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The space journey is a Pichenette case: it is most often enough to give an impulse long enough to accelerate a probe so that it then crosses the space at constant speed, by being if necessary attend by the gravity of planets on its trajectory to accelerate. This is how to travel 2, launched in 1977, was successively accelerated by Jupiter, Saturn and Uranus, to the point of reducing the duration of his trip to Neptune from thirty to twelve years.
But now, even done with small onions, gravitational assistance allows you to gain only a handful of kilometers per second. And the initial impulse, made by a reactor, can hardly last, due to lack of fuel. It would take more than a hundred thousand years for a probe like traveling to approach Alpha from the Centaur, the star closest to us, beyond the solar system. And, yet, the light of this star takes only a little more than four years to reach our telescopes, since it crosses the cosmos at nearly 300,000 km/s. Could we not travel to a tenth, even a third of this speed? As incredible as it may seem, the work is going well.
