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Comment by hinkley | Hacker News Reader

If they've started with orbits over Canada, what other countries can they serve with the same satellites?

My great circle skills are lacking, and looking at a globe it seems like a lot of water for the rest of the orbit.

You have to orbit around the center of gravity so these satellites won't just be over the arctic or anything. They have to orbit deep into the southern hemisphere to cover northern Canada so realistically there will probably global coverage at that point and this is just a pilot project of some sort.

A single great circle isn't a great way to model an orbit because it won't take into account the precession of the earth. It's a bit more accurate (but still not quite right) to say that that the constellation covers every single great circle with the same value of theta. In other words, it covers any part of the earth with equal or lower latitude.

However that's a bit of a simplification that ignores things like the need for ground stations, local laws (I will be astounded if they're allowed to broadcast over China), gaps in their orbital shells (such gaps probably don't actually exist, I haven't looked carefully at their orbits), local obstructions like mountains/valleys, etc

> gaps in their orbital shells (such gaps probably don't actually exist, I haven't looked carefully at their orbits),

Eventually they won't, right now they do.

Satellites spend most of their time near their extrema in latitude, though, so that's why the current constellation offers northern US/Canada and not areas south of there.

This is a global constellation. The initial orbital planes are arranged so that the density of satellites is maximized in middle latitudes, where most of the affluent world population lives.

With a LEO constellation, unlike GEO, you can not just serve a single area. That is why you have to go with a very big, worldwide system.

Or, of course, you can just choose not to offer a service part of the time, with satellites idling when they aren't pointed where you want them.

https://en.wikipedia.org/wiki/Meridian_(satellite)

The orbit those are doing (a Molniya orbit) means they are looking down at Russia for many hours, then they zip around the far side of the globe quickly, then back to hanging over Russia.

Geostationary is cool, but it's very expensive, and lots of Russia is very far North for which Geostationary sucks anyway. So, do cheaper orbits with more birds, but with a very eccentric orbit and voila, you've solved the problem.

Thanks, that was interesting. I skipped to the first linked https://en.wikipedia.org/wiki/Molniya_orbit

Highlights:

"[Pic of 12h orbit] Usually the period from perigee +2 hours to perigee +10 hours is used to transmit to the northern hemisphere."

"In practice, a satellite in a Molniya orbit serves the same purpose for high latitudes as a geostationary satellite does for equatorial regions, except that multiple satellites are required for continuous coverage."

I know it's an exaggeration, but it's exciting to think of some random bored person in a low-access area all of a sudden seeing a new access point in settings.

(Come to think of it, with the PSPS phenomenon here in NorCal, I might end up being that bored guy this very year!)

They haven't started with orbits specifically around Canada. It's probably just a matter of where it is easiest to go through the legal/political mess.

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