Solar eclipses occur because of a cosmic coincidence: the Sun is 400 times larger than the Moon, but it is also 400 times farther away. So when the two objects are exactly parallel in space, Earth’s satellite is … It covers the face of the star, revealing its outer layer, the solar corona. Astronomers are particularly interested in this mysterious region of the sun because it is, paradoxically, a million degrees hotter than the surface, and it is responsible for belching out violent particles and solar storms that can damage orbiting satellites or Earth’s power and communications networks. A better understanding of how it works could one day save us from disaster.
Of course, observing the solar corona is not easy. To do this, scientists use specialized telescopes on Earth and in orbit called coronagraphs. These are equipped with occultation disks and shields designed to cover the Sun in their field of view. But their effectiveness is limited by the phenomenon of diffraction, through which scattered light is filtered around the edges.
To solve this problem, European Space Agency (ESA) Plans to launch a new mission in November Proba-3It consists of a pair of probes that, when spaced 150 metres apart, will be able to produce on-demand orbital eclipses of unprecedented clarity, as if they were a giant instrument. The pair will leave India on a PSLV launch vehicle and will spend two years in orbit. Each satellite, a cube measuring one metre on each side, is comparable in size to a large refrigerator.
invisible thread
The space program, led for the first time by the Spanish company SENER, with the participation of different countries, will test a complex technology that will allow the two ships to fly together in formation as if they were connected by an invisible thread with a string. Incredible accuracy of 2 to 3 millimeters. A very technical challenge.
The Occulter and Coronagraph spacecraft will be aligned with the Sun so that the occultant, which has a 1.4-meter-diameter ring, casts a shadow on the face of the Coronograph, blocking the Sun so that the Corona is visible. During each 20-hour orbit, the ships will produce an artificial eclipse of six hours, “which is a long period and represents a huge scientific advantage,” says Diego Rodríguez, director of science and space at Madrid-based Sener Aeroespacial y Defensa, the company coordinating the consortium responsible for the mission, which also includes other Spanish companies such as Airbus, GMV and Deimos.
Proba-3 will make a very eccentric orbit, so that at one point it will be very close to the Earth, at a distance of 600 kilometers, and at another point it will be as far away as 60,000 kilometers. “At apogee (the farthest point), the speed of the two ships will decrease and the effects of gravity will decrease. Therefore, the energy consumption is lower and we will be able to maintain the formation flight for a much longer period.”
The mission has a dual objective. On the one hand, “there is great interest in studying the inner layers of the solar corona, because the main atmospheric phenomena of the Sun occur there, such as solar flares that affect terrestrial life,” emphasizes the head of SENER.
Illustration of a pair of Proba-3 satellites.
who
“We already have instruments that can study the Sun, the low corona and the high corona, and many heliophysics missions have studied the corona at different temperatures and altitudes. However, between the low and high corona is a region that is difficult to observe. “This region, where the solar wind and coronal mass ejections are generated, remains largely unexplored and extremely difficult to observe with sufficient spatial resolution and sensitivity to understand these phenomena,” notes ESA’s Proba-3 team. The three instruments on board will also address a long-standing scientific mystery: why the solar corona is significantly hotter than the Sun itself.
On the other hand, Proba-3 will develop high-precision formation flight techniques. In this scientific mission, to hide the sun, the two ships must always remain 150 meters apart, as if they were a large observatory of this size, which is impossible to send into space. He points out that “the formation flight generates virtual structures, as if the two ships were connected by a solid structure that does not exist in reality.”
But other missions may require increasing or decreasing the distance, for example, to observe at different wavelengths. “To prove that this is possible, the two spacecraft will approach and recede (rendezvous) in a completely autonomous and controlled manner, without any intervention from Earth,” says Rodriguez. In the future, giant telescopes with mirrors separated from each other but virtually connected to each other could be sent into space.
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