Escaping Earth
To send a probe to another planet, we have to define the right time to launch it towards its target. Contrary to what we might think, it is not when the 2 planets are opposite each other. First, ascending vertically from Earth’s surface requires a huge amount of energy. Second, all the bodies in the solar system are in motion relative to one another, so the target planet will not necessarily be in the right place when the probe intersects its trajectory.
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To begin with, we therefore need to take the planets’ relative motion into account when determining the launch window. The spacecraft is launched toward a point in space and then injected into a solar orbit to intersect that of the target planet at the right time to reach it. |
Journey of Europe’s Mars Express probe. Launched in June 2003, it intersected Mars’ orbit in December before going into orbit around the Red Planet.
Source : ESA
MARS EXPRESS' trajectory (ESA website)
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Our planet orbits the Sun at a speed of 108,000 kilometres per hour. An object near the equator moves at a speed of 1,650 kph with respect to the centre of the Earth. Near the poles, its velocity is virtually zero. When launching a spacecraft, it is therefore very important to takes advantag of the velocity imparted by the Earth’s rotation and by its revolution around the Sun. This is why the launch site has a direct impact on the amount of energy required. |
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The world’s main launch sites.
Europe’s spaceport in Kourou, French Guiana, is ideally situated near the equator at a latitude of 5.23° North.
Credits : CNES
