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Comment by panic | Hacker News Reader

If you zoom out a bit, there are noticeable "holes" above the North and South Poles where the density of objects is lower. Does anyone know what is causing these holes?

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I noticed the same thing.

A few ideas:

* Those spots are the furthest possible distance from the equator (in angular terms), so they should be the most expensive places to put something in orbit (either you launch from a northerly/southerly latitude or spend a lot of fuel on maneuvering into that orbit either way that's expensive)

* Maybe Earth's magnetic field interferes with electronics (less protection from the sun's radiation)

* No one really lives there so there's fewer reasons to spend a lot of money putting something in orbit

* Some kind of international agreement/rules

Maybe someone more knowledgeable could weigh in!

Most satellite footprints (imagine a cone from the satellite to the earth) are quite big I'd guess, so the need to launch into a truly polar orbit to capture all of the poles isn't needed.

That said my knowledge comes from playing KSP with the scansat mod.

I think it's just a math artifact. There's lots of "holes" in the orbit inclinations -- their distribution is actually very non-uniform. But at a frozen moment in time, the object's latitude will be anywhere from -i to +i, so the latitude distribution is "smeared out" over the whole range. The gap in the polar inclinations is the only one that's not, so that's the latitude gap you see.

Here's a histogram of the orbit inclinations where you can see this:

https://i.imgur.com/K9zsCy3.png

Here's the raw orbits data that the site uses:

http://stuffin.space/TLE.json

https://en.wikipedia.org/wiki/Two-line_element_set

Right - even though polar orbits are pretty useful, so there probably are quite a few satellites with inclinations close to 90 degrees, they spend less than 10/360 = 2.8% of their time within 5 degrees of the north pole. What's surprising is the sudden increase in the density of stuff around 80 degrees north.

One possible explanation is the combination of the iridium 33 collision debris field, which is in orbits with inclinations around 86 degrees, and Fengyun 1C debris, which is around 99 degrees (so, 81 degrees but going the opposite direction). The limit of the distributions of those two clusters might account for the clear 'edge' of the circle around the pole.

I think those are sun-synchronous imaging satellites:

https://en.wikipedia.org/wiki/Sun-synchronous_orbit

98° inclination is the same as 82° in retrograde (against the earth's rotation).

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