# Why do so few satellites pass over the poles, and why do so many focus on the equator?

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. Very few satellites (or pieces of debris) pass over the poles
2. GPS satellites seem to avoid the poles almost entirely
3. There is a high concentration of satellites around the equator.

I assume this is why Google Maps' earth view breaks down and gets blocky near the poles:

I know that the poles are the least populated places on the planet. No one but fish, whales, and other non-satellite producing layabout species live near the north pole, and the south pole is reserved for penguins, explorers with fantastic beards, and a rotating selection of scientists, some of whom have been assimilated by the Thing.

I also know that there are a few satellites dedicated to orbiting over the poles, but I would have thought there would be a more significant number of them.

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• 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. – Hohmannfan Jul 9 '16 at 18:10
• 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 – Fattie Jul 10 '16 at 12:54
• 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. – Fattie Jul 11 '16 at 14:44
• There's a good set: en.wikipedia.org/wiki/A-train_(satellite_constellation) – Fattie Jul 11 '16 at 14:46
• 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. – uhoh Jul 12 '16 at 1:36

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.

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.

I think there may be some confusion here,

1. Note that there are "geostationary satellites, and then other satellites." GEO satellites are, of course, entirely and totally about being on the equator. The term "geostationary satellite" implies "equatorial satellite".

I suspect there is simply a misreading of the data/images you present.

All I see in the images presented, is: "a big pile of satellites, distributed all over the globe - and of course one image shows our bunch of equatorial satellites."

1. Note that GPS in particular (and all the other nav constellations - GLONASS, GALILEO, etc etc) are very much evenly distributed around the globe; that's the whole point. (GPS works - in general terms - identically at the poles or anywhere else: you can see about 9 GPS satellites, at any instant, from any point at all on the ball of the Earth.)

(You can see this instantly on any awesome "Boy's Own" page about GPS satellites. Example, look at this natty animation someone bothered making, which you can find simply on the Wikipedia page for GPS.)

So again: of course, certainly and obviously, all of our "equatorial satellites" are of course … equatorial. But that's a separate category.

Regarding "all the rest", I for one don't know if there's a preference for:

• (A) sort of wobbly (from our point of view) orbits (which do not go over the poles and stay somewhat near the equator); versus

• (B) all-over-the-place orbits (like GPS); versus

• (C) orbits that specifically go over and stay over the two poles (there would certainly be some specialized need for that - which I don't know).

(Actually, this being the age of the internet, I was able to instantly find out that Iridium, for instance, uses pure polar orbits.)

Again to repeat. You may be misreading those images. All I see is a completely random even distribution (as you would expect); plus of course one image showing all our equatorial satellites.

Just to be absolutely clear, you ask in large letters:

You ask "Why do so many of our satellites orbit at or near the equator, and why do so few pass over the poles? Is it simply a matter of "No one is there, so they don't need communications, GPS, or observation?"

1. Actually GPS works flawlessly at every single point on Earth equally, very much including the two poles.

2. You mention communication. Regarding satellite phones, funnily enough our planet's satellite phone network (Iridium), is indeed … a set of polar satellites!

3. Regarding "observation" — funnily enough, it appears that observational satellites do indeed tend to be polar satellites! (Wikipedia says "To get (nearly) global coverage with a low orbit it must be a polar orbit or nearly so…", you can read all about it there.)

4. Regarding the equator: don't forget all geostationary satellites are (of course) equatorial; that's a special group.

Again, all I see in the images is that there's completely random and even coverage, plus, the equatorial satellites.

• GPS works on the poles but it is degraded compare to other areas. – Antzi Feb 3 at 15:59
• @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 :) – hobbs Sep 5 at 22:30

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:

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