This is a rather special space mission that 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 encompass? “With a demonstration mission, responds Damien Galano, ESA project directorwe want to show what a specific technology is capable of achieving in orbit, in space conditions. We want to prove that it works. » Therefore, the name “Proba” should not be compared with the diminutive of “probability” used by mathematicians, but rather with the probably Latin, meaning “test.”
One mission, but two satellites. In fact, Proba-3 will attempt to demonstrate that two spacecraft can fly in formation with diabolical precision. The Patrouille de France powers 10. The first satellite is a telescope pointed towards the Sun. The second, a round occultist 1.4 meters in diameter, a screen that 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. All this forms what astronomers call a “coronograph”, since the corona, that is, the solar atmosphere, appears as if by magic once the Sun and its blinding light have been obliterated.
With Proba-3, ESA wants to achieve for the first time, “demonstrate that we can precisely control two satellites, both their relative position and orientationexplains Damián Galano. The speed of one with respect to the other will be almost equal to zero, although both will travel several kilometers per second.” Let’s add some figures to better measure the dimension of the objective feat. The occultation satellite will be placed 150 meters from its colleague, projecting a cone of shadow towards it. This 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 student to stay in the shadows.specifies Damián Galano. If it is on the edge, light will pass through it due to diffraction. »
Cameras and laser beam.
Basically, the goal of Proba-3 is to get the equivalent of a one and a half hectometer long rigid telescope 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. To do this, several devices are used on board: cameras that take images of the other satellite; a laser beam returned by a retroreflector; Light sensors installed around the telescope entrance. If it is necessary to correct the position, it is the hider that moves very slightly thanks to small nozzles that expel nitrogen.
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