What is considered low orbit

Aha : Why do satellites orbit?

The trajectory was like that of a cannonball, because the US probe was too slow to lift the chimpanzee into orbit. After reaching an altitude of 250 kilometers, “Ham” began to fall and landed safely in the sea.

The dogs "Belka" and "Strelka" had already started in 1960. With stronger thrust. They had circled the globe 18 times in a Russian “Sputnik” satellite and returned safely.

The way into space requires a lot of energy. Only when the pace is fast enough can a satellite enter orbit and orbit the earth. “It needs enough centrifugal force to balance out gravity,” says Stephan Theil from the German Aerospace Center in Bremen.

For a low-flying satellite, the threshold is 28,000 kilometers per hour, the “first cosmic speed”. At this rate it enters a circular orbit of the earth. “If it moves faster, the orbit becomes elliptical.” 40,000 kilometers per hour are required to leave the earth's gravitational field forever.

A satellite on an elliptical course is sometimes closer to the earth, sometimes further away. If another engine ignites at the furthest point, it can be moved into a higher orbit with little effort. In this way, satellites can reach geostationary orbit at an altitude of 36,000 kilometers. Up there they run synchronously with the rotation of the earth. Seen from the ground, they stand firmly in the sky and can permanently supply an area with television programs.

Its orbit remains stable for weeks and is only corrected from time to time, for example because of the gravitational pull of the moon and sun. “In contrast, low-flying satellites quickly lose altitude due to the friction in the atmosphere,” says Theil. The international space station orbits at an altitude of 350 kilometers. It sinks by 75 meters every day and has to be lifted by space transporters several times a year.

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