Image of the solar corona, taken during a total eclipse of the Sun by the Moon, with the European Space Agency’s Proba-2 satellite, provided March 20, 2015 (ESA/Proba-2 minisatellite)
A flight with tiny precision, down to the millimeter, between two satellites, more than 60,000 km from Earth: this is the challenge of the Proba-3 mission to observe the Sun’s corona with a wealth of details, presented at the press on Wednesday in Antwerp (Belgium).
The corona, this “atmosphere” of the Sun, still largely defies understanding. Invisible to the naked eye or with simple telescopes, blinded by the brilliance of the star, it extends over a thickness of several million kilometers.
Only a total eclipse of the Sun by the Moon revealed its existence to the first astronomers, before a Frenchman, Bernard Lyot, invented the first coronagraph in the 20th century, by placing the equivalent of a lunar disk in a telescope.
This invention has flourished and the Proba-3 mission of the European Space Agency (ESA) will use it in an innovative way. Next September, an Indian rocket will release two satellites into space which will work in tandem for two years, circulating in a highly elliptical orbit, a loop taking the machines from some 600 km altitude to 60,000 km above sea level. Earth.
Equipped with a large shield measuring 1.40 meters in diameter, the first satellite will play the role of the Moon by obscuring the solar star. It will be closely followed by the second satellite, carrying the ASPIICS coronagraph, which will thus be able to observe the solar corona, in the darkness created by the occulter.
The operation will require precision never before achieved in such a formation flight exercise, carried out at a distance of 144 meters. A distance that will be respected to the nearest millimeter for optimal observation, where that of a previous experimental mission, PRISMA more than ten years ago, reached a decimeter.
The mission has a dual interest, astronomical and technological.
First, observe the solar corona as a whole, and thus complement the observations of the two probes Solar Orbiter and Parker Solar Probe, explains Raphaël Rougeot, systems engineer at ESA and specialist in the ASPIICS coronagraph, to AFP.
– Technology demonstration –
With this instrument, “we hope to be able to observe the solar corona very close to the Sun,” he says. And thus help to unravel the enigma of the temperature of this very sparse medium which is measured in millions of degrees while it peaks below, on the surface of the Sun, at only 6,000 degrees.
This phenomenon is “still poorly understood and perhaps linked to magnetic phenomena”, according to Raphaël Rougeot. Just like physics dictates that the corona is the source of the solar wind “and especially of coronal mass ejections, these gigantic waves of plasma and magnetic fields which can have impacts on the Earth and its environment”, continues the engineer. Events that could damage satellites and terrestrial installations.
Proba-3 is also a technological demonstration mission, explains Damien Galano, project manager at ESA. Formation flying allows “in principle to + build + large systems with several separate elements”, he explains to AFP. As imagined for example in preliminary projects for space interferometry or long focal length X-ray telescopes.
More prosaically, notes the expert, mastering formation flying also means “having sensors and algorithms on board allowing navigation, guidance and control of the relative position between different objects”. All in an automated and autonomous manner.
For Proba-3, this includes an optical sensor with image recognition and above all a laser sensor which will provide precise distance measurement between the two satellites. It is up to the occulting satellite to finely adjust the distance separating it from its tracking satellite using a micropropulsion system.
Such technologies could ultimately find an application for services in orbit, to repair or assemble systems, or remove them from space, specifies Damien Galano.
The Proba-3 mission is the fruit, on behalf of ESA, of a collaboration of 14 countries, led by the Spanish technology group Sener and the Belgian Spacebel, with the involvement of Airbus which built the platforms -satellites and the American company Redwire which integrated all the elements.