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Old 08-21-2014, 05:27 PM
Darth Ayebaw Darth Ayebaw is offline
Join Date: Feb 2010
Location: Big Lake. AK
Posts: 256
How many satellites do we need in geosync before we have a ring visible from the ground?

I keep hearing about geosync being crowded, satellites moving closer and closer together and so on.

I also know we can see the ISS and other satellites as point sources from the ground.

How many point sources do we need around the equator before we have a distinct line, or ring (not necessarily unbroken), visible from the ground? Either at night or in the daytime.
Old 08-21-2014, 06:08 PM
iljitsch iljitsch is offline
Join Date: Jul 2014
Location: The Hague
Posts: 1,012
I don't know what exactly makes for visibility, but remember that the ISS is roughly 100 times closer to the earth than a geostationary satellite: 420 km above the surface vs 35800 km. So to reflect the same amount of light, a geostationary satellite would have to be 100 times larger, while I'm pretty sure they're on average more like 10 times smaller.

The ISS is about 100 meters wide. You'd need about 2.5 million international space stations to completely fill up geosynchronous orbit. That would cost 2.5 million x 150 billion (wow, they really couldn't think of something better to spend the money on?) = $375000000000000000.00. (Although you'd probably get a pretty sweet deal when buying in bulk like that.)
Old 08-21-2014, 06:23 PM
filmstar-en filmstar-en is offline
Join Date: Aug 2013
Posts: 715
The Geostationary satellites are all sitting above the equator and there are photographs of them when the light catches them that shows them as a distinct ring. They are separated by 2 or 3 degrees, so there is a big gap between them. I think the separation is to keep their signals from interfering with each other. Some are in clusters, controlled and co-ordinated by the same operator. They live in a 150km box. I guess they would show up to be rather brighter.

Here is one such photograph, but rather obscured by the star trails.

I have seen better examples out there that show the ring quite distinctly.
Old 08-21-2014, 06:32 PM
eburacum45 eburacum45 is offline
Join Date: Feb 2003
Location: Old York
Posts: 2,606
Geosynchronous satellites are almost always invisible to the naked eye, so even a solid continuous ring as wide as a satellite would be difficult to see. But occasionally a GEO satellite will become breifly visible, when its solar panets catch a glint from the Sun; see

If you arrange for a ring of satellites similar to that one, with mirror-finish solar panels all pointing directly so that the Sunlight was pointing directly at you, it would be possible to make a visible ring in the sky with a magnitude of +3 or so.

They wouldn't even have to touch, since the diffraction limit of your eye would blur them all together.

The diffraction limit I quoted on an earlier thread was 0.4 minutes of arc; there are a number of other figures out there for this limit, all in the same ball park. I think this means that the satellites could be up to 4 kilometers apart without appearing as separate entities. To fill geostationary orbit you'd need 66000 satellites of this kind. Note that they would only be visible if all the mirrors were pointing right at you.

Last edited by eburacum45; 08-21-2014 at 06:33 PM.


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