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Old July 30th 17, 01:22 PM posted to uk.telecom.broadband,uk.tech.digital-tv,alt.satellite.tv.europe
Peter Duncanson
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Posts: 4,214
Default BBC News Blunder

On Sun, 30 Jul 2017 13:42:38 +0100, Java Jive
wrote:

On Sun, 30 Jul 2017 12:49:34 +0100, "NY" wrote:

Could you not have a satellite in a geostationary orbit above another line
of latitude than the equator, as long as it still rotates in a line parallel
to the equator and rotates around the earth at the same rate as the earth
spins? Or would there be a nett force dragging it towards the nearer of the
two poles - is the equator the only place for geostationary because there is
no nett force towards either pole?


The gravitational attraction between the earth and the satellite can
be considered as acting between their respective centres of gravity,
that of Earth of course being at its centre. Therefore only an orbit
around the centre of Earth is stable. An orbit around a line of
latitude other than the equator would not be stable, and would require
a constant expenditure of fuel to counterbalance the gravitational
pull towards the centre of the earth.


And I don't think that a circular path following a line of latitude is
technically an "orbit".

This constant expenditure of
fuel, as opposed to the occasional expenditure of fuel to make
corrections to maintain a stable orbit around the centre of Earth,
makes such a satellite uneconomic in the extreme.

I know less about GPS, but I believe even their satellites orbit
around Earth's centre.


They do.

The system covers the whole globe by having
many satellites whose orbits are so arranged that wherever you are on
Earth, there will always be at least two or three satellites in the
sky above you.


--
Peter Duncanson
(in uk.tech.digital-tv)