#insights

Since 2019, the United Nations has celebrated 21 June the International Day of the celebration of the Solstice, popularly known as the “Day of the Sun”.

Venerated by the oldest civilisations and studied using every possible technology, today we know much about the Sun and its influence on Earth, but there is still much more for us to discover.

To further enhance our knowledge of the Sun, how it works and its influence, we have to get close to it, even though it is 150 million km away from our planet.

The European Space Agency (ESA), in collaboration with NASA, took on that challenge and designed a space satellite, the Solar Orbiter (also known as SolO), whose perihelion can get as close as about 42 million km from the Sun (closer than Mercury’s perihelion) thanks to gravity assists provided by Venus. Its aim is to capture close-up images of the polar regions of the star, data with which to measure the composition of the solar wind and learn as much as possible about its activity.

On 10 February 2020, an Atlas V 411 rocket successfully launched the Solar Orbiter, a project in which Sener took part through various technological development contracts.

Why studying the Sun matters for the Earth

The Solar Orbiter has become the most important scientific laboratory sent to the Sun. It is not just the European satellite that has got closest to the Sun, it was also the first in the world to observe its polar regions and to provide related visual information to the Earth.

Periodically, the Solar Orbiter provides high-value information involving the origin of the solar wind, how solar flares occur, variations in the sun’s activity and other discoveries. This information is key to the Earth.

We know that any phenomenon linked to the Sun affects different elements of our planet. One of the least known factors to date has been the solar wind, which the satellite studies in as much detail as possible.

The solar wind travels through the Solar System and interacts with any element it runs into, whether it’s celestial bodies or technology that we have launched into space.

The resulting interactions can give rise to the spectacular aurora on our planet, but they can also have drawbacks; solar storms can damage electrical systems on Earth, or even in spacecraft that are orbiting at that time in space.

Understanding the solar wind is thus a priority for solar physicists. As a result, one of the main goals of the Solar Orbiter is to make it as easy as possible to study the origin of the solar wind, its evolution and characteristics.

Thanks to the equipment on the Solar Orbiter, consistingmainly of on-board instruments (which measure the solar wind and magnetic field around the spacecraft), remote sensing instruments (responsible for capturing images and data from the Sun) and the Magnetic Connectivity Tool software, it has already yielded relevant information in this area.

We already knew of the existence of the fast solar wind (which travels at over 500 km/s) and the slow solar wind (which travels below 500 km/s). A theory has also been formulated that the difference between them is in the characteristics of the different areas of the solar corona where they originate.

The fast solar wind originates in the open corona, with regions where magnetic field lines are anchored to the sun at one end and extend out into space at the other. As a result, a perfect path is created for solar material to escape into space.

The closed corona, on the other hand, is made up of regions with closed magnetic field lines, connected to the solar surface at both ends, like two large magnetic loops.

Sometimes, the loops open and solar material escapes before it closes again, giving rise to the slow solar wind, according to the theory.

The Solar Orbiter has allowed us to confirm this theory of the origin of the slow solar wind, thus achieving one of its main goals. Scientists were able to do this by measuring the composition of solar wind currents, since the combination of heavy ions in solar material depends on their origin.

The set of images of the Sun’s surface captured by the Solar Orbiter, together with the analysis of the activity on the sun’s surface and the solar wind currents, was sufficient to confirm that the slow winds come from an area where the open and closed corona come together.

“Changes in the composition of heavy ions together with electrons provide strong evidence that the variability is not only driven by the different source regions, but is also due to the re-connection processes that occur between closed and open circuits in the corona“, explains  Dr Yardley, from the research group on Solar and Space Physics at the University of Northumbria.

Sener, responsible for five Solar Orbiter contracts

Sener is responsible for five different contracts to develop the Solar Orbiter: the antennas, the feedthroughs, the nearly 5-metre long deployable boom that houses the magnetic field sensors, and two of the ten scientific instruments in the orbiter: EPD and So-Phi. This highly complex craft is one of the largest space contracts in the company’s history. The antenna subsystem alone involved over 100,000 hours of engineering.

Specifically, this subsystem includes the following elements:

• A steerable high-gain reflector, the main antenna to send all the scientific data to the Earth.
• A steerable medium-gain antenna, which serves as a secondary or back up antenna.
• Two low-gain antennas with hemispheric coverage, which help the satellite stay connected to the Earth.

For both the high- and medium-gain antennas, Sener also developed the separation booms, the deployment and pointing mechanisms, the thermal hardware and the control electronics.

The other systems developed by Sener have the following functions:

• The feedthrough subsystem provides the satellite with non-airtight protective covers for the remote sensing instruments.
• The Instrument Boom subsystem is a deployable mast with five instruments that are highly sensitive to magnetic fields. Thanks to it, these instruments are kept away from the magnetic disturbances generated by the rest of the equipment during operation.
• The remaining scientific instruments, located in different areas of the Solar Orbiter, have the essential function of analysing high-energy particles.

Sener’s participation in the Solar Orbiter is due in part to its experience in previous space projects, such as the Gaia satellite and the BepiColombo mission. For Gaia, Sener developed, manufactured and verified the satellite’s deployable sunshield; it developed the positioning subsystem for the M2 mirror; and it developed and manufactured the electronic units that regulate the deployment of the sunshield.

As for BepiColombo, it’s a mission to explore Mercury, which was used as a reference for the Solar Orbiter’s space mission. Sener was responsible for the low- and medium-gain antennas, the waveguides for routing the signal, the pointing mechanism for the high-gain antenna, and the deployable boom for the magnetometers.

Header image: ESA