became a high priority. What we want is to investigate the planet, its interior structure, what the surface is made of and also the external environment: the magnetic sphere and the exosphere. To do that, BepiColombo will make an in-depth investigation with two orbiters. It will be the first time that two orbiters simultaneously will orbit the planet Mercury. One of them will be very close to the planet and the other a little bit further away. This means that we can separate the inner and the outer components of the magnetic field and the exosphere around the planet and that we will get a better grip on the dynamics and on the gradients. Moreover, the orbiter that is closer to the planet will make a global mapping of the planet in high resolution for the first time.
-Several tests are conducted during the whole period before the launch. In which phase are these tests at the moment?
We have completed almost all of the development tests. But before we could do these tests it was important to develop new technology, necessary for this challenging mission. The surface temperatures on Mercury are extreme, up to 450 degrees Centigrade and the solar radiation is ten times higher than on Earth, so this means that everything on the outside of the spacecraft has to withstand these harsh conditions. We have never had a satellite that goes to such a hot environment, so we had to develop a lot of new materials and equipment in order to do that. An exceptional amount of development and testing was completed over a period of ten years on a lot of equipment, developing new materials, solar cells, mechanisms, antennas, coatings, etc. We have also developed an electric propulsion system based on ion engines to propel the orbiters to Mercury. All equipment was built, delivered and integrated and we are now at the final stages of the system testing.
-Are there any unpredictable factors that could put the journey in danger? Which are your safety nets in this case?
The unpredictability could be mainly in the different environments and how the materials and equipment behave in those. For this reason, we have modeled and tested everything in the best possible way. We already know a lot about the Sun, its radiation and how harsh it is at the Mercury environment, so we believe that the remaining uncertainties can be dealt with by the design margins that we have included for that purpose. For example, when you expose the solar array at Mercury, close to the Sun, the radiation is about 10 times more intense than near Earth. Such a radiation exposure in combination with the high temperatures of the solar cells, will give us uncertainties about the solar array output over its lifetime. Therefore we apply a margin on the solar array performance to account for any uncertainties in the degradation due to high intensity ultra-violet radiation, high temperature and contamination to name a few factors.
-NASA’s MESSENGER has already visited Mercury. What more will BepiColombo add to our knowledge about the planet? Is it the dual spacecraft that will make the diffference?
“Grosso modo” I would say there are three aspects related to this question. The first aspect is the one that you just mentioned: we have two orbiters so we can map in a much better way the magnetic and the exospheric environment. The second aspect is that one of the spacecrafts goes into an orbit, which will bring it very close to the planet at all times, in comparison with MESSENGER’s orbit that was only in a limited part close to the surface of Mercury. MESSENGER’s orbit was highly eccentric thus a high resolution mapping of the planet was possible only in the northern hemisphere. Instead, BepiColombo will be able to perform a close surveillance globally with imaging and spectral mapping of the surface at a much better resolution. The third aspect comes from the MESSENGER science community itself. Science progresses with new investigations but often, newly gained insights may also uncover other aspects that are not understood. And this has naturally happened with the science of MESSENGER as well. MESSENGER has provided us with fantastic new knowledge about Mercury and scientists have come up with a number of questions for further investigation and these are all areas that BepiColombo will address.
-Why is this mission a cornerstone for ESA?
We can answer this question first by addressing the issue of budget, which for a cornerstone mission would be more than 650 million euros. With a budget of 1.2 billion, BepiColombo definitely classifies as a cornerstone mission. We can then ask why the Agency would want to spend that amount of money on a mission to Mercury. This is really more of a scientific question and I think it takes us back to your first question about BepiColombo’s scientific objectives. Planetary science is important for the understanding of how life originates, how planets are formed and how planets evolve. Therefore, the Agency feels that once every so many years we must have a major planetary mission to advance the investigations on the fundamental questions of life.
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