What goes up must come down — or must it?

It's only 40 years ago that an artificial satellite was first put into orbit. Now there's so much stuff orbiting the Earth that there is a risk of collision. How does it get there? How do you make sure it stays there and does not come crashing down? Does it make any difference whether it's orbiting over the poles or around the equator? And how fast is it going?

Some satellites are 36000 km above the Earth's surface - that's six times the Earth's radius. They take all day to orbit; they're the geostationary satellites.

Others are only about 700 km above the Earth and travel so fast that it takes only 100 minutes to orbit the Earth once - that's around 15 orbits per day. They are the Low Earth Orbit (LEO) observational satellites in polar orbit.

Here you can find out what's behind all this and check up on:


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