How many satellites are needed to have real time views?

Question

how many satellites are needed to have real time views?

should cities invest in satellites over their cities?

Answer 1

I don't think you understand how satellites work.

Military and espionage surveillance is done by satellites in low Earth orbit, which means that they are constantly moving, and you may have to wait days or weeks for them to be over a specific target, and then you only have a few seconds to observe and record.

Geostationary satellites, which hover over a particular point, can only be located on the Earth's equator, so can't hover over particular cities unless the cities happen to be located on or close to the equator. Because of their high altitude, they only provide low resolution wide angle views, such as the GEOS weather satellites.

Answer 2

You can't put satellites static over a city. Only geostationary satellites (they have to be at 33000km above to be static) can be fixed and you need three of them to earth. It is not that real time though, 'cause radio waves at speed of light take finite time (in the present case it is quarter second).

A decade and a half back someone tried to solve the problem by putting a constellation of 77 LEO (low earth orbiting) satellites in 11 orbits around the Earth named 'Iridium' (in periodic table 77 is Iridium). That was near 'real time' enough. For a time we had enjoyed it but at back-breaking call rates, none could afford. So it did not recover the cost. Now, I believe American army bought it over cheaply and they have 66 (though they don't call it 'Dysprosium' the 66 th element) of them in 11 orbits.

Imagine the sheer volume of software that was needed to be written for passing bits or packets of information between satellite to satellite with all corrections, error correcting codes etc. But it is a success while it lasted (not financially though).

Answer 3

1.  How many?  Just one if you don't mind the view from geostationary orbit.  You'll need a whole constellation if you want a closer view.

2.  Should cities do it?  Heck no!  If you want to spy on a city, just put up cameras around the city.  It's a lot cheaper and more reliable, plus you can see something other than rooftops.

Answer 4

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