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The following screenshots from the website Stuff in Space, which tracks satellites and man-made debris orbiting the earth show us a few things:

  1. It appears to me that: very few satellites (or pieces of debris) pass over the poles. Am I correct, and if so, why?
  2. GPS satellites seem to avoid the poles almost entirely
  3. It appears to me that: there is a high concentration of satellites around the equator. Am I correct, and if so, why?

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Is it true that many of our satellites orbit near the equator, and few pass over the poles? If so, why?

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    $\begingroup$ Google Maps getting blocky near the poles is unrelated, that is just an artefact of the 3D view being a wrapped version of a cut off Mercator projection. $\endgroup$
    – SE - stop firing the good guys
    Jul 9, 2016 at 18:10
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    $\begingroup$ In the first instance, just to be clear. Say you want a satellite that "stays over the same place" (a geostationary satellite - they are very high up). In fact, and indeed obviously, those must be over the equator. This is explained in many places, example $\endgroup$
    – Fattie
    Jul 10, 2016 at 12:54
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    $\begingroup$ HI @Alec - - you know, that then simply is not a polar orbit!! Yes, it's absolutely commonplace, the norm, that there are satellites as you describe. Just see the "natty animation" mentioned in my answer below. (I believe you use "precession" in a non standard way there, maybe more like inclination, but I get what you mean.) the ones that happen to pass right over the poles are "polar satellites". I believe polar sats move about 20 degrees, each sweep - you know? And each sweep is 1 or 2 hours; so they sweep over the whole globe every 10 or 20 hours. $\endgroup$
    – Fattie
    Jul 11, 2016 at 14:44
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    $\begingroup$ There's a good set: en.wikipedia.org/wiki/A-train_(satellite_constellation) $\endgroup$
    – Fattie
    Jul 11, 2016 at 14:46
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    $\begingroup$ Where can I upvote stuffin.space? :) Seriously, I hope some day we can embed WebGL objects in stackexchange the same way we can put GIFs and YouTube videos. $\endgroup$
    – uhoh
    Jul 12, 2016 at 1:36

4 Answers 4

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You really asked a number of related questions, so here's the answers to some of the questions.

  • All satellites will pass over the equator at some point in time. Only a satellite passing directly over the poles will pass over the poles.
  • GPS satellites pass in regular orbits that can be seen from the whole Earth. They don't need to pass over the poles to do so.
  • Launching into a polar orbit is more difficult than launching into an equatorial orbit, due to the motion of the Earth.
  • Only a LEO satellite has any real reason to be over the poles. In fact, the diagram you showed of debris shows a near ring around the poles, indicating that a fair amount of debris comes close to the poles, but doesn't run right over it.
  • LEO satellites are frequently put into a 98 degree inclination orbit known as Sun Synchronous. This orbit will pass over Earth at the same (solar) time of day every day. That is responsible for the ring you see over the poles.
  • Google Earth's coverage of the poles isn't because they can't be seen (They can be seen from satellites), but because they simply use other data that people have used, and no one is paying for high resolution Polar pictures. Look at other sparse areas away from the poles, like the Amazon Rain Forest, remote islands, Sahara desert, etc, for comparison.
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Regarding "a high concentration of satellites around the equator":

Geostationary orbit (~36,000 km above the equator) is the only orbit where a satellite appears to be stationary in the sky, so you can communicate with it using a small, fixed dish. In all other orbits you need a dish that can rotate to track the satellite.
This makes geostationary orbit highly desirable for applications with a large number of users who don't want to pay much for the service, i.e. satellite TV.
Other applications also benefit from being stationary: communications, weather and other long-term observation, etc. And just outside geostationary orbit is another large concentration: this is a graveyard for old geostationary satellites. When a satellite is decommissioned, it is moved to a slightly higher orbit to free up its slot in geostationary orbit.

Geostationary satellites are concentrated on the equator (because that's the only place where an orbit can be geostationary) but that does not mean those satellites focus (i.e. aim their antennas and sensors) on the equatorial regions. GEO is so high, those satellites can be seen/see even high latitudes, just about everywhere except the polar regions. I'm at ~50º N, and my country benefits from geostationary communications and meteorology satellites, for example.

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There's more equator than poles!

Fraction of a sphere within 10° of the poles:

$$2 \int_0^{\pi/18} 2 \pi \ \sin \ \theta \ d \theta = 0.191, \ \text{(1.5% of the sphere)}$$

Fraction of a sphere within 10° of the equator:

$$2 \int_{8 \pi/18}^{\pi/2} 2 \pi \ \sin \ \theta \ d \theta = 2.182, \ \text{(17.4% of the sphere)}$$

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It appears to me that: very few satellites (or pieces of debris) pass over the poles. Am I correct ...

You're completely, totally wrong.

GPS satellites seem to avoid the poles almost entirely

This is completely, totally wrong.

It appears to me that: there is a high concentration of satellites around the equator. Am I correct ...

Note that geosynchronous satellites can only be on the equator.

Other than that you're completely wrong. There is no concentration whatsoever of satellites anywhere.

(All I see in the images is that there's completely random and even coverage, plus, the few geosynchronous satellites, which matches the known simple facts.)

  • By the way, there are around 400 geosynchronous satellites (thought to be "402" at time of writing).

  • There are around 6000 satellites in total. (About 1/2 are working, about 1/2 are old ones.)

  • The number is increasing quickly, estimated 10,000 working sats in about 10 years from now.

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  • $\begingroup$ GPS works on the poles but it is degraded compare to other areas. $\endgroup$
    – Antzi
    Feb 3, 2019 at 15:59
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    $\begingroup$ @Antzi that hinges on the definition of the word "degraded". GPS provides its specified level of service everywhere on earth. Even at the poles, there will always be at least 4 birds, at least 5 degrees above the horizon, with at least X amount of RF pointed your way. Accuracy is lower, for geometry and ionospheric reasons, but that just means that you're only getting as-promised service instead of the massively-better-than-promised service most of us are used to :) $\endgroup$
    – hobbs
    Sep 5, 2019 at 22:30

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