We are going to the sun. ESA launched the European observation satellite Solar Orbiter from Florida in the USA. This space probe is going to look at sides of the sun that we have not been able to see well before: the two poles of the sun.
Solar Orbiter is an ESA-led mission with strong NASA participation. It will look at never-before-seen regions of the sun, such as the poles. Space weather research is one of its main objects. It hopes to shed more light on the origins of solar wind. This can knock out power grids on the ground and disrupt operations of satellites orbiting the Earth. ESA’s new sun exploring spacecraft Solar Orbiter launched atop the US Atlas V 411 rocket from NASA’s Kennedy Space Center in Cape Canaveral, Florida, on 10 February 2020. The prime contractor is Airbus Defence and Space in Stevenage, UK. Solar Orbiter is the first ‘medium’-class mission implemented in the Cosmic Vision 2015-25 programme, the current planning cycle for ESA’s space science missions.
Facing the sun
What happens on the sun actually has consequences for our earth. And then it’s not just about the temperature. The sun and the north and south pole of the star have strong magnetic fields. And they sometimes change, resulting in a lot of solar wind. The Solar Orbiter will investigate that process. Solar Orbiter must give us more insight into how our parent star works. Also, It will investigate how intense radiation and energetic particles impact our home planet. The goal is to better understand and predict periods of ‘space weather’. Solar storms have the potential to knock out power grids, disrupt air traffic and telecommunications. Furthermore, they endanger space-walking astronauts. Notorious is a major power outage in Canada in 1989 that was the result of a solar storm. In short, it is good to know more about how solar storms exactly work and how they arrive on earth.
Polar regions of the sun
Solar Orbiter will take just under two years to reach its initial operational orbit, making use of gravity-assist flybys of Earth and Venus to enter a highly elliptical orbit around the Sun. The spacecraft will use the gravity of Venus to slingshot itself out of the ecliptic plane of the solar system, which is home to the planetary orbits, and raise its orbit’s inclination to give us new views of the uncharted polar regions of our parent star. Up until now, the poles have been out of view from earth and to other spacecraft. However, scientists think they are key to understanding the sun’s activity. Over the course of its planned five-year mission, Solar Orbiter will reach an inclination of 17° above and below the solar equator. The proposed extended mission would see it reach up to 33° inclination.
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Ten instruments
Solar Orbiter will use a combination of ten in situ and remote-sensing instruments to observe the turbulent solar surface, the Sun’s hot outer atmosphere and changes in the solar wind. Remote-sensing payloads will perform high-resolution imaging of the Sun’s atmosphere – the corona – as well as the solar disc. In situ instruments will measure the solar wind and the solar magnetic field in the vicinity of the orbiter.
Solar Orbiter Versus Parker Solar Probe
As one of two complementary spacecraft studying the Sun at close proximity, it joins NASA’s Parker Solar Probe. This is already engaged in its mission. Solar Orbiter and Parker Solar Probe function in their own respective orbits to accomplish their different, if complementary, goals. Parker Solar Probe ‘touches’ our star at much closer distances than Solar Orbiter. It is there to study how the solar wind originates. But, it does not have cameras to view the Sun directly. Solar Orbiter flies at a distance to achieve a comprehensive perspective of the sun, including both remote images and in situ measurements, and will view the Sun’s polar regions for the first time.
Contextual information
Beyond accomplishing its own science goals, Solar Orbiter will provide contextual information. This should improve the understanding of Parker Solar Probe’s measurements. By working together in this way, the two spacecraft will collect complementary data sets that will allow more science to be distilled from the two missions than either could manage on its own. Solar Orbiter builds on the legacy of missions such as the joint ESA/NASA Ulysses and Solar and Heliophysics Observatory (SOHO), to give the most advanced look yet at our star, and its influence on Earth.
Solar energy
The Orbiter runs… on solar energy. Airbus Defense and Space Netherlands contributed to the solar panels that will provide the spacecraft with energy in the coming years. Dutch meteorological institute KNMI takes action when the first measurement data from the Solar Orbiter reach our planet. The spacecraft is equipped with “jewel-like” solar panels,” said Rob van Hassel of Airbus Defense and Space Netherlands, responsible for assembling them. “The satellite will orbit the sun on nearly forty million kilometers. That sounds like a great distance, but for solar panels that is really very close. The temperature on the front of the heat shield of the Solar Orbiter can go up to five hundred degrees Celsius. While at the back, in the shade, it is only fifty degrees.”
Mercury
At its closest, Solar Orbiter will face the sun from within the orbit of Mercury. Or: approximately 42 million kilometres from the solar surface. The design of the solar panels themselves have, to a large extent, been based on panels that are already flying towards Mercury as part of the BepiColombo mission. Several solutions had to be specifically devised to prevent the Solar Orbiter from overheating. Heatshield technology must ensure the spacecraft’s scientific instruments are protected. The images are made behind moveable flaps. The heatshield will endure temperatures of up to 500°C – up to thirteen times the heat experienced by satellites in earth orbit.
Manageable temperatures
Because of the brightness of the light so close to the sun, the panels also provide sufficient power at an angle of 75 to 80 degrees to the sun. As a result, the temperature of the solar cells can be limited to a manageable 170 degrees Celsius. In addition, the hinges and the arm of the panels are all equipped with small glass mirrors and shields and titanium. The mirrors reflect sunlight everywhere, except in the direction of the satellite itself. “If those mirrors are ill-mounted only the slightest bit, those solar panels become like a magnifying glass that easily burns a hole in the satellite,” says Van Hassel.
Kapton blanket
In addition to the mirrors and shields, Airbus Defense and Space Netherlands also applied a kapton blanket. It has a conductive black layer that protects the back of the solar panels. The blanket prevents electrostatic discharges from disrupting measurements from the satellite instruments or damaging the solar panels themselves. In other words: the Solar Orbiter has its own lightning rod on board. The development of the solar panels is a collaboration between the German Airbus location in Ottobrunn and Airbus Defense and Space Netherlands. Its development took three years. The Dutch part of the development was funded by the contribution that the Dutch government made to ESA’s scientific missions.
Space weather alarm
As we become increasingly dependent on technology – for example, the signal from navigation satellites – the impact of solar wind on our society is increasing. That is why KNMI is developing a ‘space weather alarm for the Netherlands. Van den Oord: “With that new information from Solar Orbiter we are going to improve the models. This is because we want to be able to warn in time of increased solar activity. For example for aviation, emergency services and other vital sectors in our society. If we know that a major solar storm is coming, we can take timely action here on Earth to limit its impact on our society.”
