Satellite Spotting & Operations Handbook
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After teaching astronomy full time since 1994, I wish I could have a pound for every time I hear ‘Astronauts must have a great time in zero gravity’ or something to that effect. I usually reply‘I am sure it must be, but then if there is no gravity up there then why do they keep orbiting the earth and not fly away?’ The reply is almost always ‘… because of the earth’s gravity silly!’
That part is correct, the first is not. So what is going wrong? The astronauts are to blame for this misconception. They are always mentioning zero or micro gravity. Both terms are false. Gravity does indeed get weaker with distance as first proved mathematically by Robert Hooke from the Isle of Wight in 1686. He demonstrated this to Sir Isaac Newton and later included it in his famous book on gravity – The Principia… but Isaac Newton never gave Robert the credit; it was a bad habit of his.
So the next question will naturally be ‘Why do things float around in space then?’
This is down to motion; satellites are not stationary. In a roller coaster, during the fast descent phase, you may feel that you weigh virtually nothing and you begin to feel you could float out it you were not strapped in. This is a real effect. The vehicle you are in is rapidly descending and so are you. Gravity is doing its job just the same and yet you feel lighter. If you could weigh yourself at this point, you really would have been on an instant diet, kilograms have vanished. Once you reach the bottom of the ride, full weight is resumed; sorry, (unless you have thrown up). The description that is more accurate should be 'Weightlessness' rather than Zero Gravity; it's simply too confusing.
An orbit is achieved by basically throwing an object so fast forward that as the earth's gravity tries to pull it back down, it can't. The object just flies around constantly missing the earth's curvature