It's a rather special space mission which must leave Earth on Wednesday December 4. The European Space Agency (ESA), which launches it, defines, in fact, Proba-3 as a “demonstration mission”. What does this expression cover? “With a demonstration mission, responds Damien Galano, project manager at ESAwe want to show what a specific technology is capable of achieving in orbit, in space conditions. We want to prove that it works. » The name “Proba” is therefore not to be compared to the diminutive of “probability” used by mathematicians but rather to the proba Latin, which means “test”.
One mission, but two satellites. Indeed, Proba-3 will attempt to prove that two spacecraft can fly in formation with diabolical precision. The Patrouille de France power 10. The first satellite is a telescope pointed towards the Sun. The second a round occulter 1.4 meters in diameter, a screen which must be placed exactly in front of the disk of our star to hide it, exactly like the Moon “turns off” Phoebus during a total eclipse. The whole thing forms what astronomers call a “coronograph” since the corona – that is to say the solar atmosphere – appears as if by magic once the Sun and its blinding light have been erased.
With Proba-3, ESA wants to achieve a first, “demonstrate that we can precisely control two satellites, both their relative position and their orientationexplained Damien Galano. The speed of one relative to the other will be almost equal to zero even though both will go several kilometers per second.” Let's add some figures to better measure the dimension of the targeted feat. The occulting satellite will be placed 150 meters from its colleague, projecting a cone of shadow towards it. Said shadow will only measure 8 centimeters in diameter when it reaches the coronagraph whose entrance pupil has a diameter of 5 centimeters. “We want this pupil to stay in the middle of the shadowspecifies Damien Galano. If it is at the edge, light will pass through due to diffraction. »
Cameras and laser beam
Basically, the objective of Proba-3 is to obtain the equivalent of a rigid telescope measuring one and a half hectometers long with two devices floating in the vacuum of space. To achieve this virtual “rigidity”, so that the satellites do not move relative to each other, both must know their respective positions precisely and at all times. Several devices are used on board for this purpose: cameras which take images of the other satellite; a laser beam returned by a retroreflector; light sensors installed all around the telescope entrance. If the position must be corrected, it is the occulter which moves very slightly thanks to small nozzles ejecting nitrogen.
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